C astal
2005
Conferência
Hope
Proceedings
Lisboa,Portugal
24-29 de Julho de 2005
Faculdade de Ciências
Universidade de Lisboa
IBERIAN COASTAL HOLOCENE PALEONVIRONMENTAL EVOLUTION
IBERIAN COASTAL HOLOCENE
PALEOENVIRONMENTAL EVOLUTION
C astal
Hope 2005
PROCEEDINGS
Editors
Maria da Conceição Freitas & Teresa Drago
Lisbon, Portugal, 24-29 July 2005
Faculdade de Ciências, Universidade de
Lisboa
ISBN : 972-99694-OX
Cover photograph: João Moreno & Francisco Fatela
Cover design: Carlos Marques da Silva
Sponsors:
Banco Portugês de Investimento
Faculdade de Ciências da Universidade de Lisboa
Departamento de Geologia
Centro de Geologia
Instituto Nacional de Investigação Agrária e Pescas - IPIMAR
Fundação Calouste Gulbenkian
Fundação para a Ciência e Tecnologia
Associação Eurocoast-Portugal
Câmara Municipal Santiago Cacém
Câmara Municipal Lisboa
Reserva Natural das Lagoas de Santo André e da Sancha
CCDR-Alentejo
Caixa Geral de Depósitos
Co-organizing entities: Centro Geofísica – Universidade de Lisboa
Instituto Tecnológico e Nuclear
Université Bordeaux I
Universidad de A Coruña
Universidad del Pais Vasco
Organising Comittee
Maria Conceição Freitas, University of Lisbon, Portugal
Teresa Drago, National Institute of Nacional de Investigação Agrária e Pescas-IPIMAR,
Portugal
Célia Lee – Centre of Geology, University of Lisbon, Portugal
César Andrade – University of Lisbon, Portugal
Anabela Cruces- University of LIsbon, Portugal
Tânia Ferreira - University of LIsbon, Portugal
Silvia Serina - National Institute of Nacional de Investigação Agrária e Pescas-IPIMAR, Portugal
Selma Gabriel- National Institute of Nacional de Investigação Agrária e Pescas-IPIMAR,
Portugal
Scientific Committee
Alejandro Cearreta
Anabela Oliveira
Assunção Araújo
Aurora Bizarro
Cari Zazo
Carlos Vale
Cristino Dabrio
Maria Fernanda Sanchez Goñi
Fernando Rocha
Francisco Fatela
Guilhermo Francés
Jean-Marie Jouanneau
João Alveirinho Dias
João Cabral
João Cascalho
José Manuel Munhá
Luisa Santos
Maria Cristina Cabral
Maria de Fátima Araújo
Maria Helena Granja
Maria Virgínia Henriques
Mário Cachão
Jorge Miguel Miranda
Olivier Weber
Pedro Proença e Cunha
Roberto Bao
Sebastião Teixeira
Tomasz Boski
Universidade País Basco - Espanha
Instituto Hidrográfico - Portugal
Universidade do Porto - Portugal
Instituto Hidrográfico - Portugal
Museu Nacional de Ciências Naturais - Espanha
INIAP - IPIMAR - Portugal
Universidade Complutense - Espanha
Universidade de Bordéus I - França
Universidade de Aveiro - Portugal
Universidade de Lisboa - Portugal
Universidade de Vigo - Espanha
Universidade de Bordéus I - França
Universidade do Algarve - Portugal
Universidade de Lisboa - Portugal
Universidade de Lisboa - Portugal
Universidade de Lisboa - Portugal
Universidade da Corunha - Espanha
Universidade de Lisboa - Portugal
ITN - Portugal
Universidade do Minho - Portugal
Universidade de Évora - Portugal
Universidade de Lisboa - Portugal
Universidade de Lisboa - Portugal
Universidade de Bordéus I - França
Universidade de Coimbra - Portugal
Universidade da Corunha - Espanha
DRAOT Algarve - Portugal
Universidade do Algarve - Portugal
Organization
•
•
•
Centro de Geologia da F.C.U.L.
Departamento de Geologia da F.C.U.L.
INIAP – IPIMAR
PREFACE
The widely recognized value of the coastal fringe and the need to base management
instruments on sound scientific foundations encouraged, in the last decade,
multidisciplinary and integrated research, which, in the field of Earth Sciences,
enlarged the traditional short time-scale of approach to encompass the last 20 Ka.
In this context, two R&D Projects have been proposed and completed under the
auspices of FCT and fulfilled in the proponent institutions Instituto de Investigação das
Pescas e do Mar (IPIMAR) and Centro and Departamento de Geologia da Faculdade
de Ciências da Universidade de Lisboa: “Global vs Local Forcing Factors and
Paleoenvironmental Changes of Estuaries and Lagoons of SW Portugal Since the
Lateglacial” (PDCTM/MAR/15231/99) and “Late Quaternary Environmental Change
from Estuarine and Continental Shelf Sedimentary Record” (PLE/12/00).
The Coastal Hope 2005 Conference culminates work carried out by the teams
involved in both projects that included, beyond staff from both proponent institutions,
researchers from the Departamento de Geociências da Universidade de Aveiro, the
Universidad de A Coruña, the Université de Bordeaux 1, the Universidad del País
Vasco, the Museu de História Natural, the Departamento de Química do Instituto
Tecnológico e Nuclear, the Centro de Geofísica da Universidade de Lisboa, among
others, and drilling experts and facilities from the private company Teixeira Duarte, SA.
These projects shared as a common research goal the characterization of Post Glacial
sedimentary patterns in both active and silted lagoonal and estuarine environments of
Western Portugal and the identification of forcing factors of coastal modification (local
vs global) such as changes in sea level and climate, in sediment availability and
supply, in the watershed and anthropogenic influence. Research progressed under a
multi- and interdisciplinary perspective, using sedimentological, geochemical and
(paleo)biological environmentally-sensitive proxies that allowed the reconstruction of
paleoclimatic and paleoenvironmental evolution throughout the last millennia.
The widening of the geographical scope of Coastal Hope 2005 to include the whole
Atlantic Iberian façade aims to encourage discussion and exchange between
Quaternary coastal scientists and to achieve a holistic understanding of the evolution
models proposed for this littoral as well as to strengthen partnership within Iberia.
Lisbon, July 2005
Maria da Conceição Freitas, University of Lisbon
Teresa Drago, INIAP-IPIMAR
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
ÍNDICE
Isabel Abrantes, João Manuel Dias & Fernando Rocha – Matéria particulada em suspensão na Ria de Aveiro –
Variabilidade Espacial e Temporal e Fluxos na Embocadura (TALK) .................................................................................. 3
Paula Alvarez-Iglesias, Marta Pérez-Arlucea & B. Rubio – Sediment infilling and geochemical patterns of San Simón Bay
intertidal area (Rías Baixas, Galicia, Spain) (TALK) ............................................................................................................. 5
Ana Amorim, B. Dale. & A. L. Dale – Dinoflagellate cysts as environmental indicators over the past 2000 years in shallow
marine sediment cores from the Tagus deposition center (W Iberia) (POSTER) ................................................................. 7
Maria de Fátima Araújo, Ana Lobato, Anabela Cruces & Teresa Drago - Paleoenvironmental Geochemical patterns in the
holocenic evolution of minho estuary (TALK)......................................................................................................................... 8
P. Bernárdez, R. González-Álvarez, G. Francés, M.Á. Bárcena, O. Romero & R. Prego - A 4700-yr-long record from the
galician continental shelf: diatom production and riverine input (TALK) .............................................................................. 11
Tomasz Boski, Cristina Veiga-Pires, Delminda Moura & Sarita Camacho - Patterns of sedimentary infilling of estuaries
during the Holocene sea-level rise in S. Portugal (TALK) .................................................................................................... 13
Pedro Brito, Pedro Terrinha, Luís Rebêlo & Hipólito Monteiro - Deltaic sedimentary structure interpreted from highresolution seismic data: Sado estuary, Portugal (POSTER) ................................................................................................ 15
Mário Cachão, Maria da Conceição Freitas, Maria de Jesus Ribeiro, Catarina Guerreiro & Teresa Drago - PleistoHolocene Calcareous Nannoplankton Abundance Variation Pattern inside Paralic Environments of Western Iberia
(TALK) .................................................................................................................................................................................. 17
P. M. Callapez, R. Paredes, P. Dinis, R. Danielsen, A. F. Soares & M. Carvalho - Biofacies from the Holocene
paleolagoon of Leirosa (Figueira da Foz, West Central Portugal) (POSTER) ..................................................................... 19
Maria João Sacadura Carvalho - Contributo para a gestão de sistemas lagunares – o caso da Lagoa de Óbidos (TALK) .......... 21
Alejandro Cearreta - General framework of holocene sea-level/coastal changes in the Cantabrian coast (Bay of
Biscay) (TALK) ..................................................................................................................................................................... 26
F. Clemente, Marta Pérez-Arlucea, Irene Alejo, Miguel Ángel Nombela, D. González, Susana Costas, Patricia Bernárdez,
R. González & Rita González Villanueva - 3D Facies architecture and dynamics of a beach barrier-lagoon complex
(Ría de Vigo, Galicia, Spain) (POSTER).............................................................................................................................. 32
Catarina Corredeira, Maria de Fátima Araújo, A. Gouveia & Jean-Marie Jouanneau - Anthropogenic and lithogenic
continental evidences on the composition of shelf sediment cores from SW Iberia (TALK) ................................................ 34
Susana Costas, Irene Alejo, Fernando Rial, Henrique Lorenzo & Miguel A. Nombela - The evolution of a retrograding
sand barrier at Cíes islands (NW Iberian Peninsula) (TALK) ............................................................................................... 36
Cristino J. Dabrio - The last deglaciation in costal setting of southern Spain (TALK) ..................................................................... 38
Randi Danielsen - Paleoenvironmental development of the Quiaios dunes, Beira Litoral, Portugal (POSTER)............................. 40
Jorge Dinis, Virgínia Henriques, Maria Conceição Freitas & César Andrade - The holocenic evolution of the Óbidos,
Alfeizerão and Pederneira lagoons (western Portugal). Natural and anthropic forcing (TALK) ........................................... 42
Paula Diz & Guillermo Francés - La importancia de la calidad del alimento en la distribucion de foraminiferos bentónicos
en ambientes someros: la ria de Vigo como ejemplo (TALK) .............................................................................................. 44
Teresa Drago - Late Quaternary environmental changes of northern Portuguese estuaries (TALK).............................................. 46
Henrique Duarte, Luis Menezes Pinheiro, Cristina Bernardes, F.C. Teixeira, S. Bouriak & José Hipólito Monteiro - High
resoultion seismic stratigraphy of the Ria of Aveiro (Portugal) (TALK) ................................................................................ 52
Marco Ferraz, Elsa Silva, Anabela Cruces, Maria Conceição Freitas, Mário Cachão, César Andrade & Maria de Fátima
Araújo – Environmental characterization of the Albufeira lagoon (Portugal) at micro timescale using a
multidisciplinary approach (TALK)....................................................................................................................................... 54
Tânia Ferreira, Anabela Cruces, Maria Conceição Freitas, César Andrade, Maria de Fátima Araújo & Robert Bao Microscale charaterization of Lagoa da Sancha - an acidic dune slack in the Portuguese SW coast (TALK)..................... 58
Catarina Fradique, João Cascalho & Teresa Drago - Translucent heavy minerals from the Minho estuary sedimentary
record (TALK)....................................................................................................................................................................... 62
Maria da Conceição Freitas & César Andrade - Global vs local forcing factors and paleoenvironmental changes of
estuaries and lagoons of SW Portugal since the late glacial (TALK) ................................................................................... 64
Selma Gabriel, Flávio Martins, Rui Taborda & Teresa Drago - Simulation of past sedimentary dynamics in douro estuary:
first results (POSTER).......................................................................................................................................................... 71
Raquel González-Álvarez & Guillermo Francés - Paleoenvironmental conditions of the galician continental shelf during
the holocene (POSTER)....................................................................................................................................................... 74
Helena Maria Granja - Evolution of the coastal zone of NW Portugal (Minho-Mondego) since late glacial times (TALK) ............. 76
Catarina Guerreiro, Mário Cachão & Teresa Drago - Calcareous nannoplankton as a tracer of the marine influence in the
NW coast of Portugal, over the last 14000 BP (TALK) ........................................................................................................ 79
Virgínia Martins, Jean-Marie Jouanneau, Olivier Weber, João Alveirinho Dias & Fernando Rocha - Oceanic influence in
the Ria de Vigo during the last 2600 years (POSTER) ........................................................................................................ 82
Angela Alonso Millán & J. L. Pagés - La transgresion holocena en el noroeste peninsular (TALK) ............................................... 85
António M. Monge Soares & João M. Alveirinho Dias - Evidence for temporal fluctuations in ocean reservoir effect off
Portugal during the holocene (TALK) ................................................................................................................................... 89
Filipa Moreno, Maria de Fátima Araújo, P. Valério, João Moreno & Francisco Fatela - Weathering and transport on Minho
river basin (NW Portugal): some inferences from bedload geochemistry (POSTER).......................................................... 91
João Moreno & Francisco Fatela - Palaeoenvironmental evolution over the last 10 kyr BP at Caminha tidal marsh (NW of
Portugal): foraminiferal evidences (TALK) ........................................................................................................................... 94
Filipa Naughton, Maria Fernanda Sanchez Goñi, S. Desprat, J.-L. Turon, J. Duprat, E. Cortijo, B. Malaizé, C. Joli, E. Bard
& F. Rostek - Climate variability of the last 25.000 years in and off Iberia: direct land-sea correlation from the
multiproxy analysis of a northwestern Iberian margin deep-sea core (TALK)...................................................................... 97
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IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Filipa Naughton, Maria Fernanda Sanchez Goñi, Teresa Drago, J.-L. Turon, J. Duprat, E. Cortijo, B. Malaizé, E. Bard, F.
Rostek, Jean-Marie Jouanneau & Maria da Conceição Freitas - Millennial-scale climatic variability during the last
glacial-interglacial transition and the Holocene in the NW of Iberia (TALK)......................................................................... 98
Miguel Angel Nombela, Irene Alejo, P. Bernárdez, F. Clemente, Susana Costas, Paula Diz, S. Fernández-Bastero,
Guilhermo Francés, L. Gago-Duport, T. García, D. González-Alonso, R. González-Álvarez, R. GonzálezVillanueva, C. Liquete, L.D. Pena & Marta Pérez-Arlucea - Evolución sedimentaria desde el último máximo glacial
en la costa y plataforma continental de las Rías Baixas (Galicia, NW de la Península Ibérica) (TALK) ............................. 99
L.D. Pena, Guilhermo Francês, P. Diz, Miguel Angel Nombela & Irene Alejo - Oscilaciones climáticas milenarias en el
Atlántico Norte durante el holoceno: teleconexiones entre altas y bajas latitudes (TALK) ................................................ 101
Marta Pérez-Arlucea, A. Carter, F. Clemente, Miguel Angel Nombela & D. González - Long and short term denudation
rate calculations for the “Ría de Vigo” (Spain): AFTD, DEM-based analysis, river loads and sediment volume
(TALK) ................................................................................................................................................................................ 103
L. Pérez-Belmonte & E. Goubert - Multi-proxy description of major sedimentary environments in Morbihan’s gulf (NW
France) (TALK)................................................................................................................................................................... 105
Rute Ramos, Anabela Cruces, Maria da Conceição Freitas, César Andrade, Maria de Fátima Araújo & Jean-Marie
Jouanneau - The last 200 years of sedimentation in Santo André lagoon (SW Portuguese coast) – results from
sedimentological and geochemical proxies (TALK) ........................................................................................................... 106
Luís P. Rebêlo, Pedro O. Brito, Pedro G. Terrinha & Hipólito C. Monteiro - Evolution of the Tróia Peninsula: the foredunes
record (TALK)..................................................................................................................................................................... 110
Maria de Jesus Ribeiro, Mário Cachão, I. Abrantes & Fernando Rocha - Coccolithophores from the Ria de Aveiro lagoon
(NW Portugal). Implication for the circulation pattern of marine waters (TALK)................................................................. 112
Maria de Jesus Ribeiro, Mário Cachão, Maria da Conceição Freitas & Anabela Cruces - Nannoliths as a tracer of marine
influence inside coastal lagoons: the cases of Melides and Santo André (TALK) ............................................................. 113
Maria de Jesus Ribeiro, Mário Cachão, Maria da Conceição Freitas & Anabela Cruces - Nannoliths as an important tool
to mesoscale (centennial) paleoenvironmental interpretation – Santo André lagoon. Preliminary data (TALK)................ 114
Maria de Jesus Ribeiro, Mário Cachão, Maria da Conceição Freitas & Anabela Cruces - Nannoliths as an important tool
to macroscale (millennial) paleoenvironmental interpretation: the case of Melides and Santo André lagoons (TALK) ..... 115
Fernando Rocha, Teresa Drago & Paula Gonçalves - Variações ambientais Holocénicas no estuário do Minho (NW
Portugal) – Abordagem Mineralógica (TALK) .................................................................................................................... 116
Francisca Rosa, Francisco Fatela, Selma Gabriel, Silvia Serina & Teresa Drago - Late holocene palaeoecological
evolution of foraminiferal assemblages from the NW Portuguese shelf off the Douro river (POSTER)............................. 118
Emilia Salgueiro, A. Voelker, L. de Abreu, Fátima Abrantes, H. Meggers, G. Wefer & C. Lopes - Paleotemperature and
paleoproductivity off the northwestern Iberia margin during the last 140 ky (TALK).......................................................... 120
Sebastião Braz Teixeira - Evolução holocénica do litoral em regime transgressivo: o caso da costa de quarteira (Algarve,
Portugal) (TALK) ................................................................................................................................................................ 121
Sebastião Braz Teixeira, Paula Gaspar & Marcos Rosa - Holocene sea-level index points on the Quarteira coast (Algarve,
Portugal) (TALK) ................................................................................................................................................................ 125
María José Viñals - Problemas y amenazas para la conservación de las zonas húmedas mediterráneas (TALK)...................... 128
Olivier Weber, Teresa Drago, Filipa Naughton, Jean-Marie Jouanneau, Selma Gabriel & Sílvia Serina - Fine scale
sedimentary sequences of Douro muddy complex (northern portuguese continental shelf) (POSTER)Error! Bookmark not defined.
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IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
MATÉRIA PARTICULADA EM SUSPENSÃO NA RIA DE AVEIRO –
VARIABILIDADE ESPACIAL E TEMPORAL E FLUXOS NA EMBOCADURA
(TALK)
Isabel Abrantes1,3, João Manuel Dias2 & Fernando Rocha3
1
2
3
ESE/Instituto Politécnico de Viseu, R. Maximiano Aragão, 3500 Viseu, Portugal; [email protected]
Dep. Física, Univ, Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal; [email protected]
MIA (FCT), Dep. Geociências, Univ. Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal; [email protected]
A Ria de Aveiro constitui um sistema estuarino-lagunar, de águas pouco profundas, bem
misturado, que comunica com o Oceano Atlântico, através de um canal fixado artificialmente.
Com uma superfície adjacente de 250 km2, apresenta uma topografia complexa caracterizada
por extensas zonas intertidais e quatro canais principais: S. Jacinto, Mira, Espinheiro e Ílhavo. O
Rio Vouga e o Rio Antuã constituem os principais afluentes do sistema, cuja média total do
débito fluvial (durante um ciclo de maré) é de cerca de 1,8x106 m3 (Moreira et al., 1993). O
prisma de maré na embocadura é de 136,7x106 m3 em condições de maré viva máxima e de
34,9x106 m3 em maré morta mínima (Dias et al., 2000). Consequentemente, a hidrodinâmica da
Ria de Aveiro é dominada pelo forçamento da maré. A maré na embocadura é semi-diurna, com
uma amplitude média de 2 m, variando entre 0,6 m nas marés mortas e 3,2 m nas marés vivas.
As correntes de maré, condicionadas pela geometria e batimetria da laguna, são mais intensas
nos canais estreitos e profundos (troços iniciais dos canais de S. Jacinto e Espinheiro), onde
podem atingir velocidades superiores a 1 m.s-1. Apresentam maior intensidade durante as marés
vivas e no decurso da vazante (meia-vazante). Outra acção forçadora da circulação na Ria de
Aveiro é a tensão do vento à superfície que, em condições de grande intensidade e persistência
de direcção, pode alterar os fluxos provocados pelas marés e pelo débito fluvial, particularmente
nos canais que têm uma elevada superfície de água e uma profundidade reduzida (Silva, 1994;
Dias et al., 1996; Dias, 2001).
O presente trabalho teve como objectivos principais caracterizar a variabilidade espacial e
temporal da concentração e composição mineralógica da matéria particulada em suspensão
(MPS) e estimar os fluxos de MPS, que ocorrem na interface laguna-oceano. Para a prossecução
destes objectivos foram efectuadas colheitas de sedimentos em suspensão em sete locais de
amostragem (Barra e canais de S. Jacinto, de Mira, do Espinheiro e de Ílhavo) e ao longo de uma
secção transversal ao marégrafo de Aveiro.
Os sedimentos em suspensão foram colhidos ao longo de seis ciclos de maré, no Verão
(Setembro de 2001 e Junho/Julho de 2002) e no Inverno (Fevereiro de 2002), em regime de
marés vivas e de marés mortas. A amostragem, sempre que a profundidade o permitiu, foi
efectuada à superfície, a meia-água e a 1 m do fundo, com garrafa Van Dorn. A água foi filtrada,
em laboratório, numa rampa de filtração a vácuo, tendo-se utilizado filtros HA, da Millipore, com
porosidade de 0,45 µm e 47 mm de diâmetro, previamente pesados. Após secagem dos filtros
(40ºC durante 24h) foi determinada, por pesagem, a concentração do material em suspensão. A
composição mineralógica foi obtida por difractometria de raios X, adoptando-se na análise semiquantitativa os critérios recomendados por Schultz (1964) e Thorez (1976). Os fluxos
sedimentares foram estimados utilizando um modelo numérico hidrodinâmico bidimensional
integrado segundo a vertical (2DH), previamente calibrado por Dias et al. (1998), e
concentrações de material em suspensão determinadas experimentalmente.
Durante o período de estudo, a concentração de MPS variou sazonalmente com a fase e
amplitude da maré. As diferenças nos teores de MPS observadas nas estações de amostragem
denotam, provavelmente, a magnitude das correntes de maré e as características
granulométricas dos sedimentos de fundo, encontrando-se as maiores concentrações médias
nos locais que conjugam um fundo localmente rico em partículas finas com um canal estreito e
profundo. A variabilidade sazonal parece estar mais relacionada com o regime de ventos, com a
actividade biológica (indutora de floculação), com a componente biogénica (nomeadamente os
cocolitóforos) e com alguma contribuição da plataforma do que com o débito fluvial, que se
manteve abaixo dos valores médios. Apesar do Rio Vouga constituir o maior fornecedor de
sedimentos em suspensão para a laguna, a sua contribuição foi escassa devido, muito
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IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
provavelmente, aos baixos caudais registados. Na generalidade, os teores mais elevados de
MPS observaram-se durante a vazante das marés vivas quando teoricamente as correntes
possuem maior competência remobilizadora e transportadora. Contudo, algumas estações
verificaram as concentrações médias mais elevadas durante a enchente da maré morta de
Inverno, fazendo supor que factores externos à laguna (ventos e plataforma) mascararam o
efeito das correntes de maré. O Canal de S. Jacinto parece ser o que mais contribui com MPS
para a embocadura, durante os períodos de vazante.
O cortejo mineralógico identificado na MPS é dominado, em toda a coluna de água, pela
mica/ilite, acompanhada de quartzo e caulinite, sendo acessórios os feldspatos, a calcite, a opala
C/CT, a clorite e a pirite (Abrantes et al., 2003). Nas marés vivas, correntes mais energéticas são
capazes de ressuspender e manter em suspensão os minerais mais densos e/ou de forma
esferoidal, o que se traduz no aumento da percentagem média do quartzo, da opala C/CT, dos
feldspatos e da pirite. No decurso das marés mortas, a diminuição da magnitude das correntes
induz uma deposição diferencial destes minerais, verificando-se um aumento relativo das
partículas de menor densidade e/ou de forma planar, nomeadamente os filossilicatos (mica/ilite,
clorite e caulinite) e a calcite. Na generalidade dos locais de amostragem verificou-se no Verão
um aumento, por vezes muito discreto, dos teores de mica/ilite, de clorite e dos feldspatos
potássicos, enquanto a caulinite, o quartzo, as plagioclases, a calcite, a opala C/CT e a pirite
registaram aumento durante o período de Inverno. A diminuição na enchente de Inverno dos
valores de quartzo e caulinite com a distância à embocadura leva a admitir a sua entrada na
laguna através da fronteira atlântica. A calcite parece funcionar como traçador da contribuição
biogénica marinha, exibindo um padrão de distribuição semelhante ao dos cocolitóforos.
Os fluxos de sedimentos para a plataforma adjacente ocorrem particularmente durante as
marés vivas de Verão e de Inverno. Durante as marés mortas, a Ria de Aveiro parece funcionar
como uma armadilha de sedimentos pelo que o volume de sedimentos em trânsito na
embocadura é mais elevado na enchente do que na vazante (Abrantes et al., 2005). A
exportação de sedimentos para o oceano, consistente com a dominância de vazante verificada
na zona central da laguna, reflecte a amplitude da maré e, consequentemente, o efeito das
correntes na ressuspensão, transporte e deposição das partículas finas.
Bibliografia
Abrantes, I., Rocha, F. & Dias, J.A. 2003. Distribuição e composição dos sedimentos em suspensão na Ria de Aveiro. In:
4º Simpósio sobre a Margem Ibérica Atlântica, Vigo, Thalassas, 19 (2b): 27-28.
Abrantes, I., Dias, J.M. e Rocha, F. 2005. Spatial and temporal variability of suspended sediments concentration in Ria de
Aveiro lagoon and fluxes between the lagoon and the ocean. J. Coastal Research, SI 39. (aceite).
Dias, J.M. 2001. Contribution to the study of the Ria de Aveiro hydrodynamics. Tese de Doutoramento, Universidade de
Aveiro, 288p. (não publicado).
Dias, J.M., Lopes, J.F. e Dekeyser, I. 1996. Numerical modelling of tidal fluxes and passive pollutants concentration in Ria
de Aveiro, Portugal. In: Ferrante, A.J. and Brebbia, C.A. (Eds), Coastal Environments – Environments Problems in
Coastal Regions. Computacional Mechanics Publications, Southampton, 285-294.
Dias, J.M., Lopes, J.F. e Dekeyser, I. 1998. An exploratory study of the dynamics of Ria de Aveiro, Portugal. In: Kim, H.;
Lee, S.H. and Lee, S.J. (Eds), Hydrodynamics – Theory and Applications. Seoul, Uiam Publishers, 619-624.
Moreira, M.H., Queiroga, H., Machado, M.M. e Cunha, M.R. 1993. Environmental gradients in a southern estuarine
system: Ria de Aveiro, Portugal, Implications for soft bottom macrofauna colonization. Netherlands Journal of Aquatic
Ecology, 27(2-4): 465-482.
Schultz, L.G. 1964. Quantitative interpretation of mineralogical composition from X-ray and chemical data for the Pierre
Shale. U. S. Geol. Surv. Prof Paper, 391-C, 1-31.
Silva, J.J.F. 1994. Circulação de água na Ria de Aveiro: contribuição para o estudo da qualidade da água. Tese de
Doutoramento, Universidade de Aveiro, 158 pp. (não publicado).
Thorez, J. 1976. Pratical identification of clay minerals. Ed. G. Lelotte, Belgique.
4
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SEDIMENT INFILLING AND GEOCHEMICAL PATTERNS OF SAN SIMÓN
BAY INTERTIDAL AREA (RÍAS BAIXAS, GALICIA, SPAIN) (TALK)
Paula Alvarez-Iglesias, Marta Pérez-Arlucea & B. Rubio
Dpto. Geociencias Marinas y Ordenación del Territorio, Facultad de Ciencias Experimentales, Universidad de Vigo,
36310, Vigo (Pontevedra), Spain; [email protected], [email protected], [email protected]
The inner part of the Ría de Vigo (Galicia, NW Spain), the San Simón Bay is a 7.3 km long
and 3.5 km wide bay with a surface area of 19.5 km2 (Fig. 1). Its average depth is close to 7 m.
Tidal range is 2-4 m (mesotidal). Current velocities are up to 0.25 m s-1 at the surface, and 0.12 m
s-1 at the bottom in adjacent subtidal areas (Nombela et al., 1995). It constitutes a coastal
ecosystem of high biological productivity, due to upwelling processes which are common in all the
Galician Rías (Álvarez-Salgado et al., 2000). Orientation and morphological characteristics make
San Simón a low energy environment. Sediments are mainly organic-rich muds (Álvarez-Iglesias
et al., 2004). Supratidal marshes, intertidal sandy flats and Zostera nana mud flats are developed
in the innermost areas. The intertidal area is crossed by a network of tidal channels. The main
continental freshwater inputs to the Ría de Vigo are localized in its inner part (75% of the total
discharge: Nombela et al., 1995; Pérez-Arlucea et al., 2000). Three rivers enter the northern
sector of the Bay, the Oitavén-Verdugo (NE), the Ulló (N) and the Xunqueira (NW), and develop
into estuarine environments. The first of them constitutes the main fluvial fresh water source to
the Bay. These are moderately short rivers, with a seasonal variability in their discharge and
sediment yield (Pazos et al., 2000), being their suspended sediment inputs very low. Fluvial
sediment contributes to the gradual infilling of the Bay, which acts as a sediment trap. Silt and
clay settle down in the intertidal flats, while coarser sediments deposit in the river heads
(Nombela et al., 1995). San Simón Bay is an ecosystem with high ecological and economical
relevance, where cockles and clams are exploited. Antropogenic activity around the coastline has
modified the Bay sedimentary pattern, in particular, in the northern sector of the Bay by the
artificial extension of sand flats to allow bivalves culture. Bay sediment infilling is determined both
by natural inputs and antropic activities.
4680000
4675000
4670000
LATITUDE N (UTM, m)
4685000
Sediment distribution and facies analysis have been carried out from 38 cores (spaciated
every 15-20 m) along two transects (total length about 360 m TR1 and 280 m TR2) crossing from
the Oitavén-Verdugo River to the Ulló River (SE-NW direction). 40 mm wide cores were extracted
with a detachable TESS-1 suction corer (Méndez et al., 2003). Recovery varied between 1.25 m
and 6.50 m depth. Depositional architecture shows the interaction between estuarine and tidal
processes. Sediment architecture consists
of laterally continuous, multi-story channel
SAN SIMÓN
fills. Fining upward sequences, 0.5 to 2.0 m
BAY
thick, are observed. Interchannel areas
consist of tide-influenced sand flats and
MOAÑA
Rande Straits
mixed sand and mud flats in higher
REDONDELA
CANGAS
topographic areas, which are nowadays
Home Cape
being
colonized
by
Zostera
nana
A Guía
specimens, whose radicular system favours
Cíes Islands
the retention of fine-grained sediments.
14
VIGO
AMS C dating on a bivalve shell at a depth
Samil Beach
of 1.95 m collected in the intertidal area
gives a radioacarbon age of 107.93 ± 0.41%
RIA DE VIGO
of the modern 14C activity (Stuiver &
5 km
Reymer, 1993, 2005). Considering the
recent age of this sample, calibration is not
510000
515000
520000
525000
530000
possible and sedimentation rates cannot be
LONGITUDE W (UTM, m)
calculated accurately. Even so, this age
Figure 1 - Location of the study area.
may be indicative of high current
5
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
sedimentation rates in this area. 210Pb-dating in a short core collected along TR1 confirms this
point.
Surficial samples were collected for grain size analysis (dry and wet sieving), inorganic and
organic carbon contents (Elemental Analysis) and major and trace element concentrations (X-Ray
Fluorescence). Analyses were performed on the bulk sample. Surficial sediments mainly
comprise quartz, micas, feldspars and, in a lesser extent, rock fragments (granite, schist, gneiss)
and minerals sourced from granites and metamorphic rocks (Palaeozoic rocks of the Hercynian
massif). Coarse gravels and sands concentrate in the surroundings of Oitavén-Verdugo mouth
(67-99%), whereas mud prevails in the west part of the intertidal area (52-83%). Sand constitutes
the majoritary fraction in most of the samples (58.26±19.26%). Bioclastic fragments are very
scarce, shells (Cerastoderma edule, Hydrobia ulvae) mostly concentrated in estuarine channel
margins. Total inorganic carbon content (TIC) is almost negligible as previously reported for the
intertidal area (Álvarez-Iglesias et al., 2003). Total organic carbon contents (TOC, 2.98±2.16%)
are similar to values reported for sediments in the Bay (Nombela et al., 1995; Álvarez-Iglesias et
al., 2003). In general, the finer the sediments, the higher the TOC. This reflected an incorporation
of organic matter to the finest fractions of sediments by adsorption phenomena (Salomons &
Förstner, 1984). Sediments of channel borders, mud flats and Zostera nana mud flats are
characterized by high contents of mud and TOC. Considering major and trace metal content, the
most relevant characteristic is the very high Pb concentration (up to 1933 µg g-1). Pollution can be
classified from high to very high, with concentrations which surpass from 3 to 38 times the local
background levels (Rubio et al., 2000). Intense pollution by lead was also detected in the bay
intertidal area (Álvarez-Iglesias et al., 2003). Lead concentrations are higher in the northward
transect (about twice). Correlations between TOC, fractions lesser than 63 µm and trace metal
contents highlight that organic matter and fine materials tend to act as heavy metal binders
(Salomons & Förstner, 1984).
Acknowledgements
This paper is a contribution to the projects REN2003-03233 MAR, REN2003-02822 MAR, REN2003-09394/MAR and
VEM2003-20093-C03-03 of Spanish MCYT, to the projects PGIDIT03MAR30101PR and CO/085/03 of the Xunta de
Galicia and the IGCP 464 of the UNESCO. Contribution of the XM1 and XM2 (nº 349) Groups of the Universidad de Vigo.
P.A.I. are grateful to the Spanish MECD for the concession of a PhD fellowship (F.P.U.).
References
Álvarez-Iglesias, P., Rubio B., Vilas, F. 2003. Pollution in intertidal sediments of San Simón Bay (Inner Ria de Vigo, NW of
Spain): total heavy metal concentrations and speciation. Mar. Pollut. Bull., 46: 491-503.
Álvarez-Iglesias, P., Rubio ,B., Pérez-Arlucea, M. 2004. Niveles de fondo y contaminación reciente por metales pesados
en el registro sedimentario de la Ensenada de San Simón (Ría de Vigo, NO de España). Geotemas, 6(1): 315-318.
Álvarez-Salgado, X. A., Gago, J., Míguez, B. M., Gilcoto, M., Pérez, F. F. 2000. Surface waters of the NW Iberian Margin:
upwelling on the shelf versus outwelling of upwelled waters from the Rías Baixas. Est. Coast. Shelf Sci., 51: 821-837.
Méndez, G.; Pérez-Arlucea, M.; Stouthammer, E., Berendsen, H. 2003. The TESS-1 suction corer: a new device to extract
wet, uncompacted sediments. J. Sediment. Res., 373: 1078-1081.
Nombela, M. A., Vilas, F., Evans, G. 1995. Sedimentation in the mesotidal Rias Bajas of Galicia (North-Western Spain):
Ensenada de San Simón, Inner Ría de Vigo. Spec. Publs. Int. Ass. Sediment., 24: 133-149.
Pazos, O., Nombela, M. A., Vilas, F. 2000. Continental contribution of suspended sediment to an estuary: Ría de Vigo.
Scientia Marina, 64 (3): 295-302.
Pérez-Arlucea, M., Filgueira, M., Freijido, M., Méndez, G. 2000. Parámetros morfométricos e hidrológicos de las cuencas
de drenaje y ríos tributarios a la ría de Vigo. Estimación de las variaciones anuales en la cargas en suspensión y en
disolución. Cuadernos de Geología Ibérica, 26: 171-187.
Rubio, B., Nombela, M. A., Vilas, F. 2000. La contaminación por metales pesados en las Rías Bajas gallegas: nuevos
valores de fondo para la Ría de Vigo (NO de España). Journal of Iberian Geology, 26: 121-149.
Salomons, W., Förstner, U. 1984. Metals in the Hydrocycle. Springer- Verlag, Berlin Heilderberg New York Tokio, 349 pp.
14
Stuiver, M., Reimer, P. J. 1993. Extended C database and revised CALIB radiocarbon calibration program. Radiocarbon,
35: 215-230.
Stuiver, M., Reimer, P. J., Reimer, R. W. 2005. Calib 5.0. [WWW program and documentation].
6
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DINOFLAGELLATE CYSTS AS ENVIRONMENTAL INDICATORS OVER THE
PAST 2000 YEARS IN SHALLOW MARINE SEDIMENT CORES FROM THE
TAGUS DEPOSITION CENTER (W IBERIA) (POSTER)
Ana Amorim1, B. Dale2 & A. L. Dale3
1
2
3
Faculdade de Ciências da Universidade de Lisboa, Instituto de Oceanografia, Lisboa, Portugal; [email protected]
University of Oslo, Department of Geoscisences, Oslo, Norway; [email protected]
GeoResearch Consulting, Skarnes, Norway; [email protected]
Dinoflagellate cyst assemblages were analysed from a box-core and a piston-core
recovered from the Tagus deposition centre off Lisbon (Portugal, W Iberia). The studied area is
influenced by the Tagus river discharge (the longest river of the Iberian Peninsula) and by
seasonal coastal upwelling. The cores covered the last 2,000 years, including pre-industrial time
and the subsequent period most affected by human activities, namely cultural eutrophication. Cyst
assemblages were characterized by the consistent presence of warm temperate cosmopolitan
species: Lingulodinium polyedrum, Protoceratium reticulatum, Spiniferites bulloideus, S. mirabilis
and Protoperidinium conicum. Three species accounted for almost all the variance in the data: L.
polyedrum, P. reticulatum and Gymnodinium catenatum. Correspondence analysis was used to
identify ecological signals, based on previous studies of global recent cyst distributions. This
allowed differentiation between signals of climatic variability and cultural eutrophication.
7
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PALEOENVIRONMENTAL GEOCHEMICAL PATTERNS IN THE HOLOCENIC
EVOLUTION OF MINHO ESTUARY (TALK)
Maria de Fátima Araújo1, Ana Lobato1, Anabela Cruces2 & Teresa Drago3
1
Departamento de Química, Instituto Tecnológico e Nuclear, ITN, Estrada Nacional 10, 2686-953 Sacavém. Portugal;
[email protected]
Laboratório de Procost, Centro e Departamento de Geologia da FCUL. Edifício C6, 3º Piso. Campo Grande. 1749-016
LISBOA. Portugal; [email protected]
3
Instituto Nacional de Investigação Agrária e Pescas-IPIMAR; [email protected]
2
Introduction
The Minho estuary is localized in the upper most north region of Portugal (Fig. 1A) defining
at the final course the geographic border between Portugal and Spain. It is a very shallow and
large estuary that trends NNE-SSW, in a meso to micro tidal environment, with a maximum tidal
range of 4m. The drainage basin has 17000km2 and extends over different lithologies (Paleozoic
to Cenozoic) including schist, granites and greywackes. The river mouth is partially confined by a
sand barrier, tied in the left border, covered by a field dune fixed by pine trees, known as “Pinhal
do Camarido”.
A multidisciplinary study on the stratigraphic succession of Holocene sedimentary records
of Minho estuary permitted the recognition and distinction of relevant paleoenvironmental units,
which have occurred during the Late Quaternary. This paper highlights the valuable contribution
of geochemistry in the comprehension of complex evolution of transitional environments, namely
estuaries.
Methods
Two cores were collected in the Camarido region aligned cross-shore and located 200m
apart (Fig. 1B). Core 1 (seaward location) reached -29.90m depth (all depths are refereed to
Mean Sea Level - MSL) and attained bedrock at -29.56m; core 2 reached -27.54m and attained
bedrock (granite) at -25.84m.
Figure 1 - Location of the study area: A - Northern Portugal including Minho estuary B – core 1 and core 2 in Camarido.
Cores were open, described and subsampled for sedimentological, paleoecological,
mineralogical and geochemical determinations. Sedimentological analysis were perform in the
total sample at IPIMAR (texture, organic matter (OM) determined by LOI (Loss On Ignition) at
8
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450°C, during 2 hours in a furnace and carbonate content - determined by weight difference
before and after digestion with diluted hydrochloric acid) in 120 and 75 samples from core 1 and
2, respectively. Whereas geochemical analyses were carried out in the <2mm size fraction by a
multielemental technique: Energy-Dispersive X-Ray Fluorescence spectrometry, at ITN. About 21
elements (Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb and Pb) were
determined in 37 and 47 sub samples from core 1 and core2, respectively. Subsamples were
selected to characterize the different sedimentary units representative of the Holocene evolution.
Sample preparation and analytical procedures have been described in detail elsewhere (Araújo et
al., 2002). Radiocarbon dates were obtained in samples of organic matter by the AMS technique
at Beta Analytic Inc., USA.
Si (%)
Ca(%)
K(%)
14C
(cal BP)
Si (%)
% Carbonate
Ca(%)
Cl(%)
25
50
0.0
1.5
3.0
12
0
750
1500
0
100
200
0
-2
-2
-4
-4
2150
-6
-6
III
IIIB
-8
-8
-10
-10
-12
-12
IIIA
-14
-14
-16
II
-16
-18
-18
-20
-20
II
-22
11950
I
-22
-24
-24
-26
-26
-28
I
200
100
Sr(mg/kg)
0
1500
750
0
12
6
0
Al(%)
Rb(mg/kg)
9020
13400
-28
-30
Al(%)
Sr(mg/kg) Rb(mg/kg)
Figure 2 - Depth profiles on the elemental composition of core 1 and core 2, and correlation between the different units
defined for each core.
9
0.5
0
6
2
0.3
50
0
0.0
25
IV
IV
K(%)
0
60
30
0
80
40
4
0
-30
% <63µm
0
0.5
0.3
2
0.0
3.0
1.5
0.0
50
25
0
50
25
0
60
30
0
80
40
0
4
Cl(%)
Height
(m) (MSL)
% Carbonate
Units
% <63µm
Units
Height
(m) (MSL)
Results and Discussion
Elements were grouped and discussed according to specific parameters: origin (lithological,
biological, marine and anthropogenic) and also by their chemical behaviour. Al and Si are mostly
linked with textural characteristics (percentages of sand/silt/clay), Ca and Sr are associated with
the bioclastic fraction although they can be enriched in particular mineralogical phases
(plagioclases, apatite). K and Rb are indicative of a continental source and high contents
(variations) of some speficic elements, such as, Cl, Br and S can be good indicators of a marine
influence (Freitas et al., 2003). The relative variations of the above mentioned elements can
provide relevant information on the definition of lithological units and contribute to the
establishment of a paleoenvironmental evolution model.
Both in core 1 and 2, four units could be defined (Fig. 2) taking into account the downcore
elemental variations of the above mentioned elements. Al and Si profiles reflect variations
between sandy and silt/clay size layers (associated with Al). Ca and Sr depth profiles showed to
be important tools in the definition of the units, presenting anomalously large concentrations
which are high negatively correlated with the Al and Si contents. Therefore, the Ca and Sr
concentrations, also positively correlated with the carbonates indicate a local enrichment in
bioclasts (marine influence). It is worth to note, that in core 1 the Ca and Sr concentrations are
systematically higher than in core 2. Elevated concentrations of K and Rb indicate the presence
of minerals like feldspars, common in the granites of the drainage basin.
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
The depth profiles of the elements that can be considered to detect a major marine
influence (Cl, Br and S) indicate that this has a greater importance in units II and III A of the core
1 and unit II of core 2.
Conclusions
Both cores have reached the regional substrate rock (granite) and the sedimentological
infill begins with a gravelly basal unit (unit I) constituted essentially by quartzite and rounded
gravels and particulate organic matter that correspond to a fluvial environment (radiocarbon date
13400 cal BP).
After 9020 cal BP, there are variations in Al and Si related to alternate layers of sandy and
muddy sediments. In these units II higher concentration values of Ca, Sr, Cl and Br have been
measured suggesting a major marine influence. In units III this marine signal decreases and in
core 1 at the top of the unit (Unit IIIB) it is observed a sudden impoverishment in these “marine”
elements. However, these elements present always lower concentrations in core 2. The topmost
unit (unit IV) is constituted by a monotonous sequence of sands (high Si and low Al contents)
disturbed by an event with singular characteristics: a muddy organic layer with fragments of coal,
low contents of Si, K and Rb (terrrigeneous), high contents of S, Cl and Br.
Geochemistry contribution has revealed to be an important tool in a study of transitional
environments giving particular indications in the marine/terrigeneous origin of the deposited
materials and allow to recognise and evaluate some temporal changes occurred during the last
13400 years.
Acknowledgments
This work has been partially funded by FCT project PLE/12/00 “Late Quaternary ENVIronmental CHANGES from
Estuarine and Continental Shelf Sedimentary Record” (ENVI-CHANGES). A. Cruces is thankful for FCT support through
the doctoral grant (BD/21654/99).
References
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias,
J.M.A. 2002. Geochemical Tracers of Northern Portuguese Estuarine Sediments on the Shelf. Progress in
Oceanography, 52: 277-297.
Freitas, M.C., Andrade, C., Rocha, F., Tassinari, C., Munhá, J.M., Cruces, A., Vidinha, J. & Silva, C.M. 2003. Lateglacial
and Holocene environmental changes in Portuguese coastal lagoons: 1. The sedimentological and geochemical
records of the Santo André coastal area (SW Portugal). The Holocene, 13, 3: 433-446.
10
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A 4700-YR-LONG RECORD FROM THE GALICIAN CONTINENTAL SHELF:
DIATOM PRODUCTION AND RIVERINE INPUT (TALK)
P. Bernárdez1,2, R. González-Álvarez1, G. Francés1, M.Á. Bárcena3, O. Romero4 & R. Prego2
1
Universidad de Vigo. Dpto. Geociencias Marinas y O.T., Fac. Ciencias del Mar, Campus Lagoas-Marcosende s/n, 36310
Vigo Spain; [email protected]; [email protected]; [email protected]
2
Institute of Marine Research (CSIC), C/Eduardo Cabello 6, 36208, Vigo, Spain; [email protected].
3
Universidad de Salamanca, Dpto. de Geología. Fac. de Ciencias, Plaza de la Merced s/n, 37008, Spain;
[email protected]
4
Bremen University, Department of Geosciences, P.O. Box 33 04 40, 28334 Bremen, Germany; [email protected]
Introduction
The core SMP02-3 (42º02.207’N, 9º02.363’W, 260 cm, 121 m depth) was used to
reconstruct the Late Holocene paleoproductivity, the changes of the upwelling dynamics and the
fluctuations of the terrestrial input. It was retrieved from the Galicia Mud Patch (GMP), a N-S
elongate muddy sediment body deposited on the middle Galician continental shelf. In this work
we use a multivariable study based on bulk components, diatoms and other biosiliceous
components.
Material and Methods
Samples for biosiliceous components counts were prepared following the method proposed
by Bárcena and Abrantes (1998). Quantitative analyses (number of diatom valves,
silicoflagellates, sponge spicules, palynomorphs, crysophycean cysts, phytoliths and radiolaria
per gram of dry sediment) were done at 1000 magnifications using a Leica DMLB with phase
contrast illumination. Diatom valves and Chaetoceros resting spores identification has been done
at the species level when possible.
Total carbon (TC), total inorganic carbon (TIC) and total nitrogen (TN) were performed with
a Leco CN-2000 y CC-100 elemental analyser from the Research Support Service (CACTI) at the
University of Vigo. Organic carbon (TOC) was determined by the difference between TC and TIC.
Calcium carbonate content was calculated by multiplying the TIC by a constant factor of 8.33.
Additionally, the TOC/TN ratio (hereafter C/N ratio) was calculated. The amount of opal contained
in the bulk sediment was analyzed following the method of wet alkaline leaching procedure
devised by Mortlock and Froelich (1989).
Four 14C AMS dates were obtained (Geochron Lab. and Aarhus University) and corrected
using CALIB REV 5.0.1 for 13C and for a reservoir age of 400 yr, and then converted into calendar
years (Stuiver & Reimer, 1993; Hughen et al., 2004). Ages between dated levels were obtained
by linear interpolation between the nearest AMS dating points.
Results and discussion
According to the lithology, the core shows three intervals: A lower glauconitic sandy interval
with bioclast remains (4700-2500 cal yr BP) overlaid by a clayish interval (3300-1300 cal yr BP)
and an upper muddy interval (1300-200 cal yr BP). The biogenic component of the sediment is
dominated by CaCO3 (1.7-20%), followed by organic carbon (0.81-2.13%) and opal (1.2-2.0%).
High values of opal and organic carbon are recorded between 3300-2500 and 1200-500 cal yr
BP. Lowest percentages of the biogenic compounds are registered between 3000-1300,
coinciding with the clayish interval.
Diatom abundance follows the downcore variations described for both TOC and opal,
especially in the upper part of the core. Two levels barren of diatoms (4700-3300 and 2500-1200
cal yr BP) evidence a change of the diatom preservation conditions. Although absolute
abundance of diatoms is relatively low, the number of species is relatively high. All diatom species
with well-documented ecological requirements were assigned to one of the following groups:
freshwater, benthic, coastal planktonic and upwelling markers. Diatom assemblages are
dominated by four species: Chaetoceros resting spores (mostly C. affinis) are a marker of
upwelling; Leptocylindrus danicus resting spore is linked to nutrient depletion, upwelling relaxation
and stratification; Paralia sulcata indicates coastal upwelling and/or poor preservation and
11
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Thalassionema nitzschioides var. nitzschioides is typical from areas with weaker upwelling and/or
river discharge.
The most remarkable feature is the high abundance of T. nitzschioides var. nitzschioides at
1200-500 cal yr BP. In the same interval maximum percentages of freshwater forms (4-5%) and
benthic diatoms (around 4%) also occurred, pointing out an increase in the river discharge. The
same interpretation is invoked for 3300-2500 cal yr BP period, although the fluvial influence was
weaker. Other terrestrial input proxies (C/N ratio, the abundance of crysophycean cysts,
phytoliths, palynomorphs) also peaks between ca. 3300-2500 and 1200-500 cal yr BP. The most
probable source for this material is the Miño River. According to these facts a significant part of
organic carbon and opal preserved into the sediments has a continental provenance. Our
interpretation agrees with those of Pena et al. (2003) and Álvarez et al. (2005) for the nearby Rias
de Muros and Vigo. These authors identify wetter periods at similar ages. More intense
precipitations over the northwest of Iberia increased the rivers discharge and would have
enhanced the terrestrial sediment supply to the continental shelf. Probably, the growth of the
GMP is related to these rainy phases.
For the most recent period, the abrupt increase of diatoms related to coastal upwelling
(Chaetoceros resting spores), as well as the drastic decrease of L. danicus, point to a change in
the hydrographical setting that involves the upwelling reinforcement and therefore enhances
marine primary production. This phenomenon has been pointed out by Soares (1993), Diz et al.
(2002) and González-Álvarez et al. (2005) in the region at around 1000-1200 cal yr BP. According
to our age model the upwelling intensification in the continental shelf took place during the last
500 years. Upwelling markers in the continental shelf sediments may be blurred by other
processes, as the river influence. The Miño River has a stronger discharge than the little rivers
flowing into the rias.
References
Álvarez, M.C., Flores, J.A., Sierro, F.J., Diz, P., Francés, G., Pelejero, C. & Grimalt., J. 2005. Millennial surface water
dynamics in the Ría de Vigo during the las 3000 years as revealed by coccoliths and molecular biomarkers.
Palaeogeography, Palaeoclimatology, Palaeoecology, 218: 1-13.
Bárcena, M.A. & Abrantes, F. 1998. Evidence of a high productivity area off the coast of Malaga from studies on surface
sediments. Marine Micropaleontology, 35: 91-103.
Diz, P., Francés, G., Pelejero, C., Grimalt, J.O. & Vilas, F. 2002. The last 3000 years in the Ría de Vigo (NW Iberian
Margin): climatic and hydrographic signals. The Holocene, 12: 459-468.
González-Álvarez, R., Bernárdez, P., Pena, L.D., Francés, G., Prego, R., Diz, P. & Vilas, F. 2005. Paleoclimatic evolution
of the Galician continental shelf (NW of Spain) during the last 3,000 years: from a storm regime to present conditions.
Journal of Marine Systems, 54: 245-260.
Hughen K.A., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C., Blackwell, P.G., Buck, C.E., Burr, G., Cutler,
K.B., Damon, P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Kromer, B., McCormac, F.G.,
Manning, S., Bronk Ramsey, C., Reimer, P.J., Reimer, R.W., Remmele, S., Southon, J.R., Stuiver, M., Talamo, S.,
Taylor, F.W., van der Plicht, J. & Weyhenmeyer, C.E. 2004. Marine04 Marine Radiocarbon Age Calibration, 0–26 Cal
Kyr BP. Radiocarbon, 46: 1059-1086.
Mortlock, R.A. & Froelich, P. 1989. A simple method for the rapid determination of biogenic opal in pelagic marine
sediments. Deep-Sea Research, 36: 1415-1426.
Pena, L.D., Francés, G., Diz, P., Liquete, C., González-Álvarez, R., Bernárdez, P., Nombela, M.A., Alejo, I. & Vilas, F.
2003. Forzamiento solar en el régimen de lluvias durante los últimos 3000 años en el noroeste de la Península Ibérica.
Thalassas, 19 (2a): 119-120.
14
Soares, A.M. 1993. The C content on marine shells: evidences for variability in coastal upwelling off Portugal during the
Holocene. Proceedings of an International Symposium on Applications of Isotope Techniques in the Studying Past and
Current Environmental Changes in the Hydrosphere and the Atmosphere. International Atomic Energy Agency, Vienna,
471-485.
14
Stuiver, M. & Reimer, P. J. 1993. Extended C database and revised CALIB radiocarbon calibration program.
Radiocarbon, 35: 215-230.
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PATTERNS OF SEDIMENTARY INFILLING OF ESTUARIES DURING THE
HOLOCENE SEA-LEVEL RISE IN S. PORTUGAL (TALK)
Tomasz Boski, Cristina Veiga-Pires, Delminda Moura & Sarita Camacho
CIMA – Centro de Investigação Marinha e Ambiental, Universidade do Algarve, 8000-117 Faro, Portugal; [email protected]
Guadiana is a major river on the Iberian Peninsula and the terminal segment of its valley is
cut deeply into the impervious and faulted Upper Carboniferous schists and graywacks.
Boreholes and seismic profiles indicate that the paleovalley is 600 m wide and 70 m deep below
mean sea level, ca 7 km inland from the mouth (Boski et al., 2002). The depth of the incision
which is exceptional for the Gulf of Cadiz, allows a good insight into the sedimentary record with a
high resolution timescale. Several cored boreholes that reached the pre-Holocene substratum
were drilled in recent years in order to recognize the architecture of sedimentary facies and to
quantify the organic carbon content trapped in sediments accumulating during the drowning of the
Guadiana fluvial valley. The materials described in the present study were obtained from a borehole drilled down to ca 53 meters near the confluence of Beliche and Guadiana Rivers, located in
the intertidal zone of the latter. Three 14C datings performed on the recovered samples indicate
that the entire sedimentary sequence accumulated over a period of ca 13-14 kyrs, representing
one of the longest postglacial sedimentary records in the non glaciated areas. About 80% of the
Holocene sedimentary sequence was accumulated in the first phase of the sea level rise, with a
rate of ca 80 cm per century, which terminated ca 6700 cal yrs BP and was followed by a much
slower rate of vertical accretion. The 10 lowermost meters, of this sequence which is lying on top
of a polimictic gravels, are mostly sandy with intercalation of silty clay. The basal sands are
mineralogically and texturally immature but become progressively more quartzic and devoid of
mica towards the top of the horizon. The foraminifera fauna is almost absent in this interval and
when present, it consists of scarce inner linings of benthic foraminifera. This environment maybe
interpreted as belonging to the transitional fluvial – estuarine phase observed also in the basal
sections of other boreholes in Guadiana area (Boski et al., 2002). In the remaining upper, almost
entirely fine grained section of the borehole, marking differences were found with respect to
several faunistic and geochemical parameters.
The lower segment extending to ca –15 m depth is characterized by a low abundance of
calcareous benthic foraminifera, lower sulfur content and predominance of phytoplancton
molecular biomarkers (Gonzalez Vila et al., 2002). These features may be representative of
mudflat facies experiencing frequent submergence and in which reducing conditions prevailed.
The upper segment which comprises the top 15 meters of the sediment column is very rich in
calcareous benthic foraminifera, high in sulfur and in resin biomarkers. This information indicates
saltmarsh conditions in a fully marine water regime and may also correspond to the increased
erosion on land covered by conifer forests.
The Boina-Arade Estuary lies in a junction of 2 valleys, in the confluence of two rivers
draining Southern slopes of the world famous nepheline syenite massive intruded into the
Carboniferous schists. The paleovalley of Boina-Arade which experiences, the same as
Guadiana, terminal stage of infilling, is cut into calcareous rocks and therefore its maximum depth
does not exceed 30 m. We present here data from 2 boreholes drilled across the Holocene
sedimentary sequence. The borehole P5 is situated in the 2 km from se river junction in the
terminal, intertidal part of Boina valley, a high gradient mountain river renowned for its flash–
floods. The Holocene sedimentary record embraces about 8000 yrs and starts (as in case of
Guadiana) with a series of sand/gravel and clay intercalations which correspond to transitional,
fluvial/estuarine, period. Sharp boundaries separating texturally distinct layers indicate pulses of
fluvial sediments transported and deposited during occasional floods. However, due to the
incertitude of 14C data it is difficult to ascribe time boundaries to this transitional horizon, which is
followed by a 6 m thick clayey sequence, rich in foraminifera and accumulated under the mudflat
regime. This low energy environment lasted until ca 6500 yrs cal BP when the estuary started to
fill with a coarser material of inland and coastal origin. There is a rather similar sequence of
events inferred from the sedimentary record in the borehole P2 in Arade valley. However because
Arade valley is more open to the sea and not affected by mountain flash floods, the 8 m thick
13
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mudflat horizon dates back to ca 8000 yrs cal. BP. It has abundant benthic foraminifera fauna in
which Haynesina germanica, Trochamina inflata, and Cibicides lobatulus predominate. As
observed in P5 borehole, sand and silt infilling was dominating during the Upper Holocene, in part
due to the anthropogenic causes (Chester & James, 1991).
The area of Gilão-Almargem estuary is is part of the Ria Formosa lagoon-barrier islands
system. The two rivers considered in this study are slightly different in length and outflow although
they both converge to the same actual salt marsh system. Gilão River has a NW-SE course over
more than 30 km whereas Almargem River flows N-S for less than 20 km and has a smaller
outflow. According to the literature and to ancient maps (Algarve Region bibliographic
contribution), Gilão and Almargem River mouths were draining into the same estuary until the
sixteenth century. Until then, it seems that the estuary was more opened to the ocean via the
broad tidal inlet later subjected to narrowing due to the accelerated accretion of sand bars. Three
cores were retrieved from the surroundings of the actual inlet of the Gilão River. Although the
geographical positions of the cores are relatively close to each other, the sedimentary sequences
are very different showing therefore facies complexity characterising estuarine environments
(Frey & Howard, 1986).
Despite the marked differences in the pattern and chronology of Holocene infilling of the
estuarine valleys in S Portugal which are caused by hydrodynamic, topographic and
morphological factors it is possible to recognize several phases of environmental change acting
on a regional/global scale and namely:
Bulk of fine sediments which filled the estuarine valleys accumulated fast during the Lower
Holocene until ca 6500 – 7000 yrs cal. BP with a rate of ca 0.8 m/century.
This phase of infilling is interrupted by either a climatic event (transition from Boreal to
Atlantic ?) or first anthropogenic impact, which corresponded to higher erosion in the river basin.
During the Upper Holocene, coarser sediments either shelf derived or eroded inland,
completed the process of infilling of the estuaries.
References
Boski, T., Moura, D., Camacho, S., Duarte, R.D.N., Scott, D.B., Viga-Pires, C., Pedro, P. & Santana, P. 2002. Postglacial
sea level rise and sedimentary response in the Guadiana Estuary, Portugal/Spain border. Sedimentary Geology,
150:103-121.
Chester, D.K. & James, P.A. 1991. Holocene Alluviation in the Algarve, southern Portugal: case for an anthropogenic
cause. Journal of Archeological Science, 18: 73-87.
Frey, R.W. & Howard, J.D. 1986. Mesotidal estuarine sequences: a perspective from Georgia Bight. Journal of
Sedimentary Petrology, 56: 911-924.
Gonzalez-Vila, F.J., Polvillo, O., Boski, T. & Andres, J.R. 2002. A biomarker approach to the organic matter deposited in
coastal estuarine sediments during Holocene: a case study in the Guadiana River estuary. Organic Geochemistry (in
press).
Goy, J.L., Zazo, C., Somoza, L., Dabrio, C.J., Lario, J., Borja, F., Sierro, F.J. & Flores, J.A. 1996. Global and regional
factors controlling changes of coastlines in South Iberia (Spain) during Holocene. Quaternary Science Reviews, 15: 773
–780.
14
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DELTAIC SEDIMENTARY STRUCTURE INTERPRETED FROM HIGHRESOLUTION SEISMIC DATA: SADO ESTUARY, PORTUGAL (POSTER)
Pedro Brito1, Pedro Terrinha2, Luís Rebêlo3 & Hipólito Monteiro4
1
Dep. de Geo. Marinha, INETI. Estrada da Portela, 2720-866 Amadora; [email protected]
Dep. de Geo., FCUL/LATTEX. Campo Grande edifício C6, 1149-016 Lisboa; [email protected]
Dep. de Geo. Marinha, INETI. Estrada da Portela, 2720-866 Amadora; [email protected]
4
Dep. de Geo. Marinha, INETI. Estrada da Portela, 2720-866 Amadora; [email protected]
2
3
Introduction and study area
A high-resolution seismic reflection
survey was carried out in the Sado estuary
(Fig. 1) to investigate the sedimentary
bodies that resulted from interactions
between estuarine and shelf processes in
this area, since the last glacial maximum
(LGM). This work presents the first results
based on the interpretation of these seismic
lines focusing on the seismic-stratigraphic
features that can be found in the Sado
Metric coordinates
Hayford-Gauss,
estuary ebb delta and their significance in
Datum Lisboa
the context of the transgression that
followed the LGM.The Sado estuary is
located on the west Portuguese coast,
50km to the south of Lisbon. It is a
mesotidal bar-built estuary, with a mean
depth of 5m, a submerged area of 180km2
and a spring tidal prism of 4x108m3. The
1 – Location of the surveyed seismic lines in the
estuary is connected with the ocean by an Figure
Sado estuary. Tc020 segment is represented as a dotted line.
approximately 30m-deep and 2km-wide
inlet, which is constrained to the south by
the Tróia peninsula, a large sand spit
nourished by a local northward littoral drift, and to the north by the Arrabida chain that protects the
estuary from the predominant NW swell. Evidence from historical documents (e.g. CasteloBranco, 1926) and morphologic interpretation (Quevauviller, 1985; Psuty & Moreira, 2000),
suggest that the Tróia Peninsula was an island during the Roman period. Therefore, other inlet(s)
should have existed southward of the present-day one. The Sado ebb delta is a submerged sand
body, which extends approximately 5km offshore from the inlet gorge. It has an area of 47km2 and
a roughly triangular shape, ending abruptly to the offshore in a ≈2.5º slope that connects the delta
surface (-5m) to the foot of the delta front (-40m). This shoal is cut by a navigation channel that is
regularly dredged.
Methods
322km of high-resolution single-channel seismic reflection profiles were collected in 2003
within the Sado estuary and adjacent coastal shelf, during the Tesa cruise carried out onboard the
UAM Fisália (Fig. 1). Dip and strike oriented profiles were collected on the shelf, with a line
spacing ranging from less than 1km to 5km and trackline positioning done with a differential GPS.
A Boomer unit (EG&G 230-1 UNIBOOM) was used as seismic source, operated with an energy
output of 100J or 200J depending on the water depth. The digitally recorded seismic signal has
a frequency spectrum of 200-1850Hz, with an estimated vertical resolution of 2m. Seismic
processing included frequency band pass filtering, predictive and spike deconvolution and trace
mixing.
15
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Results, Discussion and conclusion
Interpretation of a sector of the seismic line Tc020, surveyed along the navigation channel
that crosses the delta (Fig. 1), leads to the identification of two major discontinuity surfaces,
S1and S2, and the individualization of three seismic units, U1 to U3, (Fig. 2).Unit U1 was
subdivided in two subunits (U1a, U1b), and is limited at the top by a seaward dipping erosive
surface (S1), while its base was not imaged. Subunit U1a shows oblique sub-parallel reflections
dipping seaward, in contrast with the oblique landward dipping reflections of subunit U1b. Unit U2
is limited by the surfaces S1 and S2, respectively at the base and top, and is characterized by
oblique seaward-dipping reflections that downlap on top of S1. The thickness of U2 decreases
seaward and the unit becomes almost reflection-free. Unit U3 sits on top of the S2 discontinuity
and outcrops at the sea floor where sand waves develop; the geometry of the U3 reflectors
downlapping on top of S2 discontinuity are typical of a progradant clastic body, i.e. a delta.
Nevertheless, internal and frontal surfaces suggest a complex history of the delta growth. The
geometry of S1, an irregular but continuous surface persistent down to a water depth exceeding
100m, suggests that it could correspond to the Flandrian transgression surface. Thus, unit U1
should be older than the trangressive ravinement, on top of which the present day ebb delta
started building up. Subunit U1b possibly corresponds to a paleo-valley cut into U1 unit. The
limited offshore extend of S2, present only in the submarine delta area, suggests that it could
correspond to a tidal/wave ravinement surface, probably related to the closure of former inlet(s)
located southward of the present-day one, to the onset of stronger currents in the modern inlet
area. The subsequent deposition of the unit U3 probably occurred under conditions similar to the
present-day ones.
Figure 2 – Segment of the seismic line Tc020 (top) and interpretative sketch (bottom), showing 3 seismic units (U1
to U3) and 2 major discontinuity surfaces (S1 and S2). Location of the seismic line segment in Fig. 1.
Acknowledgments
Thanks are due to the FCT (Portuguese Science and Technology Foundation) for financing the INGMAR project (without
reference), the STELIS project (POCTI/CTA/41754 /2001) and Pedro Brito’s PhD scholarship (SFRH/BD/11748/2003) that
supported this work. C. Andrade reviewed and added valuable comments to an early draft of this abstract.
References
Castelo-Branco, F. 1926. Da origem e do desaparecimento de Tróia de Setúbal. Las Ciencias de Madrid, Ano XIX(2):
445-461.
Psuty, N.P. & Moreira, M.E.S.A. 2000. Holocene sedimentation and sea level rise in the Sado estuary, Portugal. Journal of
Coastal Research, 16(1): 125-138.
Quevauviller, P. 1985. Estuário do Sado - Costa da Galé análise geomorfológica e estudo de alguns aspectos
sedimentológicos, Direcção Geral do Ordenamento, 85 p.
16
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PLEISTO-HOLOCENE CALCAREOUS NANNOPLANKTON ABUNDANCE
VARIATION PATTERN INSIDE PARALIC ENVIRONMENTS OF WESTERN
IBERIA (TALK)
Mário Cachão1,2, Maria da Conceição Freitas1,2, Maria de Jesus Ribeiro2, Catarina Guerreiro2 &
Teresa Drago3
1
Department of Geology, Faculty Sciences, Univ. Lisbon, Building C6, Campo Grande, 1749-016 Lisboa, Portugal;
[email protected]; [email protected].
2
Centre of Geology Univ. Lisbon, Building C6, 6.4.67, Campo Grande, 1749-016 Lisboa, Portugal; [email protected];
[email protected]
3
INIAP, IPIMAR, CRIPSUL Olhão, 8700-305 Portugal; [email protected]
Calcareous nannoplankton biogenic structures (coccoliths) that can be recognizable by
optical petrographic microscopy, are exclusively marine. Advected by waves and coastal currents
towards the shore, coastal high bottom hydrodynamics prevent coccoliths from depositing except
inside protected sectors of paralic (paleo) environments (Ferreira & Cachão, 2005).
Cores retrieved from completely siltup sectors of paralic environments from the
southwestern coast (lagoons of Santo André and Melides; Cearreta et al., 2003; Freitas et al.,
2003) the western coast (the Tagus estuary; Freitas et al., 1999) and northwestern coast (the
Douro and Minho estuaries; Cachão et al., 2002; Drago et al., 2002; Drago et al., 2003; Drago et
al., subm.; Guerreiro et al. subm.) of Portugal allowed the recognition of an overall similar pattern
of coccolith abundances, both by semi-quantitative (coccolith abundance index, CAI) and
quantitative (coccolith per gram) methods, although these sedimentary sequences display, in
general, considerable variation of facies from high energy coarse sediments to very fine sand and
silty-clay, which may induce pronounced disturbances in the coccolith record.
This pattern is composed by 5 sectors according to abundance and persistence of
coccoliths in sets of sequential core samples. The model was developed combining and
interpolating all data from the previously mentioned areas since significant changes from core to
core were found, due to the location and the particular and distinct spatial evolutionary history of
the paralic environments while evolving to present day estuaries or lagoons. The comparison with
sedimentology, geochemistry and other paleontological proxies (opp. cit.) allows to interpret these
sectors as follows, from base to top:
Sector I – The lowermost samples of the cores generally display no coccolith content
although microfossils such as pollens and fresh water diatoms may be present. This sector is
interpreted as composed by a sequence of fluvial sediments deposited while sea level was rapidly
rising after Termination I that marks the end of the Würm glaciation, but the coast line was still far
away;
Sector II – This short sector is characterized by the beginning of the record of coccoliths in
the core. Coccolith diversity is low (less than 5 taxa, in general) while intermittent abundance
varies from few to dozens of specimens. It represents the moment coast line rapidly transgresses
the core location, through estuarine like paleoenvironmental conditions;
Sector III – This sector is characterized by a more or less extended sequence of samples
with diverse, abundant (hundreds to thousands of CAI or coccoliths per gram) and generally
persistent content in coccoliths. It represents sedimentation in neritic conditions similar to present
day marine inner shelf produced by rapid transgression into a fluvial valley changing it temporarily
to a ria;
Sector IV – This sector is characterized by a return to low diversity and irregular coccolith
abundances produced when middle Holocene decreasing rate of sea-level rise and the
subsequent development of a sandy barrier, partially restricts marine influence, marking the return
to a fluvial dominated lagoonal ou estuarine (paleo)environment;
Sector V – This sector is composed by the topmost barren samples deposited by rivers or
silt up from adjacent emerged areas that followed severe recent to present day restriction of the
marine influence inside the paralic environment.
Recently, the study of a lithologically homogeneous core from the Mira estuary
(Southwestern Portugal) not only allowed to confirm the symmetrical pattern of the above
17
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
taphonomical and paleoecological model (Alday et al., subm.), but also opens the way to further
paleoecological analysis of the calcareous nannoplankton in the context of the evolution of the
coastal environments that followed Late Glacial global climate change.
Acknowledgements
This work was funded by FCT projects «Global vs local forcing factors and paleoenvironmental changes of estuaries and
lagoons of SW Portugal since the Late Glacial» (POCTI/MAR/15231/1999) and «Canal» (POCTI/PAL/32724/2000).
References
Alday, M., Cearreta, A., Cachão, M., Freitas, M.C., Andrade, C. & Gama, C. submitted. Micropalaeontological Record of
Holocene Estuarine and Marine Stages in the Corgo do Porto Rivulet (Mira River, SW Portugal). Estuarine, Coastal and
Shelf Science.
Cachão, M., Drago, T., Silva, A., Moita, T., Oliveira, A. & Naughton, F. 2002. The secret (estuarine ?) life of Helicosphaera
th
carteri: preliminary results. 9 INA Conference, Parma 2002, Journal Nannoplankton Research, 24 (2): 76-78.
Cearreta, A., Cachão, M., Cabral, M.C., Bao, R. & Ramalho, M.J. 2003. Late Glacial and Holocene Environmental
Changes in Portuguese coastal lagoons: 2 - The Santo André coastal area (SW Portugal) during the last 14 000 years
based on micropaleontological multiproxy evidence. Holocene, 13 (3): 447-458.
Drago, T., Naughton, F., Moreno, J., Rocha, F., Cachão, M., Sanchez Goñi, M.F., Oliveira, A., Cascalho, J., Fatela, F.,
Freitas, C. & Andrade, C. 2002. Geological record of environmental changes in the Douro estuary (NW Portugal), since
the Late Glacial. Proceedings, LITTORAL 2002, Eurocoast, Vol. III: 341-346.
Drago, T., Freitas, C., Cachão, M., Moreno, J., Cascalho, J., Oliveira, A., Naughton, F., Fradique, C., Silveira, T. & Fatela,
th
F. 2003. Douro estuary sedimentary record and sea level rise evolution in the last 14 000 years. 4 Symposium on the
Atlantic Iberian Continental Margin, Vigo, Thalassas, 19(2a): 101-103.
Drago, T, Freitas, C., Rocha, F., Cachão, M., Moreno, J., Naughton, F., Fradique, C., Araújo, F., Silveira, T., Oliveira, A.,
Cascalho, J. & Fatela, F. submitted. Paleoenvironmental evolution of estuarine systems during the last 14000 years –
the case of Douro estuary (NW Portugal). Journal of Coastal Research, SI 39, 7p.
Ferreira, J. & Cachão, M. 2005. “Calcareous nannoplankton from the Guadiana estuary and Algarve continental shelf
(Southern Portugal)”. Thalassas, 21 (1): 35-44.
Freitas, M.C., Andrade, C., Moreno, J.C., Munhá, J.M. & Cachão, M. 1999. The Sedimentary record of recent (last 500
years) environmental changes in the Seixal Bay marsh, Tagus estuary, Portugal. Geologie en Mijnbouw, 77: 283-293.
Freitas, M. C., Andrade, C., Cruces, A. & Cachão, M. 2003. Sedimentary response to sea-level changes of Portuguese
lowlands since the Late Glacial - a multidisciplinary approach. IX Congresso da Associação Brasileira de Estudos do
Quaternário & II Congresso do Quaternário dos Países de Língua Ibérica – 12-19 Outubro, Recife, Brasil, edição CDROM, 5 p.
Guerreiro, C., Cachão, M. & Drago, T. submitted. Calcareous Nannoplankton in coastal sediments, NW of Portugal, over
the last 14000 BP. Journal of Nannoplankton Research.
18
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BIOFACIES FROM THE HOLOCENE PALEOLAGOON OF LEIROSA
(FIGUEIRA DA FOZ, WEST CENTRAL PORTUGAL) (POSTER)
P. M. Callapez1,2, R. Paredes1, P. Dinis1, R. Danielsen3, A. F. Soares1 & M. Carvalho4
1
Departamento de Ciências da Terra, Universidade de Coimbra, Apartado 3014, 3001-401 Coimbra, Portugal;
[email protected]
2
Museu Mineralógico e Geológico, Secção do Museu de História Natural da Universidade de Coimbra.
3
CIPA, Instituto Português de Arqueologia, Avenida da Índia, 136, P-1300-300, Lisboa; [email protected]
4
Rua Ferreira Borges, 175, 1º, 3000-180, Coimbra, Portugal; [email protected]
The beach of Leirosa is located a few kilometers south of the coastal town of Figueira da
Foz, in Central Portugal. Within this area it is possible to recognize the single Holocene former
coastal lagoon of the sector of Cabo Mondego – Nazaré known till now. Some studies focusing on
the mineralogy and sedimentology of these sediments have been presented recently, but no
special attention was given to the biofacies and fossil content of lagoonal sediments (Rocha &
Bernardes, 1997; Bernardes et al., 2001).
The lagoonal unit is a single bed, less than 1.20 m thick, of dark sandy mud interbedded
within a thick succession of beach and aeolian sands. This unit is currently covered by present
day beach and dune sands but sometimes may be exposed at low tide after erosional storm
events. Radiocarbon dates by Bernardes et al. (2001) suggest an early Sub-Atlantic age
(2950±100 yrs to 2060±60 yrs), younger than the group of lagoon and beach examples from the
northwest coastal zone of Portugal (Granja & Carvalho, 1995).
Blocks of sandy mud sediment are usually found along the beach west and south of
Leirosa for more than 2 km. Many of these samples are perforated and bioeroded by Pholadidae
bivalves, sometimes with articulated shells of the species Pholas dactylus (Linné, 1758), Barnea
candida (Linné, 1758) and Petricola pholadiformis (Retzius, 1786) already preserved inside. In a
few blocks, the external surface and the interior of perforations was colonized by encrusting
bryozoans of species Electra pilosa (Linné, 1758). The occurrence of these modern epizoans and
bioeroders is an evident sign that the lagoonal deposits are periodically exposed in the infralittoral
bottom situated in front of the beach, but above the base of storm waves.
The lagoonal biofacies are very rich in aquatic molluscs, pollen and other microfossils. The
pollen content indicates a local deciduous oak forest with some pine. Of special interest are
occurrences of Triticum, a sign of agricultural activities in the Mondego drainage basin or even in
the near vicinity of the paleolagoon. The mollusc content paleofauna comprises a wide variety of
well preserved individuals (Callapez et al., 2005), yielding: Ostrea edulis (Linné, 1758), Ostrea
stentina (Payraudeau, 1826), Crassostrea angulata (Lamarck, 1819), Loripes lacteus (Linné,
1758), Cerastoderma edule (Linné, 1758), Parvicardium exiguum (Gmelin, 1791), Eastonia
rugosa (Elbling, 1779), Gastrana fragilis (Linné, 1758), Abra alba (Wood, 1802), Littorina littorea
(Linné, 1758), Peringia ulvae (Pennant, 1777), Rissoa ventricosa (Desmarest, 1814), Bittium
reticulatum (Da Costa, 1778), Hinia servaini (Locard, 1887), Turbonilla acutissima (Monterosato,
1884), Retusa truncatula (Bruguière, 1792), and Haminoea hydatis (Linné, 1758).
This molluscan association as well the absence of fresh water species suggests a brackish
palaeoenvironment periodically opened to significant marine influences. A semi-enclosed
lagoonal or estuarine environment with restricted fluvial input may be proposed, with possible
connections to the southern branch of Mondego estuary.
When compared with the modern molluscan faunas of the Mondego and other estuaries
and lagoons of the Portuguese west coast, it is also interesting to note that a few taxa of Leirosa
are already extinct or in risk of extinction in these areas. Hinia servaini (Locard, 1887), for
example, is presently known from Ria Formosa and replaced elsewhere by Hinia reticulata (Linné,
1758). Also ostreids like Ostrea edulis (Linné, 1758) and, specially, Crassostrea angulata
(Lamarck, 1819) are in accentuated regression of population effectives. On the contrary, the
common and widespread brackish water bivalve Scrobicularia plana (Da Costa, 1778) seems to
be absent from Leirosa.
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References
Bernardes, C. M., Noivo, L. M. & Corrochano, A. 2001. Evolution of Holocenic coastal dunes at Leirosa, south of Cape
Mondego, Portugal. Thalassas, 17: 45-56.
Callapez, P. M., Paredes, R,. Dinis, P., Danielsen, R., Soares, A. F. & Carvalho, M. 2005. The paleolagoon of Leirosa
(Figueira da Foz) and the Holocene brackish malacofauna of West Portugal. Congresso Nacional de Malacologia,
Portugalla, 5: 17-18.
Granja, H. & Carvalho, G. S. 1995. Sea-level changes during the Pleistocene-Holocene in the NW coastal zone of
Portugal. Terra Nova, 7: 60-67.
Rocha, F. & Bernardes, C. 1997. Caracterização mineralógica dos níveis lodosos no sistema de dunas costeiras a sul do
Cabo Mondego (Leirosa, Portugal). Estudos do Quaternário, 1: 67-72.
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CONTRIBUTO PARA A GESTÃO DE SISTEMAS LAGUNARES – O CASO DA
LAGOA DE ÓBIDOS (TALK)
Maria João Sacadura Carvalho
Universidade de Évora-Dep.
[email protected]
Biologia,
Universidade de Évora, Largo dos Colegiais, 7001 Évora Codex;
Introdução
A Lagoa de Óbidos localiza-se na costa oeste Portuguesa, cerca de 90 km a norte de
Lisboa. Ocupa cerca de 7 km2 e a bacia de drenagem envolvente estende-se por cerca de 440
km2 através de 7 concelhos, com relevância para os de Óbidos, Bombarral, Cadaval e Caldas da
Rainha; nesta envolvente destacam-se as sub-bacias do Arnóia e do Real, pela sua extensão e
carga poluente e, pela última razão, as do Cal, Ameal, Porto do Carro e Ferraria.
É uma região com elevado e diversificado interesse ambiental e cultural, ilustrado pelo
património arqueológico (Consulmar-Nemus, 2000), classificação como biótopo CORINE,
inclusão na proposta de sítios da Rede Natura 2000 e no Inventário Nacional de Zonas Húmidas,
elaborado de acordo com a Convenção de Ramsar (Farinha & Trindade, 1994). Os PDMs de
Caldas da Rainha e de Óbidos, prevêem regime de protecção para a Lagoa de Óbidos,
compatível com o estatuto de Área de Paisagem Protegida de Âmbito Regional, e o POOC
Alcobaça-Mafra, refere-a como área de protecção integral (PATO, 2005). Para além da protecção
oferecida pela legislação do Domínio Público Hídrico aos leitos e margens da Lagoa,
instrumentos mais recentes insituiram ali os refúgios de caça OBD-1 e CDR-2 e o Dec.-Lei nº
149/2004 reconhece a Lagoa e respectiva envolvente como zona sensível, nomeadamente ao
lançamento de águas residuais e susceptível de eutrofização nos dois braços interiores.
Enquadramento geológico
A laguna ocupa o flanco NW do anticlinal do Vale Tifónico de Caldas da Rainha/Óbidos; do
centro para a periferia do vale tifónico afloram as seguintes formções:
• formações pliocénicas de preenchimento recente, arenosas e arenítico-argilosas com
linhitos e diatomitos;
• formações hetangianas do infra-Lias, margosas, salíferas e gipsíferas, que afloram em
toda a margem Norte da laguna;
• formações calcárias do Lusitaniano – Camadas de Alcobaça, com alternância de
arenitos, margas e calcários, margas avermelhadas e níveis areníticos e margo-calcários;
Camadas de Montejunto com alternância de margas e calcários;
• Formações com alternância de arenitos e argilas do Lusitaniano – Grés Superiores - a
montante da laguna;
• Formações areniticas argilosas Cretácicas aflorantes na margem Sul da laguna.
Para montante, a bacia atravessa o Vale Tifónico, onde afloram essencialmente
asformações areníticas Lusitanianas (Zbyzewski & Almeida, 1960).
Toda a região se caracteriza pela existência de diversos aquíferos e relativa abundância
de água, associada essencialmente a níveis arenosos, areníticos e calcários.
O contacto entre os calcários Jurássicos e as margas Hetangianas, promovido pelas falhas
que bordejam a estrutura anticlinal, promove um efeito de barreira hidráulica que força as águas
infiltradas nos calcários Lusitanianos da Serra dos Candeeiros a subir, ainda com alguma da
temperatura que tinham em profundidade, dada a velocidade da ascensão. O facto de existirem
níveis de evaporitos intercalados e, nódulos de pirite nos calcários, promove o enriquecimento
em carbonatos, sulforetos, cloretos, etc. (Graça, 2004). O tempo de percolação estimado pela
Geostudos em 1983 para o aquífero termal de Caldas da Rainha, é de 450 anos (Graça, 2004). A
diferenciação em vários tipos de mineralização, é promovida pelas diversas litologias
atravessadas, o que distingue as nascentes termo-medicinais existentes na região.
Aspectos sócio-económicos
O uso de solos na bacia hidrográfica é predominantemente agrícola e florestal, com
predominância de eucalipto e vinha (PATO, 2005). A caracterização da população residente na
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envolvente lagunar indica envelhecimento, elevada taxa de analfabetismo (10-14% em 2001)
mas desemprego abaixo da média nacional. As principais actividades são agricultura, pecuária,
apanha de bivalves, pesca, turismo, cerâmica, comércio e serviços, com predominância do
sector terciário; as actividades extractivas repartem-se por uma mina de gesso e duas pedreiras
de calcário; as indústrias principais são a cerâmica, produtos alimentares, mobiliário, moagem,
alumínios, velas, metalomecânica, confecções, perfumes e rolamentos; das actividades
exclusivamente dependentes da laguna vivem 128 pescadores e mariscadores sendo as
espécies com maior valor comercial o berbigão (Cerastoderma edule), a ameijoa-boa (Ruditapes
decussatus ) e a ameijoa-macha (Venerupis pullastra e Venerupis aurea) (PATO, 2005).
Biodiversidade
Em termos de diversidade biológica do espaço lagunar, merece realce a grande
abundância de fitoplâncton, que ocasionalmente promove “marés vermelhas” e blooms de
microalgas conduzindo à elevação das concentrações de toxinas em bivalves (ICTM, Set. 1994).
Existem mais de 200 espécies inventariadas de macrofauna bentónica (Pereira, 2004), das quais
40 são anelídeos (poliquetas), 21 artrópodes (7 anfípodes, 5 isópodes, 2 misidáceos e 7
decápodes) e 40 de moluscos (22 bivalves, 16 gastrópodes e 2 poliplacóforos) (PATO, 2005).
Foram inventariadas 55 espécies de ictiofauna, das quais 30 com importância económica, que
incluem residentes, anádromos, catádromos e ocasionais (PATO, 2005); contam-se 10 espécies
de anfíbios, 3 de répteis (PATO, 2005) e são de referir alguns endemismos de herpetofauna
(Consulmar-Nemus, 2000). Estão também contabilizadas 175 espécies de aves (PATO, 2005)
das quais 5 beneficiam de estatuto de conservação (Consulmar-Nemus, 2000), 8 constam do
Anexo I da Directiva Aves e 4 são de ocorrência ocasional (Consulmar-Nemus, 2000); 4
espécies figuram no Anexo II da Convenção de Berna, das quais 2 figuram também no Anexo da
Convenção de Bona. Foram inventariadas 20 espécies de mamíferos, entre as quais se contam a
lontra (Lutra lutra) e 7 são quirópteros de entre os quais 2 espécies constam do Anexo II da
Convenção de Berna (PATO, 2005; Consulmar-Nemus, 2000); 3 espécies de mamíferos constam
do Anexo B-II da Directiva Habitats e 4 outras espécies do Anexo B-IV da mesma Directiva.
Perturbação
Os principais elementos de perturbação do sistema incluem a poluição da água e dos
sedimentos, por esgotos industriais e domésticos, por pesticidas e resíduos abandonados por
pescadores e visitantes. A extracção de inertes e deposição de dragados nas margens. O
assoreamento, acelerado pela descarga sólida das linhas de água afluentes e potenciado pela
plantação de espécies vegetais nas margens que favorecem a sua erosão. A pressão antrópica
(com relevo para o turismo), traduzida pelos edificados em dunas marginais, pela redução do
caudal do rio Arnóia, devido à construção recente de uma barragem e pela actividade do Clube
Aeronáutico sobre a avifauna; utilização do espelho de água para desportos náuticos a motor;
apanha ilegal, excessiva e não controlada de bivalves por turistas; introdução não regulamentada
de espécies exóticas para fins comerciais; circulação de veículos motorizados e pisoteio na
envolvente arenosa da laguna, particularmente em zonas sensíveis; caça ilegal e queima do
caniço .
O ritmo de assoreamento no interior do sistema lagunar entre 2000 e 2004 foi estimado em
200000 m3/ano (Fortunato et al., 2005). De 1995 até ao presente, verificou-se um substancial
assoreamento do corpo central da laguna até junto à confluência dos braços da Barrosa e do
Bom Sucesso, e, actualmente, a zona de entrada dos braços resume-se a um canal muito
estreito, com tedência para fechar. Em 1999 construíu-se um dique de guiamento de correntes a
montante da aberta; nos últimos anos e com possível mas não provada relação com o dique
construído, tem aumentado substancialmente o processo de assoreamento (Fortunato et al.,
2005) acompanhado de erosão da margem sul, perto do Gronho até à primeira semana de Julho
de 2005, data em que houve temporais de Verão e a aberta voltou a derivar para Norte, perto da
zona intermédia entre as duas praias – Foz do Arelho e Bom Sucesso.
No sentido de contribuir para o conhecimento deste espaço lagunar e respectiva
envolvente, de modo a adquirir dados que possam ser úteis na integração em intervenções
futuras ou planos de gestão da Lagoa de Óbidos, efectuaram-se alguns trabalhos de campo
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sobre a propagação da maré, características dos sedimentos de fundo e qualidade ecológica dos
afluentes, que complementam informação já existente, apresentando-se neste trabalho, os
primeiros resultados obtidos.
Metodologia
A evolução temporal da altura da maré no interior da Lagoa de Óbidos foi avaliada em
ciclo de águas vivas e mortas (Julho e Agosto de 2004, respectivamente), em 4 estações,
localizadas na aberta, junto ao dique de guiamento e a montante dos 2 braços (Barrosa e Bom
Sucesso), que distam respectivamente 500, 1000, 5125 e 6125m da boca da barra. As
observações consistiram em leituras espaçadas de 15 minutos, em réguas graduadas
previamente cravadas no fundo. Foi também efectuada uma campanha de recolha de
sedimentos de fundo em 19 pontos de amostragem no corpo lagunar, para avaliação do teor em
metais, do conteúdo em matéria orgânica indiferenciada, do valor de pH e das características
sedimentológicas, com vista ao mapeamento destas variáveis e à identificação de fontes
sedimentos e de cargas poluentes.
Realizou-se ainda uma campanha de caracterização da qualidade ecológica das principais
linhas de água afluentes à laguna, usando os índices QBR – Índice de Qualidade Riparia (Munné
et al., 2000) e BMWP’ – Índice de Qualidade Ecológica de Águas Superficiais (Pinto et al., 2004;
Alba-Tercedor & Sánchez-Ortega, 1988).
Resultados
Maré
A análise dos dados de maré indica em todas as estações de medida dominância de
enchente – as enchentes são mais curtas e, portanto, associam-se a maior velocidade média de
escoamento – que se traduz por um resíduo líquido do transporte sedimentar para o interior da
laguna e seu aprisionamento definitivo. Aubrey & Friedrichs (1988) referem para este tipo de
sistemas geometrias instáveis e pouco profundas (por comparação com a amplitude das marés),
características morfológicas observáveis no caso de Óbidos, em que os fundos intertidais,
aplanados, têm pouca capacidade de armazenamento de água, quando alagados. Estes autores
indicam a excedência do limiar de 0,3 para a razão Amplitude / Profundidade como indicativo
desta situação. Na lagoa de Óbidos os resultados usando as amplitudes observadas e os dados
batimétricos locais constantes do relatório elaborado pelo LNEC, referidos ao zero hidrográfico
(0ZH ~ -2 NMM), em Fevereiro de 2005 são: 0,32 na Barrosa, 0,26 no Bom Sucesso, 0,40 no
dique de guiamento e 1,02 na aberta. Todos estes valores excedem o limite proposto por Aubrey
& Friedrichs (1988), excepto no Braço do Bom Sucesso onde a profundidade é bastante superior
à média da laguna. Com o aumento da profundidade relativa ou aumento das áreas de
armazenamento intertidais, aumenta a influência da vazante (Aubrey & Friedrichs, 1988). Este
efeito pode ser conseguido pela dragagem e rebaixamento generalizado dos rasos de maré ou,
em alternativa, pela construção de canais oblíquos a um eixo de escoamento principal, que
veiculem um prisma idêntico ao conseguido pela primeira solução, com a vantagem de minimizar
as perturbações nos habitats associados (Fortunato & Oliveira, 2004).
Sedimentos
A zona central do corpo lagunar apresenta, em morfoscopia, a maior diversidade
mineralógica, o que indica que é aqui que se faz a transição entre os diversos regimes. A
salinidade nos troços finais dos braços é ainda suficiente para a cristalização de halite no fim do
Bom Sucesso. A esfericidade elevada indica vários ciclos de transporte o que é condizente com
a origem predominantemente sedimentar dos materiais que compõem as diversas sub-bacias de
drenagem. As curvas granulométricas permitem distinguir 4 ambientes de sedimentação
distintos: Praia - areias médias a grosseiras, lavadas, moderadamente calibradas, indiciando
regime de transporte intenso e boa selecção dimensional. A amostra colhida junto ao dique de
guiamento, semelhante às de praia em calibre e ausência de finos reflecte, contudo,
bimodalidade, cuja origem é, neste momento, discutível. Na zona de transição para ambientes
fluviais, os sedimentos apresentam-se também livres de finos e são bimodais, mas mostram
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composição mais variada que as anteriores. Na zona montante do corpo lagunar principal
encontram-se areias médias, muito mal calibradas e multimodais. A entrada no Braço da Barrosa
é marcada por diminuição na dimensão média das partículas e melhor calibragem embora
persistam 2 modas. Os sedimentos das embocaduras das linhas de água têm características
granulométricas e composicionais diferentes em todas as estações, o que é interpretado como
reflexo de assinatura textural de cada sub-bacia. As amostras destes pontos têm deficite de
finos.
Qualidade ecológica das linhas de água
Da análise do QBR verifica-se uma forte predominância de troços fluviais com muito fraca
qualidade ripária em todas os casos analisados, embora nos rios da Cal e do Porto do Carro,
existam segmentos com qualidade boa a muito boa, que deveriam ser preservados, melhorados
e utilizados como viveiros para recolonização de troços dos mesmos rios e de outros, a
recuperar. Nas estações dos rios Real e Arnóia, todas muito idênticas, os valores embora maus,
deixam prever a possibilidade de recuperação destas linhas de água com alguma facilidade. Os
salgueiros foram contabilizados como autóctones e algumas opiniões sugerem que esta espécie
seja usada na recolonização de zonas ripárias, tanto dos afluentes à Lagoa de Óbidos como
também dos que afluem à Baía de S. Martinho do Porto. Embora não se disponha ainda de
elementos quantitativos sobre macro-invertebrados para cálculo do BMWP’, as observações
efectuadas no terreno sugerem a predominância de oligoquetas e quironomídeos, o que indicaria
forte contaminação das águas afluentes à laguna.
Conclusões
É necessário regulamentar os usos de solos na bacia de drenagem e o uso do plano de
água pelo menos conseguir uma utilização concertada pelas diversas actividades, deforma a que
estas não colidam, estando presentemente elaboração o Plano de Gestão do Plano de Água e a
NOSTRUM apresentou uma proposta de execução do Zonamento das Margens.
É urgente a eliminação das fontes de poluição das águas e dos solos, nomeadamente de
origem doméstica, agro-pecuária e industrial.
É urgente mitigar os processos de assoreamento no interior do corpo lagunar e de erosão
na bacia, assim como diminuir a importância relativa ou mesmo inverter a dominância de
enchente na aberta e restante espaço lagunar, para aumentar a longevidade da laguna e evitar
a sua colmatação rápida.
Há necessidade de controlar as espécies alóctones e planear a re-introducção e
repovoamento com autóctones, tanto vegetais como animais, no interior do corpo lagunar e nas
respectivas margens.
Alguns agentes económicos consideram que é necessário e urgente o apoio e reintrodução de actividades tradicionais na laguna e em seu redor, como a pesca, apanha de
bivalves, agricultura tradicional, pastoreio, etc., menos impactantes e que traduzem redução no
desemprego em populações com baixos níveis de instrução e fracas possibilidades de
reconversão no emprego. Outros têm opinião adversa e argumentam que não se consegue esse
objectivo e simultaneamente preservar a qualidade ambiental mantendo o turismo, uso balnear
etc., havendo que fazer opções. Seria necessário promover estudos de avaliação económica dos
valores e funções ambientais presentes no sistema lagunar e, aplicar instrumentos económicos
como análise SWOT e análise custo-benefício das diversas actividades e dos seus
constrangimentos.
Finalmente é necessário encontrar o equilíbrio entre todas estas necessidades e usos do
mesmo espaço e, hierarquizá-las, de modo a possibilitar tomadas de decisão em termos de
ordenamento, servidões e incentivos e regulamentação, visto que muitas são, pela sua natureza,
incompatíveis.
Referências
Alba-Tercedor & Sánchez-Ortega, 1988. Avaliação da qualidade de um curso de água doce através da determinação do
Índice B.M.W.P, http://geographyfieldwork.com/indexda.htm.
Aubrey, D.G., Friedrichs, C.1988. Seasonal climatology of tidal non-linearities in a shallow estuary. WHOI.
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IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Consulmar – Nemus 2000. Projecto de Execução para a recuperação das Margens da Lagoa de Óbidos e Concha de S.
Martinho – Relatório Base, Estudo Prévio e projecto de Execução da Lagoa de Óbidos”, Setembro.
Farinha, J.C. & Trindade, A.1994. Contribuição para o Inventário e Caracterização de Zonas Húmidas em Portugal
Continental, Instituto da Conservação da Natureza, Dezembro.
Fortunato, A., Matos, R.S., Portela, L., Sancho, F., Oliveira, A. & Clímaco, M. 2005. Revisão do Plano de Gestão
Ambiental da Lagoa de Óbidos – Relatório 3: Plano de Intervenção – Volume 2: Dragagens e Dique de Guiamento –
Relatório 24/05, LNEC, Feveveiro.
Fortunato, A. & Oliveira, A. 2004. Promoting ebb dominance in coastal lagoons. 29th ICCM Proceedings.
Graça, H. 2004. Novos conhecimentos sobre o aquífero mineral das Caldas da Rainha. Centro Hospitalar de Caldas da
Rainha.
Munné, A., Solà, C., Bonada, M., Plans, M., Rieradevall, M. & Prat, N. 2000. QBR: un índice rápido para la evaluación de
los ecosistemas de ribera. Alquibla – Boletín Informativo de la Asociación Española de Limnología, nº 31.
Nature Conservancy Council. Site Management Plans for nature conservation – a working guide. England.
PATO, Associação de Defesa do Paúl de Tornada 2005. Área de Paisagem Protegida de Âmbito Regional da Lagoa de
Óbidos – Dossier Técnico de Candidatura à Classificação – Plano de Gestão do Espelho de Água – Versão preliminar.
Pinto, P., Graça, M., Morais, M., Formigo, N., Cortes, R., Hughes, S., Rafael, T. & Pádua, J. 2004. Método de
amostragem dos invertebrados bentónicos – Draft – 4ª versão, Janeiro.
Zbyszewski, G. & Moitinho de Almeida, F. 1960. Carta Geológica de Portugal, Notícia Explicativa da Folha 26-D de
Caldas da Rainha na escala 1:50000.
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GENERAL FRAMEWORK OF HOLOCENE SEA-LEVEL/COASTAL CHANGES
IN THE CANTABRIAN COAST (BAY OF BISCAY) (TALK)
Alejandro Cearreta
Departamento de Estratigrafia y Paleontología. Facultad de Ciencia y Tecnología. Universidad del País Vasco/EHU.
Apartado 644, 48080 Bilbao, Spain; [email protected]
The northeastern coast of Spain (named Cantabrian coast) is characterized by MesozoicCenozoic sedimentary rocks forming high cliffs interrupted by short, narrow estuaries that are
separated from the open sea by sandbars, beaches and dune deposits. The morphology and
extent of the different estuarine sedimentary environments are constantly altered by erosion and
deposition of sediments, and they are sensitive to even small changes in sea level. The Holocene
transgressive episode caused the deposition of large volumes of well preserved estuarine
sediments that can be studied to understand environmental and sea-level changes during this
interglacial.
8
7
FRANCE
45º
SPAIN
6
BAY OF BISCAY
44 º
Bordeaux
5
44º
Cantabrian Sea
1
2
3
4
Bilbao
1º
Figure 1 - Geographical location of the coastal areas referred to in the text. Key: 1-Santoña estuary; 2-Bilbao estuary; 3Gernika estuary; 4-Bidasoa estuary; 5-Aquitaine coastal dunes; 6-Arcachon bay; 7-Gironde estuary; 8-La Perroche
marsh.
Different boreholes drilled on the main estuarine environments have been studied during
recent years. In the Santoña estuary (Fig. 1), Cearreta and Murray (1996) analyzed three long
boreholes for their foraminiferal content and recognized two different upward-shallowing
sequences (near-marine intertidal to low marsh) separated by a transgressive overlap boundary
(TOB). They concluded that the relative rise of sea level appeared to be stepped rather than
smooth in that estuary. Attemps to date the TOB identified using indigenous foraminiferal tests
(Cearreta & Murray, 2000) produced unreliable results due to significant reworking of
foraminifera associated with the transgressive episode.
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The foraminiferal assemblages recorded in the sedimentary successions of several
boreholes drilled in the Bilbao estuary (Fig. 1) were analyzed by Cearreta (1998) and Leorri &
Cearreta (2004). Palaeoenvironmental interpretation of these assemblages defined the Bilbao
estuary infill as a depositional sequence within a fourth-order eustatic cycle in the sense of Vail et
al. (1991). This sedimentary sequence comprises a wide range of foraminiferal assemblage
zones (FAZ) that are organized into three systems tracts as defined by Allen and Posamentier
(1993). Each systems tract is composed of a distinct suite of FAZs separated by continuous
stratigraphic surfaces that constitute good correlation markers.
The major structure of the Bilbao estuary infill is shown schematically in figure 2. During
Lateglacial low sea-level conditions, sedimentation was represented by fluviatile gravels and
coarse sands almost barren of foraminifera (lowstand systems tract-LST). During marine
transgression (8500-3000 cal years BP), these coarse sediments were trapped in the upper and
middle estuarine areas by the landward migrating estuarine deposits, whereas in the lower
estuary former LST materials were reworked and included into this transgressive systems tract
(TST). Great volumes of mainly near-marine sediments were deposited in the lower estuary,
alternation of brackish and near-marine sediments were accumulated in the middle estuary, and
brackish materials were sedimented in the upper estuary. The final part of the TST is represented
by open-marine sediments (dominant exotic foraminifera) limited below by the tidal ravinement
surface (TRS) and above by the maximum flooding surface (MFS). The highstand systems tract
(HST) deposited during the upper Holocene (3000 cal years BP-19th century human reclamation)
represented brackish intertidal and supratidal conditions as the sedimentary infill was taking place
under stabilized sea-level.
SEA FRONT
LOWER ESTUARY
MIDDLE ESTUARY
UPPER ESTUARY
+10
+5
0
Bay
?
5
10
?
0
15
5
20
10
25
Fill
HST
TST+HST
TST
LST
Basement
30
35
LST reworked
15
20
Age (cal yrs BP)
25
8000
6000
4000
2000
Figure 2 - Sequence-stratigraphic interpretation of the Bilbao estuary Holocene deposits. Vertical lines indicate borehole
locations on the right bank of the estuary drilled during the geological study for the Bilbao Metropolitan Subway. LST:
lowstand systems tract; TST: transgressive systems tract; HST: highstand systems tract. Depth with reference to local
ordnance datum. Box represents estuarine floor depth through time. Black dots, triangles and crosses are radiocarbon
data from boreholes SM1, SM11 and SM13 respectively, located in the left bank of the lower estuary (after Leorri &
Cearreta, 2004).
27
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Pascual et al. (1998, 1999, 2000, 2001 and 2002) analyzed the sedimentological and
microfossil (foraminifera and ostracoda) content of nine short cores (maximum length 7.26 m;
basement not reached) along the Gernika estuary (Fig. 1). Here three different phases in the
infilling of this estuarine area were distinguished. The first one is characterized by a mixture of
marine and estuarine conditions dated from at least 6410±70 to 3740±60 conventional years BP.
The second phase represents a transgressive shift that took place during 3410±60 and 3250±40
conventional years BP. The final phase is marked by an active sedimentation characterized by
the filling of estuarine channels, the increase of salt marshes and a decrease in diversity of the
microfaunas.
Finally, in the Bidasoa estuary (Fig. 1), Cearreta (1994) studied the microfossil content
(foraminifera) of two long boreholes and found a comparable transgressive boundary (TOB)
separating two upward-shallowing sequences. The upper sequence shows shallowing to the
present marshes. In the lower sequence the basal deposits were radiocarbon dated to 7810±130
conventional years BP showing that the estuary was forming by then. A single date from above
the TOB gave an age of 2740±90 conventional years BP.
Different curves from the Bay of Biscay show that sea-level reached approximately its
present position at about 3000 cal years BP (Pirazzoli, 1991). The sedimentary response to this
stabilization of sea level was the turnaround from eustatic transgression to relative regression,
with deposition of estuarine materials similar to those of the underlying TST but containing
brackish and shallower foraminiferal indicators. The uppermost FAZs in the boreholes comprise
the highstand systems tract (HST). The surface between the HST and the TST represents the
maximum flooding surface (MFS). Radiocarbon dates obtained from HST materials were younger
than 2810 cal years BP. Box in figure 2 represents variation of the estuarine floor depth through
time based on radiocarbon dated samples from boreholes located in the left bank of the lower
Bilbao estuary. The topographic location of dated samples shows two different phases in the infill
process. A rapid initial phase that chronologically corresponds to the TST is followed by a second
slower phase, topographically close to datum, that represents the HST.
On the other side, the eastern area of the Bay of Biscay (known as Aquitaine coast) is
mainly a straight and continuous sandy beach backed by a coastal dune system fixed during the
19th century. These extensive dune fields formed when sand deposits on the continental shelf
were reworked during the Holocene sea-level rise. Two different generations of dunes have been
identified: primary dunes, that initiated around 3000-2300 cal years BP, and modern dunes, that
were active between 1500 and 200 cal years BP (Tastet & Pontee, 1998).
A set of short cores (basement not reached) obtained in the northern part of the Arcachon
bay (Fig. 1) allowed to recognize three filling stages in this lagoon during the last 5000 years
(Klingebiel & Gayet, 1995). Initially, marine sands and muddy intertidal sediments were deposited
between 5000 and 2500 conventional years BP, that were followed by transgressive tidal
channels filled with shelly sand sequences dated between 2600 and 1500 conventional years BP.
Finally, more restricted intertidal organic mud flats and present-day tidal channels developed.
They concluded that, on the whole, a gradual sea-level rise, having become very slow during the
last 2000 years, predominated along the Atlantic coast of France, where no reliable evidence
suggests the occurrence of a sea level higher than the present one.
Based on a compilation of core, borehole and hydrological data, Allen and Posamentier
(1993) described the lithofacies and stratal architecture of the incised-valley fill of the Gironde
estuary (Fig. 1) during the Holocene. They proposed a sequence-stratigraphic model for this
estuarine area organizing the wide range of lithofacies into three systems tracts separated by
continuous stratigraphic surfaces. No dating was presented and, consequently, this environmental
evolution was not located in time. However, following Fairbanks (1989), they considered that the
maximum flooding in the estuary was reached at about 4000 years BP. More recently, Diot &
Tastet (1995) and Pontee et al. (1997) studied the palynology and sedimentology of six short
vibration cores (maximum depth 7.7 m; basement not reached) showing the progressive infilling
of tributary tidal channels in the lower estuary of Gironde (Medoc peninsula) during the last 6700
years. They concluded that this area became a continental marsh during the last 2000 years,
following the formation of a transgressive shelly ridge (named Cordon de Richard). This
28
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
calcareous deposit is composed of sand, pebbles and shells, and it was dated at 2575±120 and
1421±162 conventional years BP.
Observations from the inner shelf (around 50 m water depth) adjacent to the mouth of the
Gironde estuary showed that mud deposition on that area began around 2000 cal years BP
(based on radiocarbon dating and palynological analyses, in Lesueur et al., 1996), illustrating that
fluvial sediments from the Gironde began to reach the continental shelf at that time (Lesueur et
al., 2002).
Finally, the sediment and microfossil (ostracoda) content of the Holocene sequence in the
La Perroche marsh (Fig. 1) was studied by Clavé et al. (2001) by means of eight long boreholes,
that showed the progressive marine invasion of the area containing a final transgressive event
dated between 3600 and 2100 cal years BP. This event was correlated with the Richard-shelly
ridge and interpreted as an episode of rising sea level or/and increased storminess. After 2100 cal
years BP the definitive isolation of the marsh occurred, and extensive peat developed suggesting
a final period of stable sea level.
Origin of main sea-level variations may be found both in the global eustatic motion, like the
Holocene rise due to deglaciation during the last 10000 years, or in local subsidence or uplift of
the continental margin, due to tectonic activity related to plate movements (Klingebiel and Gayet,
1995). Although neotectonic uplift movements have been invoked to explain aspects of the
evolution of the southern Bay of Biscay margin during the Neogene and Pleistocene (Mary, 1983),
unfortunately, no research on Holocene neotectonics has been undertaken so far in this region.
However, on the Aquitaine coast, tectonic subsidence contribution to the transgressive trend has
been evaluated in the order of 0-0.7 mm year-1 (Klingebiel & Gayet, 1995). Hence, significant
interferences between eustatic and tectonic vertical movements may have occurred in the Bay of
Biscay during the Holocene.
Consequently, it can be concluded that different coastal sedimentary sequences and
radiocarbon datings obtained during recent years from the Bay of Biscay indicate that, following
postglacial sea-level rise, modern estuaries in the region began to develop around 8500 cal years
BP. Furthermore, a final transgressive event was dated at around 3000 cal years BP when sea
level reached approximately its present position after a second upward-shallowing sequence
commenced.
Exploitation of abundant local iron ore led to the early industrial development of the
Cantabrian coast, in the mid-19th century. As a consequence, the original estuaries were reduced
rapidly in size, through land reclamation, to form tidal channels as navigable watercourses;
likewise, to provide space for urban, industrial and port developments. Furthermore, during the
last 150 years, the Cantabrian estuaries have received wastes from many sources (mineral
sluicing, industrial wastes and urban effluents); these have degraded, significantly, their
environmental quality (Cearreta et al., 2000). Records of environmental change are often
preserved in sediments obtained from sub-tidal and inter-tidal mudflats and salt marshes. Study of
these sediments allows an assessment to be made of the scale of pollutant inputs, from past
industrial and urban development.
Cearreta et al. (2000) have examined the recent history of pollution in the Bilbao estuary.
Geochemical data and benthic foraminifera from surface sediment samples and sediment cores,
collected from the highly polluted intertidal flats, were investigated. 210Pb and 137Cs determinations
were also undertaken, to provide a chronology for the pollutant inputs and ecological changes in
the Bilbao estuary. The sediment characteristics, geochemistry and foraminiferal content of
surface and cored samples have indicated clearly that the environmental conditions in the area
have been degraded heavily, over at least the past 40 years. Other indirect evidence of this longlasting pollution impact, on the estuarine environment, was the absence of bioturbation
throughout the short cores.
In order to study the complete industrial record of the Bilbao estuary, Cearreta et al. (2002)
used benthic foraminiferal assemblages and geochemical data; these were contained in long
sediment cores, collected from the highly polluted intertidal flats. Sediment cores, from 6 to 10 m
in length, were taken from six intertidal areas, throughout the estuary. The composite results
obtained from microfaunal and geochemical proxies reflect a long lasting record of anthropogenic
inputs, which have led to the disappearance of the indigenous microfauna and to the significant
29
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
pollution of the sediments. Three different zones could be identified in the recent sedimentary
record (Fig. 3), reflecting initially the pre-industrial estuarine conditions with abundant and diverse
foraminiferal assemblages and baseline levels of metals, followed by the industrial-period
sedimentary record, when high concentrations of metals in the estuarine environment allowed the
development of abundant foraminiferal assemblages during the older industrial zone (period
1850-1950) that disappeared during the younger industrial zone (period 1950-2000) due to
complete defaunation of the Bilbao estuary caused by minimum oxygen levels during this period.
Obtained data provide important information in planning the restoration of the Bilbao estuary,
because sediments have proven to be an important storage reservoir for pollutants and
microfossils.
BILBAO ESTUARY PERCUSSION CORES
LOWER ESTUARY
Gobelas
UPPER ESTUARY
Simondrogas
Galindo
Erandio
Asua
NR
NR
Zorroza
+2
+1
NR
NR
0
1
2
NR
3
4
5
6
7
Industrial without
microfauna
8
Industrial with
microfauna
Pre-industrial
9
Figure 3 - Environmental interpretation of the recent Bilbao estuary percussion cores based on the combination of
microfaunal and geochemical data. N.R.= not recovered (after Cearreta et al., 2002).
References
Allen, G.P. & Posamentier, H.W. 1993. Sequence stratigraphy and facies model of an incised valley fill: The Gironde
Estuary, France. Journal of Sedimentary Petrology 63: 378-391.
Cearreta, A. 1994. Análisis micropaleontológico e interpretación paleoecológica del relleno sedimentario holoceno en el
estuario del Bidasoa (Golfo de Bizkaia). Geobios, 27: 271-283.
Cearreta, A. 1998. Holocene sea-level change in the Bilbao estuary (north Spain): foraminiferal evidence.
Micropaleontology, 44: 265-276.
Cearreta, A., Irabien, M.J., Leorri, E., Yusta, I., Croudace, I.W. & Cundy, A.B. 2000. Recent anthropogenic impacts on the
Bilbao estuary, northern Spain: geochemical and microfaunal evidence. Estuarine, Coastal and Shelf Science, 50: 571592.
Cearreta, A., Irabien, M.J., Leorri, E., Yusta, I., Quintanilla, A. & Zabaleta, A. 2002. Environmental transformation of the
Bilbao estuary, N. Spain: microfaunal and geochemical proxies in the recent sedimentary record. Marine Pollution
Bulletin, 44: 487-503.
30
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Cearreta, A. & Murray, J.W. 1996. Holocene paleoenvironmental and relative sea-level changes in the Santoña estuary,
Spain. Journal of Foraminiferal Research, 26: 289-299.
Cearreta, A. & Murray, J.W. 2000. AMS 14C dating of Holocene estuarine deposits: consequences of high-energy and
reworked foraminifera. The Holocene 10: 155-159.
Clavé, B., Massé, L., Carbonel, P. & Tastet, J.-P. 2001. Holocene coastal changes and infilling of the La Perroche marsh
(French Atlantic coast). Oceanologica Acta, 24: 377-389.
Diot, M.-F. & Tastet, J.-P. 1995. Paleo-environnements holocenes et limites chrono-climatiques enregistres dans un
marais estuarien de la Gironde (France). Quaternaire, 6: 63-75.
Fairbanks, R.G. 1989. A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger
Dryas event and deep-ocean circulation. Nature, 342: 637-642.
Klingebiel, A. & Gayet, J. 1995. Fluvio-lagoonal sedimentary sequences in Leyre delta and Arcachon bay, and Holocene
sea level variations, along the Aquitaine coast (France). Quaternary International, 29/30: 111-117.
Leorri, E. & Cearreta, A. 2004. Holocene environmental development of the Bilbao estuary, northern Spain: sequence
stratigraphy and foraminiferal interpretation. Marine Micropaleontology, 51 : 75-94.
Lesueur, P., Tastet, J.-P. & Marambat, L. 1996. Shelf mud fields formation within historical times: examples from offshore
the Gironde estuary, France. Continental Shelf Research, 16: 1849-1870.
Lesueur, P., Tastet, J.-P. & Weber, O. 2002. Origin and morphosedimentary evolution of fine-grained modern continental
shelf deposits: the Gironde mud fields (Bay of Biscay, France). Sedimentology, 49: 1299-1320.
Mary, G. 1983. Evolución del margen costero de la Cordillera Cantábrica en Asturias desde el Mioceno. Trabajos de
Geología 13: 3-35.
Pascual, A., Weber, O., Rodríguez-Lázaro, J., Jouanneau, J.-M. & Pujos, M. 1998. Le comblement de la ria de Gernika
(golfe de Gascogne) à l’Holocène terminal. Oceanologica Acta 21: 263-269.
Pascual, A., Weber, O., Caballero, F., Rodríguez-Lázaro, J. & Jouanneau, J.-M. 1999. Análisis integral
(micropaleontología y sedimentología) de un sondeo supramareal Holoceno en la ría de Gernika (Golfo de Vizcaya).
Geogaceta, 26: 75-78.
Pascual, A., Weber, O., Rodríguez-Lázaro, J. & Jouanneau, J.-M. 2000. Evolución sedimentaria del pólder Anbeko
(Reserva de Urdaibai, Golfo de Vizcaya) durante el Holoceno. Geogaceta, 28: 113-116.
Pascual, A., Rodríguez-Lázaro, J., Weber, O. & Jouanneau, J.-M. 2001. Cambios paleogeográficos durante el Holoceno
en las marismas de Forua, Reserva de la Biosfera de Urdaibai. Geogaceta, 30: 191-194.
Pascual, A., Rodríguez-Lázaro, J., Weber, O. & Jouanneau, J.-M. 2002. Late Holocene pollution in the Gernika estuary
(southern Bay of Biscay) evidenced by the study of Foraminifera and Ostracoda. Hydrobiologia, 475/476: 477-491.
Pirazzoli, P.A. 1991. World Atlas of Holocene Sea-Level Changes. Elsevier, Amsterdam, 300p.
Pontee, N.I., Tastet, J.-P. & Massé, L. 1997. Morpho-sedimentary evidence of Holocene coastal changes near the mouth
of the Gironde estuary and on Médoc peninsula, S.W. France. Guide of the Fieldmeeting on Holocene coastal changes
in the Aquitaine region, relationships with human settlements, Bordeaux.
Tastet, J.-P. & Pontee, N.I. 1998. Morpho-chronology of coastal dunes in Médoc. A new interpretation of Holocene dunes
in Southwestern France. Geomorphology, 25: 93-109.
Vail, P.R., Audemard, F., Bowman, S.A., Eisner, P.N. & Perez-Cruz, C. 1991. The stratigraphic signatures of tectonics,
eustacy, and sedimentology-an overview. In: Einsele, G., Ricken, W., Seilacher, A. (Eds.), Cycles and Events in
Stratigraphy. Springer-Verlag, Berlin, 617-659.
31
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
3D FACIES ARCHITECTURE AND DYNAMICS OF A BEACH BARRIERLAGOON COMPLEX (RÍA DE VIGO, GALICIA, SPAIN) (POSTER)
F. Clemente, Marta Pérez-Arlucea, Irene Alejo, Miguel Ángel Nombela, D. González, Susana
Costas, Patricia Bernárdez, R. González & Rita González Villanueva
Dpto. Xeociencias Mariñas y O.T. Facultade de Ciencias, Universidade de Vigo. 36.200 Vigo, Spain; [email protected];
[email protected]; [email protected]
Tidal-fluvial estuarine processes and interactions have been studied by monitoring tidal
stages, current velocities, river discharges, water slopes, grain size, and transport rates during
several tide cycles in the beach barrier-lagoon complex located in A Ramallosa. The sedimentary
complex is located in Baiona Bay, at the southeast corner of the Ria de Vigo. The beach barrier
(Playa Ladeira) is a north-south, 800 m long and 88-120 m wide feature, located to the west of the
complex. Behind the beach barrier a 0.88 km2 intertidal flat is developed. Three rivers enter the
complex toward the north and east, the Miñor, Groba and Guillade-Belesar. All of them merge
and connect to the open sea by a narrow inlet located to the south. An ebb tidal delta is
developed at the mouth. Tidal range is mesotidal (2-5 m). During high tides the complex evolves
to a shallow lagoon, flooding about 90% of the complex in average tides. Tidal deposits consist of
sub to intertidal sand flats and mid-channel ramps, mixed intertidal mud-sand flats and intertidal to
supratidal marshes.
The Minor River has a single, 22 m wide, meandering channel at the upstream reach.
Further downstream, about 3 km from the coast, it develops into an estuary entering the
Ramallosa Complex from the north. The estuarine reach shows a fairly straight, 54 m wide
channel with several alternate
bars evolving downstream to
a
multi-channel
braided
system where mid-channel
bars
and
tidal
ramps
dominate. The Groba River is
a moderately sinuous channel
about 9 m wide at the
upstream reach. It enters the
complex on the southern
margin showing a discrete
anastomosing
pattern.
Individual channels are about
35 m wide. The Minor and the
Groba rivers merge close to
the narrow outlet located at
the north end of the beach
(Ladeira). Current velocities
and current directions have
been recorded in 0.02 to 0.10
Figure 1 - Digital elevation model for the Ramallosa beach barrier-lagoon
m flow cells across the entire
complex. 1 Miñor River entry; 2 Groba River and inner marshes; 3. Ebbriver and estuarine sections
tidal delta and 4. Tidal ramps in the Miñor estuary area.
with a 4 beam acoustic
Doppler profiler. River discharges and tidal flow have been established at several points along the
rivers and tidal inlet at different tidal stages to establish tide influence along the rivers. Tide curves
have been recorded at 3 locations over 90 hours at 5’ intervals with pressure transducers. Fluvial
discharges and stage fluctuations were obtained over several years to construct a rating curve.
Measured fluvial discharges obtained at the Miñor and Groba Rivers were 0.57 m3s-1 and 0.14
m3s-1, very low values in relation to average figures obtained for the Miñor (2.7 m3s-1 during 97-98
and 6.7 m3s-1 during 2000/2001; Pérez-Arlucea et al., 2005).
Transport conditions have been calculated for both flood and ebb currents in estuarine
channels and intertidal areas. Transport rates have been directly measured with Helley Smith
32
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
sediment traps. Fluvial currents showed extremely low stages and flow regime over the current
year, so the present conditions show the minimum possible fluvial influence in the intertidal areas.
Even under these conditions grains can be
transported in and out of the complex by
fluvial and tidal currents. Tidal currents
flood and ebb through a 50 m wide inlet
into the inner intertidal area, causing a
funnel effect. Flood tidal currents show
maximum velocities of 0.95 m.s-1 and ebb
currents of 0.89 m.s-1. Calculated flow
competence indicates movements of
sedimentary particles up to 8 mm, which
accumulate on an ebb tidal delta. Flood
currents allow 10 mm particles to move
and accumulate in tidal ramps in the
intertidal areas. Sediment transport values
obtained with Helley-Smith sediment traps
gives values from 0.01 to 0.4 kg m-1s-1,
Finally,
a
model
for
tide
distributions has been generated from a
DEM obtained with a Nikon DTM-330
Total Station (Fig. 2). About 90% of the
complex interior is located in the intertidal
area. Facies distributions show sand
dominated environments toward the west
and north (estuaries, sand flats and tidal
Figure 2 - Tide flood model (0.20 m intervals).
ramps) and inner vegetated marshes
toward the east (muddy sand and fine
sands). From the digital topographic model and sediment distribution maps a threshold for mud
deposition have been established for the sedimentary complex at about 2.0-2.5 m of elevation.
1.8m
2.4m
3.0m
1.4m
1.6m
2.0m
2.2m
2.6m
2.8m
3.2m
3.4m
Acknowledgements
This research work has been possible thanks to grants from OMA (Universidade de Vigo) and projects: UNESCO IGCP464, CO-085-03 (Xunta de Galicia) y REN2003-09394/MAR (MCYT).
References
Méndez, G.; Pérez-Arlucea, M.; Stouthammer, E. and Berendsen, H. 2003. The TESS-1 suction corer: a new device to
extract wet, uncompacted sediments. Journal of Sedimentary Research, 373:1078-1081.
Pérez-Arlucea, M.; Méndez, G.; Clemente, F.; Nombela, M.;Rubio B. and Filgueira M. 2005. Hydrology, sediment yield,
erosion and sedimentation rates in the estuarine environment of the Ria de Vigo, Galicia, Spain. In: A general study of
the Spanish North Atlantic boundaries: an interdisciplinary approach. Journal of Marine Systems, Spec. vol. 54, 209226
33
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
ANTHROPOGENIC AND LITHOGENIC CONTINENTAL EVIDENCES ON THE
COMPOSITION OF SHELF SEDIMENT CORES FROM SW IBERIA (TALK)
Catarina Corredeira1, Maria de Fátima Araújo1, A. Gouveia1 & Jean-Marie Jouanneau2
1
2
QAA, Química, Instituto Tecnológico e Nuclear, E.N. 10, 2686-953 Sacavém; [email protected], [email protected]
DGO-UMR 5805 CNRS, Université Bordeaux I, Av. des Facultés, 33405 Talence Cedex, France
Introduction
The Guadiana River basin flows westward
through southcentral Spain and southeastern
Portugal to the Gulf of Cadiz and the Atlantic Ocean
(Fig. 1) draining an arid mining area (Iberian Pyrite
Belt). In the Southwest Iberian Peninsula mining
activities have been developed since prehistoric
times and an industrial exploitation is reported at
least since the Roman Period. In this paper we
investigate the spatial and temporal elemental
distribution patterns in shelf sediment cores
collected at the fine deposits adjacent to Guadiana
estuary. Our aim is the determination of the
influence of the sediment load carried by the
Guadiana river basin (influenced by lithology,
anthropogenic and mining activities) into the
continental shelf marine environment as well as the
understanding of sedimentation processes and
sources of shelf sediments.
Figure 1 – Sediment cores location.
Methology
Three sediment cores (~3-4 m long) were collected with a vibro-corer at the Iberian
Continental Shelf (12 – 92 m bathymetric lines) during the cruise CRIDA 07/02 in July, 2002.
Chemical analyses were carried out in selected fractions by Energy Dispersive X-Ray
Fluorescence Spectrometry (EDXRF) and Instrumental Neutron Activation Analysis (INAA). The
selected fractions were chosen according to the core granulometric description. The detailed
methodology has been described elsewhere (Araújo et al., 2002).
Core 1
Core 8
Core 5
34
Depth (cm)
Depth (cm)
Depth (cm)
Results and discussion
Cu/Al
Cu/Al
To assess the extent of
Cu/Al
0
5 10 15 20
0
5 10 15 20
0
5
10 15 20
anthropogenic contamination, metal
0
0
0
20
20
20
concentrations were normalised
40
40
40
60
60
60
against a conservative element (Al),
80
80
80
100
100
100
figure 2. The upper layers of
120
120
120
140
140
140
160
sediments are clearly heavy metal
160
160
180
180
180
200
200
enriched (Pb also exhibits a similar
200
220
220
220
240
240
behaviour). These enhanced values
240
260
260
260
280
280
280
are certainly due to anthropogenic
300
300
300
320
C u/Al
320
320
C u/Al
sources, particularly the mineral
C u/Al
340
340
340
Zn/Al
Zn/Al
360
360
Zn/Al
360
wastes of mining activities and
380
380
380
0 10 20 30 40 50
0
10
20
30
40
50
0 10 20 30 40 50
industrial plants as a result of the
Zn/Al
Zn/Al
Zn/Al
ore exploitation carried out along the
Iberian Pyrite Belt. In cores 1 and
Figure 2 – Cu and Zn normalised distribution patterns.
5 this enrichment/contamination
reaches ~ 40 cm of the core depth, although in core 1 a sudden increase is measured at about 80
cm depth. This increase might be due to a, until now, non identified event. In core 8, levels of
pollution are slightly higher and reach much deeper layers, the geochemical background is
reached at ~80 cm depth. It is worth to note, that core 8 is located closer to the coastal area, in a
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
different fine sedimentary deposit, in which the deposition rates are much higher (preliminary
experiments revealed that excess of 210Pb was still found down to the 30 cm). The value of the
sedimentation rate determined by the same method for core 5 was 0.12 cm/yr.
The ES–normalised REE results are rather similar for all the cores (Fig. 3). The (La/Yb)n
have a consistent value of about
0.9, indicating a slight HREE’s
REE
enrichment. The ∑REE for the three
sediment cores is depleted to shale
2
(∑REE shale = 204.0; ∑REE Core 1
1.6
= 131.8; ∑REE Core 5 = 138.4;
Core 1
1.2
∑REE Core 8 = 138.4). This
Core 5
0.8
depletion, can be attributed to a
Core 8
dilution with carbonated enriched
0.4
sediments
in
the
area
(~
0
Ca=6.1%).The
Mediterranean
La Ce
Nd
Sm Eu
Tb
Yb Lu
characteristics present in the SW
Figure 3 – REE normalised distribution patterns.
Iberian Continental shelf seems to
favour a much higher biological
productivity. The common negative Eu-anomaly is not observed in the three analysed cores (Fig.
3). This unusual behaviour is probably associated with the volcanic rocks present in the drainage
basin (Munhá, 1983 in Oliveira, 1992).
Conclusions
Shelf sediments adjacent to Guadiana estuary show an important continental contribution,
which is stronger in the sediment cores located closer to the coastline. However, we also note
that core 8 may be influenced by the longshore drift, following W-E along the coast. The heavy
metal (e.g. Cu, Zn, Pb) enrichment determined for the upper layers of the three studied sediment
cores indicate a continental contaminated source due to the mineral wastes of mining activities
and industrial plants of the ores exploitation along the Iberian Pyrite Belt. Contaminated
sediments have been transported, probably by Guadiana river and the anthropogenic signatures
at the shelf sediments seem to be able to last for several centuries. The absence of the common
negative Eu-anomaly, and the depletion in ΣREE observed in the three analysed cores differ of
that observed for shelf sediments, influenced by large river basins along the Iberian coastal area
(Araújo et al., 2002, Araújo et al., in press). Thus the continental influence on the shelf is also
detectable by the REE distribution patterns.
Acknowledgements
The present work is a contribution of the project (CRIDA) - PLE/8/00 C. Corredeira thanks the FCT-Portugal for the
doctoral grant (BD/14144/2003).
References
Araújo, M.F., Corredeira, C., Gouveia, A. in press. Rare Earth Elements Distribution in Sediments of the Northwestern
Iberian Continental Shelf. Journal of Radioanalytical and Nuclear Chemistry.
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias,
J.M.A. 2002. Geochemical Tracers of Northern Portuguese Estuarine Sediments on the Shelf. Progress in
Oceanography, 52 (2-4): 277-297.
Oliveira, J.T. 1992. Carta Geológica de Portugal (1/200000) – Notícia explicativa da folha 8, Serviços Geológicos de
Portugal, Lisboa, 91p.
35
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THE EVOLUTION OF A RETROGRADING SAND BARRIER AT CÍES
ISLANDS (NW IBERIAN PENINSULA) (TALK)
Susana Costas1, Irene Alejo2, Fernando Rial3, Henrique Lorenzo4 & Miguel A. Nombela5
1,2,5
Dpto. Xeociencias Mariñas e O.T. Facultade de Ciencias do Mar, Universidade de Vigo. 36310 Vigo;
[email protected]; [email protected]; [email protected].
2,4
Dpto. Enxeñería dos Recursos Naturais e Medio Ambiente, Universidade de Vigo. Campus A Xunqueira s/n. 36005 4
Pontevedra; [email protected]
3
[email protected]
Barriers are dynamic and ephemeral constructions changing as they are modified by
waves, winds and water currents. In this sense, retrograding barriers are the youngest of these
coastal sedimentary environments. These barriers are controlled by storm overwash and tidal
inlet deposition, and are associated with coastal recession. Here we present an example of a
retrograding sand barrier located at the NW Coast of the Iberian Peninsula. The internal structure
and the recent evolution of this barrier are analysed in detail using ground penetrating radar
(GPR) and geo-rectified aerial photographs to investigate accretion/recession trends and rates at
this coastline sector.
Following the criteria proposed by Bristow (1995) and Bristow et al. (2000) we identified
four different radar facies, which were related to specific sedimentary regimes: 1) Radar Facies
Washover Sheet (RWS), characterized by sub-horizontal reflectors gently dipping landward, 2)
Radar Facies Washover Delta (RWD), characterized by high angle reflectors dipping landward, 3)
Radar Facies Beach Face (RBF), characterized by high angle reflectors dipping seaward, 4)
Radar Facies Barrier Top (RBT), characterized by sub-horizontal reflectors indicating transition
from the beach to the backbarrier environment (Fig. 1).
Figure 1 - a) Crosshore GPR profile T7 from beach face to the backbarrier. b) Interpretation of the profile radar
stratigraphy including the succession of radar facies and discontinuity surfaces.
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From the beach towards the lagoon, the barrier presents a gradual succession of the radar
facies. On the other hand, the vertical radar facies succession is controlled by an erosive
bounding surface resulting in a discordant bounding that separates RWS and RBF, so beach
deposits overlap washover deposits (Fig. 1). This discordant succession of radar facies indicates
that the barrier is migrating landward due to the advance of the beach face over washover
deposits.
Aerial photo analysis, covering the period from 1956 to 2003 indicates that the evolution of
the studied feature is non linear. From 1956 to 1985 the barrier experienced erosion and the
shoreline retreated around 25 m. Maximum landward retreat was recorded in 1985. The position
of the shoreline in this year coincides with the location of the discordant bounding surface in GPR
profiles. From 1985 to 2003, the barrier presented a prograding trend, with seaward advance of
the primary foredune. This reversal in the migration trend of the shoreline is recorded in GPR
profiles as a seaward advance of the beach face.
Taking into account these results it was possible to develop an evolutionary model
describing the behavior of the sand barrier throughout the last decades. In this sense, the barrier
displayed a cyclical evolution in spite of net shoreline retreat during the studied period. The
reversal of the evolution trend coincides with the sharp change in the North Atlantic Oscillation
index (NAO) around the mid-1970s, from negative towards positive phase (Hurrel, 1995). On the
other hand, the shoreline retreat rate observed at the studied area for the period between 1956
and 2003 was one order of magnitude higher than the expected using the approximation of the
Brunn Rule (Bruun, 1954). The approximation takes into account the eustatic sea level rise, which
was measured at Ría de Vigo tide gauge from 1942 to 2001 (2.91 mm/yr, Marcos et al., 2005),
and the mean beach face slope (β = 6º). These differences could be explained by the
combination of two factors: (1) sand mining activities carried out in the studied barrier during fifties
and sixties, and (2) the present negligible sediment input towards the sedimentary complex, which
could have enhanced the effect of erosion at the study area increasing the observed retreat rate.
Acknowledgements
This research work has been possible thanks to grants from OMA (Universidade de Vigo) and projects: UNESCO IGCP464, CO-085-03 (Xunta de Galicia) y REN2003-09394/MAR (MCYT).
References
Bristow, C.S. 1995. Facies analysis in the Lower Greensand using ground-penetrating radar. J. Geol. Soc. London, 152:
591-598.
Bristow, C.S., Chroston, P.N. & Bailey, S.D. 2000. The structure and development of foredunes on a locally prograding
coast: insights from gound-penetrating radar surveys, Norfolk, UK. Sedimentology, 47: 923-944.
Hurrel, J.W. 1995. Decadal trends in the North Atlantic Oscillation and relationships to regional temperatures and
precipitations. Science 269: 676–679.
Marcos, M., Gomis, D., Monserrat, S., Álvarez, E., Pérez, B. & García-Lafuente, J. 2005. Consistency of long sea-level
time series in the Northern coast of Spain. Journal of Geophysical Research, 110:, C03008,
doi:10.1029/2004JC002522.
37
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
THE LAST DEGLACIATION IN COSTAL SETTING OF SOUTHERN SPAIN
(TALK)
Cristino J. Dabrio
Departamento de Estratigrafía and Instituto de Geología Económica-CSIC, Universidad Complutense, 28040-Madrid,
Spain; [email protected]
In collaboration: C. Zazo, J.L. Goy, T. Bardají, F. Borja, A. Cabero, B. Ghaleb, C. Hillaire-Marcel, J. Lario, N. Mercier, E.
Roquero, P.G. Silva
Introduction
The onset of the worldwide rise of sea level following the Last Deglaciation was recorded in
coastal and coastal-related sedimentary environments of southern Spain by diverse
morphostratigraphic units. Some of these environments evolved from terrestrial to marine or
estuarine, but others were never drowned and persisted as terrestrial, although in a more
proximal position. Changes in aridity and vegetal cover largely controlled the sedimentary supply
to the coastal areas, and a substantial part of the record occurs under aeolian facies.
This review presents updated results from aeolian coastal dunes and alluvial fans,
estuarine and peat bog deposits, and a coastal plain in the almost-tideless Mediterranean coast,
each of which illustrates a part of the dramatic events that accompanied the shift from glacial to
interglacial conditions. It is the result of various projects involving many Institutions and
researchers.
Material and methods: proxies
The present study is supported by morphostratigraphic studies including geological
mapping based on aerial photographs at various scales, sedimentary facies analysis,
palaeocurrent measurements and soft-sediment deformation features, analyses of paleosols,
palaeontological and neotectonic features, subsurface data from hydrological drillings,
radiocarbon measurements (AMS, conventional), and Optically Stimulated Luminescence (OSL).
Aeolian and Alluvial realms: Abalario and Barbate-Trafalgar
The Abalario area is a morphological dome elongated in a NW–SE direction that separates
the Neogene Guadalquivir basin from the Atlantic Ocean. The 28 km-long Asperillo cliff exposes
the internal structure of the dome including a record of the last 130Kyr. A major
morphosedimentary element in the area is the sin-depositional Torre del Loro gravitational fault
(TLF). Its downthrown block trapped aeolian sediments and laterally discontinuous sand layers
rich in organic matter. Three units (U1 to U3) were identified which, according to radiocarbon and
OSL ages ,and regional geological data, accumulated during the last part of the Last Interglacial
period (U1), Last Glacial (U2) and Last Deglaciation- earliest part of Holocene (U3).
Sedimentation of aeolian unit 3 (U3) took place during the Last Deglaciation (16–12 kyr cal
BP, radiocarbon and OSL ages), under humid conditions that evolved towards arid conditions as
demonstrated by mud–cracking of organic layers found at the upper part of the unit, and dated as
13,870–11,950 kyr cal BP, suggesting that such arid climate may represents the Younger Dryas
event.
A surface enriched in iron oxide fossilizes the fault trace sealing the two fault blocks. This
supersurface developed in OIS 1 during the Holocene Climatic Optimum, coinciding with a moist,
temperate climate (9 kyr cal BP–6.5 kyr cal BP).
Younger semi–mobile and mobile aeolian dunes (U4, U5 and U6) accumulated mostly after
the Middle Holocene covering the supersurface and growing to topographic elevations above 100
m. The mobile dunes record a general trend to aridity that began ca. 5 kyr cal BP. A remarkably
arid event occurred at ca. 2.7 kyr cal BP marked by the beginning of accumulation of aeolian U5
and progradation of the emergent spit bars at estuary mouths.
Along the Trafalgar-Barbate littoral alluvial sedimentation recorded more humid conditions
during the Last Deglaciation. A marked arid period occurred at about 9-8 kyr cal BP triggered
alluvial sedimentation inactivity.
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The Present Interglacial in this coast includes five to six aeolian systems since 8 kyr cal BP
accumulated under prevailing south-westerly winds and more arid conditions, which increased in
the last 700-800 yr. Besides, multidisciplinary studies in aeolian facies allowed exploring the
feedback relationships among sea-cliff generation, sea-level changes, sea-cliff degradation and
the consequent succession of littoral landscapes over time.
The estuarine realm: Odiel-Tinto and Guadalete
The interpretation of the Late Pleistocene and Holocene evolution of the estuaries in the
Gulf of Cadiz is based on drill cores, logs, trenches, and scores of radiocarbon data, and the
results compared with the shelf. The paleo-Odiel, Tinto and Guadalete Rivers incised coarsegrained deposits of supposed IS 3 during the last main lowstand at ca 21 kyr cal BP, when sea
level dropped to 120 m and the coastline lay 14 km seawards from the present. The resulting
erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise,
overlain by the valley fill deposits of the transgressive and highstand phases of the last fourthand fifth-order depositional sequences recognised in the shelf. The first marine influence in the
estuaries during the transgression was detected in drill cores 25-30 m below present sea level, at
ca 10,000 years BP. According to fossil assemblages, the transgressed basins changed from
brackish to more open marine as the sea rose until ca 6500 years BP, when it reached the
maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy
central basins. Then, the rate of eustatic rise decreased drastically, and the estuarine filling
followed a two-fold pattern governed by the progressive change from vertical accretion to lateral
centripetal progradation. Isolated layers of somewhat coarser, more marine sediments found in
Doñana estuary may represent episodes of high energy related to tsunamis.
At ca 4000 years BP the fluvial input surpassed the already negligible rate of rise, causing
partial emergence of tidal flats and spit barriers in the largely filled estuarine basins. Prevalence of
coastal progradation upon vertical accretion at ca 2400 years BP caused accelerated expansion
of tidal flats and rapid growth of the sandy barriers. Further changes since the 16th century reflect
widespread anthropic impacts.
Beach ridge complexes
1-Mediterranean: Roquetas (Almeria)
Six units (H1 to H6) have been distinguished in the prograding beach-ridge complex of
Campo de Dalías (Almería) since 7400 yr cal BP. H-units are deposited during periods of high
relative sea level and increased sediment input to the coast. They are bounded by large swales or
erosional surfaces associated with lower sea levels and reduced input of sediment to the coast;
these correspond to short periods of increased aridity inside the general arid trend recorded in the
Western Mediterranean since 5.4 kyr. Changes in the flux of Atlantic superficial waters into the
Mediterranean Sea, and relative strength of the W/SW winds account for the recorded oscillations
of relative sea level.
The deposition of a beach-ridge and the adjacent swale follows a decadal periodicity that is
very likely related to fluctuations of the North Atlantic Oscillation (NAO) index and to variations of
solar activity. The quasi-millennial periodicity duration of H units is punctuated by short (hundred
years) episodes of reduced progradation or erosion that represent events of increased aridity
likely to be related to Bond´s Holocene cold events.
2-Atlantic- Doñana (Huelva)
Two exposed H units, H5 and H6 (see Mediterranean nomenclature) separated by a very
large swale were generated since 2 kyr cal BP. Strong erosives processes recorded between
650-675,450-500, and at 350 yr cal BP are interpreted as storm periods under SW winds
intensification.A periodicity of 50 yr for 4 beach-ridges generation has been deduced based on
radiocarbon and archaeological data. Periods of increasing aridity occurred at 1.3 kyr cal BP, and
ca 1.0 kyr cal BP, the older maybe related to 1.38 kyr cal BP cold Bond event.
Acknowledgments
Research financed by Projects: BTE2002-1691, BTE2002-1065.
39
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PALEOENVIRONMENTAL DEVELOPMENT OF THE QUIAIOS DUNES, BEIRA
LITORAL, PORTUGAL (POSTER)
Randi Danielsen
Universidade do Minho, Braga / Laboratório de Paleoecologia e Arqueobotânica (IPA-Programa CIPA), Lisboa;
[email protected]
The coastal region between Cape Mondego and Mira is characterized by its large plain of
Holocene sand dunes. A string of shallow lakes is found at the transition between young
transverse E-W oriented dunes to the west and the Gândara plain with Pleistocene dunes to the
east (Carvalho, 1964). The western dunes are believed to have formed since 3000 BP by a
progradation of the coast 6-7 km due to the groyne effect provided by the natural promontory of
Cape Mondego (Noivo, 1996, Dias et al. 1997). These dunes have, since the beginning of the 20th
Century, been afforested and today support a large pine forest dominated by Pinus pinaster. Little
is known about the past vegetation cover. Different theories about the development of the region
in what concern past vegetation changes, genesis of the lakes, coast line dynamics and dune
systems, have been proposed, but are diverging.
The current palynological investigation of some of these lakes is intended as a contribution
to a wider understanding of the evolution of the region. Cores from two lakes (Lagoa da Vela and
Lagoa das Braças) and a dried out paleolake (Terra de Areia) have so far been analyzed for
pollen, algae and other microfossils. The length of the lake cores are ca 80 cm. The core from the
paleolake is ca 3 m. An iron pan (surraipa) below the bottom sand layer, is probably a truncated
podzol encountered in large sections of the Gândara region and dated to 3160 – 1650 BP (Granja
et al., 1996). No 14 C-datings are yet available for the cores. The iron pan found inside the lakes
indicates their formation to post-podzol.
The pollen and microfossil content at the base of the cores reflect open scrub vegetation
dominated by Erica umbellata and E. scoparia initially with a relatively high content of Cistacea
spp. like Halimium halimifolium. Extremely low values of arboreal pollen (< 5%) indicate that
forest vegetation in the region was scarce. Pinus and Quercus are the only representatives of the
regional arboreal pollen. Around the lakes a riparian zone containing Alnus existed. The
Ericaceae heath land predominated until the time of the planting, but with fluctuations between
the different species. Corema album becomes dominant before and during the planting period.
In the lakes the afforestation level is found at around 30 cm below sediment surface. In the
paleolake, however, it appears at around 80 cm below surface. Here a layer of aeolian sand
above indicates that some sand movement occurred even after the establishment of the pine
forest. In all the cores the percentages of Pinus pollen rapidly increases from ca 0.5% to ca 50%
at this level. Pollen grains from exotic trees like Eucalyptus, Acacia, Platanus and Casuarina
appear and agricultural indicators like Zea mays, Triticum sp., Secale cereale and Olea europaea
become abundant. An eutrophication trend can be detected through changes in the algal flora.
The quantity and diversity of algae increase after the afforestation.
There are different theories concerning the formation of the lakes. Noivo (op. cit.) defines
them as remnants of an old marshy littoral zone. Almeida (1995), however, suggests that they
were formed synchronously and as a direct result of the last dune generation believed to have
originated due to the climatic deterioration and sea level regression during the Little Ice Age.
Sand dunes are thought to have blocked natural drainage channels seawards and caused
flooding and lake formation in the lower parts to their immediate eastern limit (Almeida, op. cit.).
The preliminary results of this investigation seem to point more in the direction of Almeida´s
theory. The limited extension of the cores with ca 40 % of their depth representing the time after
the planting (initiated in 1924), already indicates a recent origin of the lakes. The vegetation cover
reflected contributes further to this idea.
At Leirosa beach, a similar dune area south of Cape Mondego, a 1.2 m thick organic
lagoonal deposit has been encountered under the present beach sand and its origin dated to
2900 BP (Bernardes et al. 2001). A preliminary study of the pollen and microfossil content from
blocks of this deposit appearing on the beach has been carried out (Danielsen, in prep.). It
indicates a forest (> 40% arboreal pollen) dominated by deciduous Quercus with some pine and
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an under vegetation of Erica scoparia, E. arborea, Calluna vulgaris, Myrica and Pteridium. The
investigated block has not been dated, but probably originates from a period some time after 2900
BP. The contemporaneous vegetation north of Cape Mondego was most likely similar. The
vegetation cover reflected by the pollen content of the lake sediments therefore apparently is
more recent in origin.
So far no indication of a past coast line near the lakes, as proposed by Noivo (op. cit.) and
Dias et al. (op. cit.), has been registered. Cysts of Dinoflagellates (“Histrix”) and other marine
indicators so abundant in the Leirosa sediment, are absent in the lake sediments. This may be
due to their recent origin and does not contradict the existing theories.
References
Almeida, A.C. 1995. Dunas de Quiaios, Gândara e Serra da Boa Viagem. Uma abordagem Ecológica da Paisagem. PhD
thesis. Coimbra University. 305 p.
Bernardes, C., Noivo, L.M. & Corrochano, A. 2001. Evolution of Holocenic coastal dunes at Leirosa, south of Cape
Mondego, Portugal. Thalassas, 17 (2): 47-56.
Carvalho, G.S. 1964. Areias da Gãndara (Potugal). Uma formação eólica Quaternária. Public. Mus. Lab. Mim. Geol. Fac.
Ciências do Porto, 81 (4): 3-32.
Dias, J.M.A., Rodrigues, A. & Magalhães, F. 1997. Evolução da linha de costa, em Portugal, desde o Último Máximo
Glaciário até à actualidade: Síntese dos conhecimentos. Estudos do Quaternário 1, APEQ, Lisboa, 53-66.
Granja, H.M., Carvalho, G.S., De Groot, T., Soares, M.S. & Parish, R. 1996. Geochronology and the Recent
Geomorphological Evolution of the Northwest Coastal Zone of Portugal. Proceedings of 3rd International Symposium
Eurocoast-Litoral 96, Portsmouth, 297-308.
Noivo, L.M. 1996. Morfologia e dinâmica sedimentar das dunas de Quiaios, Portugal. Master thesis. Aveiro University.
169 p.
41
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THE HOLOCENIC EVOLUTION OF THE ÓBIDOS, ALFEIZERÃO AND
PEDERNEIRA LAGOONS (WESTERN PORTUGAL).
NATURAL AND ANTHROPIC FORCING (TALK)
Jorge Dinis1, Virgínia Henriques2, Maria Conceição Freitas3 & César Andrade3
1
Department of Earth Sciences & Geosciences Centre, University of Coimbra, Largo Marquês de Pombal, 3000-272
Coimbra, Portugal; [email protected]
2
Department of Geosciences, University of Évora, Rua Romão Ramalho 59, 7002-554 Évora, Portugal;
[email protected]
3
Laboratory of Coastal Processes, Center & Department of Geology, Faculty of Sciences, University of Lisbon, Bl. C6, 3º
Piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected], [email protected]
In the coast of Central Portugal three lagoons were probably created by the Holocene
flooding of coastal depressions (Dias et al., 2000; Granja, 2002) but experienced afterwards a fast
sediment accumulation clearly forced by anthropic activities, with a strong feedback on the human
communities. Such depressions are related with the diapiric activity of the Caldas da Rainha Leiria fault (Dinis & Bernardes, 2004), and the erosion in their watersheds depends on climatic
and anthropic changes; especially, demographic rises increase agriculture and deforestation, and,
thus, sedimentation in the lagoons; in what concerns climate, works of Martinez-Cortizas et al.
(1999) and Desprat et al. (2003) recognised in north-western Iberia the First Cold
Subatlantic/Neoglacial Period, the Roman Warm Period, the Dark Ages cold period, the Medieval
Warm Period, the Little Ice Age and the 20th century warming.
Narrow rocky inlets (Pederneira and Alfeizerão) or detrital barriers created by the
deceleration of sea-level rise in the Middle Holocene (around 6-5 ka BP, Dias et al., 2000)
(Óbidos and Pederneira), provided sheltering to these lagoons. The proposed Middle Holocene
transgressive maximum roughly matches the boundary of recent alluvial deposits at 7-10 m
elevation and is usually marked by a clear slope break (Henriques et al., 2002). Unfortunately no
reliable dating on the Holocenic infill is available, but we believe that the evolution of the lagoons
can be evaluated using archaeological to historical remains and documentary information. The
lagoon’s shoaling and surface reduction appears to follow a pattern similar to other small
Portuguese coastal lagoons (Freitas et al., 2002; Granja, 2002). Currently, the S. Martinho do
Porto lagoon is a relict of the former Alfeizerão feature, the Óbidos lagoon is greatly reduced and
the Pederneira one is fully silted.
Archaeological remains from Neolithic to Roman times in the studied region concentrate
along the proposed maximal extension of the lagoons (Henriques et al., 2002; Moreira, 2002).
Romanization increased agriculture, favoured during the Roman Warm Period (250 BC- 450 AD),
and led to watershed erosion and accumulation of the released sediment probably restricted to
the stream’s mouths, as shown by the location of the Eburobrittium harbour in a branch about 8
km East of the current Óbidos lagoon shore (Moreira, 2002). Several Visigoth watch towers later
built along the margins of Pederneira and Alfeizerão lagoons, also suggest little reduction of the
immersed area.
Political and social instability characterized this sparsely populated region during the late
Roman time, the barbarian kingdoms and the Muslim occupation. This large period includes also
the cold Dark Ages (450 to 950 AD) and the Oort solar minimum (essentially the 11th century).
Consequently, the main changes in the lagoons were largely due to the sudden increase of
agriculture and deforestation following the definitive Christian Reconquest (late 12th century AD),
driven by the monks of the Cistercian Alcobaça Abbey in most of the Pederneira and Alfeizerão
lagoons drainage basins (Barbosa, 1992), throughout the Medieval Climatic Optimum (Brown,
1995). The Pederneira lagoon was also reduced by the southward progradation of dune fields,
stopped by pine-tree plantation in the late 12th and 13th centuries. Most of the forest of the Óbidos
lagoon basin was better preserved until the end of the 14th century due to its status as royal
hunting reserve (Devy-Vareta, 1985).
Population was severely reduced in mid 14th century by the Black Death and social and
agricultural crisis (Gonçalves, 1989), probably linked with the Wolf Solar Minimum, favouring the
regain of natural vegetation and slowing the lagoons infill. The 15th to 17th centuries are marked
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by demographic growth and great increase in timber cut, as needed for trade and exploration
vessels during the Discoveries Era (Devy-Vareta, 1985, 1986). In this period the inner harbours
declined very fast and had to be relocated seaward (e.g. from Pederneira or Valado to Ponte das
Barcas; from Alfeizerão to Salir do Porto), and large areas were reclaimed to farming.
Since the 14th century, the Óbidos lagoon was reduced to 1/3 of its maximum extension,
and, according to the documentary record, needs artificial opening, after the change of forest
regime of its basin allowed increased agriculture and timber cut. A sedimentation rate of 1.2
cm/year was calculated to the 1917 - 1980 period (Freitas, 1989). Empirical quantification of soil
loss in the watershed points to accumulation rates between 0.5 and 2.4 cm/year (Cruces, 2001).
We presume a regular decrease of the lagoonal volumes during the 17th to 18th centuries,
due to social and climatic reasons. The available data on regional demography points to
stagnation during the 17th century and a reduced to moderate growth during the 18th and first half
of the 19th centuries (Serrão, 1993). The region kept its agricultural character, and the Little Ice
Age climate did not help in the recovery of the vegetation cover. By the end of the 18th century,
the Alfeizerão and Pederneira lagoons had acquired their present-day configuration.
The global warming marks the 20th century. Yet, any possible contribution to reducing the
erosion was largely overstepped by the improvement of farming techniques, as well as a great
increase in the population of the region, surely reflected in a growth of the deposition rate in these
lagoonal systems.
In synthesis, we conclude that the human activities, that appear to be in tune with climatic
oscillations deduced from regional and global data during the last millennium, greatly accelerated
the natural silting trend of the lagoons.
Acknowledgements
This work was funded by the project «Global vs local forcing factors and paleoenvironmental changes of estuaries and
lagoons of SW Portugal since the Late Glacial» (POCTI/MAR/15231/1999).
References
Barbosa, P.G. 1992. Povoamento e estrutura Agrícola na Estremadura Central (Sec. XII a 1325). Instituto Nacional de
Investigação Científica, Lisbon, 397 p.
Brown, N. 1995. The impact of climate change. Some indications from History, 250-1250 AD. OCEES Research Paper,
Oxford, 61 p.
Cruces, A. 2001 Estudo a micro e meso-escala temporal de sistemas lagunares do SW Alentejano (Portugal): as lagunas
de Melides e Santo André. Dissert. Mestrado Geologia, FCUL, 228 p.
Desprat, S., Sanchez-Goñi, M.F., Loutre, M.-F. 2003. Revealing climatic variability of the last three millennia in
northwestern Iberia using pollen influx data. Earth and Planetary Science Letters, 213, 63-78.
Devy-Vareta, N., 1985. Para uma geografia histórica da floresta portuguêsa - As matas medievais e a “coutada velha” do
Rei. Revista da Faculdade de Letras, Geografia, Porto, I Série Vol. I, 47-67.
Devy-Vareta, N. 1986. Para uma geografia histórica da floresta portuguêsa – Do declínio das matas medievais à política
florestal do Renascimento (Sec. XV e XVI). Revista da Faculdade de Letras, Geografia, Porto, I Série Vol. II, 5-37.
Dinis, J.L., Bernardes, C. 2004. Upper Jurassic outcrops along the Caldas da Rainha diapir, Portugal. A regional
geoheritage overview. Rivista Italiana di Paleontologia e Stratigrafia, 110, 407-415.
Freitas, M.C. 1989. A evolução da Lagoa de Óbidos nos tempos históricos. Geolis, 3, 105-117.
Freitas, M.C.; Andrade, C., Cruces, A. 2002. The geological record of environmental changes in southwestern Portuguese
coastal lagoons since the Lateglacial. Quaternary International, 93-94, 161-170.
Gonçalves, I. 1989. O património do Mosteiro de Alcobaça nos séculos XIV e XV. Faculdade de Ciências Sociais e
Humanas, Universidade Nova de Lisboa, 586 p.
Granja H. M. 2002. Reconstituição paleoambiental da zona costeira, a norte da laguna de Aveiro, desde a Idade Média
até à Actualidade. In: O litoral em perspectiva histórica (sec. XVI a XVIII). Instituto de História Moderna, Porto, pp. 93109
Henriques, M.V., Freitas, M.C., Andrade, C., Cruces, A. 2002. Alterações morfológicas em ambientes litorais desde o
último máximo transgressivo – exemplos da Estremadura e do Alentejo. Publicações da Associação Portuguesa de
Geomorfólogos, Vol. I, Lisbon, 99-109.
Martínez-Cortizas, A., Pontevedra-Pombal, X., García-Rodeja, E., Nóvoa-Muñoz, J.C., Shotyk, W. 1999 Mercury in a
Spanish peat bog: archive of climate change and atmospheric metal deposition. Science, 284, 939-942.
Moreira, J.M. 2002. A Cidade Romana de Eburobrittium – Óbidos. Editora Mimésis, Porto, 175 p.
Serrão, J.V. 1993. O quadro humano. In: Mattoso, J. (Coord.), História de Portugal, Vol. IV- O antigo regime (1620-1807),
Círculo de Leitores, Lisbon, pp. 49-69.
43
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
LA IMPORTANCIA DE LA CALIDAD DEL ALIMENTO EN LA DISTRIBUCION
DE FORAMINIFEROS BENTÓNICOS EN AMBIENTES SOMEROS:
LA RIA DE VIGO COMO EJEMPLO (TALK)
Paula Diz1,2 & Guillermo Francés2
1
School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, U.K.;
[email protected]
2
Universidad de Vigo. Dpto. Geociencias Marinas y O.T. Fac. Ciencias del Mar, As Lagoas-Marcosende, s/n, 36200
Vigo, España; [email protected]
Introducción
Para la correcta interpretación paleoecológica es necesario tener un exhaustivo
conocimiento de las variables que determinan la presencia/ausencia o la abundancia de
determinadas especies en las comunidades vivas. El objetivo de este trabajo es precisamente
profundizar en este conocimiento a través del análisis de la distribución de los foraminíferos
bentónicos vivos en la Ría de Vigo (NW de España) y su relación con determinadas variables
ambientales.
En ambientes someros el número de variables que pueden controlar la distribución de
foraminíferos bentónicos es elevado. Por esta razón, en ocasiones, es difícil de aislar cuál de
esas variables, o el conjunto de cuáles, es la que determina la distribución espacial o vertical de
los foraminíferos bentónicos (ver revisión en Loubere y Fariduddin, 1999). Generalmente se
considera que en este tipo de ambientes la competencia por los recursos es mínima y que las
asociaciones están dominadas por taxones altamente oportunistas y con un elevado potencial de
reproducción (Jorissen, 1999).
El estudio de los foraminíferos bentónicos vivos en la Ría de Vigo, un ambiente marino
somero afectado por upwelling estacional, nos ha permitido poner de manifiesto la influencia de
la disponibilidad del carbono orgánico en ambientes eutróficos sobre la abundancia y
composición de las asociaciones. Los resultados se discutirán mediante dos ejemplos: El primero
(Ejemplo 1) resulta de comparar las asociaciones de foraminíferos bentónicos vivos en el sector
externo de la ría de Vigo bajo dos situaciones contrastadas, la de downwelling o de baja
productividad y la de upwelling, que comporta la llegada de materia orgánica lábil al fondo. En el
segundo se comparan, bajo condiciones de upwelling, las asociaciones que habitan la superficie
del sedimento con las que viven asociados al poliqueto Maldane glebifex Grube, el cual
proporciona un tipo de carbono orgánico diferente del derivado directamente del afloramiento
(Ejemplo 2).
Las estaciones seleccionadas para este estudio fueron muestreadas mediante una box
corer (Fig. 1A) en enero (condiciones de downwelling) y en septiembre (condiciones de
upwelling) de 1998. Se han considerado todos los individuos vivos (teñidos con Rosa de
Bengala) >63 µm contenidos en 50 cm3 de sedimento del centímetro superficial. En aquellas
estaciones en las que durante el muestreo se observó la presencia de M. glebifex, el tubo del
poliqueto fue extraído y tratado de la misma manera que las muestras de sedimento.
Ejemplo 1 (upwelling vs. downwelling)
Durante la campaña de septiembre la densidad de foraminíferos vivos se incrementa
notablemente en todas las estaciones del sector externo de la ría con respecto al muestreo de
enero, excepto en la estación 13 (Fig. 1B). Ello está causado por el incremento en la abundancia
absoluta de las especies típicas de este sector (B. spathulata/dilatata y S. fusiformis, Fig. 1C),
pero también por la presencia espacialmente heterogénea de especies ausentes durante la
campaña de invierno (B. translucens, N. Stella, N. turgida y L. scottii). La respuesta de los
foraminíferos bentónicos a la llegada de materia orgánica lábil procedente del afloramiento
sugiere que: 1) a pesar del alto contenido en Corg de los sedimentos (Fig. 1B), la abundancia y la
composición de las asociaciones está determinada por la llegada al fondo de carbono orgánico
de alta calidad; 2) el carbono orgánico debe sedimentar heterogéneamente provocando
diferencias en la calidad nutritiva de unas estaciones a otras. De este hecho se aprovechan las 4
especies oportunistas que colonizan rápidamente los agregados de materia orgánica según sus
preferencias nutricionales específicas (Fig. 1C). Esta respuesta específica de cada especie a la
44
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
ingestión de carbono orgánico ha sido también demostrada en experimentos de laboratorio por
Nomaki et al. (2005).
Ejemplo 2 (sedimento superficial vs. M. glebifex)
Las especies encontradas en los tubos de M. glebifex difieren de las que habitan el
sedimento superficial (Fig. 1C). Estas diferencias se deben fundamentalmente a la ausencia en
los tubos del poliqueto de las 4 especies oportunistas, a los bajos porcentajes de S. fusiformis y a
la mayor abundancia de B. gibba/elongata. Estos contrastes son una expresión de las
preferencias específicas de cada especie por diferentes calidades de carbono orgánico. Las
especies que se relacionan con la llegada de materia orgánica lábil aportada por el afloramiento
habitan preferentemente en la superficie del sedimento y no lo hacen, por el contrario, en los
tubos de M. glebifex. En estos, la materia orgánica debe ser de diferente naturaleza,
probablemente de origen bacteriano y/o menos lábil de la que se aprovechan especies con un
carácter oportunista menor, como B. gibba/elongata y B. spathulata/dilatata.
4680000
B
Enero 1998
26
4
22
C org
18
13
individuals/50 cm
3
Latitud (UTM)
7
4670000
A
1400
1200
1000
800
600
400
200
0
3.5
3
2.5
2
1.5
1
4
4665000
505000
510000
515000
% C org
12
4675000
Septi embre 1998
7
13
12 18
Station
520000
22
26
26
20
B. gibba/elongata
25
10
0
0
7
13
100
12
18
22
5
0
0
13
12 18
Station
22
26
13
12
18
22
0
200
12
18
22
10
50
0
0
13
12
18
22
26
40
N. stella
30
100
20
50
10
0
7
13
12
18
22
26
Enero 1998
100
7
150
4
20
4
13
30
L. scottii
150
7
0
26
%
3
Individuals/50 cm
%
50
13
0
4
10
7
10
0
20
100
20
R. phlegeri
25
26
B. translucens
4
10
50
7
150
26
N. turgida
4
200
7
0
%
3
Individuals /50
5 cm
4
0
4
50
%
22
Septi embre 1998
%
18
%
12
Individuals/50 cm3
50
13
20
3
0
7
40
%
20
S. fusiformis
500
400
300
200
100
0
Individuals/50 cm
%
40
4
3
Individ uals/50 cm
60
I ndividuals/50 cm 3
B. spathulata/dilatata
500
400
300
200
100
0
I ndividuals/ 50 cm3
Individuals/50 c m
3
Longitud (UTM)
12 18
Station
22
% Enero 1998
% Septiembre 1998
M. glebif ex
C
26
Figura 1- A: Localización de las muestras. B: Abundancia absoluta de foraminíferos bentónicos vivos (enero y
septiembre) y porcentaje de carbono orgánico (septiembre) en el sedimento superficial. C: Abundancia absoluta (barras)
y relativa de las especies más significativas en el sedimento (líneas negras) y en los tubos de M. glebifex (línea roja).
Bibliografía
Jorissen, F.J. 1999. Benthic foraminiferal microhabitats below the sediment-water interface. In: Sen Gupta, K. (Ed.),
Modern Foraminifera. Kluwer Academic Pub. 161-179.
Loubere, P. & Fariduddin, M. 1999. Benthic Foraminifera and the flux of organic carbon to the seabed. In: Sen Gupta, K.
(Ed.), Modern Foraminifera. Kluwer Academic Pub. 181-199.
Nomaki, H., Heinz, P., Nakatsuka, T., Shimanaga, M. & Kitazato, H. 2005. Species-specific ingestion of organic carbon by
deep-sea benthic foraminifera and meiobenthos: In situ tracer experiments. Limnology and Oceanography, 50(1): 134146.
45
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LATE QUATERNARY ENVIRONMENTAL CHANGES OF NORTHERN
PORTUGUESE ESTUARIES (TALK)
Teresa Drago
Instituto Nacional de Investigação Agrária e Pescas-IPIMAR; [email protected]
In collaboration with: Adriano Bordalo-Sá, Ana Lobato, Anabela Cruces, António Caetano Alves, Catarina Fradique,
Catarina Guerreiro, César de Andrade, Conceição Freitas, Fátima Araújo, Fernando Rocha, Filipa Naughton, Filipa
Moreno, Francisca Rosa, Francisco Fatela, Jean Marie Jouanneau, João Cascalho, João Moreno, Maria Fernanda Goñi,
Mário Cachão, Miguel Miranda, Olivier Weber, Paulo Silvestre, Pedro Silva, Selma Gabriel & Sílvia Serina
Introduction
Estuaries are, for excellence, the “meeting place” between marine and continental
influences. This makes them ideal environments for studying sea-level and other environmental
changes. Following the studies of the Portuguese northern continental shelf published in the 90’s
(e.g. Rodrigues et al., 1991; Magalhães & Dias, 1992; Cascalho & Galopim, 1993; Araújo et al.,
1994; Fatela et al., 1994; Drago, 1995; Magalhães, 1999), the Douro and Minho estuaries
(including the Coura marsh), were selected as target areas with the aim of enlarging the scope of
studies on paleoenvironmental changes since the last deglaciation to the northwest Portuguese
margin, based on sedimentary data. This study was done under the auspices of the EnviChanges Project, which involved several researchers and institutions. The results obtained,
essentially based in paleoenvironmentals
indicators, show a succession of
Minho estuary
environments in relation with sea-level
rise associated with the Holocene
CPF1
transgression.
Caminha
Coura
Cabedelo
marsh
Study Areas
Core1
Core2
The Douro estuary is located in the
NW Portuguese coast and the city of
Camarido
Oporto extends along its northern margin
(Fig.1). It is a narrow funneled estuary,
partly barred by the Cabedelo sand spit
that develops northward and shelters the
Oporto
S.Paio Bay. One 25m-long core has been
taken from the Cabedelo sand barrier
Douro estuary
(Core 2-Fig.1) and two other have been
Core
retrieved from the back-barrier (cores 1
2 S.Paio
and 1B, spaced 0.5m apart - Fig. 1),
Bay
inside de S. Paio Bay and combined to
Cores 1
+1B
produce a composite column. Cores 1 and
1B (+3.5 to -15.16m relative to mean sea
level-msl) and 2 (-15.16 to -39.66m msl)
can be considered as representative of
Figure 1 – Location of study areas.
the sedimentary infill present in the
southern margin of Douro estuary.
The Minho estuary is a very wide and shallow estuary following a general NNE-SSW trend.
It is also partially barred by a complex sand beach-and-dune ridge barrier, known as Camarido, at
present densely covered by pine trees. Two cores aligned cross-shore and located 200m apart,
were retrieved from this sand barrier (Fig. 1). Core 1 (seaward location) reached bedrock at 29.66m depth msl and core 2 stopped in granite basement at -25.84m msl.
Finally, the third study area was the Coura marsh. It is located along the margins of river
Coura, which meets the Minho estuary in its southern margin, east of the village of Caminha (Fig.
1). One 13m -long core (CPF1–Fig. 1) was collected from this marsh and stopped at -11.62m msl
without reaching basement.
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Methodology
The present study was supported by multi-proxies analyses of the cores cited above. They
were collected using rotary (Douro and Minho estuaries) and percussion methods (Coura).
The cores were sub-sampled for several studies: sedimentological (texture, mineralogy of
fine and coarse fraction, organic matter, carbonates and water content), micropaleontological
(foraminifera, calcareous nannoplankton and pollens) and geochemical (major and minor
elements).
Sediments were classified according to Flemming (2000). Several samples at specific
levels were dated by 14C AMS (Beta Analytic Inc.). Datings results were converted to calendar
years following Stuiver et al. (1998).
Results and discussion
Overall results from this study show a succession of environments in relation with sea-level
rise, in particular with the Holocene transgression, and regional environmental changes occurred
since the Lateglacial. However, local forcing factors seem to have played a decisive role in
controlling local sedimentation patterns, contributing to an enormous variety of sedimentary facies
and to record similar environmental episodes at different depths in both estuaries.
Two main units with different environmental significance and corresponding with major time
intervals were found, which may be subdivided in several stages as follows:
A – The last deglaciation
The basal sediments in core 2 of both estuaries have been dated from the last deglaciation
period; the base of core 1 of Minho estuary yielded a date of cal BP 9020.
Fluvial Stage
In both estuaries, a fluvial environment is well recorded in the lower section of the cores
cited above (Fig. 2).
In the Douro estuary, this stage began at or before cal BP 16480. Sediments are basically
slightly muddy sand with few interbedded layers of sandy mud, muddy sand and gravel. The
fluvial signature is supported by the total absence of biogenic components, namely mollusks,
foraminifera and calcareous nannoplankton, and significant abundance of plant remains. The
suite of heavy minerals, together with the high contents in Al, Ca (derived from Apatite), Sr and Zr
(Araújo et al., in press) and the clay mineral association corroborate this interpretation suggesting
evidence of direct erosion of the formerly outcropping basement (Fradique & Cascalho, 2004;
Rocha et al., in press); sedimentation in this stage relates with clastic fluvial input, and bears a
strong provenance signal of the watershed.
In the Minho estuary, a single date of the same stage yielded an age of cal BP 13400 at
core 2 (Fig. 2). Sediment is mainly represented by somewhat muddy grain-supported coarse
gravel with abundant rounded quartzite and few quartz and granite elements; the thickness of this
layer varies between 0.84m in core 1 and circa 5m in core 2.
From the climatic point of view, pollen assemblages in this stage encompass a succession
of the Bölling Allerød, Younger Dryas and early Holocene well known climatic events (Naughton
et al., this volume). The climatic amelioration that characterized this last time interval event is
quite well identified at -33.16m msl by the expansion of Quercus deciduous and Fraxinus sp.. The
onset of the Holocene may therefore be dated in this estuary slightly before cal BP 12120 (32.33m msl).
B- The Holocene transgression
Evidences of the Holocene transgression in the sedimentary record may occur in the
following stages (Fig. 2):
Estuarine I stage
This stage correspond to the earliest signals of marine influence related with sea-level rise
in the study area and has been clearly recognized in the Douro estuary, while in the Minho
estuary it has been barely sampled in the bottom levels of core 2 and only identified in the
abundance profile in nannoplankton (Guerreiro et al., this volume). Accordingly, the following
description relies essentially upon data from the Douro.
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This stage is represented in both cores (2 and 1B) although with somewhat different facies.
In core 2 it is essentially represented by a succession of slightly sandy mud, sandy mud and
muddy sand layers, the youngest sediment dated cal BP 10150; textural evidences and lateral
correlation with core 1B suggest that the correspondent sequence may have been truncated in
this location. Core 1B contains a record equivalent to the missing section in the previous core and
consists of interbedded layers of muddy sand and sandy mud, dated between cal BP 10720 and
cal BP 6890.
In both locations this stage is characterized by incipient marine influence, initially
discontinuous and sparse to the base, and growing in consistency towards the top. The earlier
marine influence is represented in core 2 at -27.77/-27.66m msl by brackish and estuarine-mouth
foraminifera, added by peaks in mollusk and “other biogenics” shell, corresponding to an
interpolated time period circa cal BP 11300. The marine signature is also supported by the
increase in Carbonate/Detrital ratio (C/D) and concomitant decrease in Kaolinite/Ilite ratio in the
fine fraction (<63µm) (Rocha et al., in press), particularly above -22.74m, where increase in Ca
and Sr are also observed (Araújo et al., in press). The presence of calcareous nannoplankton is
only recorded later, at -22.37m depth, corresponding to an approximate age of cal BP 10400.
Further upwards, and until -8.68m (circa cal BP 6890) both nannoplankton and foraminifera
appear more consistently but showing, at specific levels, drastic decrease in abundance or even
interruption. These perturbations are simultaneous with increases in terrigenous indicators,
especially plant and wood remains. Thus, these intervals were attributed to continental inputs
which seem to have been short-lived and probably related with flood episodes.
The pollen assemblages are in agreement with the climatic amelioration that characterizes
the Holocene (Naughton et al., this volume), showing that the early Holocene was characterised
by a warm and humid climate as testified by a well-established Pinus-Quercus-Alnus regional
forest (Naughton, 2002; Naughton et al., 2002).
In particular, XRD data put in evidence a climate evolution towards more temperate
conditions, with less precipitation and, therefore, less favorable to the development of hydrolysis
in source areas (along core 2-Douro estuary) but with a progressive increase of these hydrolysis
conditions, i.e., towards a warmer and more humid climate, with seasonal contrast,
simultaneously with an evolution towards a lower hydrodynamics (along core 1B) (Rocha et al., in
press).
Marine stage
This stage is characterized by the onset of a fully marine environment in studied areas,
similar to present day open gulfs or “rias” when the coastline standing landward of the sites cored.
In the Douro estuary, this stage is testified by an evident increase in marine proxies,
particularly noticed in the topmost layers of core 1B between cal BP 6890 (-8.35m) and cal BP
6530 (-5.75m) (Fig. 2). Sediments contemporaneous of this period consist of (biogenic) gravel,
sandy mud and muddy sand and contain a foraminifera assemblage with clear presence of
continental shelf species and minor representation of brackish forms, growing nannoplankton
diversity and abundance and evident increase of the C/D ratio (Drago et al., in press).
In the Minho estuary, the onset of an equivalent stage was dated cal BP 9020 in core 1 (27.80 m msl) and cal BP 11950 in core 2 (-20.39m msl). This same stage is represented, in Core
1, by a high-frequency alternation of sand with slightly muddy sand (between circa -28m and 14.87m) and, in core 2, by a tick slightly muddy sand layer (between circa -20.39m and -12.76m)
(Fig. 2). Contrarily to Douro estuary, the abundance and diversity of marine proxies is fairly
constant along the sedimentary record: both the foraminifera and nannoplankton assemblages
show rather uniform vertical abundance profiles with just a few or none interruptions. In addition,
salinity paleoindicators such Cl, Br or S are quite well represented (Araújo et al., this volume). Ca
and carbonate contents also match the downcore profile of ecological proxies.
In this estuary, paleoecological data and radiocarbon dating suggest an older age for the
beginning of this stage in core 2, un unexpected result given the short distance between
boreholes; this can only be understood if an erosive episode took place in core 1 location. It is
worth to note, that in core 1 the Ca and Sr concentrations are systematically higher than in core 2
and that Ca and Sr concentrations are positively correlated with carbonate, indicating a local
enrichment in bioclasts (Araújo et al., this volume). If this is taken as an indication of core 1 being
48
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more proximal to the main channel and core 2 to the margin, the erosive episode mentioned
above may gain some consistency.
Similarly, a significant time offset in the initiation of marine stage in both estuaries has been
recorded. This stage apparently began earlier in Minho and a possible explanation is also to
invoke different distances of coring sites in relation to the main channel.
In Coura river sedimentation in this stage (below -5.3m) reflects its location upstream the
main Minho estuarine basin (Fig. 2); it is represented by slightly sandy mud, sandy mud and
muddy sand. Paleoecological indicators suggest the persistence of brackish and low energy
environment during most of this stage; this is supported by the dominancy of brackish/brackishmarine intertidal to subtidal foraminifera, followed by mouth-estuary and shelf assemblages; in
addition, the observed nannoplanton population should have been majority transported (Moreno &
Fatela, this volume). An evident increase of outer continental shelf and mouth-estuary
foraminifera is recorded late in this stage, between cal BP 7610-7485 and cal BP 6624-6410
between -6.82 and -5.52m msl and this should correspond to the maximum transgression.
Douro estuary
Depth 4
(m)
2
0
Cal BP 1500
Cal BP 6890
Coura marsh
Sand
barrier
Sand
barrier
-2
-4
-6
Cal BP 6530
Minho estuary
Barrier
(gravel)
Cal BP 2150
Cal BP 6624_6410
-8
-10
Estuarine
Intertidal
Marine
Estuarine
II
Estuarine
I
Marine
-12
-14
Estuarine/
Marine
-16
-18
-20
-22
-24
-26
Cal BP 14462
Cal BP 11950
-28
Fluvial
-30
Cal BP 13400
-32
-34
Fluvial
-36
-38
Cal BP 16480
-40
Figure 2 - Environmental stages synthesis corresponding depths and ages in the different study areas.
Estuarine II/ Gravel-Barrier stage
After the Holocene transgressive maximum and in consequence of the deceleration of sealevel rise rate, local forcing factors seem to have acquired predominancy in determining the
morpho-sedimentary responses in both estuaries.
Following the full marine conditions, a second stage of estuarine environment was recorded
in the Minho estuary. It is characterized by an alternation of continental and marine signature,
starting above -14.85m in core 1 and -12.3m in core 2. Nannoplankton and estuarinemouth/marine foraminifera assemblages are now discontinuous and appear as isolated peaks.
Other proxies as: biogenic sand components (mollusks, benthics foraminifers and echinoderms
debris), Ca and carbonate contents which steadily diminish upcore corroborate the decrease of
marine influence. In constrast, a high content of charcoal (that may reach 50-80%) testifies higher
continental influence. This stage remained at least until circa cal BP 2150 (Fig. 2). At the Douro
estuary the deceleration of sea-level rise rate has been responsible for the emplacement of a
gravel-barrier, with 5.23m and 1.17m thickness (core 1/1B and in core 2, respectively), post cal
BP 6530 that remained until cal BP 1500 (Fig. 2); gravels are essentially of rounded quartzite,
probably fluvial- sourced and subsequently reworked by the sea (Naughton et al., 2002); this
hypothesis is supported by the presence of rounded, spherical and ellipsoidal grains of garnet,
andalusite and tourmaline in the gravel layer in core 2 (Fradique et al., 2004; Fradique et al., in
press). The growth of the gravely barrier has been possibly accompanied by the northward
relocation of the Douro channel, leaving its former position fossilized as a paleovalley located
49
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
south of the present-day thalweg (Carvalho & Rosa, 1988). The formation of this gravel-barrier is
contemporaneous of similar features (though sandy) found in the SW Portuguese coastal lagoons
of Albufeira, Melides and Santo André (Freitas & Andrade, 2001).
Sand barrier stage
In Douro estuary, after cal BP 1500 and until present, the formation of a sand barrier
occurred, represented essentially by clean coarse sand; at its bottom some muddy layers were
found and in the lowest one (-1.69m) micropaleontological data (foraminifera and nannoplankton)
suggest a brackish signature. With the exception of this layer, where a small percentage (<1%) of
mollusks is present, no biogenic sand components have been detected upcore. This facies
includes a significative percentage of amphibole in the heavy mineral suite of the top of the unit,
which is probably of terrestrial source (Fradique & Cascalho, 2004).
The pollinic study of the muddy layers indicate radical changes in vegetation with an almost
exclusive presence of local, herbaceous plants; this can be attributed to the relocation of the
Douro river towards north, as a consequence of the ancient valley infill and gravely barrier
development (Naughton et al., 2002). At the surface, pollens of Juglans, Eucalyptus, Castanea
and the increase of Pinus define clearly anthropogenic influence (Naughton et al., 2002).
The accumulation of the estuarine spit and sedimentation in the estuarine domain sheltered
by the barrier progressed at a high rate, allowing the marine signal to fade away in the topmost
section of the sedimentary record of this place. Therefore, a forced regressive facies was
constructed here in spite of a persistent eustatic positive trend.
In Minho estuary, the same stage (after cal BP 2150) (Fig. 2) is characterized by extremely
low contents of marine mollusks till 2m above msl. The sedimentary record ends with the
emplacement of a dune field characterized by high and uniform contents of sand (almost 100%),
exclusively constituted by terrigenous components (quartz, mica and some charcoal).
Relatively to Coura river, sediment accumulated after the transgressive maximum remained
fine grained, evolving to a estuarine/intertidal one contemporaneously to the emplacement of both
stages estuarine II and sand barrier further seaward. In this location, upward -5.2m (6360-6150 y
cal BP), sediment is barren in nannoplankton and foraminifera drop drastically in density or
completely disappear in some zones, suggesting a complete change in environmental conditions
(Moreno & Fatela, this volume). Above 1.62m a few species characteristic of high intertidal, low
marsh and high marsh occur in relation with the onsetting of the present day salt marsh.
Conclusions
Several environmental stages can be distinguished in the study areas. They are principally
controlled by global factors as sea-level rise and climatic changes. However, local factors seem to
have played an equal important role in sedimentation patterns and recorded events in different
time stages. Although the general aspects of paleoenvironmental evolution can be recognized in
all field areas, their expression in the geological record may vary from site to site. In fact, the
onset of a determined stage both in different places of the same estuary and in different estuaries,
may have been recorded in the sediment infill at different depths and in association with different
ages, if not completely obliterated by post-depositional processes. Whatever the reasons that
future work may bring to detail reasons explaining these differences, the data available are
enough to conclude that site effects are not negligible in the reconstruction on paleoenvironmental
changes and forcing factors from the sedimentary record in this area.
The sedimentary record begins, in both studied estuaries, by a fluvial stage, which is
contemporaneous of the last deglaciation. With the arrival of first marine influence at coring sites,
in relation with the Holocene transgression, an estuarine environment developed in the Douro
estuary, which is barely represented in Minho; the following stage, of marine character, is well
recorded in Minho estuary but modestly expressed in the Douro one. Following sea-level rise
deceleration circa cal BP 6500 a gravel barrier formed in Douro estuary; simultaneously, a second
estuarine stage was ongoing in the Minho estuary. More recently, both estuaries developed sand
barriers that persist until present.
50
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This global evolution shows particular signatures in the Coura marsh, which are lateral
equivalents of more seaward sedimentation, given its upstream location in the Minho fluvial
system. The earliest stage identified in this location is contemporaneous of the marine stage
recorded in seaward cores and it may be considered as estuarine/marine. The following estuarine
intertidal stage is contemporaneous of stages “estuarine II” and “sand barrier”, once again
identified in more seaward locations.
Acknowledgments
This work was undertaken as a part of the ENVI-CHANGES project (PLE/12/00) funded by Fundação para a Ciência e a
Tecnologia (Portugal). The author which to address a special thanks to C. Freitas and C. Andrade for enlightening
discussions and the carefully revision of this paper.
References
Araújo, M.F., Dias, J.M.A. & Jouanneau, J.-M. 1994. Chemical characterization of the main fine sedimentary deposit at the
northwestern portuguese shelf. Gaia: 9, 59-65.
Araújo, M.F., Rocha, F., Lambéria, M., Gouveia, A. & Drago, T. in press. Geochemical and Mineralogical
Palaeoenvironmental Patterns in the Douro Estuary. Memórias e Notas da Universidade de Coimbra
Araújo, M.F., Lobato, A., Cruces, A., Drago, T. this volume. Paleoenvironmental Geochemical patterns in the holocenic
evolution of minho estuary.
Carvalho, A.F & Rosa, M.M.P. 1988. Localização do Paleovale do Rio Douro. Anais do Inst. Hidrográfico, 9: 77-82.
Cascalho, J. & Galopim de Carvalho, A.M. 1993. Proveniência dos minerais pesados da plataforma continental
portuguesa a norte do paralelo de Espinho, Gaia, 6, Univ.Lisboa, 10-25.
Fatela, F., Duprat, J. & Pujos, A. 1994 - How southward migrated the polar front, along the west Iberian Margin, at 17,800
years BP? Gaia, 8: 169-173.
Flemming, B.W. 2000. A revised textural classification of gravel-free muddy sediments on the basis of ternary diagrams.
Cont. Shelf Res., 20: 1125-1137.
Drago, T. 1995. La vasière Ouest-Douro sur la plateforme continentale nord portugaise. Rôle, fonctionnement, evolution.
Tese de Doutoramento, Univ.de Bordéus I, 300p., 116 figs, 29 tabelas.
Drago, T., Freitas, C., Rocha, F., Cachão, M., Moreno, J., Naughton, F., Fradique, C., Silveira, T., Oliveira, A., Cascalho,
J. & Fatela, F. in press. Paleoenvironmental data of the sedimentary record Douro estuary in the last 14 000 years.
Journal of Coastal Research
Fradique, C. & Cascalho, J. 2004. Sedimentary processes in Douro estuary (Portugal) – A heavy mineral study.
Thalassas, vol.20 (2):v61-68
Fradique, C., Cascalho, J., Drago, T., Rocha, F. & Silveira, T. in press. The meaning of heavy minerals in the recent
sedimentary record of the Douro estuary (Portugal); Int. Coastal Symposium.
Freitas, M.C. & Andrade, C. 2001. Marcadores ambientais na evolução dos espaços lagunares do SW português durante
o Holocénico: a formação das barreiras arenosas e a influência antrópica. Proceedings of V Reunião Quat. Ibérico,
113-116.
Guerreiro, C., Cachão, M. & Drago, T. this volume. Calcareous nannoplankton as a tracer of the marine influence in the
NW coast of Portugal, over the last 14000 BP.
Magalhães, F. 1999. Os sedimentos da plataforma continental portuguesa: contrastes espaciais, perspectiva temporal,
potencialidades económicas. PhD thesis, Univ. Lisboa, (unpublished), 500p.
Magalhães, F. & Dias J.M.A. 1992. Depósitos sedimentares da plataforma continental a norte de Espinho, GAIA, 5, Univ.
Lisboa, 6-17.
Moreno, J. & Fatela, F. This volume. palaeoenvironmental evolution over the last 10 kyr BP at Caminha tidal marsh (NW
of Portugal): foraminiferal evidences
Naughton, F. 2002. Evolução Morfodinâmica do Estuário do Douro com base no registo polínico e sedimentológico.
Master Thesis, Lisbon University, 131 p. (not published).
Naughton, F., Drago, T., Rocha, F.& Sánchez Goñi, M.F. 2002. Holocene Environmental changes in Douro Estuary (NW
Portugal). Actas da III Assembleia Luso-Espanhola de Geodesia e Geofisica, Valencia.
Naughton, F., Sanchez Goñi, M.F., Drago, T., Turon, J.-L., Duprat, J., Cortijo, E., Malaizé, B., Bard, E., Rostek, F.,
Jouanneau, J.-M. & Freitas, M.C. this volume. Millennial-scale climatic variability during the last glacial-interglacial
transition and the Holocene in the NW of Iberia.
Rocha, F., Drago, T., Naughton, F. & Silveira, T. in press. Paleoenvironmental analysis of Douro estuary based on
mineralogical parameters. Thalassas
Rodrigues, A., Magalhães, F. & Dias, J.M.A. 1991. Evolution of the north portuguese coast in the last 18000 years. Quat.
Int., 9: 67-74.
Stuiver, M. & van der Plicht, H. 1998. Intcal98 Radiocarbon Age calibration, Radiocarbon, 40 (3): 1041-1083
51
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HIGH RESOULTION SEISMIC STRATIGRAPHY OF THE RIA OF AVEIRO
(PORTUGAL) (TALK)
Henrique Duarte1,2, Luis Menezes Pinheiro1, Cristina Bernardes1, F.C. Teixeira2, S. Bouriak2 &
José Hipólito Monteiro2
1
2
Dep. Geociências, Universidade de Aveiro, Campus Santiago 3810-193 Aveiro; [email protected]
Dep. Geologia Marinha e Costeira, INETInovação
Introduction
The Ria of Aveiro is a 50 km2 barrier type lagoon, located in Northwestern Portugal at the
mouth of the Vouga River. Onshore geology reveals dune, beach and lagoonal sediments of
Quaternary age, composed essentially of unconsolidated sands and clays. Core data and seismic
reflection profiles show that these sediments are less than 10 metres thick to the East, and over a
100 meters thick to the West (the deeper sediments are probably Neogene), and that they have
an erosive lower boundary, locally channelized, mostly flat and gently dipping less than 1º
westwards (Marques da Silva 1992; Teixeira & Pinheiro, 1998). Where it is thinner, the lower
boundary of the Quaternary sediments cuts through Mesozoic clays and limestones (probable
Upper Cretaceous). In 2002 and 2003, three high-resolution seismic surveys (with Chirp and
Boomer systems) were conducted in the Ria to investigate the sedimentation, structural control
and evidence of gas and gas seepage. Here we present an example of the interpreted seismic
stratigraphy, based on seismic data acquired during these surveys.
Material and Methods
Three surveys, RIAV02, RIAV02A and RIAV03, were conducted in this area, on board “Ria
Azul” of the Aveiro Harbour Authorities. 177km of Chirp profiles (Datasonics, CAP-6000W) were
digitally acquired during RIAV02 and RIAV02A; the signal bandwidth was 1.5-10 KHz, the output
power was 1KW and the chirp length 10 ms (approximate vertical resolution of 15 cm). 47km of
Boomer profiles (EG&G Uniboom) were digitally acquired during the RIAV03 cruise; the energy
was 100-watt s-1 and a single-channel streamer with 24 hydrophones was used. The signal
frequency spectrum ranged from 250 to 1400 Hz (estimated vertical resolution <2 m). Seismic
processing included frequency band pass filtering, time variant amplitude gain correction,
predictive deconvolution, spiking deconvolution and trace mixing. The total survey grid covers
most of the navigable channels of the Ria, and separation between profiles ranges from 10 to 75
m (Fig. 1). Positioning of the profiles was done with differential GPS, except where differential
correction was not available
(approx. 60 km of Chirp
profiles).
Results
The following seismic
units were interpreted (see
figure 2): Unit U1(a,b) is the
uppermost unit with oblique
tangential to sigmoid reflections that downlap a
channel-like truncation surface;
Unit U1a is partially filling a
modern channel; Unit U1b is
totally filling a paleo-channel;
Unit U2 has few irregular
reflections that downlap or
Figure 1 - A – Boomer and Chirp seismic coverage of the Ria of Aveiro (in
onlap the lower boundary
black). B – Detail of survey grid. Grey lines: Chirp profiles; Black lines:
which is an ubiquitous
Boomer profiles; Dotted line: profile RIAV03-P02A (figure 2).
truncation surface that dips
slightly to the west; this unit is limited above either by the sea bottom or by unit U1; Unit U3 is
52
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mostly transparent with few, cross, oblique parallel reflections with poor continuity that onlap the
lower truncation surface which is an approximately 1.5 km wide, NNW-SSE oriented channelterrace feature; it is limited above by unit U2; Unit M is characterized by strong, continuous,
parallel reflections, folded and faulted but generally dipping to the west (steeper the lower
boundary of unit U2); the lower boundary of this unit was not imaged.
Discussion and Conclusions
Lithological data from hydrogeology cores (Marques da Silva, 1992) allows the correlation
of unit M with shales and limestones, probably of the Upper Cretaceous (Fig. 2). This unit was
partially eroded most probably during the last glacial maximum (LGM), in sub-aerial conditions, as
indicated by the M-U3 erosive boundary, and possibly, by parts of the M-U2 boundary. Unit U3 is
interpreted as valley infill sediments deposited after the LGM, and prior to the wave/tidal erosion
that is suggested by the U3/U2 boundary. Unit U2 is interpreted as marine/tidal channel
sediments deposited after the sea level reached a depth near the U2 lower boundary, and,
possibly, before the artificial opening of the tidal inlet, which would be marked by the U2/U1
boundary. Units U1 are interpreted as tidal channel infill sediments probably deposited after the
artificial opening of the tidal inlet (which caused the development of new tidal channels).
Figure 2 - Top – Segment of Boomer profile RIAV03-P02A (location in Figure 1); Bottom – interpreted section. Thin black
lines - reflections; Dotted lines – unit boundaries; U1:U3 post-last glacial maximum units; M – Up. Cretaceous unit; F –
faults.
Acknowledgements
H. Duarte’s Ph.D. work is supported by a FCT scholarship (FSRH/BD/2017/2004). The seismic data collected in the Ria of
Aveiro was possible thanks to the EICOS Project (PRAXIS/2/2.1/MAR/1750/95), the INGMAR Project (FCT-PLE/4/98) and
Ciência Viva actions (FCT). Thanks also the Administration of the Harbour of Aveiro (APA) who provided the ship time,
and to Cmd. Francisco Pontes, Mr. Licínio Rama, Master of “Ria Azul”, and the crew and scientific parties of cruises
RIAV02, RIAV02A and RIAV03.
References
Marques da Silva, M. A. 1992. Camadas-guia do Cretácico de Aveiro e sua importância hidrogeológica. Geociências,
Rev.Univer.Aveiro 7 (1/2): 111-124.
Teixeira, F. C. & Pinheiro, L. M. 1998. Contribuição para o estudo da evolução geológica da Ria de Aveiro e da
Plataforma Continental Adjacente. V Cong. Nac. de Geologia, Lisboa, 84 (1): 43-46.
53
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ENVIRONMENTAL CHARACTERIZATION OF THE ALBUFEIRA LAGOON
(PORTUGAL) AT MICRO TIMESCALE USING A MULTIDISCIPLINARY
APPROACH (TALK)
Marco Ferraz1, Elsa Silva1, Anabela Cruces1, Maria Conceição Freitas1, Mário Cachão1, César
Andrade1 & Maria de Fátima Araújo2
1
Laboratório de Processos Costeiros, Centro e Departamento de Geologia da Faculdade de Ciências da Universidade de
Lisboa. Edifício C6, 3º Piso. Campo Grande. 1749-016 LISBOA. Portugal; [email protected],
[email protected], [email protected], [email protected], [email protected], [email protected].
2
Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém. Portugal;
[email protected]
Introduction
The Albufeira lagoon is located 20km south of Lisbon, in the coastal arc of Trafaria-Espichel
(Fig. 1A) and is formed by two main bodies – Lagoa Grande and Lagoa Pequena (Fig. 1B); its
major axis is oblique to the coast (trending NE-SW), the flooded surface is 1.3km2 and its
maximum length, width and depth are 3.5km, 625m and 15m, respectively. It is usually isolated
from the ocean by a welded sand barrier, where a tidal inlet is artificially opened once a year,
allowing the renewal of the lagoonal water. In consequence, the lagoonal water becomes
homogeneous and similar to marine water. When the inlet is closed, the lagoon essentially
collects freshwater from the tributaries leading to stratification of the water column.
In the late 70’s an intensive raft culture of mussel (Mytilus edulis) was introduced at
Albufeira lagoon. The intensive culture of filtering organism in low-energy environments may raise
particular sustainability problems, such as changes in sedimentation rates (Schettini et al., in
press), in sediment organic content and in nutrient cycles.
The main goal of this work is to characterize the Albufeira lagoon at micro timescale using a
multidisciplinary approach; a number of parameters that are important to establish present day
environmental conditions and to understand actual dynamics of this lagoon have been assembled
to build an integrated data base; in turn, these elements are of crucial importance to the
interpretation of past sedimentary registers and help to build models of paleoenvironmental
evolution of lagoonal areas.
Methods
The micro timescale approach referred to in this work relied upon the study of bottom
sediments sampled in 2003 during two surveys – february/march, shortly before barrier breaching
at the end of a long period of isolation from the ocean, and june, following a period of inlet activity
and exchange with the ocean. In each survey, 20 sediment samples were collected (Fig. 1b)
using a Van Veen grab sampler operated from a small boat.
4264.5
N
A.
¿
LISBOA
LISBON
Tagus
Estuário
Estuary
do Tejo
4264
Atlânti
c
Ocean
Trafaria
Albufeira
Lagoon
Espichel
Cabo Espichel
Cape
100
0 100km
© http://geocid-snig.igeo.pt
B.
go
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4263.5
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d
an
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e
9
10
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13
14
15
16
17
a
go
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a
ibnid
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A
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iddaa
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5
0
10
20km
4263
4262.5
4262
484
1
4
2
3
5
484.5
485
18
19
20
8
485.5
486
486.5
487
487.5
488
Figure 1 - A - Location of Lagoa de Albufeira in the coastal arc of Caparica-Espichel; B – The main bodies of Lagoa de
Albufeira and location of sediment samples (UTM Coordinates, European Datum 50).
Sedimentological analysis (texture, pH - determined using the electrometric method
according to Head (1980) and classified following Pratolongo (in Costa, 1999), organic matter
54
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
(OM) - determined through oxidation with potassium-dichromate followed by titration using ironsulphate (Standard E-201, LNEC, 1967) and CaCO3 content - determined gasometrically using an
Eijkelkamp calcimeter) have been performed in all samples, whereas geochemical analysis
(major and trace elements determined by EDXRF – Araújo et al., 2002) and quantification of the
calcareous nannoplankton using the "settling" technique (Ferreira & Cachão, 2003) were carried
out only in the first and second surveys, respectively. Dimensional and sorting (textural)
classification of sand follows Friedman and Sanders (1978). The Enrichment Factor (EF),
describing the relative concentration of elements in a given sample was calculated by Loring &
Rantala, 1992:
⎞
EF = ⎛⎜ [Metal ]sample [Al ]
⎟
sample ⎠
⎝
([Metal ]AverageShale
[Al ]AverageShale )
In order to evaluate the impact of the Mytilus edulis farming in this lagoonal system,
particles settling through the water column have been collected in sediment traps, suspended
during 7 days close to the bottom right under a raft in two occasions (July 2003): A – open-inlet
conditions, at 11m depth and (B) – closed- inlet conditions, at 10m depth. This material was
analyzed for sedimentological and paleocological purposes.
Results and Discussion
Similar textural and compositional results have been found in sediment collected in both
surveys: in central and deeper zones of Lagoa Grande and Lagoa Pequena prevail muddy,
neutral to subalkaline (pH 7.3 to 7.6) sediment, with important bioclastic (CaCO3 ranging between
3 and 29%) and OM (3 to 7%) contents; in the vestibular area and fluvial fans of Apostiça and
Aiana rivulets the sediment is essentially sandy, subalkaline (pH 7.6 to 8.5) with low content in
OM (<2.1%) and CaCO3 (<5%) (Fig. 2A,B). In the vestibular zone, coarse moderately to well
sorted sand predominates, while in the alluvial fans sand is medium, moderate (Aiana) to
moderately well sorted (Apostiça).
4264.5
4264.5
4264
A.
6.3
12.8
29.6
34.4
2.4
98.4
54.9
20.3
10 0
4264
21.5
90
B.
5.0
80
7.2
4263
98.2
98.6
0.0
2.1
5.4
5.3
4.9
4263.5
36.8
21.39.5
17.4
70
50
15.0
4263
0.0
0.0
30
4262.5
7
4.9
6
6.3 6.0
40
33.9
4262.5
5.8
5
6.5
4
5.5
3
0.0
20
2
10
484.5
485
485.5
486
9
8
5.8
60
99.2
4262
484
10
5.1
10.3
4263.5
5.5
3.8
4.2
486.5
487
0
4262
487.5
484 488
1
0
484.5
485
485.5
486
486.5
487
487.5
488
Figure 2 – Distribution of some sedimentological parameters in lagoonal bottom sediments collected in the second survey
(June 2003): A – percentage particles >63µm; B – percentage of organic matter.
Values of major elements such as Si and Al are related to sediment mineralogy, and may
be used as indirect markers of texture: essentially sandy sediments exhibit the highest values of
Si (41-45%) and the lowest values of Al (1-3%), while muddy sediments are comparatively
enriched in Al (4-9%), K and Rb (probably associated with mica) and naturally associate with
other elements bearing affinity for organic and silt-clay fractions (e.g. heavy metals). Sediment
with important bioclastic component is clearly identified by the highest concentrations in Ca
(>1,6%) and Sr (>100mg/kg). As expected, fine sediment accumulated under the influence of the
tidal inlet is enriched in marine-borne elements (Cl, Br and S).
To distinguish natural concentration from anthropogenic enrichment, Loring & Rantala
(1992) suggested plotting concentrations of metals versus Al, and values that plot above the trend
line of linear regression are considered as contaminated. Cr, Ni and Cu in Albufeira lagoon show
high correlation values with Al (R2 0.75, 0.89 and 0.88, respectively), suggesting natural
occurrence for these elements, while Zn and Pb (especially the samples of Lagoa Grande and
near Aiana alluvial fan) show lower correlation values (Fig. 3A), with enrichment factors that reach
2.4 and 5.1, respectively (Fig. 3B), indicating possible anthropogenic influence.
55
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
R2 = 0.4706
0
1
2
3
4
5
Al (%)
6
7
8
9 10
R2 = 0.5322
0
1
2
3
4
5
6
Al (%)
7
8
9 10
Cr Lagoa
Ni Pequena
Cu
Zn
Pb
Lagoa Grande
5
4
Aiana
6
B.
200
180
160
140
120
100
80
60
40
20
0
Enrichment Factor
80
70
60
50
40
30
20
10
0
Zn (mg/kg)
Pb (mg/kg)
A.100
90
Apostiça
Calcareous nannoplankton content in bottom sediment displays a longitudinal gradient with
maximum values (6.2x106 coccoliths/g) under the influence of tidal inlet and decreasing upstream.
The identified assemblage was mainly composed by Gephyrocapsa oceanica, Gephyrocapsa
muellerae, Gephyrocapsa ericsonii and Emiliania huxleyi with maximum values of 2.25 x106, 1.38
x106, 9.69 x105, and 7.62 x105 coccoliths/g, respectively. Sediment collected east of the outlet of
Aiana rivulet is completely barren of coccoliths.
During the active-inlet period the materials collected in the trap located under the raft are
essentially muddy (silt+clay >56%), subalkaline (pH 8.0-8.1), with OM content between 16 and
19% and exhibiting 16.5x106 coccoliths/g. In closed-inlet conditions these deposits enriched in
mud (silty+clay >75%) and OM content (22-25%), pH decreased of to neutral values (7.2-7.4) and
the calcareous nannoplankton content dropped to 8.1x106 coccoliths/g. The values obtained at
11m depth (active inlet) and 10m depth (inlet absent) for the flux of particulate suspended matter
were 0.142 and 0.092 kg/m2.day, respectively.
3
2
1
0
1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 20 14 18 19
Sampled stations
2
Figure 3 - A - Plot of Pb and Zn versus Al in bottom lagoonal sediment, and correlation coefficient (R ); B – Enrichment
Factor of bottom lagoonal sediments in different sampling sites.
Conclusions
Textural, compositional and geochemical results obtained from bottom sediment allow the
definition of areas with different dynamic conditioned mainly by the efficiency of the tidal inlet and
fluvial discharge. In the lagoonal central, low energy zones, muddy sediment predominate
enriched in organic matter and bioclasts, and show high concentrations in Al, Ca and Sr, as well
as in heavy metals. The proximity to the ocean and to a fluvial source, locally increase energy
levels and the deposits accumulated there are essentially sandy and rich in Si. Zn and Pb are the
only elements that suggest some degree of anthropogenic contamination, mainly in the Lagoa
Grande, reaching FE of 2.4 and 5.1, respectively.
Mytilus edulis are filtering organisms responsible for the increase of vertical flux of OM from
the water column to sediment in the lagoonal system. The results obtained in the Albufeira lagoon
suggest that particulate suspended matter near the rafts is enriched in OM and coccoliths
comparatively to bottom sediments elsewhere in the lagoon. When the lagoon looses capacity of
mass exchange with the ocean the number of coccoliths in trapped sediment decreases and the
OM content increases.
Acknowledgments
This work was funded by the FCT project «Global vs Local Forcing Factors and Paleoenvironmental Changes of Estuaries
and Lagoons of SW Portugal Since the Lateglacial » (POCTI/MAR/15231/99). The authors thank skipper Hernani
Rodrigues for the use of his fishing boat and M. J. Balsinha, A. L. Rodrigues, G. Costa, L. Matos and M. L. Santos for help
in sedimentological analysis of samples collected in the first survey.
References
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias,
J.M.A. 2002. Geochemical Tracers of Northern Portuguese Estuarine Sediments on the Shelf. Progress in
Oceanography, 52: 277-297.
Costa, J.B. 1999. Caracterização e constituição do solo. Fund. Cal. Gulbenkian. Lisboa, 4ª ed., 527p.
Head, K. 1980. Manual of soil laboratory testing. Volume 1: Soil classification and compaction tests. Pentech Press,
London, 334p.
Ferreira, J. & Cachão, M. 2003. Nanofósseis calcários em fácies costeiras: revisão de técnicas de estudo. Ciências da
Terra (UNL), Lisboa, nº esp. V, CD-ROM, A76-A78.
Friedman, G.M. & Sanders, J.E. 1978. Principles of Sedimentology. John Wiley & Sons, New York, 792p.
L.N.E.C. – Laboratório Nacional de Engenharia Civil 1967. Especificação E 203, Solos – Determinação do pH.
Documentação normativa, Outubro de 1967. 2p.
56
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Loring, D.H. & Rantala, R.T.T 1992. Manual for the geochemical analyses of marine sediments and suspended particulate
matter. Earth-Science Reviews, nº 32. Elsevier Science Publishers, Amsterdam. 235-283.
Schettini, C.A.F., D’ Aquino, C.A. & Carvalho, C.E.V. in press. Fine sediment dynamics under blue mussel aquaculture
plots in a semi sheltered bight: the Armação do Itapocoroy, SC, Brasil. Proceedings ICS 2004, Journal of Coastal
Research, SI 39.
57
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
MICROSCALE CHARATERIZATION OF LAGOA DA SANCHA - AN ACIDIC
DUNE SLACK IN THE PORTUGUESE SW COAST (TALK)
Tânia Ferreira1, Anabela Cruces1, Maria Conceição Freitas1, César Andrade1, Maria de Fátima
Araújo2 & Robert Bao3
1
Laboratório de Processos Costeiros, Centro e Departamento de Geologia da Faculdade de Ciências da Universidade de
Lisboa. Edifício C6, 3º Piso. Campo Grande. 1749-016 LISBOA. Portugal; [email protected], [email protected],
[email protected], [email protected]
2
Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém. Portugal;
[email protected]
3
Departamento de Xeologia, Facultade de Ciencias, Universidade da Coruña, Campus da Zapateira s/n, 15071 A
Coruña, España; [email protected]
Introduction
The Tróia-Sines littoral stretch (Fig. 1A), located in the SW coast of Portugal, contains
numerous and diverse wetlands such as small estuaries, lagoons and dune slacks. Lagoa da
Sancha, located 5km north of Sines (Fig. 1B), occupies the most external dune slack in a PleistoHolocene coastal dune complex and is isolated from the ocean by a sand barrier, which is
occasionally overwashed.
This elongated depression shows maximum length and width of 1km and 200m,
respectively. Margins are colonized by dense reed-swamp vegetation consisting mainly in
Phragmites australis. This is a peculiar interdune slack in Portugal and its uniqueness derives
from the highly acidic character of the water, an iron-rich crust at the sediment-water interface,
resistant to submersion of well developed desiccation cracks in the bottom sediment surface and
a large catchment surface that reaches 35km2.
Despite the ecological and geological value of Lagoa da Sancha, the existing knowledge on
its origin, evolution and dynamics is poor. In this context, the main objective of this paper is to
present first results of a pioneer study concerning the sedimentological, geochemical and
paleoecological caracterization of the Lagoa da Sancha bottom sediments, which will contribute to
build environmental models of this coastal system.
Figure 1 - A: Location of the Tróia Sines stretch in the
Portuguese coast. B: Location of Lagoa da Sancha, in the
Tróia-Sines coast. C: Sampling points in Lagoa da Sancha.
58
Methods
Physical-chemical
parameters
(salinity, dissolved oxygen, pH, Eh and
temperature) of the water body were
measured in two surveys (June 2001 and
August 2002). The classification of water in
what concerns salinity and pH followed
Barnes (1980) and Teodorovich (in
Pettijohn, 1975), respectively.
In June 2001 8 bottom sediment
samples were collected (Fig. 1B) using a
Van Veen grab. Sedimentological analysis
(texture, pH – determined by the
electrometric method according to LNEC
(1967a) and classified following Pratolongo
(in Costa, 1999), organic matter (OM) determined
through
oxidation
with
potassium-dichromate followed by titration
using iron-sulphate (Standard E-201, LNEC,
1967b) and classified according to Costa
(1999) and CaCO3 content – determined
gasometrically
using
an
Eijkelkamp
calcimeter) have been performed in all
samples. Textural classification followed
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Flemming (2000). Major and trace elements have been determined by EDXRF (Araújo et al.,
2002) and paleoecological analyses (diatom content) were performed according to standard
procedures (Battarbee et al., 2001).
Results and Discussion
The water column varies seasonally and did not exceed 1m in June 2001 and 0.2m in
August 2002, a time during which the flooded area was much reduced; these circumstances
explain the homogeneity found in physical-chemical parameters and thus maximum values
recorded in each survey have been used for the water column characterization. In both surveys
an acidic (pH 3.2 and 3.5), oxidant (Eh max. +546mV), subsatured-satured in oxygen (6.5 and
9.5mg/l) and freshwater (salinity 0.9 and 3.8‰) environment has been found.
The bottom sediment is free of CaCO3, hyperacid (pH 2.66 - 3.18), highly organic (OM
varying between 11.9 and 18.3%) mud (%>63µm >97.5%), except in the overwash influenced
zone consisting of muddy sand (Fig. 2A).
The concentration of major and trace elements (including heavy metals) in sediment
presents longitudinal and transversal gradients. The former is displayed by elements associated
to texture: concentration values of Si, K, Rb and Zr, increase northward suggesting the
incorporation of minerals such as quartz, mica (muscovite, biotite) and zircon, sourced from the
nearby beach and foredune sand and deposited via overwash; Br also increases northward as a
consequence of marine influence. The latter gradient is displayed by Fe, Mn and Cr, which occur
in higher concentrations in the southwestern zone of the wetland (Fig. 2); this pattern is probably
a consequence of more frequent exposure of bottom sediments in this section of the slack,
favouring precipitation of iron oxides/hydroxides at the surface; the presence of a thin iron crust at
water-sediment sediment interface and the iron coating of plant steams close to free surface of
water support this interpretation. Sediments show extremely high concentrations in Fe (up to
17%) (Fig. 2A), unusual in lagoonal/lake sediments. Mn and Cr have similar behaviour to Fe,
indicating their preferential association with this element. In contrast, they are extremely
impoverished in Ca (<0,1%) and Sr (<100 ppm), evidencing an acidic environment and eventual
leaching of bioclasts that may develop in, or be carried into, the slack.
55 diatom species were identified. According to data published on diatom autoecology (e.g.
Denys, 1991; Kjemperud, 1982; DeNicola, 2000 and Sabater et al., 2003), the majority of diatoms
that occur in these sediments are benthonic (>77%) or ticoplantonic (1 to 22%) and euplantonic
taxa are lacking, suggesting a shallow water column. Most of the diatoms have an oligohalobous
(salinity values under 5‰) character (58 to 82%), though some mesohalobous taxa (17 to 39%)
and even some marine Chaetoceros resting spores (which could be originated from overwash
events) occur. pH species classification showed a dominance of acidobionte diatoms (38 to 69%)
(Fig. 2B). A small percentage can be classified as alcaliphilous, indicating a possible allocthonous
origin (watershed) for these species.
The extreme environment conditions registered in both water and sediments of Lagoa da
Sancha dune slack share similarities with the Acid Sulphate Soils described by several authors
(e.g. Costa, 1999; web reference) and may result of the following sequence of events: 1)
deposition of bottom sediments rich in sulphur (marine sulphate and organic matter are the S
source) that remain stable as sulphides under anoxic conditions; 2) when these sediments are
exposed to atmosphere in a dehydration event, the oxidation of iron sulphides releases sulphur
and iron, among other metals; 3) soon after water becomes available sulphuric acid will be
formed; if Ca is available, a small decrease in pH is observed; otherwise, the strong decline in pH
(reaching values < 3) leads to extreme acidic conditions.
Conclusions
Lagoa da Sancha presents a very homogeneous acidic, oxidant, freshwater body, where
salinity and water input are mainly controlled by groundwater flow and evaporation, although there
are sedimentological, geochemical and paleocological evidences of contributions from overwash.
Bottom sediments consist essentially of acidic organic mud sourced on the surrounding
slopes, in the watershed, from in situ production and fallout.
59
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
The concentration of major and trace elements (including heavy metals) displays
longitudinal and transversal patterns. Two relevant results are: unusually high concentrations in
Fe (17%) that can be related with underground leaching and remobilization in acidic environment,
followed by precipitation of Fe-oxide films in oxidant conditions near surface and extreme low
concentrations in Ca and Sr.
Diatom taxa in sediment reveal an acidic, oligohalobous, shallow water environment, which
is in conformity with results from other proxies. Some of the taxa may have an allocthonous origin,
especially from the watershed.
100
80
60
%
40
20
0
<63µm-70.46
%O.M. –15.0
pH - 3.18
Fe (%)
<63µm-98.96
%O.M. –18.3
pH - 2.6
<63µm-97.81
%O.M. –16.9
pH - 2.71
<63µm-99.01
%O.M. –12.6
pH - 3.07
2.3
<63µm-97.60
%O.M. –17.5
pH - 2.68
<63µm-99.08
%O.M. –17.2
pH - 3.09
<63µm-98.09
%O.M. –15.4
pH - 2.72
Legend:
Desconhecido
Unknwon
Acidobionte
philous
Acidofilo
A
100
80
60
%
40
20
0
100
80
60
%
40
20
0
100
80
60
%
40
20
0
<63µm-98.65
%O.M. –11.9
pH - 2.75
100
80
60
%
40
20
0
100
80
60
%
40
20
0
100
80
60
%
40
20
0
100
80
60
%
40
20
0
Circumneutral
Alcalifila
B
Alcalibionte
philous
Indiferente
Figure 2 - A: Distribution in bottom sediments of %Fe, % O.M., pH and texture. B: Values and
distribution of pH autoecology inferred from diatoms.
We hypothesize that extreme conditions recorded in the study area may be similar to
environmental constrains leading to formation of Acid Sulphate Soils.
Acknowledgments
This work was funded by the FCT project «Global vs Local Forcing Factors and Paleoenvironmental Changes of Estuaries
and Lagoons of SW Portugal Since the Lateglacial » (POCTI/MAR/15231/99). The authors thank Ana Vidal, Director of the
“Reserva Natural da Lagoa de Santo André e da Sancha” for the facilities in the field work.
References
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias,
J.M.A. 2002. Geochemical Tracers of Northern Portuguese Estuarine Sediments on the Shelf. Progress in
Oceanography, 52: 277-297.
Barnes, R. S. K. 1980. Coastal lagoons. Cambridge University Press, 106 p.
Battarbee, R. W., Jones, V.J., Flower, R. J., Cameron, N. G., Bennion, H., Carvalho, L. & Juggins, S. 2001. Diatoms. In:
Smol, J. P., Birks, H. J, Last, W. M. (Eds) Tracking Environmental change using lake sediments. Vol. 3 Kluwer
Academic Publishers.
DeNicola, D. M. 2000. A review of diatoms found in highly acid environments. Hidrobiology, 433: 111-122.
Costa, J.B. 1999. Caracterização e constituição do solo. Fund. Cal. Gulbenkian. 4ª ed., 527 p.
Denys, L. 1991. A check-list of the diatoms in Holocene deposits of the western Belgian coastal plain with a survey of their
apparent ecological requirements- I- Introduction, ecological code and complete list. Ministere des affaires
economiques, Service Geologique de Belgique. 41p.
Flemming, B.W. 2000. A revised textural classification of gravel-free muddy sediments on the basis of ternary diagrams.
Continental Shelf Research 20: 1125-1137.
60
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Kjemperud, A. 1982. Late Weichselian and Holocene shorline displacement in parts of TrØndelag, Central NorwayAppendix:diatoms tables. Dr. scient. Thesis, Dept. of Geology, Univ. of Oslo.
L.N.E.C. - Laboratório Nacional de Engenharia Civil 1967a. Especificação E 203, Solos – Determinação do pH.
Documentação normativa, Outubro de 1967. 2 p.
L.N.E.C. - Laboratório Nacional de Engenharia Civil 1967b. Especificação E 201, Solos – Determinação do teor em
matéria orgânica. Documentação normativa, Outubro de 1967. 3 p.
Pettijohn, E. J. 1975. Sedimentary rocks. Harper & Row Publishers, Third edition, 628 p.
Sabater, S., Buchaca, T., Cambra, J., Catalan, J., Guasch, H., Ivorra, N., Muñoz, I., Navarro, E., Real, M. & Romani, A.
2003. Structure and fuction of benthic algal communities in an extrremely acid river. Journal of Phicology, 39: 481-489.
Web references:
http://www.ozestuaries.org/indicators/ls_acid_soils_f.html
61
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TRANSLUCENT HEAVY MINERALS FROM THE MINHO ESTUARY
SEDIMENTARY RECORD (TALK)
Catarina Fradique1, João Cascalho2 & Teresa Drago3
1
Instituto Hidrográfico, Lisboa; [email protected]
Museu Nacional de História Natural da Universidade de Lisboa; [email protected]
3
INIAP-IPIMAR, Olhão; [email protected]
2
This work focus the study of heavy minerals present in the sand fraction of one core (Minho
I) that represents about 30m of the sedimentary infilling record thickness, collected from the
Minho estuary in the scope of the Envi-Changes project.
The main objectives of this work are the determination of the main primary source for the
minerals identified, as well as the deduction of the main sediment sorting mechanisms operating
during the Holocene infill of the Minho estuary (Camarido coastal plain).
The heavy minerals study was carried out in 44 samples of the Minho I core in three grainsize sand classes, medium (0.5 – 0.25mm), fine (0.25-0.125mm) and very fine (0.125-0.063mm).
The heavy minerals were separated using sodium polytungstate (density 2.82), weighted and
mounted on microscope slides in Canada balsam. Between 300 and 400 grains per fraction were
identified and counted under the polarizing microscope. Eleven main translucent species were
counted and identified. The results are expressed on table 1.
Table 1: Mean content and standard deviation (STD) of the main translucent heavy minerals for the sand grain size
classes analysed (data from Minho I core).
HEAVY MINERALS
Mica
Andalusite
Tourmaline
Garnet
Staurolite
Amphibole
Apatite
Zircon
others
MEAN
STD
83.6
6.2
3.8
2.5
2.0
1.1
0.2
0.2
0.4
13.8
5.4
3.1
3.4
2.5
0.9
0.4
0.3
0.5
The relative abundance of the main translucent mineral species defines a provenance
signal compatible with the igneous and metamorphic rocks outcropping in the Minho basin. In
truly the extensive granite outcrops rich in mica minerals in the Minho basin (Liñán et al., 1994,
1980 and Oliveira et al., 1992), are the feasible source of mica found on the sediments analysed.
The presence of important outcrops of andalusite hornfels (Teixeira & Assunção, 1961; Castañon,
et al., 1981) can justify the relative abundance of this silicate found in the heavy mineral suite.
Other translucent minerals like for example tourmaline, apatite and zircon also attest the granite
provenance signal. Finally, the heavy mineral suite composed by garnet, staurolite and amphibole
has most likely a source related with the presence of shists, hornfels and other metamorphic
rocks in the Minho basin.
From the weight percentage of the total heavy minerals the median grain size was
computed. The data obtained was compared with the entire sand median grain size (Fig. 1).
Apparently the total heavy mineral content (Fig. 1, left) doesn’t show a visible correlation
with the median values of the heavy minerals and sand grain size. Nevertheless the significant
increase in the total heavy mineral percentage registered above -10m (Fig. 1, left) can be
interpreted as an important terrigenous input signal.
The median grain-sizes differences between heavy minerals and the entire sand fraction
show considerable variability along the core analysed (Fig. 1, left). In the deepest levels the
difference is high (more than 0.2mm). These levels fit in to the unit I of the Holocene infill of the
62
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Camarido costal plain defined by Drago et al. (2004). These median differences can be
interpreted as the result of a sorting process by previous bedload transport, because this
transport mode can involve the repeated grain entrainment which may amplify the size differences
between heavy and light minerals (Slingerland, 1977; Komar, 1989).
Minho I
5
5
0
0
-5
-5
-10
-10
depth (m)
depth (m)
Minho I
-15
-15
-20
-20
-25
-25
-30
-30
0
1
2
heavy mineral (%)
0.0
3
0.2
0.4
0.6
0.8
median grain size (mm)
Figure 1 – Left: variation of the heavy mineral percentage in the sand fraction; right: variation of grain size median values
with depth (heavy minerals in full line; sand in dashed line).
Between -28m and -2.5m the grain-size differences are considerably shorter and in some
cases are nearly zero. These values most likely indicate a previous sorting process promoted by
suspended load transport which is compatible with the existence of several levels composed by
muddy sand or sandy mud sediments, corresponding to the units II and III defined by Drago et al.,
2004). Above –2.5 m the median differences turn again higher revealing again sorting process by
previous bedload transport. These levels fit in the unit IV proposed by Drago, op. cit.
Acknowledgments
This paper is a contribution of the FCT project – Envichanges (PLE/12/00).
References
Castañón, L.G.C., Floor, P., Gómez, H.A., Hurtado, J.A., Dones, D.V.P., Palenzuela, J.M.Z. & Salinas, F.G. 1981. Mapa
Geologico de España (escala 1:50 000). Hoja de Pontevedra (4-10(185)). Instituto Geologico y Geominero de España,
Madrid, 45p.
Drago, T., Freitas, C., Andrade C., Fernandes P., Serina, S. & Gabriel S. 2004. Holocene sediments of na estuarine
coastal plain – The case of the Minho River (North Portugal). 23rd IAS Meeting of Sedimentology, 15-17 September
2004, Coimbra, Portugal.
Komar, P.D. 1989. Physical processes of waves and currents and the formation of marine placers. Aquatic Sciences, 1
(3): 393-423.
Liñán & collaborators 1994. Mapa Geológico de la Península Ibérica, Baleares y Canárias (1:1000000).Instituto
Tecnológico Geominero de España & Instituto Geológico e Mineiro de Portugal.
Oliveira, J.T., Pereira, E., Ramalho, M., Antunes, M.T. & Monteiro, J.H. & collaborators 1992. Carta Geológica de Portugal
(1:500000). Instituto Geológico e Mineiro.
Slingerland, R. L. 1977. The effects of entrainment on the hydraulic relationships of light and heavy minerals in sands.
Journal of Sedimentary Petrology, 47: 753-770.
Teixeira, C. & Assunção, C.T. 1961. Notícia explicativa da folha 1-C (Caminha) da Carta Geológica de Portugal na escala
1:50 000. Serviços Geológicos de Portugal, Lisboa, 41p.
63
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
GLOBAL VS LOCAL FORCING FACTORS AND PALEOENVIRONMENTAL
CHANGES OF ESTUARIES AND LAGOONS OF SW PORTUGAL SINCE THE
LATE GLACIAL (TALK)
Maria da Conceição Freitas & César Andrade
Departmento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Bloco C6, 3º piso, Campo Grande, 1749-016
Lisboa, Portugal; [email protected], [email protected]
Introdution
The project “Global vs local forcing factors and paleoenvironmental changes of estuaries
and lagoons of SW Portugal since the Late Glacial” (POCTI/MAR/15231/99) has been proposed
in 1999, initiated in October 2000 and will end in August 2005.
The main objective of this proposal was the identification of patterns of evolution and
sedimentary responses of estuarine and lagoonal environments of the SW Portuguese coast
since the Late-Glacial until present, using a multi and pluridisciplinar methodology adequate to
assess and separate the relative contributions of global vs local conditioning factors (sea-level
and climate changes, sediment availability and fluvial basin changes, anthropic influence).
Specific objectives were the study of past and present sedimentation patterns and rates in active
or silted estuarine/lagoonal structures using a suite of proxies of geochemical and
(palaeo)ecological nature, to detect palaeoclimatic and palaeoenvironmental changes that took
place throughout the last millennia. A complementary (but of primary importance) objective was
the attempt to understand, model and link processes/patterns of coastal change when studied in
different time-scales, ranging from the micro to the macroscale.
The results of this project link with the ones obtained in other national R&D project that
analyzed a different segment of the Portuguese coast, using similar methodologies - Late
Quaternary Environmental Changes from estuarine and shelf sedimentary record – PLE/12/00.
The exchange of results among scientists that worked in complementary field areas allowed the
comparison between the northern and southern sectors of the Portuguese coast and contributed
to an insight of the large-scale regional patterns of evolution of the coast as a whole.
Study Area
The coast under study extends along 180 km south of Lisbon (Fig. 1) and is high energy
and high-mesotidal. It comprehends: (1) two broad homothetic arcuate segments – TrafariaEspichel and Tróia-Sines – which include the coastal lagoons of Albufeira, Melides and Santo
André and the “Poços do Barbaroxa”, “Poço do Pinheirinho” and Lagoa da Sancha dune slacks;
(2) – an essentially rocky stretch, dominated by sea cliffs, where the Mira and Aljezur estuaries
are located.
The lagoon of Albufeira is located 20 km south of Lisbon (Fig. 1) and presents a flooded
surface, maximum width and length of 1.3 km2, 625 m and 3.5 km, respectively. It has an
elongate shape, its major axis trending northeast-southwest aligned with the Apostiça valley. The
lagoons of Melides and Santo André are located 20 and 15 km north of Sines (Fig. 1). The
Melides lagoon occupies an elongated flooded surface of 0.4 km2 while the Santo André lagoon
extends across 2.5 km2 and displays a complex shape (Fig. 1). The average depth and stored
volume of water vary seasonally, the Melides lagoon being generally shallower throughout the
year. All these lagoons are separated from the open ocean by reflective welded sand barriers
and most of the water exchange with the ocean is ensured by periodic artificial opening of an
inlet, in order to prevent euthrofication and drain the tributary alluvial plains that have been
reclaimed for agricultural purposes.
The Lagoa da Sancha, located 5 km north of Sines (Fig. 1), is the most external dune slack
in a Pleisto-Holocene coastal dune complex and is isolated from the ocean by a sand barrier,
which is occasionally overwashed. This N-S elongated depression shows maximum length and
width of 1 km and 200 m, respectively. The “Poços do Barbaroxa” and “Poço do Pinheirinho”,
located south of Lagoa de Santo André, are smaller slacks of the same dune complex.
The Mira River is located 30 km south of Sines in the Alentejo coast of Portugal (Fig. 1).
Its maximum width is 400 m and the depth varies between 5-10 m in the lower and medium
64
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
zones and less than 3 m in the upper reach. The Corgo do Porto is a small rivulet and incised
tributary on the right bank of the Mira River and discharges circa 3.5 km upstream of its mouth
which locates at Vila Nova de Milfontes. Its thalwegs, runs close to the left and scarped
embankment of an asymmetric flat-floored valley infilled due to extensive siltation by terrigenous
sediment, which forms an alluvial plain reclaimed for agriculture and aquaculture.
The Aljezur rivulet is located 60 km south of
Sines; in its terminal section the valley widens allowing
Tagus
estuary
the thalwegs, to meander in an alluvial plain 275 to 670
m wide; it meets the ocean in the southern extreme of
N Trafaria
the Amoreira beach.
¿
Albufeira
a
bid
Atlanti
c Oce
an
lagoon
rrá
aA
Methods
ra d
Tróia
Ser
A multidisciplinary approach have been
Espichel Cape Sado estuary
systematically used, involving sedimentary (texture, pH,
organic matter, CaCO3 content, morphoscopy, mineral
Melides lagoon
composition, XRay imagery), geochemical (major, minor
Serra de
Santo André lagoon
and trace elements, including heavy metals and stable
Grândola
Poços Barbaroxa
Baixo, Meio, Cima
isotopes), geophysical (magnetic properties, electrical
Lagoa da Sancha
resistivity surveys) and paleoecological (pollen, diatoms,
Sines
foraminifera, ostracoda, calcareous nannoplankton and
macrofauna) environmentally sensitive proxies. Dating
relied on 14C radiometric determination on thin slices of
Mira estuary
organic sediment performed by Beta Analytic Inc;
conversion to calendar years followed Stuiver et al.
(1998) when supplied by that laboratory and Stuiver et
al. (2005) in other cases. Recent sedimentation rates
have been evaluated by means of determination of
Aljezur estuary
210
Pb and 137Ce and complemented with estimates
derived from quantitative evaluation of the rate of soil
loss in catchments.
The methodology adopted addresses coastal
responses to spatial variability and to different time5
0
10 20km
scales. In what concerns the time variable, micro-,
meso- and macro-temporal scales have been
Figure 1 – Location of study areas.
considered.
The micro-scale approach is typical of engineering and planning and concerns short-term
processes varying from hours to decades. This approach relies on observation and measurement
of active processes and products in present-day active environments, including descriptive
parameters ob both sediment and water and morphological analysis. This scale of approach is
important to characterize and quantify present-day environmental conditions and to understand
the actual dynamics of coastal environments; the data assembled contribute to build an
integrated data-base describing actual analogues used to interpret past sedimentary registers
and to construct models of paleoenvironmental evolution.
Mesoscale comprehends the century dynamics. The study at this time-scale relies heavily
in the interpretation of documentary sources (iconographic and written elements) to which we
added high resolution processing and interpretation of short cores taken from the lagoonal
bottom, representing the last 200 years of sedimentation. This scale of approach provides both
qualitative and quantitative data and is important to assess the extension and nature of
anthropogenic influence and to sort out the coastal morphological evolution during historical
times.
Macroscale is typical of geology, and addresses processes/responses operating at
millenary periods, especially, in this study, those occurred since the Late-Glacial. In the SW coast
of Portugal, no outcrops of that age are found, so this study must use coring methods to collect
the sedimentary sequences accumulated in lowlands. Each area has been extensively cored
using light hand-operated equipment and this information was used to get an insight into the
100
65
0 100km
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
lithostratigraphical features and local variation and helped to select location to perform deep
boreholes mechanically assisted.
In what concerns spatial variability related to estuaries and lagoons, three main
sedimentary and morphodynamic systems have been considered: littoral, lagoonal/estuarine (ss)
and fluvial.
The littoral system comprehends the area most proximal to the ocean and where wave-,
tide- and wind-driven processes govern the dynamics; it contributes with marine water and
sediment and includes the barrier system (beach/dune/backbarrier), the inlet and inlet related
deposits (tidal deltas) and washovers. Boreholes performed in this area are referred below as
“littoral”.
The fluvial system extends through the drainage network and watershed, contributing with
fresh-water and terrestrial sediment; it includes the thalwegs, embankments and flood plains of
tributaries and also terminal alluvial fans accumulated in the interface with the lagoonal basin.
Boreholes in this area are referred below as “alluvial proximal” if drilled in the alluvial plain close
to the normal limit of lagoonal/estuarine flooding, and “alluvial distal” if performed in a more
upstream location.
The lagoonal/estuarine system (ss) stands in between and receives contributions from
both. It shows a great sensitivity in relation to the presence/absence of an active inlet and
exchange with the ocean and to meteorological conditions. Tides, tidal currents, locally winddriven waves and fresh-water input are the main forcing factors in this system.
Results
A. Lagoons/estuaries
A.1 – One littoral and four alluvial proximal long cores, retrieved from estuarine/lagoonal
areas, have been studied:
MB and MIGM, taken in the Melides lagoon, the former in the back-barrier and the latter in
the alluvial plain of the main tributary;
LSA, retrieved from the alluvial plain of the main tributary of Santo André lagoon;
MIRA, drilled at the Corgo do Porto alluvial plain;
ALJ, retrieved from the alluvial plain of the Aljezur rivulet.
The geological record associated to these systems consists of sedimentary sequences
where several units with paleoenvironmental significance may be considered (Fig. 2):
Unit I – this basal unit is characterized by 1 to 10 m of minerogenic sediment (minimum and
maximum thickness are found in MIRA/ALJ and Melides area, respectively), always barren in
micro and macrofossils and virtually free of organic matter; the texture varies from gravel to mud
in relation to the local energy level; marine-borne elements (I, Cl, Br, S) exhibit values under the
detection limit and the 87Sr/86Sr ratio is high. The oldest date found in this unit is 16.9 ka cal BP
(LSA).
Unit II – in general, sediments found in this unit are finer (sand to mud), with higher
proportion of both organic matter and bioclasts (shell and shell debris); marine-affiliated elements
occur in measurable quantities and the 87Sr/86Sr ratio is low. The paleoecological signature
indicates deposition in an environment open to the ocean, with assemblages typical of brackish to
marine water, the latter showing higher abundance and diversity of species; usually, the marine
influence increases to the top of the unit, reaching the maximum expression found in the whole
core. These materials were mainly deposited after 11 ka cal BP and until 5.5 ka cal BP. The
thickness of this unit varies significantly from core to core, between 14 m at MIRA and 1 m at ALJ.
Unit III – this unit is 7 to 9 m thick and consists of mud and fine sand in alluvial cores and of
essentially coarse to fine sand in the littoral core MB. Bioclasts and organic matter content are
usually high and pyrite (denoting anoxic conditions) may occur. Fossil assemblages indicate
alternating brackish and freshwater conditions.
Unit IV – this top unit is characterized by 1 to 5 m of minerogenic sediment, varying from
sand to mud, similar to those of Unit I in what concerns fossil content and values of marinerelated elements but occasionally more organic; these sediments are younger than 3 ka cal BP in
cores retrieved in alluvial plains of the lagoonal main tributaries (LSA and MIGM) but older in
66
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
cores MIRA and ALJ, associated to estuaries. An exception is found at MB, where this unit is
exclusively made of coarse, almost barren sand.
14400
16700
16900
-15
-16
-21
-24.5
-10.5
9030
10150
-11
-14.6
-0.09
AM
C-14
cal age
+4.6
Fluvial
+2.5
Fluvial
Fluvial
4830
7960
C-14
cal age
2800
MC
C-14
cal age
+1.8
+3.2
840
1500
8330
3450
Fluvial
-16
6290
-10
7010
7860
+2.2
APO
Fluvial
-6.9
4475
C-14
cal age
Fluvial
5580
-3
ALJ
Estuarine
Fluvial
3380
Estuarine
-1.7
Alluvial distal
+2.4
Estuarine/Marine
-10
540
Estuarine/Marine
11450
Lagoonal
Fluvial
7955
Estuarine/Marine
-8.8
C-14
cal age
MIRA
-0.1
Fluvial
-18
-21
-1.5
C-14
cal age
Fluvial
12340
MIGM
+3.4
Fluvial
10430
Estuarine/Marine
Estuarine/Marine
-14
8995
1520
3860
6190
Fluvial
-37
-11.5
7930
8020
C-14
cal age
Fluvial
Barrier
-27
LSA
-2.5
-13
-17
+2.7
2565
Fluvial
Height (msl) - m
+0.3
C-14
cal age
Lagoonal
MB
Fluvial
Alluvial proximal
Littoral
+2.8
5910
6650
7370
9180
7790
-5.5
-3.5
7950
6300
+1
Figure 2 – Schematic representation (out of scale) of the facies succession found in cores referred in text (msl – mean sea
level).
A.2 - Three alluvial distal long cores, retrieved from estuarine/lagoonal areas, have also
been studied:
APO and AM, drilled in the alluvial plain of eastern tributaries of Albufeira lagoon;
MC, taken from the alluvial plain of the main tributary of the Melides lagoon.
These cores exhibit only two contrasting sedimentary units:
- at APO and AM, the lower unit consists of circa 5 m of organic mud and peat deposited
after circa 8 ka cal BP in terrestrial environment, in relation with variable phreatic surface,
indicated by the pollen record: water table remained higher until circa 4.9 ka cal BP, lower
between 4.9 and 3.2 ka cal BP and intermediate until 2.8 ka cal BP at APO, and 0.7 ka cal BP at
AM. Pollen of dune vegetation occurs only after 5.9 ka cal BP, increasing significantly to the top of
this unit. At MC the unit consists of 2 m of organic material (organic matter content reaching
90%); the phreatic surface would have been lower between 6.3 and circa 3.9 ka cal BP and
higher between 3.9 and 0.8 ka cal BP;
- in all cores the top unit is made of 1 to 2 m of minerogenic sediments, similar to those of
Unit IV in LSA and MIGM.
B. Dune slacks
Sediment accumulated in all the studied slacks (PP- Poço do Pinheirinho, BC, BM, BB –
Poços do Barbaroxa de Cima, do Meio, de Baixo, respectively and LS – Lagoa da Sancha) rests
upon dune sand and consist of one or two lithostratigraphical units: a basal unit corresponding to
carbonate-free peaty material and organic mud (25-77% organic matter), which may extend up to
the surface; texture and composition of this material suggests in situ sedimentation in close
dependence of variation in the water level within the slack: organic deposits associate with
persistent very shallow reed swamp facies whereas organic silt-clayey sedimentation indicates
permanence of higher levels of inundation, leading to the recession of the vegetation towards the
marginal slopes; in cases, a top unit is present (LS), consisting essentially of minerogenic mud in
agreement with the increase in concentration of Al, Si, K, Ti, Rb and Zr, suggesting a change
towards an external source. Dating results of the basal peats range between > 30000 BP and 5.4
ka cal BP and are compatible with a westward prograding coast built through the accretion of
successive beach ridges.
Discussion and conclusions
Results obtained from the infill of distinct wetlands of the SW Portuguese coast disclose a
succession of sedimentary episodes controlled by distinct environmental constrains. Pleistocene
sedimentation corresponds invariably to terrestrial facies and is represented by fluvial materials
67
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
deposited closer or farther the main channel, contemporaneous of a low sea level (at least 30 m
below present) and of a distal shoreline. The persistence of a low base level must have favored
incision of deep valleys and the development of an uneven landscape. During Early Holocene the
inherited erosive depressions were rapidly drowned by the Holocene transgression, creating rialike environments and wide open marine gulfs, the transgressive maximum being recorded
between 6.5 and 5.5 ka cal BP, with the exception of ALJ where it was dated earlier (circa 8.3 ka
cal BP).
Following this stage all indicators point to a change to transitional environments. In cases,
this change translates into sedimentation of lagoonal facies implying the emplacement of terminal
sandy barriers favored by the deceleration of sea-level rise rate. Data obtained at MB favors a
mechanism of widening of an aggrading barrier rather than roll-over of the whole structure. Since
this time onwards the lagoons alternated periods of complete isolation from the sea with others
when barrier breaching allowed connection and exchanges with the ocean. In other cases, the
decelerating sea-level rise promoted the establishment of estuarine conditions that became more
restricted through time.
Both lagoons and estuaries evolved as such until present, reducing their depth and
extension essentially at the expense of terrestrial sediment entrapped in marginal alluvial fans
and floodplains. The silting process occurred in time probably with different intensities; in fact,
archeological and documentary data suggest that the flooded surface experienced minimum
changes between the Holocene transgressive maximum and circa 1500 BP, in spite of a relatively
stable base level.
The Pleistocene and Holocene sedimentary record of the studied region indicates the
existence of a complete sedimentary cycle; this cycle includes a transgressive phase followed by
a regressive one, both associated to positive eustatism. Assuming negligible neotectonic effects
in this section of the coast, it may be concluded that prior to 6.5 ka cal BP the eustatic forcing
factor translated by rapid sea level rise dominated the pattern of coastal change in the SW of
Iberian Peninsula. The deceleration of the sea level rise rate post 6.5-5.5 ka cal BP triggered the
dominance of local forcing factors (e.g. sediment availability, permeability of barriers,
anthropogenic influence), which became preeminent over global factors in controlling coastal
changes. The balance between the sea level rise rate and the amount of sediment delivered to
these areas is negative, leading to the regression expressed by the two topmost sedimentary
Units, despite the positive eustatism that persists throughout the Late Holocene.
The relative sea level rise rate along the Portuguese coast increased to +1.5 mm/year
(Dias & Taborda, 1992) since the early 19th century in consequence of global warming driven by
anthropogenic activity (IPCC, 2001). This figure is similar to average rate of change reported
elsewhere in the world and significantly higher than the one characterizing the Late Holocene.
Throughout the 20th century the Portuguese coast displayed signals of increasing sediment
starvation which resulted from the cut off of terrestrial sediment sources and led to widespread
erosion of significant ribbons of exposed coast. However, the evolution of Portuguese
southwestern wetlands is still towards siltation, therefore maintaining the regressive signal in spit
of the acceleration of the sea level forcing.
Acknowledgements
This work was funded by the FCT project «Global vs local forcing factors and paleoenvironmental changes of estuaries
and lagoons of SW Portugal since the Late Glacial » (POCTI/MAR/15231/1999) co-financed by FEDER (EU).
References
Alday, M., Cearreta, A., Cachão, M., Freitas, M.C., Andrade, C. & Gama, C. accepted. Micropalaeontological Record of
Holocene Estuarine and Marine Stages in the Corgo do Porto Rivulet (Mira River, SW Portugal). Estuarine, Coastal and
Shelf Science.
Andrade, C. & Freitas, M.C. 1998. Architecture and recent development of an estuarine detached beach. The Alfeite sand
spit (Tagus estuary, Portugal). Proceedings, Littoral’98 - Eurocoast Fourth International Conference – Sustainable
waterfront and coastal developments in Europe: socioeconomics, technical and environmental aspects, 101-109.
Andrade, C. & Freitas, C. 2000. An example of rapid coastal change associated with an extreme event: the Algarve coast
of Portugal. In: Smith, D.; Raper, S.; Zerbini, S.& Sanchéz-Arcilla, A. (Eds.) - Sea level change and coastal processes.
Implications for Europe. Research results and recommendations. Energy, Environment and Sustainable Development,
European Comission, 139-150.
68
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Andrade, C. & Freitas, M.C. 2001. Transformação litoral e equilíbrios perturbados: exemplos do litoral Português. In:
Moreira, M.; Moura, A.; Granja, H. & Noronha, F. (Eds.). Homenagem (in honorium) Professor Doutor Gaspar Soares
de Carvalho, Braga, 195-212.
Andrade, C. & Freitas, M.C. 2004. Stratigraphical evidence of Late Holocene barrier breaching and extreme storms in
lagoonal sediments of Ria Formosa, Algarve, Portugal. Marine Geology, 210: 339-362.
Bao, R., Freitas, M.C. & Andrade, C. 1997. Análisis Paleoambiental de la Sedimentación Tardiholocénica de la Lagoa de
Albufeira (Portugal) - Resultados Preliminares. In: Cuaternario Ibérico, Associação Espanhola para el Estudio del
Cuaternario, J. Rodríguez Vidal, Ed., Huelva, 171-175.
Bao, R., Freitas, M.C. & Andrade, C. 1999. Separating eustatic from local environmental effects: a late holocene record of
coastal change in Albufeira lagoon, Portugal. The Holocene, 9, 3: 341-352.
Brito, P., Amorim, A., Andrade, C., Freitas, M.C. & Monteiro, H. 2003. Assessment of morphological change in estuarine
systems – a tool to evaluate responses to future sea level rise. The case of the Sado Estuary (Portugal). II Congresso
sobre Planejamento e Gestão da Zona Costeira dos Países de Expressão Portuguesa - 12-19 Outubro, Recife, Brasil,
edição em CD-ROM, 5 p.
Cearreta, A., Alday, M., Freitas, M.C., Andrade, C. & Cruces, A. 2002. Modern and Holocene foraminiferal record of
alternating open and restricted environmental conditions in the Santo André lagoon, SW Portugal. Hydrobiologia,
475/476: 21-27.
Cearreta, A., Cachão, M., Cabral, M.C., Bao, R. & Ramalho, M.J. 2003. Late Glacial and Holocene Environmental
Changes in Portuguese coastal lagoons: 2 - The Santo André coastal area (SW Portugal) during the last 14 000 years
based on micropaleontological multiproxy evidence. Holocene, 13 (3): 447-458.
Cruces, A., Freitas, C. & Andrade, C. 1999. Factores forçadores globais versus locais na evolução tardiglaciar e
holocénica de sistemas lagunares do litoral SW português. Encontros de Geomorfologia, Universidade de Coimbra,
105-113.
Cruces, A., Freitas, M.C., Andrade, C., Munhá, J., Tassinari, C., Vale, C. & Jouanneau, J.-M. in press. The importance of
geochemistry in multidisciplinary studies of lagoonal environments at different time scales: the case of Santo André
lagoon (SW Portugal). Journal of Coastal Research, SI 39: 7p.
Cruces, A., Freitas, M.C., Araújo, M.F., Andrade, C. & Ferreira, T. in press. Caracterização geoambiental da depressão
interdunar da LAGOA DA SANCHA (SW Portugal). Proceedings, Interdisciplinary Symposium on Wetlands, 2005, 15 p.
Dias, J.A. & Taborda, R. 1992. Tidal Gauge Data in Deducing Secular Trends of Relative Sea Level and Crustal
Movements in Portugal. Journal of Coastal Research, 8: 655-659.
Dinis, J.L., Costa, P., Henriques, V., Freitas, M.C. & Andrade, C. submitted. Natural to anthropogenic forcing in the
Holocenic evolution of three coastal lagoons (Caldas da Rainha valley, western Portugal). 2005, Quaternary
International.
Drago, T., Naughton, F., Moreno, J., Rocha, F., Cachão, M., Sanchez Goñi, M.F., Oliveira, A., Cascalho, J., Fatela, F.,
Freitas, C. & Andrade, C. 2002. Geological record of environmental changes in the Douro estuary (NW Portugal), since
the Late Glacial. Proceedings, Littoral 2002 - Eurocoast, Vol. III: 341-346.
Drago, T., Freitas, C., Cachão, M., Moreno, J., Cascalho, J., Oliveira, A., Naughton, F., Fradique, C., Silveira, T. & Fatela,
F. 2003. Douro estuary sedimentary record and sea level rise evolution in the last 14 000 years. 4th Symposium on the
Atlantic Iberian Continental Margin, Vigo, Thalassas, 19(2a): 101-103.
Drago, T, Freitas, C., Rocha, F., Cachão, M., Moreno, J., Naughton, F., Fradique, C., Araújo, F., Silveira, T., Oliveira, A.,
Cascalho, J. & Fatela, F. In press. Paleoenvironmental evolution of estuarine systems during the last 14000 years – the
case of Douro estuary (NW Portugal). Journal of Coastal Research, SI 39, 7p.
Freitas, M.C. 1989. Evolução da Lagoa de Óbidos nos tempos históricos. GEOLIS, vol. III, Fasc. 1 e 2: 105-117.
Freitas, M.C. 1989. Natureza dos sedimentos de fundo da Lagoa de Óbidos. GEOLIS, vol. III, Fasc. 1 e 2: 144-153.
Freitas, M.C. 1990. Lagoa de Albufeira. Estudo preliminar. GEOLIS, vol. IV, fasc. 1 e 2: 153-172.
Freitas, M.C. & Andrade, C. 1994. Tidal inlet evolution and hydraulic characteristics at Albufeira lagoon. Proceedings,
Littoral 94 - Eurocoast - Second International Symposium, vol. I: 257-271.
Freitas, M.C. 1996. Lagunas costeiras: ambientes em evolução. Seminário sobre Lagunas Costeiras e Ilhas-barreira da
Zona Costeira de Portugal. Associação Eurocoast - Portugal, 107-123.
Freitas, M.C. & Andrade, C. 1997. Sistemas fluvio-lagunares a Sul do Tejo: evolução a escalas temporais diferentes.
Colectânea de Ideias sobre a Zona Costeira de Portugal. Associação Eurocoast-Portugal, 525-545.
Freitas, C. & Andrade, C. 1998. Evolução do litoral português nos últimos 5000 anos. Alguns exemplos. Almadan, Centro
de Arqueologia de Almada, 64-70.
Freitas, M.C., Andrade, C. & Jones, F. 1992. Recent evolution of Óbidos and Albufeira coastal lagoons. Proceedings,
International Coastal Congress - ICC'92, Kiel, 167-186.
Freitas, M.C., Cachão, M., Fonseca, L.C., Caroça, C. & Carvalho, A.M.G. 1994. Unusual co-ocorrence of Serpulids and
Bryozoa in a lagoonal system (Albufeira coastal lagoon - Portugal). Gaia, nº 8: 39-46.
Freitas, M.C., Cruces, A. & Andrade, C. 1999. As lagunas de Melides e Santo André: evolução e comportamento
morfodinâmico. In: G. Soares de Carvalho, F. Veloso Gomes & F. Taveira Pinto (Eds) - A zona costeira do Alentejo.
Associação Eurocoast-Portugal, 27-44.
Freitas, M.C., Andrade, C., Moreno, J.C., Munhá, J.M. & Cachão, M. 1999. The Sedimentary record of recent (last 500
years) environmental changes in the Seixal Bay marsh, Tagus estuary, Portugal. Geologie en Mijnbouw, 77: 283-293.
Freitas, M.C., Andrade, C. & Cruces, A. 2000. A importância do conhecimento geológico no ordenamento de ambientes
lagunares: exemplos do litoral SW de Portugal. Seminário Associação Eurocoast-Portugal “Perspectivas de gestão
integrada de ambientes costeiros”. Coimbra, 127-142.
Freitas, M.C., Andrade, C. & Cruces, A. 2002. The geological record of environmental changes in southwestern
Portuguese coastal lagoons since the Lateglacial. Quaternary International, vol. 93-94 (C): 161-170.
Freitas, M.C., Andrade, C. & Cruces, C. 2002. Estudo Integrado do Sistema Lagunar de Santo André – Monte Velho.
Colecção Estudos sobre Alentejo, 1, DRAOT Alentejo, 80 p.
69
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Freitas, M.C., Andrade, C., Cruces, A., Amorim, A., Cearreta, A. & Ramalho, M.J. 2002. Coastal Environmental Changes
at Different Time-Scales: the Case of the Melides Barrier-Lagoon System (SW Portugal). Proceedings, Littoral 2002,
Eurocoast, Vol. III: 397-402.
Freitas, M.C., Andrade, C., Cruces, A. & Cachão, M. 2003. Sedimentary response to sea-level changes of Portuguese
lowlands since the Late Glacial - a multidisciplinary approach. IX Congresso da Associação Brasileira de Estudos do
Quaternário & II Congresso do Quaternário dos Países de Língua Ibérica – 12-19 Outubro, Recife, Brasil, edição CDROM, 5 p.
Freitas, M.C., Andrade, C. & Cruces, A. 2003. Middle/Late Holocene alluviation of SW Portuguese lagoons – causes,
sediments and rates. Coastal Sediments’03 – The fifth International Symposium on Coastal Engineering and Science of
Coastal Sediment Processes, 18 - 23 May, Clearwater Beach, Fl., edição em CD-ROM, 14 p.
Freitas, M.C., Andrade, C., Rocha, F., Tassinari, C., Munhá, J.M., Cruces, A., Vidinha, J. & Silva, C.M. 2003. Lateglacial
and Holocene environmental changes in Portuguese coastal lagoons: 1. The sedimentological and geochemical
records of the Santo André coastal area (SW Portugal). The Holocene, 13, 3: 433-446.
Freitas, M.C., Cachão, M., Andrade, C. & Cruces, A. 2003. O ciclo sedimentar do Tardiglaciar e Holocénico. Exemplos do
litoral SW português. VI Congresso Nacional de Geologia, Ciências da Terra (UNL), Lisboa, nº esp. V, CD-ROM, H61H64.
Freitas, M.C., Cruces, A. & Andrade, C. in press. A importância do conhecimento geológico no ordenamento de
ambientes lagunares: o exemplo da Lagoa de Santo André. 2º Encontro sobre a Lagoa de Santo André, 2000.
Freitas, M.C. & Ferreira, T. 2004. A Lagoa de Albufeira. Geologia. Instituto da Conservação da Natureza/Centro de Zonas
Húmidas, 11-52.
IPCC 2001. Third Assessment Report – WG2 Technical Summary Climate Change 2001: Impacts, Adaptation and
Vulnerability, 20-73.
Henriques, M.V., Freitas, M.C., Andrade, C. & Cruces, A. 2002. Alterações morfológicas em ambientes litorais desde o
último máximo transgressivo: exemplos da Estremadura e do Alentejo. Actas, 1º Seminário de Geomorfologia.
Contribuições para a dinâmica geomorfológica, APGeom, Vol. 1: 99-109.
Pinto, C., Freitas, M.C. & Andrade, C. 2000. Elementos sobre a evolução tardi-holocénica da restinga da Ponta da
Passadeira (Barreiro – Estuário do Tejo). Livro de Actas, Pangea 2000 - I Jornadas de Jovens Geólogos. D. Carapinha,
H. Alvalade & J. Ferrer (Eds.), 200-211.
Santos, L., Sanchez Goñi, M.F., Freitas, M.C. & Andrade, C. 2002. Climatic and environmental changes in the Santo
André coastal area (SW Portugal) during the last 15,000 years. In: Zapata, M.B.R.; Valiño, M.D.; Rodríguez, A.V.;
García, M.J.G.; Azcárate, T.B.; Gutiérrez, I.B. & Mendizábal, I.M. (Eds.) Quaternary climatic changes and
environmental crises in the Mediterranean Region Meeting, 175-179. also edited in CD-ROM.
Silva, A., Remédio, A., Ramos, R., Miranda, T., Freitas, M.C., Andrade, C., Cruces, A., Ferreira, T., Piedade, M.
submitted. Caracterização dos depósitos holocénicos da planície aluvial da ribeira da Cascalheira (Lagoa de Santo
André). Pangea'05 - VI Jornadas Ibéricas de Jovens Geólogos, Universidade de Évora, 2005, 7p.
Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, F.G., Van de Plicht, J. &
Spurk, M. 1998. INTCAL98 Radiocarbon age calibration 24,000-0 cal BP. Radiocarbon, 40: 1041-1083.
Stuiver, M., Reimer, P. & Reimer, R. 2005. CALIB 5.0 (www.program and documentation).
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SIMULATION OF PAST SEDIMENTARY DYNAMICS IN DOURO ESTUARY:
FIRST RESULTS (POSTER)
Selma Gabriel1, Flávio Martins2, Rui Taborda3 & Teresa Drago1
1
INIAP – IPIMAR. Av. 5 de Outubro 8700 Olhão, Portugal; [email protected], [email protected]
HIDROTEC - Escola Superior de Tecnologia, Universidade do Algarve, 8005-117 Faro, Portugal; [email protected]
3
Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Ed. C6, 1749-016,
Lisboa, Portugal; [email protected]
2
Objectives
The main objective of this work is to model the sedimentary dynamics in the Douro paleo
estuary, using a hydrodynamic model coupled with a sedimentary transport model. This numerical
model will be validated with the results obtained by multidisciplinary studies made on the Douro
estuary (Drago et al. 2002; Drago et al. 2004) that provide additional information on the
paleoenvironmental evolution of the NW Portuguese coast. These studies are based on a
multi-proxy approach which includes several analyses such as sedimentological (texture,
mineralogy of sand and clay, water content, carbonates and organic matter), micropaleontological
(counting and identification of foraminifera, calcareous nannoplankton and pollen associations)
and radiocarbon dating.
Settings
The Douro has a long (22 km) and narrow (maximum width of 1300 m) estuary trending
approximately W-E, located in the north-western Portuguese coast (Fig. 1). At the river mouth, in
the southern margin, it develops a sand barrier (approximately 1 km long) perpendicular to the
estuary axis known as Cabedelo, with a highly variable geometry modulated by local
hydrodynamics. The river discharge is controlled by Crestuma reservoir, located 22 km upstream
of the mouth (Water Institute Report vol. II, 2003).
Douro river is the one of the main contributors of freshwater and suspended sediment to
the Iberian continental shelf. In this sector, the shelf is flat and narrow, the width varies between
35 and 50 km and it is possible to distinguish some topographic features like the Oporto canyon
and other minor slope valleys that must had great importance in the sedimentary transfer to major
depths (Rodrigues & Dias, 1989; Vitorino et al. 2002).
Cabedelo
barrier
Methods
The proposed work will be
performed in two stages: the first
consists in the implementation of a
N
numerical sediment transport model for
present day conditions; in the second,
OPORTO
the calibrated model will be applied to
past conditions, where sea level was at
Douro river
lower levels.The numerical model used
Figure 1 - Location of the
in the present study is the MOHID
study area.
modelling system that includes a 3D
baroclinic hydrodynamic module for the
water column linked to both eulerian and
1Km
lagrangian transport modules (Martins et
al. 2003; Martins et al. 2004).
The sediment transport model uses several formulations for the vertical sediment velocity,
includingflocculation, deposition and ressuspension and can be used for both cohesive sediments
and sands. The sediment transport model interacts with the bottom model that manages the
sediment mass in the bottom and can include sediment consolidation.
MOHID was developed to be used directly in short time scale approaches (up to a few
years). In this work the objective is to apply successively the model starting by the older scenario
71
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and project the results forward in time to aid the definition of subsequent scenarios. Before that,
the model must be calibrated and validated for present estuary conditions using currentometry
and salinity available data.
In present simulation River discharge values are based on four complete consecutive years
of hydrographic data series taken from the Water Institute site, that point out to an annual average
flow rate of 390m3/s. The bathymetry was based on Hydrographic Institute bathymetrical maps
(sheet nº 26402-INT 1871 of 2000 in the scales1/10000 and 1/30000) and included the
development of a Digital Terrain Model (DTM) with an horizontal grid with 105 x 157 cells, with a
variable grid spacing between 100 and 50 m, covering an area of 6.8 by 9.8 km, which extents
from the inner shelf (around the 30 m) to the Arrabida bridge (Fig. 2)
Bathymetry (m)
Figure 2 - Actual bathymetry
and horizontal grid of the
Douro estuary.
The simulation of past sedimentary dynamics of the Douro estuary will be performed
using the calibrated model with the paleo-bathymetry based on the interpretation of available shelf
seismic release data profiles, converted in isopacs and isobaths maps (Carvalho & Rosa, 1988;
Rodrigues & Dias, 1989; Rodrigues, 2004).
Results and future work
So far, the work has focused on present hydrodynamics conditions, using a 2D
hydrodynamic model. Although the first results seem very promising, as the model seem to
express the main hydrodynamic features of the estuary including the vortexes related to the
development and present configuration of the Cabedelo sand barrier (Fig. 3), validation is still in
progress.
0
1
2Km
0
1
2Km
Figure 3 – Hydrodynamics conditions of Douro Estuary during ebb (left) and flood (right). The colours represent the water
level, between 0m and 5.5m. The arrows represent the resultant of Instantaneous Velocities u and v (m/s).
For a more complete approach of the complex dynamism of this estuary, a 3D model is
being implemented will try to recreate the vertical stratification of the river. The final stage
72
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includes the imposition of the ancient bathymetry in order to reach the evolution model for Douro
estuary.
Acknowledgments
This work was made in the ambit of the project ENVI-CHANGES-PLE/12/00 financed by Foundation for Science and
Technology (FCT).
References
Carvalho, A. F. & Rosa, M. 1988. Localização do Paleovale do Rio Douro. Anais do Instituto Hidrográfico, 9: 77-82.
Dias, J.M.A. 1987. Dinâmica sedimentar e evolução recente da plataforma continental setentrional portuguesa. Ph. D.
Thesis (not published).
Drago, T., Freitas, M.C., Rocha, F., Moreno, J., Cachão, M., Naughton, F., Fradique, C., Araújo, F., Silveira, T., Oliveira,
A., Cascalho, J. & Fatela, F. 2004. Paleoenvironmental evolution of estuarine systems during the last 14000 years – the
case of Douro estuary (NW Portugal). Journal of Coastal Research, Special Issue 39.
Drago, T., Naughton, F., Moreno, J., Rocha, F., Cachão, M., Sanchez Gõni, M.F., Oliveira, A., Cascalho, J., Fatela, F.,
Freitas C. & Andrade, C. 2002. Geological Record of Environmental Changes in the Douro Estuary (NW Portugal)
Since the Late Glacial. Littoral 2002, The Changing Coast. EUROCOAST / EUCC, Porto – Portugal. 341-346.
Martins, F., Pina, P., Calado, S., Delgado, S. & Neves, R. 2003. A coupled hydrodynamic and ecological model to
manage water quality in Ria Formosa coastal lagoon. In: E. Tiezzi, C.A. Brebbia & J.L. Usó (ed.). Ecosystems and
sustainable development, vol 1. Advances in Ecological Sciences series 18. WITpress, 93-100.
Martins, F., Reis, M.P., Neves, R., Cravo, A.P., Brito, A. & Venâncio, A. in press. Molluscan Shellfish bacterial
contamination in Ria Formosa coastal lagoon: A modelling approach. Journal of Coastal Research, Special Issue 39.
Rodrigues, A. 2004. Tectono-Estratigrafia da Plataforma
Continental Setentrional Portuguesa. Ph. D. Thesis,
Documentos Técnicos do Instituto Hidrográfico, nº 35, 227p.
Rodrigues, A. & Dias, J.M.A. 1989. Evolução Pós-Glaciária da Plataforma Continental Portuguesa a Norte do Cabo
Mondego. Anais do Instituto Hidrográfico, 10: 39-50.
Vitorino, J., Oliveira, A., Jouanneau, J.M. & Drago, T. 2002. Winter dynamics on the northern Portuguese shelf. Part 1:
physical processes. Progress in Oceanography, 52: 129-153.
Water Institute Report, June 2003. Water Quality in Portuguese Estuaries, Volume II - Douro Estuary.
73
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PALEOENVIRONMENTAL CONDITIONS OF THE GALICIAN CONTINENTAL
SHELF DURING THE HOLOCENE (POSTER)
Raquel González-Álvarez & Guillermo Francés
Universidad de Vigo. Dpto. Geociencias Marinas y O.T. Facultad Ciencias del Mar, As Lagoas-Marcosende, s/n, 36310
Vigo, España; [email protected], [email protected]
4740000
This
paper
presents
sedimentological, biogeochemical and
planktonic foraminifera data from Galician
Iberian
Peninsula
continental
shelf
(NW
of
Iberian
Peninsula) during the last 10 kyr. We have
analysed the vibro core ZV-27 (42º8.67’N,
8º55.73’W, 73 m depth, 428 cm length) in
order to reconstruct the regional
paleohydrology. The study focuses on the
water surface dynamics, mixing and
stratification, and their linkages to
productivity in the surface water column.
The studied core presents two
clearly different sections. From the bottom
up to 205 cm, it is composed by pebbles
ZV-27
floating in a coarse-medium sandy matrix.
MIÑO RIVER
This section is interpreted as a fluvial
sediment deposited during the Last
Glacial Maximum (Liquete et al., 2003).
10 km
From 205cm up to the core top the
sediment has a marine origin. This marine
455000
475000
495000
515000
535000
unit was sampled in 1 cm-thick slices
LONGITUDE W (UTM, m)
every
6cm
to
perform
micropaleontological, biogeochemical and
Figure 1 – Location of the vibro core anlysed.
grain size analyses. Evaluation of total
carbon (TC), total nitrogen (TN) and total
inorganic carbon (TIC) content were performed with a Leco CC-100 and CN-2000 (CACTI,
Universidad de Vigo). Total organic carbon (TOC) was estimated by subtracting the TIC to the
TC. Calcium carbonate content (CaCO3) was calculated by multiplying the TIC by a constant
factor of 8.33. Additionally, the TOC/TN ratio (C/N ratio) was calculated. Counts on planktonic
foraminifera fauna were conducted on the >150 µm residue and they were identified following the
classification of Kennett and Srinivasan (1983).
Relative abundance is expressed as the percentage of each species in relation to the total
specimens counted. The absolute abundance is the number of planktonic foraminifera per gram
of dry sediment. The total number of benthic foraminifera in each sample was also counted to
determine the planktonic/benthic foraminiferal ratio (PF/BF).
The chronological framework of the marine unit is based on five AMS-14C ages (Geochron
Laboratories, Cambridge, Massachusetts USA). Raw radiocarbon ages were calibrated using the
CALIB Rev 5.0 program (Stuiver & Reimer, 1993) and the Marine04 calibration dataset (Hughen
et al., 2004). The marine unit spans from 9370 cal yr BP to 1015 cal yr BP. According to the age
model, the mean sedimentation rate is 22 cm/kyr, although higher values have been estimated for
the lower 50 cm (40 cm/kyr).
This increase in the sedimentation rate from 205 to 150 cm coincides with the interval of
higher sand content (more than 85%). From 150cm up to the core top, the sand content shows a
general decreasing trend marked by three fining upward sequences, although the coarser
fractions tend to increase. This particular pattern is mainly controlled by the decrease of very fine
sand, the most abundant fraction, and the parallel increase of silt and clay. A sharp lithologic
change is observed between 150-145 cm. Below this level the sediment is mostly composed of
100
150
200
10
00
50 0
1500
4660000
4680000
4700000
S
XA
AI
4720000
B
AS
LATITUDE N (UTM, m)
RÍ
74
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quartz and glauconite grains. The low content of calcium carbonate (~10%) is supplied by
foraminifera tests. Above this level, carbonate increases up to a maximum value of 40%,
glauconite and quartz are almost absent and the abundance of other biogenic particles
(ostracods, spicule remains, gastropods and reworked bioclasts) increase rapidly. A weaker
change occurs at 50cm. Towards the top of the core biogenic particles and, therefore, total
calcium carbonate decrease and glauconite grains increase. The organic carbon content varies
between 0.5% and 1% along the core following the pattern displayed by the mud fraction, in
particular by that of clay and fine silt.
Three species of planktonic foraminifera account for the 85% of the total assemblage:
Globigerina bulloides d’Orbigny, Neogloboquadrina pachyderma (Ehrenberg) (right-coiling) and
Globorotalia inflata d’Orbigny. These species are typical of subpolar and transitional zones (Bé,
1977) and we interpret their abundances following ecological preferences described in Bé (1977)
and Pujol and Vergnaud-Grazzini (1995). Changes observed in the relative abundance of
planktonic foraminifera as well as in the other analysed markers, allow us to define four main
periods for the last 9000 years.
From 9400 to 8000 cal yr BP the calcium carbonate and organic carbon record the lowest
values, whereas quartz and glauconite show the highest abundance. N. pachyderma is the
dominant species in the planktonic assemblage, G. bulloides represents less than 35% and the
percentage of G. inflata varies around 10%. The progressive decrease of terrigenous particles
and N. pachyderma (left-coiling) reveal a progressive rise of the sea level and the warming of
surface waters. A sea-level lower than nowadays inhibits the mixing of the water column and
therefore the productivity is relatively low.
From 8000 to 4860 cal yr BP the gradual increase of G. bulloides and the organic carbon
content may reflect the progressive establishment of high productivity conditions in the Galician
continental shelf, reaching the maximum level at the end of this period (6400-4860 cal yr BP). An
event of relative mixing of the water column, with warmer and less productive surface waters, has
been described between 7530 and 6860 cal yr BP, when G. inflata peaks and the organic carbon
percentage falls. At this time sand size quartz and glauconite grains disappear, indicating lower
environmental energy levels and an enhanced influence of marine sources of sediment.
The third period spans from 4860 to 3230 cal yr BP. The inverse correlation between N.
pachyderma and G. inflata, as well as relative low values of G. bulloides and total organic carbon
reveal a strong stratification of the water column and low nutrient levels. This interval is
interpreted as representing the warmer and drier conditions that characterized the Sub-Boreal
period (e.g. van Geel et al., 1999).
The most recent period is identified to be from 2950 to 1000 cal yr BP. High percentages of
G. bulloides and G. inflata and the decrease of N. pachyderma indicate strong upwelling
conditions and vertical mixing of the water column. This high productivity conditions are also
supported by the recovery of organic carbon values. The decrease of calcium carbonates and the
parallel increase of glauconite and quartz grains are also tracers of more energetic sedimentary
processes and enhanced terrestrial influence.
References
Bé, A.W.H. 1977. An ecological, zoogeographical and taxonomic review of recent planktonic foraminifera. In: A.T.S.
Ramsay (Ed.), Oceanic Micropaleontology, vol. 1. Academic Press, London, 1-100.
Hughen, K.A., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C.J.H., Blackwell, P.G., Buck, C.E., Burr, G.S.,
Cutler, K.B., Damon, P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Kromer, B., McCormac,
F.G., Manning, S.W., Bronk Ramsey, C., Reimer, P.J., Reimer, R.W., Remmele, S., Southon, J.R., Stuiver, M., Talamo,
S., Taylor, F.W., van der Plicht, J. & Weyhenmeyer, C.E. 2004. Marine04 Marine radiocarbon age calibration, 26-0 ka
BP. Radiocarbon, 46: 1059-1086.
Kennett, J.P. & Srinivasan, M.S. 1993. Neogene Planktonic Foraminifera. A Phylogenetic Atlas. Hutchinson Ross Pub.,
Stroudburg, PA. 265 p.
Liquete, C., González-Álvarez, R., Diz, P. & Francés, G. 2003. The onset of marine sedimentation on Galician continental
shelf and Holocene environmental evolution. Geophysical Research Abstracts 5: 13672.
Pujol, C. & Vergnaud-Grazzini, C. 1995. Distribution patterns of live plankton foraminifers as related to regional
hydrography and productive systems of the Mediterranean Sea. Marine Micropaleontology, 25: 187-217.
14
Stuiver, M. & Reimer, P.J. 1993. Extended C database and revised CALIB radiocarbon calibration program.
Radiocarbon, 35: 215-230.
van Geel, B., Raspopov, O.M., Renssen, H., van der Plicht, J., Dergachev, V.A. & Meijer, H.A.J. 1999. The role of solar
forcing upon climate change. Quaternary Science Reviews, 18: 331-338.
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EVOLUTION OF THE COASTAL ZONE OF NW PORTUGAL (MINHOMONDEGO) SINCE LATE GLACIAL TIMES (TALK)
Helena Maria Granja
Universidade do Minho, Departamento de Ciências da Terra, Campus de Gualtar, 4710-057 Braga, Portugal;
[email protected]
Introduction
The coastal zone of northwest Portugal can be subdivided into two major,
geomorphologically distinct areas. The northern one, between the Minho river and Espinho,
consists predominantly of a rocky substrate with a thin veneer of pebble and sand beaches,
limited landwards by a narrow dune fringe. The coast is intersected by several estuaries that
formed protected areas for more or less complete sediment successions. The southern area that
extends between Espinho and the Mondego Cape, is dominated by wide sandy beaches and
extensive dune fields. No estuaries are found, but several lagoons in different phases of closure
are present. Due to their different geomorphology, both areas reacted differently to the global
changes since the Last Glacial, i.e. climate change and sea-level changes. Since human
occupation began, the coast has been subjected to additional forcing. The impact of human
activities on this coastal zone has been rapidly increasing for more than a century and – locally –
has been exceeding natural impacts.
Northern area (Minho River – Espinho)
Sedimentology and sea-level changes
The occurrence close to the surface of hard rock basement has controlled the amount of
sedimentation in the coastal zone during the Quaternary. In most of the area, the beaches are
relatively thin and the dune systems poorly developed, except in some segments, like at Amorosa
(south of Viana do Castelo) and Aguçadoura (Póvoa de Varzim) where parabolic dunes extend
inland. Beaches were formed by extensive pebbly deposits, forming high beach ridges in some
places (like in Belinho), that have been covered by beach and aeolian sands. It is still unclear how
the pebble layers were formed (e.g. fluvial origin, reworked into shingle beaches by wave action
during early Holocene sea-level rise) nor when they were covered by beach sands. Present
coastal lagoons are not represented on this area.
By contrary, during Holocene, a wide paleolagoon system was set in on the area; the
residual lagoon of Apúlia is the only one that still subsists. Their age is comprised between cal BC
3253 (Belinho, 5m depth, peat) and cal AD 1511 (Apúlia paleolagoon, 2.55m depth, peat). In
some of these lagoons, a thin soil with trees developed (species still under research), when they
dried up. This lagoonal system was partially flooded by sea (16th century ?), and later on covered
by aeolian dunes (17th-19th centuries, OSL datings).
Though there are not yet enough data and datings concerning the estuaries, one can admit
that numerous estuaries (e.g. Minho, Cávado, Douro) were flooded during Holocene. On Cávado
paleoestuary, there are an indicator of a sudden marine flooding (5.50-6.80 m depth; diatom
analysis in Cávado estuary) prior to cal AD 249 (Marachão, 4.44 m depth, peat, the oldest
available dating of this site). Accepting a mean infilling rate of 2 mm/yr, this flooding event would
have taken place about 931 BC; however, more datings are needed.
Environmental proxies
Diatom and foraminifer analysis; vegetational history based on pollen diagrams and tree
species identification, climatic extrapolation; sedimentology.
Coastal changes in the twentieth century
Coastal erosion is uncovering more and more the pebble layers on top of the hard rock,
and the hard bedrock is being exposed more and more. Some sandy beaches were completely
replaced by shingle beaches (between Pedra Alta and Belinho) and new equilibrium dynamics
took place.
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Southern area (Espinho – Mondego Cape)
Sedimentology and sea-level changes
From boreholes made in the area of Espinho, it appears that the Late Glacial sediments
were formed under (wet) aeolian conditions (Granja et al. in prep.). It is assumed that this is also
the case for most of the area, although additional evidence from boreholes is missing at present.
In most of the area, aeolian activity continued till the present day, and has been dominant inland.
However, at its maximum ca. 5000 yrs BP, Holocene sea-level rise advanced close to the present
day coastal position. Behind a fringing dune barrier, breaching at several places created
extensive lagoons (e.g. Aveiro, Esmoriz are the present day largest remains), surrounded locally
by more or less extensive beach deposits. These lagoons extended seaward of present coastline
and have been exposed, for short periods, into beaches, due to erosive processes (e.g. Torrão do
Lameiro).
In most cases, the lagoons are not part of a drainage system and only the Aveiro lagoon
forms the downstream part of the Vouga River. Tentatively, the oldest age of the lagoons can be
placed at cal BC 3324 (Paramos, 8.40 m depth, shells). Some of them were flooded by sea (cal
AD 260-324), and later on covered by parabolic dunes (from 7th century onwards).
From about cal AD 883 (Silvalde, intertidal outcrop, wood) onwards, several of the lagoons
were gradually filled-in and, at the same time, cut-off from regular marine influence (e.g. Esmoriz).
Partially contemporaneous of the lagoon system (cal BC 3324-389), a podzol formed south
of Espinho (cal BC 1859 – cal AD 59).
Environmental proxies
Foraminifer analysis; vegetational history based on pollen diagrams and tree species
identification, climatic extrapolation; sedimentology.
Coastal changes in the twentieth century
The coastal position has been fairly stable for several centuries and perhaps millennia,
despite the human presence in the area. However, human impact on the coastal zone has
increased above background levels since the nineteenth century. In the second half of the
twentieth century, human impact has become problematic for the stability of the coast, through
the building of hard engineering structures to protect towns and harbours from coastal erosion.
This has destabilised coastal equilibrium in several areas (e.g. the Espinho area) and increased
erosion over large stretches. It is still a matter of debate to what extent this erosion had been
initiated in the first place by the renewed sea-level rise following the actual global climate change.
References
García-Amorena, I., Granja, H.M., Pissarra, J., Estela Silva, R., Rubiales, J.M. & Soares de Carvalho, G. accepted. Late
Quaternary palaeoenvironmental reconstruction in the northwest coast of Portugal: an example of a geo-site archive
exploration. IV International Symposium Progeo on the Conservation of Geological Heritage, Braga, September 2005.
Gomez-Orellana, R.L., Ramil-Rego, P. & Sanches, S.M. 2001. Landscape modifications during the Upper Pleistocene –
Holocene in the NW Atlantic margin of Iberian Peninsula. Estudos do Quaternário, Journal of the Portuguese
Association for Quaternary Research, 4:79-96.
Granja, H.M. 1999. Evidence for Late Pleistocene and Holocene sea-level, neotectonic and climatic indicators in the
northwest coastal zone of Portugal. Geologie en Mijnbouw, Kluwer Academic Publishers, 77 (3-4): 233-245.
Granja, H.M. 2002. Reconstituição paleoambiental da zona costeira, a norte da laguna de Aveiro, desde a Idade Média
até à actualidade. In: O Litoral em Perspectiva Histórica (Séc. XVI a XVIII). Instituto de História Moderna, Universidade
do Porto, 93-109.
Granja, H.M., Ribeiro, I., Carvalho, G.S. & Senos Matias, M. 1999. Some neotectonic indicators in Quaternary formations
of the northwest coastal zone of Portugal. Physics and Chemistry of the Earth, Elsevier Science, Ltd., 24(4): 323-336.
Granja, H.M., de Groot, T.A.M. & Costa, A.L. in prep. Evidence for Pleistocene wet aeolian dune and interdune
accumulation, S. Pedro de Maceda, NW Portugal.
López Cancelo, L. 2004. Cambios paleoambientales en el NW peninsular durante el Holoceno determinados a partir del
estudio de foraminíferos bentónicos. PhD thesis, Universidade de Coruña, 293p.
Loureiro, E. & Granja, H.M. 2000. Praias de seixos do litoral de Esposende. Actas do 3º Simpósio sobre a Margem
Continental Ibérica-Atlântica, Faro, 121-122.
Loureiro, E. & Granja, H.M. 2001. Short-term morphodynamics of a shingle beach (Esposende, northwest Portugal). In:
Packham, Randall, Barnes and Neal (eds.), Ecology and geomorphology of coastal shingle, 148-159.
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Ribeiro, I. 2003. Deformação neo-tectónica pós-plistocénica na zona costeira entre os rios Minho e Ave. PhD thesis,
Universidade do Minho, 355 p.
Ribeiro, I. & Granja, H.M. 2000. Evolução holocénica paleoambiental quaternária dos sectores costeiros das Marinhas e
Belinho (Esposende): evidências de flutuações do nível do mar. Actas do 3º Simpósio sobre a Margem Continental
Ibérica Atlântica, Faro, 123-124.
Soares de Carvalho, G. & Granja, H. accepted. As mudanças da zona costeira pela interpretação dos sedimentos
plistocénicos e holocénicos (metodologia aplicada à zona costeira do noroeste de Portugal). In: Livro de homenagem à
Professora Doutora Rosa Fernanda Moreira da Silva, Faculdade de Letras, Universidade do Porto.
Thomas, P.J., Murray, A.S., Granja, H.M. & Jain, M. in revision. Optical dating of Late Quaternary coastal deposits in
Northwest Portugal.
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CALCAREOUS NANNOPLANKTON AS A TRACER OF THE MARINE
INFLUENCE IN THE NW COAST OF PORTUGAL, OVER THE LAST 14000 BP
(TALK)
Catarina Guerreiro1, Mário Cachão1,2 & Teresa Drago3
1
Centre of Geology Univ. Lisbon, Building C6, 6.4.67, Campo Grande, 1749-016 Lisboa,
Portugal; [email protected]
Dep. Geology, Fac. Sciences, Univ.Lisbon, Building C6, 6.4.55, Campo Grande, 1749-016 Lisboa, Portugal;
[email protected]
3
INIAP, IPIMAR, CRIPSUL Olhão, 8700-305 Portugal; [email protected]
2
Introdution
According to Baumann et al. (2002), nutrients transported by upwelling promote a high
biologic productivity along coast, such as the Portuguese west coast, mainly in the proximity of
capes; the production of filaments is frequently observed, as a result of the offshore transport in
coastal waters. In such an upwelling coastal region as this, phytoplankton assemblages are
controlled by certain trophic axis, probably related with the turbulence intensity, nutrients
availability (Margalef, 1978) and light intensity (Margalef, 1997).
Therefore, regions located in the proximity of continental margins, which are characterized
as having some turbidity are associated with situations where nutrient enrichment conditions may
occur (Cachão & Moita, 2000). On the other hand, to know the physical, geological and biological
processes that occur in the Continental Mid-Shelf is also important to understand and quantify the
material flows that are being produced into the shelf-break zone (Oliveira et al., 2002), as well as
its possible influence in both water column and sediment record, as far as Calcareous
nannoplankton is concerned.
Most of Calcareous nannoplankton sedimentary record is strongly conditioned by the highly
hydrodynamic bottom conditions (Rooth et al., 1975) leading to the ressuspension and dispersion
of the nannoliths, preventing them to deposit on coarser sediments of the inner shelf. Although
diluted by high sedimentation rates, their deposition occurs, on one side, on the middle and outer
sectors of the shelf, and on the other side, on paralic low energy inlets of estuaries and lagoon
coastal systems (Ferreira & Cachão, 2005).
Using data from the NW Portuguese coast and shelf, the present study aims to add
additional support to the use of Calcareous nannoplankton in this multi-proxy studies as a natural
tracer of the marine sedimentation inside paralic systems.
Methodology
A total of 380 samples were analyzed for the present study: (1) 8 surface samples from the
Minho estuary; (2) 201 samples selected from cores CPF1 (11.5 m thick), M1 (28.7 m thick) and
M2 (21 m thick), recovered in the Minho Estuary; (3) 108 samples from D1 (0 – 7.9 m depth), D1B
(10.1 – 19.7 m depth) and D2 (20 - 40 m depth), all recovered from the Douro Estuary; and (4) 35
samples selected from FF1MG92 core (2.7 m thick) and 38 samples from POS287 core (3.7 m
thick) both recovered from the Portuguese Mid-Shelf, off Oporto, at 100 m and 81 m depth,
respectively. Sample interval varied from 10 to 20 cm, depending on lithology and texture of the
sediments (silty-clay richer sectors were more detailed sampled).
A coccolith abundance index (CAI) was determined on randomly selected 30 mm row of the
smear slide as a preliminary recognition and a semi-quantitative estimate of its abundance
(Cachão & Moita, 2000).
Absolute abundances were determined on all samples that presented nannoliths by the
previous method. Slides were prepared according to the random settling procedure (Flores &
Sierro, 1997) adapted for neritic (continental shelf) and paralic (estuaries and lagoons) facies
(Ferreira & Cachão, 2003) by modifying sediment weights and the pipetted volumes.
Slides were observed under optical polarizing microscopy (Olympus BX-40), at 1250x
magnification.
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Results
During the Late Holocene, Calcareous nannoplankton assemblages were similar to those
found on present day neritic conditions. Main species comprised Gephyrocapsa spp.,
Helicosphaera carteri, Emiliania huxleyi and Cocolithus pelagicus braarudi. An unexpected and
extremely high amount of Helicosphaera carteri in Douro estuary’s mouth was probably related to
a certain local confinement, which probably has provided an adequate nutrient concentration that
allowed this type of opportunistic behavior from H. carteri.
Maximum values of main species abundances are (in decreasing order): Gephyrocapsa
spp. - with the predominance of G. oceanica (1.3x106 nanno/gr), followed by G. muellerae
(6.4x105 nanno/gr) and finally, G. ericsonii (4.7x105 nanno/gr), Helicosphaera carteri (8.2x105
nanno/gr), Emiliania huxleyi (6.2x105 nanno/gr), Calcidiscus leptoporus (8.8x104 nanno/gr),
Syracosphaera spp. (1.8x104 nanno/gr), Umbilicosphaera sibogae (1.8x104 nanno/gr),
Coccolithus pelagicus (1.4x104 nanno/gr) and Braarudosphaera bigelowi (5.4x103 nanno/gr). Both
CPF1 and M2 cores present G. oceanica as the most abundant species, followed by H. carteri. In
the M1 core this situation is inverted, with H. carteri showing slightly higher abundance.
The FF1GM92 and POS287 cores present the calcareous nannofossil assemblages that
typically characterize the shelf. The presence of both temperate (G. muellerae, E. huxleyi) and
subtropical (G. oceanica and C. leptoporus) species is in accordance with the shelf location in the
Atlantic Oriental neritic boundary, between the biogeographic zones of temperate and subtropical
coccolithophores.
Attending to the low resistance and robustness of E. huxleyi and G. ericsonii their presence
and abundance values similar to G. oceanica, G. muellerae and H. carteri, indicate that nannolith
assemblages reflect depositional conditions rather than post-depositional diagenesis.
Discussion and Conclusions
Although Calcareous nannoplankton is mainly registered on ocean facies, the results
obtained from the NW Portuguese littoral indicate that they can be an additional proxy for
interpreting palaeoenvironmental variations and the relative predominance of ocean and land
driven sedimentation that have affected the Portuguese coast, as a result of the eustatic sea level
rise that followed the last deglaciation.
Despite the obvious difference between the amounts from the estuaries and the shelf, it is
possible to define variations on nannolith content for the last 14 000 yrs on this section of the
shelf, which are probably related to dilution by variable sedimentary rates, caused by changes in
fluvial discharge. Marine driven sedimentation inside the present day estuarine environments from
NW Portugal changed in time as indicated by variations on the total Calcareous nannoplankton
assemblages complementarily registered in all six cores. Palaeogeographically, the pattern of
variation in time of nannolith abundances on coastal sediments can be interpreted as follows: (1)
a basal set of barren samples represent fluvial sedimentation during first stages of sea level rise
but with the coastline in a still distant position; (2) a gradual (and oscillatory) increase in the
content of nannoliths testifies the moment the coast line first crosses the core location while the
palaeoenvironment changes into an estuary; (3) persistently higher amounts of nannoliths
(reaching 2x107 nannoliths per gr) are related to marine palaeoenvironmental conditions
produced by the flooding of pre-existing valleys into rias; (4) an upwards gradual increase on the
intermittency of nannoliths abundances indicates a regressive trend due to the recover of the
estuarine conditions; (5) followed by an upper set of barren samples indicating an evolution
towards a fluvial regime.
The above cycle of increase – decrease of the nannolith abundance is correlative of a
global positive eustatic trend. The “fluvial I - estuarine I - ria” increase stage is interpreted as a
response to an initially rapid sea level rise, while the “ria – estuarine II – fluvial II” decrease was a
response to a deceleration of the sea level rise rate that seemed to happen from about 6000 to
4500 BP. This leads to a change on coastal morphology, mainly by the building-up of barriers
(Fig. 1).
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Calcareous
nannoplankton
-
Transgression Stage
Regression Stage
STAGES
V
+
M1+ M2 CPF1
D1A
FF1GM92 + PO287
FLUVIAL II
ESTUARY II
IV
III
Sand bar
RIA
SHELF
II
ESTUARY I
I
FLUVIAL I
D2
D1B
Figure 1 - Schematic diagram representing the proposed Holocene paleoenvironmental evolution model for the studied
sector of the Portuguese Continental Shelf.
Acknowledgments
This paper is a contribution of the FCT project – Envichanges (PLE/12/00).
References
Baumann, K.H, Meggers, H. & Freudenthal, T. 2002. High-resolution coccolith studies on climate variability in the eastern
boundary current region off NW Africa. Journal of Nannoplankton Research, 24: 69.
Cachão, M. & Moita, T. 2000. Coccolithus pelagicus, a productivity proxy related to moderate fronts off Western Iberia.
Marine Micropaleontology, 39 (1/4): 131-155.
Ferreira, J. & Cachão, M. 2003. Nanofósseis calcários em fácies costeiras: revisão de técnicas de estudo. Ciências da
Terra (UNL), Lisboa, nº esp. V, CD-ROM: A76-A78.
Ferreira, J. & Cachão, M. 2005. Calcareous nannoplankton from the Guadiana estuary and Algarve Continental Shelf
(Southern Portugal). Thalassas, 21 (1): 35-44.
Flores, J.A. & Sierro, F.J. 1997. Revised technique for calculation of calcareous nannofossil accumulations rates.
Micropaleontology, 43 (3): 321-324.
Margalef, R. 1978. Life-Forms of Phytoplanktonas survival alternatives in an unstable environment. Oceanolog. Acta 1 (4):
493-509.
Margalef, R. 1997. Our Biosphere. Excellence in Ecology. Publish. 1997 by Ecology Insitute, D – 21385 Oldendorf/Luhe
Germany, 176 p.
Oliveira, A., Dias, J.M., Jouanneau, J.M. & Weber, O. 1994. Characterization of plumes connected with rivers from
northern Portugal (Minho, Lima, Cávado, Ave and Douro). Gaia, 1º Simpósio sobre a Margem Continental Ibérica
Atlântica, 7-9.
Oliveira, A., Vitorino, J., Jouanneau, J.M., Dias, J.A. & Weber, O. 2002. Nepheloid layer dynamics in the northern
Portuguese shelf. Progress in Oceanography vol.52: 195-213.
Roth, P. & Berger, W. 1975. Distribution and dissolution of coccoliths in the south and central Pacific. In: Sliter, W.V. (Ed.)
Dissolution of Deep sea carbonates, Cushman Fond. Foraminif. Res., Spec. Publ., 87-113.
81
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OCEANIC INFLUENCE IN THE RIA DE VIGO DURING THE LAST 2600
YEARS (POSTER)
Virgínia Martins1, Jean-Marie Jouanneau2, Olivier Weber2, João Alveirinho Dias3 & Fernando
Rocha1
1
Research Centre Industrial Minerals and Clays, Univ. of Aveiro, 3810-193 Aveiro, Portugal; [email protected],
[email protected]
2
Department of Geology and Oceanography, Univ. of Bordeaux I/CNRS, France; [email protected],
[email protected]
3
Univ. of Algarve, P-8000-117 Faro, Portugal; [email protected]
Introduction
During recent years several works based on micropalaeontological studies of sedimentary
sequences have been approached to establish the Holocene evolution of NW Iberian coastal
systems (e.g. Cearreta et al., 2002; Leorri & Cearreta, 2004). In this work benthic foraminiferal
proxies were compared with textural and mineralogical data acquired along the core KSGX 24,
obtained from the outer sector of the Ria de Vigo (Spain), in order to identify Holocene periods of
higher and lower oceanic influence within this coastal system.
Material and Methods
The studied OMEX (Ocean Margin Exchange Project) core KSGX 24, with a length of 236
cm, was collected on the outer sector of the Ria de Vigo (42°12’48 N, 8°51’90 W, 39 m depth).
Sediment samples (1cm thick) were collected every centimetre along the core and used for
mineralogical and textural studies. Mineralogical analysis was carried out on <2µm sediment
fraction using X-ray diffraction techniques. Grain size analysis was carried out by Laser Diffraction
Particle Size Analysis (Malvern Instruments). More than 300 relatively well-preserved benthic
foraminifera were counted and identified per sample using a binocular microscope, on sediment
fraction >63µm from samples collected every 2 cm. Radiocarbon dating based on mixed benthic
foraminiferal shells from the sedimentary layers 71-72 cm, 143-144 cm, 193-194 cm were
analyzed by AMS (Accelerator Mass Spectrometry) at Beta Analytic Inc. In order to identify
periods of higher oceanic influence in the Ria de Vigo, the abundance of benthic foraminifera
species was distinguished between the species more characteristic of inner to middle shelf
environments, on one side, and of middle to outer continental shelf environments, on the other
side. These depth plots were contrasted with the down-core evolution pattern of some textural
and mineralogical (illite/kaolinite ratio) data.
Results
Radiocarbon results of selected layers provided the following calibrated (cal) ages before
present (BP): 1515±95 yrs cal BP for 71-72 cm, 2070±90 yrs cal BP for 143-144 cm, 2595±125
yrs cal BP for 193-194 cm. The age model was based on these intercalated ages after correction
for the local reservoir effect of ~400 years.
The KSGX 24 core, a Holocene sedimentary sequence recording the last ~2,6 ka, has a
mean grain size varying between 13-26 µm. Fine fraction represents 76-92 % of the bulk
sediment. Illite (46-72%), kaolinite (18-43%), chlorite (2-10%), and smectite+mixed-layers illitesmectite (0-17%) compose clay minerals assemblages. Major minerals, illite and kaolinite, show
an opposition pattern along the core. Most of the foraminiferal shells are broken and poorly
preserved, being probably affected by reworking and/or dissolution. A total of 202 benthic
foraminiferal taxa were identified and consist mainly of a remobilized oceanic fauna.
Autochthonous specimens only represent about 5-25% of the benthic foraminiferal assemblages
along the core KSGX 24.
The depth plot data presented in figure 1 show an increase around 2-1.2 ka cal BP in the
group of marine benthic foraminifera typical of middle to outer shelf environments, like
Amphicoryna scalaris, Bolivina/Brizalina spp. (B. compacta, B. difformis, B. dilatata, B. ordinaria,
B. seminuda, B. skagerrakensis, B. striatula, B. variabilis, B. translucens, B.spathulata, B.
subaenariensis), Bulimina spp. (B. aculeata, B. alazanensis, B. elongata/gibba, B. exilis, B.
marginata), Buliminella tenuata, Cancris auriculus, Cassidulina spp., Epistominella vitrea,
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Fursenkoina loeblichi, Melonis barleeanum, Nonion fabum, Nonionella spp., Paumotua terebra,
Stainforthia spp., Trifarina angulosa, Uvigerina peregrina and Valvulineria bradyana.
Simultaneously, the group of species characteristic of high hydrodynamic conditions and/or
unstable environmental conditions (frequent in sediments of the inner to middle shelf
environments) decreased in the samples, like Ammonia beccarii, Asterigerinata mamilla, Bolivina
pseudoplicata, Cibicides spp., Discorbis mira, Discorbis williamsoni, Eggerelloides scaber,
Elphidium spp. (E. crispum, E. discoidale, E. excavatum, E. macellum, E. pulvereum, E.
complanatum) Eoeponidella pulchella, Glabratella millettii, Haynesina depressula, Lamarckina
haliotidea, Lobatula lobatula, Neoconorbina parkerae, Planorbulina mediterranensis,
Quinqueloculina seminulum and Rosalina anglica. During this period, the fine fraction increased
inducing a decline in sediment mean grain size. Values of kaolinite/illite ratio also decreased in
the same interval.
Fine fraction
(63 µm ; %)
Depth (cm)/ Calibrated ages BP (x10 3)
Sedim ent m ean
grain size (µm )
age /cm 10
0
10
20
0.5 30
40
50
60
1
70
80
90
100
110
1.5 120
130
140
150
160
170
2
180
190
200
210
2.5 220
230
16
22
28
0
10
20
30
40
50
60
70
80
90
100
110
120
130
1 670±90 140
Cal BP 150
160
170
180
190
200
210
220
230
75
85
Middle to outer shelf
benthic foram inifera (%)
95
25
40
0
10
20
30
40
50
60
1 115±95 70
Cal BP
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
55
Inner to m iddle shelf
benthic foram inifera (%)
30
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
45
2 195±120
Cal BP
0.2
60
Kaolinite/Illite
ratio
0.5
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
0.8
HOI
Figure 1 – A period of higher oceanic influence (HOI) in Ria de Vigo was identified.
Discussion/Conclusion
Benthic foraminiferal assemblages from the studied site are composed mainly of
allocthonous shells. The increase in benthic foraminiferal tests supplied from deeper waters
between ~2-1.2 ka cal BP should be related to a period of higher oceanic influence in the Ria de
Vigo during which a more intense intercommunication between the ria and the ocean occurred.
Most of the main species during this period are known to be linked with a higher flux of organic
matter, suggesting the occurrence of higher oceanic productivity. During this interval kaolinite
supply to the sediments decreased giving place to a higher deposition of illite.
Illite is the most abundant clay mineral in the NW Iberian continental shelf as well as in
fluvial sediments of northern Portugal that represent the main source of sediments to this marine
area (Oliveira et al., 2002). Also, there are important kaolinite deposits in the northwestern littoral
region of Portugal where highly fractured granites and schists are intensely weathered. Short
periods characterized by rapid changes in the clay mineral composition of sediments should be
connected in this coastal system with a change in currents activity and source areas. Whereas
the increase of illite should reflect an important local and/or a more open oceanic contribution, a
higher supply of kaolinite should be a proxy of an important southern influence in this ria. So
mineralogical, textural and benthic microfaunal data agree with an occurrence of a higher oceanic
influence, between ~2-1.2 ka cal BP, which could be related probably with a higher eustatic sea
level and/or a period of prevalence of upwelling regime, and a reduction of southern influence in
the outer sector of the Ria de Vigo.
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References
Cearreta, A., Irabien, M.J., Leorri, E., Yusta, I., Quintanilla, A. & Zabaleta, A. 2002. Environmental transformation of the
Bilbao estuary, N. Spain: microfaunal and geochemical proxies in the recent sedimentary record. Marine Pollut. Bulletin,
44: 487–503.
Leorri, E. & Cearreta, A. 2004. Holocene environmental development of the Bilbao estuary, northern Spain: sequence
stratigraphy and foraminiferal interpretation. Marine Micropaleontology, 51 (1-2): 75-94.
Oliveira, A., Rocha, F., Rodrigues, A., Jouanneau, J., Dias, A., Weber, O. & Gomes, C. 2002. Clay minerals from the
sedimentary cover from the Northwest Iberian shelf. Progress in Oceanography, 52 (2-4): 233-247.
84
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LA TRANSGRESION HOLOCENA EN EL NOROESTE PENINSULAR (TALK)
Angela Alonso Millán & J. L. Pagés
Sección Ciencias de la Tierra. Facultad de Ciencias. Universidad de A Coruña; [email protected]
Introduccion
Se presenta en este documento el estado actual de la investigación sobre la transgresión
holocena en el NW de la Península, alcanzado a partir de Proyectos de Investigación que dieron
comienzo en el año 1999.
Entre los años 2000 y 2003, la investigación se centró principalmente en el análisis del
registro del Pleistoceno final, desde el Ultimo Interglacial hasta el comienzo de la deglaciación.
Se definieron y dataron cuatro unidades estratigráficas para este periodo, que van desde el OIS 5
al 2, ambos inclusive. Así mismo, se inició el estudio del Holoceno, mediante la datación y
análisis de los escasos afloramientos y de varios sondeos. Complementariamente, se estudió la
influencia de la actividad antrópica sobre los sistemas naturales, los procesos erosivos actuales
en la costa y el comienzo y desarrollo de la contaminación por metales e hidrocarburos en los
sedimentos estuarinos.
ASTURIAS
GALICIA
Situación de las localidades citadas en el texto.
El proyecto en curso se centra en la determinación de las pautas evolutivas y las
condiciones ambientales y paleogeográficas que caracterizaron la última etapa de deglaciación y
toda la transgresión holocena, hasta la actualidad, en la costa del noroeste, incluyendo las
provincias de A Coruña y Lugo y el occidente de Asturias. El proyecto se denomina “Evolución de
las condiciones climáticas durante el Holoceno en el noroeste de la Península Ibérica: Estudio
multidisciplinar del registro sedimentario litoral y de las tendencias a corto y medio plazo”, y el
equipo multidisciplinar que participa abarca diversos aspectos: Micropaleontología (diatomeas,
foraminíferos, polen); Geoquímica (isótopos de C, O, S, metales); Sedimentología (facies,
procedencia); Paleobotánica (macrorrestos y microrrestos). La interpretación e integración de
todos los datos se espera proporcionen un cuadro claro de la evolución de las condiciones
climáticas durante ese periodo.
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Datos Disponibles
Ante la escasez de afloramientos, el estudio del registro holoceno se ha abordado
fundamentalmente mediante testigos de sondeos:
•
Testigos de sondeos realizados por diversas empresas para estudios geotécnicos,
(viaductos, túneles de carreteras y edificios) distribuidos desde las rías del Golfo
Ártabro en A Coruña hasta la ría de Villaviciosa en Asturias Oriental y emplazados
en el centro y márgenes de las rías. Se han estudiado un total de 55 columnas de
sondeos, de los cuales 18 han sido analizados detalladamente al disponer de
registro continuo.
•
Los escasos afloramientos se limitan a algún corte observable en turberas
aflorantes (Baldaio, Corrubedo) y sedimentos fluviales en zonas de
desembocadura donde han sido expuestos por la acción erosiva del mar (Coido de
Cabalar). Se ha recurrido a sondeos manuales para acceder a afloramientos
temporalmente cubiertos (turbera de Barreiros) o sedimentos en zonas internas de
las rías (Ortigueira, Cedeira, El Barquero).
•
Para un estudio más preciso de la segunda mitad del Holoceno y de la señal
antrópica se han realizado sondeos mecánicos específicos en depósitos de
lagunas (laguna de Traba) y con sonda de succión en las zonas internas de los
estuarios de Viveiro, Barqueiro y Ortigueira.
La Transgresión Holocena: Estado del Conocimiento
Golfo Ártabro. La mayoría de los sondeos (17) han cortado facies características de sistemas
de barra-lagoon, que incluyen arenas de playa, dunas eólicas y fangos negros con conchas. Las
facies finas son más abundantes en las zonas internas, Betanzos y Ferrol. Los espesores oscilan
entre los 10 y los 20 m. Las dataciónes más antiguas corresponden en Betanzos a un nivel de
suelo en la base del sondeo (16.000 a. BP) y en Sada a un nivel situado a -18,60 m. (9.500 a.
BP).
Rías Altas (Cedeira, Ortigueira y Viveiro). La serie mas completa es la obtenida en un sondeo
en Viveiro, donde aparece representado todo el Holoceno. Los materiales tienen un espesor
máximo de 24 m y están formados por arenas muy finas bioclásticas y limos, pasando hacia
techo a arenas gruesas con algunos cantos. En la base se dató un fragmento de madera que dio
una edad de 9.700 a. BP.
Asturias. En la ría de Navia los sondeos cortaron un máximo de 30 m de sedimentos,
principalmente arenas finas bioclásticas con niveles de limos y acumulaciones de conchas sobre
zócalo metamórfico edafizado y con restos de maderas. La base del registro está datada en
8.900 a. BP. En la ría de Pravia los sondeos, situados en el estuario interno, perforaron 32
metros de sedimentos. Los 14 metros basales son gravas fluviales del Tardiglacial, sobre ellas
comienzan los niveles bioclásticos. La datación de una muestra situada a -17,35 m proporcionó
una edad de 8.400 a. BP. Los sondeos de la ría de Villaviciosa se han realizado en la parte
interna del estuario. Cortan una serie de 8 m que comienza con 2,5 m de gravas y arenas
(canales fluviales) sobre las que aparecen limos y arenas finas con niveles de conchas,
foraminíferos y restos vegetales. La base de los sedimentos marinos ha sido datada en 7.200 a.
BP. En la base de la formación se encontró un importante yacimiento de macrorrestos vegetales.
Holoceno superior. Lagunas y turberas. El sistema sedimentario de la laguna de Traba está
formado por arenas dunares y fangos orgánicos, cuyo análisis mostró que la laguna fue de agua
dulce desde su origen. La datación de los niveles basales dio una edad de 5.740 a. BP. La
formación de la laguna fue, por tanto, coetánea con la deceleración de la tasa de subida del nivel
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del mar sugerida para los 5.000 a. BP por diversos autores en la costa atlántica de la Península
Ibérica. El modelo evolutivo establecido para la laguna de Traba puede aplicarse a la
generalidad de las lagunas litorales de Galicia haciendo salvedad de características particulares
(tamaño, tipo de desagüe, configuración geológica, etc.).
Además, existen algunos afloramientos de turberas que están siendo destruidas por la erosión
actual, que han sido datadas alrededor de los 5.000 a. BP. Otras turberas, de formación muy
reciente (Medievo), como las de Baldaio y Corrubedo, se presentan con gran tamaño y buena
conservación.
Holoceno Reciente. La señal antrópica. El estudio del Holoceno reciente se está realizando en
los estuarios y lagunas litorales. Se ha abordado mediante diversas técnicas: Polen (indicación
de cambios en la vegetación, diferenciando los de origen antrópico de los debidos a procesos
autocíclicos o climáticos); Variaciones en la tasa de sedimentación (tanto las debidas a la subida
del nivel del mar como las ocasionadas por el cambio de usos del suelo); Contenido en metales e
hidrocarburos (determinando los niveles de base y el comienzo de la actividad industrial).
Conclusiones Provisionales
Del registro sedimentario estudiado hasta el momento, y de las dataciones realizadas, se
establece una secuencia modelo de la evolución de la transgresión holocena en la costa
noroeste peninsular:
• La etapa tardiglacial se manifiesta por la existencia de sedimentos fluviales en las zonas
internas de los estuarios y el vaciado e incisión de las zonas externas de los mismos.
• A los 9.500 a. BP las zonas externas de los estuarios habían sido inundadas. Las zonas
internas fueron alcanzadas hacia los 7.500 a. BP, e incluso más tarde (Ferrol).
• La subida del nivel del mar se produjo a pulsos de diferente ritmo, lo que se refleja en el
relleno sedimentario, que es una secuencia de somerización formada por la progradación
de los subsistemas estuarinos. No se detectan momentos de bajada del nivel del mar.
• Considerando las tasas de sedimentación como indicador relativo, hasta los 6.000 a. BP
la subida del nivel del mar fue rápida, luego se produjo una ralentización claramente
agudizada alrededor de los 5.000 a. BP, lo que originó la formación de las turberas y
lagunas litorales.
• En el momento actual, el nivel del mar en esta zona está subiendo a un ritmo de 2,5
mm/a según los datos del MSLPS. Los procesos erosivos, tanto en acantilados como en
playas son activos. La gestión antrópica del litoral está acelerando puntualmente estos
procesos.
• La señal antrópica se detecta de varias formas: En torno a los 3.000 a. BP mediante
cambios en la vegetación; Alrededor de los 1.000 - 800 a. BP en el incremento en la tasa
de sedimentación por la agudización de roturaciones e incremento de usos agrícolas.
• La tasa de sedimentación reciente, determinada a partir de la identificación del comienzo
de la actividad industrial (metales, etc), es de 0,9 – 1,0 cm/a en las Rías Altas.
Línea de Investigación
En el momento actual, partiendo del esquema evolutivo anteriormente expuesto como hipótesis
de trabajo, se persigue, mediante aproximaciones detalladas desde diferentes campos, modificar
o confirmar el modelo con la suficiente precisión como para identificar ciclos (Hallstadtzeit,
Suess), y obtener una visión predictiva de las tendencias evolutivas del mismo.
En esta perspectiva de investigación se ha creado un equipo de investigación con posibilidad de
abordar los siguientes aspectos:
87
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
•
•
•
•
•
Geológicos:
Cronoestratigrafía,
sedimentología,
análisis
de
procedencia,
reconstrucciones paleogeográficas y dataciones.
Biológicos: Interpretaciones paleoambientales basadas en el análisis de restos
micropaleontológicos y macrorrestos vegetales.
Químico – biológico: El estudio de las variaciones de la concentración del CO2
atmosférico en el pasado, a través de la respuesta inversa que la densidad de estomas
presenta a la variación del CO2 atmosférico en algunas especies arbóreas. Es una
innovadora línea de estudio para conocer con precisión las variaciones de este gas de
efecto invernadero.
Geoquímicos: Estudio de la composición isotópica, tanto en conchas de foraminíferos
como de la materia orgánica. Estudio especiado de metales para la determinación de la
contaminación tanto en el sector cantábrico como en el atlántico.
Mineralógico: Estudio preferente de los minerales de arcilla, (sensibles a los cambios
climáticos y con alta capacidad de adsorción), por lo que son de interés en el análisis de
la contaminación.
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EVIDENCE FOR TEMPORAL FLUCTUATIONS IN OCEAN RESERVOIR
EFFECT OFF PORTUGAL DURING THE HOLOCENE (TALK)
António M. Monge Soares1 & João M. Alveirinho Dias2
1
2
Dep. de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém; [email protected]
Fac. de Ciências do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8000-117 Faro; [email protected]
Introduction
As it is known the ocean reservoir is deficient in radiocarbon compared with the
atmosphere – so, a reservoir age exists for the ocean. A parameter, denoted as ∆R, can be
defined as the difference between the reservoir age of the mixed layer of the regional ocean and
the reservoir age of the mixed layer of the average world ocean in AD 1950 (Stuiver et al., 1986).
Along the western coasts of Europe, active upwelling is, at present, practically restrict to the
Atlantic coast of the Iberian Peninsula, particularly from Cape Finisterra to Cape São Vicente. In
the Portuguese southern coast (Algarve) it can also be recognized.
As upwelled waters are depleted in 14C relative to sea surface water, the 14C content of
marine shells that inhabit coastal regions can be used as an upwelling proxy. Since rates of
regional upwelling can vary in the course of time and the intensity of the radiocarbon depletion in
the mixed layer depends upon the wind-driven coastal upwelling, it is likely that values of ∆R also
can vary in the course of time. A ∆R value higher then the modern value (that one in AD 1950)
will represent a period of higher than modern upwelling rates and, conversely, periods of lower
than modern ∆R value will probably represent periods of weaker coastal upwelling. So, as a
measure of the regional enhancement or depletion of radiocarbon in sea water, ∆R can also be
used as an upwelling proxy, which provides the most direct signal of upwelling activity
(Diffenbaugh et al., 2003).
Materials and methods
Two sets of samples were used in this work: (i) shells collected alive before 1950 from the
Portuguese coast and (ii) charcoal or bone/shell pairs from excavated archaeological sites,
representing different periods of time in the Holocene. Archaeological samples from each context
were collected from the same level in a restricted area (samples closely associated). It is
assumed that the deposition of both types of samples was simultaneous.
Measurement of 14C content of the samples was by means of the liquid scintillation
technique described elsewhere (Soares, 1989). Stable isotope enrichment values (δ13C) were
determined for the CO2 gas produced at the initial stage of benzene synthesis.
Measurements of the first group of samples intend to calculate the modern value of ∆R for
the Portuguese coast. Radiocarbon dating of the archaeological samples, representing different
periods of time in the Holocene, allowed not only to clarify the eventual variability of the coastal
upwelling off Atlantic Iberia but also to identify episodes of abrupt shifts in oceanic circulation,
probably coupled with abrupt climatic change.
Results
The modern value of ∆R for the Portuguese coast – 250±25 years – is in accordance with
the occurrence of an active upwelling off Portugal.
A great variability for the ∆R values was determined with the pairs of archaeological
samples (see Fig. 1):
Figure 1 - ∆R values plotted against time.
89
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Concluding remarks
This considerable variation suggest a significant fluctuation in the strength of the Iberian
coastal upwelling, which can be the result of fluctuations in the latitudinal migration of the
subtropical front or of the North Atlantic Oscillation – the strength of northerly and northwesterly
winds depends of these factors – or of the summer insolation – increases in summer insolation
result in increased sea breezes that increased the northerly component of the wind.
On the other hand, as it is known, the North Atlantic’s Holocene climate has undergone a
series of abrupt reorganizations, each with sufficient impact to force a strong increase of debrisbearing drift ice which can be recognized in deep-sea sediment cores collected at different
locations in the North Atlantic (Bond et al., 1997). Also sea sediment cores collected off West
Africa document a series of abrupt, millennial-scale cooling events resulting from increased
southward advection of cooler temperature or subpolar waters to these subtropical locations
(deMenocal et al., 2000). These cooling events – North Atlantic IRD events – at high latitudes
(“Bond events”) were identified at about 1.4, 2.3, 4.2, 5.9, 8.1, 9.4, 10.3 and 11.1 ka ago (events
numbered 1 to 8, respectively), while off West Africa were identified at 10.2, 8.0, 6.0, 4.6, 3.0, 1.9,
0.80 and 0.35 ka (“deMenocal events”), which documents a strong, in-phase link between
millennial-scale variations in high and low latitude climate during the Holocene.
If the ∆R data determined to the Portuguese coast are plotted versus time five peaks can
be observed, namely at 7810±90 BP, 5640±100 BP, 3990±60 BP, 1140±45 BP and 870±90 BP
(8410-8980 cal BP, 6210-6710 cal BP, 4250-4790 cal BP, 960-1170 cal BP and 660-950 cal BP,
respectively). These values are significantly higher than the modern value (250±25 years), while
the remaining ones that were determined in this study are lower. In a first approach those peaks
or the most part of them can be correlated with “Bond events” (those high values can be due to
the huge amounts of fresh water inject in the North Atlantic at high latitudes), while the other ∆R
values are related to the strength of the coastal upwelling prevailing at the corresponding time.
All these data suggest that off the Portuguese coast, during the Holocene, a more dynamic
upwelling regime prevailed than previously thought and, consequently, the Holocene climate
exhibit a significant variability that only recently has also been recognized.
References
Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hadjas, I. & Bonani, G.
1997. A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates. Science 278: 1257-1266.
Diffenbaugh, N.S., Sloan, L.C. & Snyder, M.A. 2003. Orbital suppression of wind-driven upwelling in the California Current
at 6 ka. Paleoceanography 18, 1051, doi: 10. 1029/2002PA000865.
deMenocal, P., Ortiz, J., Guilderson, T. & Sarnthein, M. 2000. Coherent High- and Low-Latitude Climate Variability During
the Holocene Warm Period. Science 288: 2198-2202.
Soares, A.M.M. 1989. O Efeito de Reservatório Oceânico nas Águas Costeiras de Portugal Continental. ICEN/ INETI,
Sacavém.
Stuiver, M., Pearson, G.W. & Braziunas, T. 1986. Radiocarbon Age Calibration of Marine Samples back to 9000 cal yr BP.
Radiocarbon 28, 980-1021.
90
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WEATHERING AND TRANSPORT ON MINHO RIVER BASIN (NW
PORTUGAL): SOME INFERENCES FROM BEDLOAD GEOCHEMISTRY
(POSTER)
Filipa Moreno1, Maria de Fátima Araújo1, P. Valério1, João Moreno2 & Francisco Fatela3
1 Grupo de Química Analítica e Ambiente, Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional
10, 2686-953 Sacavém, Portugal
2 Centro de Geologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
3Centro e Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande,
1749-016 Lisboa, Portugal
Introduction
The chemistry of clastic sediments depends upon several related factors, which separation
of their cumulative effects is very complex. Thus, interpreting the extent to which terrigenous
sediment composition is controlled by source-area composition or modified by source-area
weathering, mineral fractionation and/or tectonic setting must be done with caution (Bauluz et al.,
2000). Furthermore, the mineral sorting during transport and deposition of sediments results in
chemical differences between bed and suspended loads with the resulting deviation from the
source-rock composition (Singh & Rajamani, 2001). Despite these limitations, sediments have
been extensively used as source of information in the attempt of reconstructing the weathering
history of river systems all over the world.
In Iberia, the Minho river basin covers an area of about 17,081 km2, spread over Spain
(16,235 km2) and Portugal (846 km2). At present, the region has a temperate humid climate,
receiving 1600 mm of average annual rainfall. The Minho River originates in the Meira Mountain
(Spain) at an elevation of 750 m above sea level and extends approximately 300 km until reach
the Atlantic Ocean, close to the village of Caminha (NW Portugal). The main lithologies underlying
the lower section of the drainage basin include granites related with Hercinic orogeny and
metassediments (“Complexo Xisto-Grauváquico”) from Paleozoic, essentially formed by
alternating schists and greywackes, locally covered by Plio-Quaternary deposits (Pereira et al.,
1992).
This work presents results concerning geochemistry of estuarine and fluvial bottom
sediments from the lower reach of Minho River (until 30 km upstream from the mouth). The
geochemical data, obtained in two cruises separated by a time span of ten years, are briefly
discussed with the aim of characterize chemical weathering and transport in the river basin and to
assess relative mobility of elements.
Sampling and methods
Bottom sediments were collected with a grab sampler at approximately the same sampling
locations (Fig. 1), in February 1993 (24 samples) and April 2003 (22 samples), on the surface
layer (upper 10 cm) and in the middle stream. Samples were taken from the central part of the
grab, to avoid metal contamination, and deep-frozen until oven-drying prior to analysis. In the
laboratory, sediment sub-samples of grain size <2 mm were ground in an agate mortar to a grain
size <63 µm after homogenisation. These sub-samples were analysed by Energy Dispersive XRay Spectrometry (EDXRF) as pellets made by pressing the ground material with an organic
binder. Details about operational conditions, precision and accuracy of analytical results can be
found in Araújo et al. (2003).
Results and discussion
Figure 2 shows Harker variation diagrams of some major and trace elements from
estuarine and fluvial sediments collected in 1993 and 2003 in Minho river/estuary system. Values
of average Upper Continental Crust (UCC) from Taylor and McLennan (1985) are also
represented. Comparison of sediment geochemistry with UCC suggests significant loss of Mg, K
and Sr during weathering. However, and since analysed sediments have higher SiO2 abundance,
variations in these elements will be somewhat due to quartz dilution. The richness in Si is
91
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
expressed by the textural characteristics of sediments (mainly sands). The absence of carbonates
in the drainage area is in the origin of great Ca depletion.
14a,b 13
Valença
N
15
Spain
18
19
42º00’
16
17
Portugal
20
41º55’
22
23
21
11 10 9
8
12
Minho
River
6
57
2 34
Caminha
1
8º50’
5 km
8º45’
8º40’
Figure 1 - Sampling locations in Minho River lower reach and its estuary.
Considering the data of both sampling campaigns, some aspects about temporal variation
of bottom sediment geochemistry are worth mentioning:
1) The slight depletion in SiO2 and the increase in Al2O3 between 1993 and 2003, which
only might be a reflection of changes in morphodynamics of depositional environments;
2) The general enhance of MgO, CaO, Rb and Sr levels (belonging to the group of the most
easily mobilised elements to solution during weathering) in channel-bed sediments from the lower
reach of the river in a period of ten years. These results may point out to a bigger proximity of
source-area rocks. Short transport implies less chemical weathering and occurrence of more
immature clastics in bedload. However, estuarine bottom sediments located close to the river
mouth show an impoverishment in Ca and Sr, suggesting weakens of marine influence in Minho
estuary;
3) No temporal trend on the K2O levels from bottom sediments. This observation is
probably attributable to the K lower mobility, related to its tendency to form into secondary clay
minerals and some is found in rather weathering-resistant minerals such as muscovite;
4) The strong enrichment of sediments in Ti and Zr with time. This is almost certainly
associated with hydraulic sorting and trapping in estuary, related with widespread siltation, that
dictates the accumulation of heavy mineral phases like rutile, ilmenite and zircon in the
river/estuary bedload;
5) The increase in Ni and Cr content of sediments. The fact that both transition trace
elements, in 2003 sampling, are well correlated with Al (rNi= 0.93 and rCr= 0.65, n= 22, p < 0.05)
seems to indicate a grain-size control of their distributions.
Final remarks
The available data indicate changes in bottom sediment geochemistry mainly related with
textural features imposed by transport and weathering. The sediments accumulated in the final
reach of Minho River and its estuary are, at present, richer in Ti, Al, Mg, Ca, Sr, Rb, Zr, Fe, Cr
and Ni than at ten years ago. The evidence of increasing levels of the so-called “immobile”
elements Al, Fe and Ti (generally associated with high weathering intensity and abundance of
clay minerals) and Mg, Ca, Sr and Rb (suggesting more chemically unweathered material) could
be a reply to the action of two processes: 1. Estuarine retention of fines (responsible, for instance,
for higher values of Cr and Ni in sediments) due to strong and very active widespread siltation; 2.
92
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Dams growing influence, which prevent the arrival at these sites of sediments from distal sourceareas. At this stage, however, is not feasible to advance with more precise conclusions. Some
studies (ex.: Duzgoren-Aydin, 2003) have proved the need of applying integrated approaches,
meaning the inclusion of mineralogical, petrographical and geochemical characterizations, in the
study of weathering signatures, since the behaviour of chemical elements may not be systematic
and not entirely controlled by the degree of weathering.
TiO2%
1.0
„ Sampling cruise 1993
† Sampling cruise 2003
0.8
0.6
Al 2O3%
25
20
UCC
1.5
10
1.0
0.2
5
0.5
0.0
0
UCC
45
55
65
75
85
UCC
2.0
15
0.4
MgO%
2.5
0.0
45
55
65
SiO2%
75
85
45
55
SiO2%
CaO%
1.0
UCC CaO=4.2%
0.8
K2O%
4
Fe 2O3%
8
3
6
2
4
1
2
0
45
55
65
75
85
UCC
0
45
55
65
SiO2%
75
MnO%
Zr (mg/kg)
1000
0.00
UCC
75
0
45
85
55
65
SiO2%
Rb (mg/kg)
75
200
60
150
45
85
45
55
50
15
0
0
75
85
65
75
85
SiO2%
Cr (mg/kg)
Ni (mg/kg)
60
50
40
30
UCC
30
UCC
65
75
SiO2%
250
55
UCC Sr =350 mg/kg
25
0
45
Sr (mg/kg)
150
50
200
100
85
100
400
0.05
65
75
75
UCC
55
65
125
600
45
55
SiO2%
800
0.15
0.10
45
85
SiO2%
0.20
85
UCC
0.4
0.0
75
SiO2%
0.6
0.2
65
UCC
20
10
0
45
55
65
SiO2%
SiO2%
75
85
45
55
65
75
85
SiO2%
Figure 2 - Harker variation diagrams for major (as w% oxides) and some trace elements (mg/kg) from estuarine and fluvial
sediments collected in 1993 (solid squares) and 2003 (open squares) in Minho river/estuary system. UCC-Upper
Continental Crust.
Acknowledgements
This work was developed in the aim of CRIDA (PLE/8/00) and ENVICHANGES (PLE/12/00) projects, with the financial
support of Foundation for Science and Technology (FCT).
References
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias,
J.M.A. 2002. Geochemical tracers of northern Portuguese estuarine sediments on the shelf. Progress in Oceanography,
52: 277-297.
Bauluz, B., Mayayo, M.J., Fernandez-Nieto, C. & Lopez, J.M.G. 2000. Geochemistry of Precambrian and Paleozoic
siliciclastic rocks from the Iberian Range (NE Spain): implications for source-area weathering, sorting, provenance, and
tectonic setting. Chemical Geology, 168: 135-150.
Duzgoren-Aydin N.S. 2003. Comparative study of weathering signatures in felsic igneous rocks of Hong Kong. Chemical
Speciation and Bioavailability, 14:1-18.
Pereira, E., Ribeiro, A., Carvalho, G. & Monteiro, H. 1992. Carta Geológica de Portugal. Notícia Explicativa da Folha 1,
Serviços Geológicos de Portugal, Lisboa.
Singh, P. & Rajamani, V. 2001. Geochemistry of the floodplain sediments of the Kaveri River, Southern India. Journal of
Sedimentary Research, 71: 50-60.Taylor, S.R. & McLennan, S.M. 1985. The Continental crust: its composition and
evolution. Blackwell Scientific Publications, Oxford.
93
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PALAEOENVIRONMENTAL EVOLUTION OVER THE LAST 10 KYR BP AT
CAMINHA TIDAL MARSH (NW OF PORTUGAL): FORAMINIFERAL
EVIDENCES (TALK)
João Moreno1 & Francisco Fatela2
1
Centro de Geologia, Fac. Ciências Univ. Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
Centro e Departamento de Geologia, Fac. Ciências Univ. Lisboa, Campo Grande, 1749-016 Lisboa, Portugal;
[email protected]
2
Microfossil data from the CPF1 core have been interpreted using the living foraminifera
zonation of local estuarine domains. Two main units have been recognized as a response to
climate, sea-level and tidal range changes during the Late Quaternary, showing a variation from
terrestrial, marsh, intertidal and subtidal estuarine environments.
Unit I (11450-11250 to 6540-6330 yr cal BP) shows a sequential shifting from
brackish/brackish-marine intertidal to subtidal assemblages. The first marine signal is recorded by
a brackish intertidal association at the core bottom (13.40 m depth; probably 11450-11250 yr cal
BP). An intensification of marine conditions is present, with the sea-level maximum being
probably achieved at 7460-7320 yr cal BP (8.40 m depth), but extending this tendency until 68506660 yr cal BP (7.60 m depth). An increase of brackish conditions is found at the top of this unit,
probably related with the formation of a sand barrier across the mouth of the Minho River and the
prevalence of estuarine conditions. This trend follows the palaeoenvironmental evolution of the
Portuguese coast, where a decline of climate is recorded by the increase of fluvial activity and the
accumulation of sediments [1, 2], which took place when the rise of relative sea-level slowed
down. Some of these brackish events can be correlated with the advance of Alpine glaciers,
mainly at 8.5 kyr BP and 7.5 kyr BP [3], around 9600-9500 and 8500-8400 yr cal BP after our
data, suggesting their association with periods of climatic cooling.
Unit II (6360-6150 yr cal BP to Present) is interpreted as a result of the sediment
accumulation on vegetated marsh, fringe marsh and terrestrial environments, showing long
periods of low foraminiferal density poorly preserved microfaunas and barren zones. At the end of
the Atlantic Optimum, 5.4-4.9 kyr BP (around 6300-6100 and 5700-5300 yr cal BP, after our data)
the climatic decline corresponds in general to a great humidity in western Europe, and it is
characterized by a drop of temperature, expressed by the advance of Alpine glaciers at 5.3 to 5.0
kyr BP; 4.7 to 4.4 kyr BP; 3.5 to 3.0 kyr BP [3, 4] (around 6200-6000 to 5800-5600 yr cal BP;
5400-5200 to 4900-4700 yr cal BP; 3800-3700 to 3200-3100 yr cal BP, after our data). A
correlated increase of rainfall and the consequent higher Minho inputs of freshwater could be
responsible of the low microfaunal density and even foraminiferal barren zones. The low-marsh
agglutinated species present in the residual assemblages could also reflect poor preservation of
the calcareous species under such environmental conditions. The middle salt marsh assemblages
suggests a climatic improvement or a sea-level rise tendency at 3160-3080 yr cal BP, which
occurs during an important coal event that extends until 2630-2580 yr cal BP. Natural fires or
anthropogenic influence should be taken into account at this period. Transitional salt marsh
foraminiferal assemblages suggests that drier conditions and marine influence (saltwater input)
prevail between 2540-2490 and 1700-1670 yr cal BP, with a freshwater episode at 1980-1940 yr
cal BP. This agrees with the trend of warmness and increasing dryness in Europe through Roman
times [5], and it is consistent with the sea-level rise. A transition to less saline environments at the
end of the Roman period is marked by the presence of Haplophragmoides manilaensis in the
residual species group, a low-salinity high-marsh indicator. A climate decline and a possible
lowering of the sea level seem to have ruled the period between 1510-1480 and 660-650 yr cal
BP. The low specimens density and the two barren zones (1230-1200 to 1040-1020 yr cal BP and
760-740 yr cal BP) could indicate an increase of freshwater input. The CPF1 site should be at the
limit of the tidal influence and periodically undergone the transition to a terrestrial environment.
This pattern is consistent with severe climate aggravation in Europe and Alpine glaciers advances
(600-700 AD; 850 AD), during the Dark Ages (450-950 AD) [5]. From 660-650 yr cal BP to
Present, the marsh assemblages are similar to the modern living faunas and represent a high
marsh environment. A marsh fringe and a high marsh with a clear freshwater input are present
94
C860cm
14
cal BP7610to 7485
C730cm
14
cal BP6625to 6410
C250cm
14
cal BP2365to 2320
Depth (cm)
II
I
95
Freshwater
Marine
Brackish
Barrenzones
%
IIAlowmarsh zone
%
normal salinity
Upper intertidal/middle marsh
%
Intertidal (brackish)
Estuary mouth
%
(brackish to normal salinity)
At
Hg
Hm
Hm
n<45
species
Residual
Cassidulinaspp.; will - E. williamsoni
beccarii; Bol - Bolivinaspp.; Cass -
At - A. tepida; Am- Ammoniasp; Abec - A.
Hg- H. germanica; Amx - A. mexicana;
Ti - T. inflata; Tc - T. comprimata;
Mf - M. fusca; Pg- P. guaratibaensis;
Hm - H. manilaensis; Jm- J.macrescens;
%
Outer shelf/continental slope
Zonation
Paleoecological interpretation
Tides
MHW
NT- meanhighwater neaptides
MHW
ST- meanhighwater springtides;
IA- highmarsh; HHW- Highest highwater;
water; IIA/IB- transitionlowtohighmarsh; IBa
AC- continental environment; FW- fresh
IT- intertidal; SUT- subtidal; LM- lowmarshl;
Assemblages
LM ( ? )
Figure1- Benthic foraminiferal assemblages distributionintheCPF1core, duringthelast 10000yearscal BP, andpalaeoecological interpretation.
0
178
%
IA1high marsh zone
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
between 660-650 and 470-460 yr cal BP, preceding an increase of salt water until 180 yr cal BP.
The highest freshwater input is achieved at 90 yr cal BP. The Medieval Warm Period (900-1000
AD to 1200-1300 AD) corresponds in our record to a low density foraminiferal and a barren
zones, followed by a strong input of freshwater assemblages (660-650 to 90 yr cal BP), probably
corresponding to the humidity increase of the Little Ice Age (1342-1849 AD) in the north-western
Iberia [6].
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Acknowledgments
This is a contribution of the project ENVI-CHANGES-PLE/12/00 financed by Foundation for Science and Technology (FCT).
References
[1] Freitas, M.C., Andrade, C. & Cruces, A. 2002. The geological record of environmental changes in southwestern Portuguese
coastal lagoons since the Lateglacial. Quat. Int. 93-94: 161-170.
[2] Drago, T., Freitas, C., Rocha, F., Cachão, J., Moreno, J., Naughton, F., Fradique, C., Araújo, F., Silveira, T., Oliveira, A.,
Cascalho, J., & Fatela, F. in press. Paleoenvironmental evolution of estuarine systems during the last 14000 years – the case of
Douro estuary (NW Portugal). J. Coast. Res., Special Issue 39.
[3] Ehlers, J. 1996. Quaternary and Glacial Geology. John Wiley & Sons. Chichester, 578p.
[4] Starkell, L. 1997. Environmental changes in central Europe 5000-3000 BP. In Third Millennium BC Climate Change and Old
World Collapse, Ed. H.N. Dalfes, G. Kukla, and H. Weiss. NATO ASI Series vol. 149, Springer-Verlag Berlin Heidelberg, 531550.
[5] Lamb, H. H. 1997. Climate History and the Modern World. London and New York, Routledge, 433p.
[6] Desprat, S., Goñi, M.F.S. & Loutre, M.-F. 2003. Revealing climatic variability of the last three millennia in northwestern Iberia
using pollen influx data. Earth Planet. Sci. Lett., 213: 63-78.
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CLIMATE VARIABILITY OF THE LAST 25.000 YEARS IN AND OFF IBERIA: DIRECT
LAND-SEA CORRELATION FROM THE MULTIPROXY ANALYSIS OF A
NORTHWESTERN IBERIAN MARGIN DEEP-SEA CORE (TALK)
Filipa Naughton1,2,3, Maria Fernanda Sanchez Goñi4, S. Desprat4, J.-L. Turon1, J. Duprat1, E. Cortijo5, B.
Malaizé1, C. Joli1, E. Bard6 & F. Rostek6
1
DGO, UMR-CNRS EPOC 5805, Bordeaux 1 University, 33405 Talence, France
INIAP, IPIMAR, CRIPSUL, Instituto Nacional de Investigação Agrária e Pescas, Av. 5 de Outubro, 8700-305 Olhão, Portugal
3
Departamento de Geologia -Universidade de Lisboa, Bloco C2, 5º piso, Campo Grande, 1749-016 Lisboa, Portugal
4
EPHE, DGO, UMR-CNRS EPOC 5805, Université Bordeaux 1, 33405 Talence, France
5
Laboratoire des Sciences du Climat et de 1’ Environnement, Domaine du CNRS, 91198 Gif-sur-Yvette, France
6
CEREGE, UMR-CNRS 6635, Europole de l'Arbois BP80 13545, Aix-en-Provence, France
2
Climate variability is a global phenomenon, primarily triggered by changes in solar radiation, which
involves changes in the different Earth’s reservoirs (ice, ocean, atmosphere, biosphere and land
surfaces). Shifts in these five reservoirs modulate, in turn, climate throughout feedback mechanisms. For
understanding the frequency, amplitude, mechanisms and consequences of the natural climate variability
we need to reconstruct in detail the climatic patterns of the past. This reconstruction can be achieved by
the correlation of deep-sea, ice and continental archives. However, it is well known that continental
sequences are frequently discontinuous; usually cover short time periods and their pollen data generally
represent local rather than regional vegetation from the surrounding areas. Furthermore, the
establishment of independent age models in marine and terrestrial sequences prevents an accurate and
reliable correlation between the responses of both environments to a given climate change. Marine
sequences, in turn, usually present continuous and long records and pollen grains preserved in their
sediments are the only proxy that allows a direct correlation between marine and terrestrial stratigraphies.
Previous studies on the modern pollen rain in oceanic sediments from north western and north
eastern Atlantic, western African margin, Mediterranean Sea and Pacific Ocean have demonstrated the
reliability of marine pollen records to reconstruct an integrated image of the regional vegetation and,
therefore, the climate of the adjacent continent. The comparison between present-day continental
(including coastal systems) pollen signatures and marine (including shelf and slope) pollen assemblages
retrieved in and off the Iberian Peninsula allows us to show that marine pollen signal from the western
Iberian margin represents the regional vegetation of the adjacent continent. Further, our study shows that
marine pollen spectra clearly discriminate both the Mediterranean and the Atlantic plant communities from
southern and northern Iberian margin samples, respectively. This study also allows understanding the
present-day patterns of pollen dispersion in the Iberian margin by using the distribution of total pollen
concentration.
Direct correlation between terrestrial (pollen) and marine climatic indicators and ice volume proxy
from the high resolution deep-sea core MD99-2331, retrieved off northwestern Iberia (42° 09’N, 09° 41’W,
2120 m depth and c. 100 km from the present-day coast line) provides a record of the climatic variability of
the last 25.000 years detected elsewhere in the North Atlantic region. It also accurately documents the
regional vegetation changes in NW of Iberia during Heinrich 2, Heinrich 1 and Younger Dryas cold events,
the Last Glacial Maximum, the Bölling-Alleröd interstadial, and the Holocene interglacial.
Acknowledgments
This paper is a contribution of the FCT project – Envichanges (PLE/12/00), IMAGES V and Artemis and Eclipse CNRS-INSU
projects.
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MILLENNIAL-SCALE CLIMATIC VARIABILITY DURING THE LAST GLACIALINTERGLACIAL TRANSITION AND THE HOLOCENE IN THE NW OF IBERIA (TALK)
Filipa Naughton1,2,3, Maria Fernanda Sanchez Goñi4, Teresa Drago2, J.-L. Turon1, J. Duprat 1, E. Cortijo 5,
B. Malaizé 1, E. Bard 6, F. Rostek 6, Jean-Marie Jouanneau 1 & Maria da Conceição Freitas3
1
DGO, UMR-CNRS EPOC 5805, Bordeaux 1 University, 33405 Talence, France
INIAP, IPIMAR, CRIPSUL, Instituto Nacional de Investigação Agrária e Pescas, Av. 5 de Outubro, 8700-305 Olhão, Portugal
3
Departamento e Centro de Geologia -Universidade de Lisboa, Bloco C6, 3º piso, Campo Grande, 1749-016 Lisboa, Portugal
4
EPHE, DGO, UMR-CNRS EPOC 5805, Université Bordeaux 1, 33405 Talence, France
5
Laboratoire des Sciences du Climat et de 1’ Environnement, Domaine du CNRS, 91198 Gif-sur-Yvette, France
6
CEREGE, UMR-CNRS 6635, Europole de l'Arbois BP80 13545, Aix-en-Provence, France
2
Millennial scale climatic variability, known as the Dansgaard/Oeschger (D/O) cycles, have been
detected in several ice, marine and continental records all over the world. These 1.500 year oscillations
are recorded in North Atlantic deep-sea cores by the presence of ice rafted detritus deriving from northern
Ice-sheets (Laurentide, Hudson Bay and Fennoscandian) during the last glacial-interglacial transition and
the Holocene. Bond et al. (1997) have defined eight cold episodes within the Holocene interglacial which
occurred at 9.800, 9.100, 8.600, 7.400, 5.200, 4.000, 2.700, 1.600 years BP in the North Atlantic Ocean.
These sea surface temperatures cooling are of low amplitude (less than 2°C) and the corresponding cool
episodes are short (inferior to 100 years) usually preventing the detection of this millennial-scale
variability.
The aim of this work is to document the vegetation response to this climatic variability in the
northwestern Iberian Peninsula during the last glacial-interglacial transition and the Holocene. For this,
pollen analysis has been performed in a high-rate sedimentary deep-sea core (MD99-2331, 42°09’00 N
and 09°41’90W) retrieved in the northwestern Iberian margin and in two cores from Douro estuary
(41°09’00 N and 08°38’00 W) covering the last glacial-interglacial transition and the Holocene. We have
also analysed the pollen content of a core from the shelf (Po 287-13-2G, 41°09’39 N and 09°00’72 W)
which covers the last 1000 years.
Both MD99-2331 and Douro estuary sequences record drastic vegetation changes during the last
glacial-interglacial transition which characterise the Bölling-Alleröd interstadial, the Younger Dryas cold
event and the beginning of the Holocene. Climate amelioration that characterises the beginning of the
Holocene is marked by the settlement of an oak forest in the northwestern Iberian Peninsula.
During the Holocene two major changes in the percentages pollen diagram at around 7.400 (8.2
cold event) and 4.500 years BP are represented in the marine deep sea core (MD99-2331). The second
deciduous forest reduction is related to a decrease of alkenones derives sea surface temperatures while
the first one is contemporaneous to the maximum warmth in the ocean. This apparent contradiction can
be result of the low resolution apply to the alkenone analysis. 8.2 cold event is also supported by changes
in Planktic foraminifer’s assemblages.
Core2 from the Douro estuary possibly detects two slight cold episodes between 10350 and 9450
BP.
Po 287-13-2G, 41°09’39 N shelf core presents no changes in the pollen percentages curves.
However pollen concentrations jointly with changes of granulometry have allowed us to detect the well
known historical episodes: the Little Ice Age and the Medieval Warm Period in the northwestern of Iberia.
Acknowledgments
This paper is a contribution of the FCT project – Envichanges (PLE/12/00), IMAGES V and Artemis and Eclipse CNRS-INSU
projects.
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EVOLUCIÓN SEDIMENTARIA DESDE EL ÚLTIMO MÁXIMO GLACIAL EN LA
COSTA Y PLATAFORMA CONTINENTAL DE LAS RÍAS BAIXAS
(GALICIA, NW DE LA PENÍNSULA IBÉRICA) (TALK)
Miguel Angel Nombela, Irene Alejo, P. Bernárdez, F. Clemente, Susana Costas, Paula Diz, S.
Fernández-Bastero, Guilhermo Francés, L. Gago-Duport, T. García, D. González-Alonso, R. GonzálezÁlvarez, R. González-Villanueva, C. Liquete, L.D. Pena & Marta Pérez-Arlucea
Grupo XM1, Dpto. Xeociencias Mariñas e O.T., Fac. Ciencias Do Mar, Universidade de Vigo; [email protected]
Introducción
En este trabajo se presenta una síntesis de los datos obtenidos durante los últimos años por el
grupo de investigación XM1 de la Universidad de Vigo. La actividad de este grupo se ha centrado en los
sedimentos marinos del Cuaternario en la costa occidental gallega y en la plataforma continental
adyacente. Más concretamente, se presentan resultados de los complejos playa-barrera-lagoon de La
Ramallosa (Baiona) y Rodas (Islas Cíes), de las playas de Patos y Moaña, todos ellos localizados en la
Ría de Vigo, así como de diferentes sondeos marinos extraídos en las rías de Vigo y Muros y en la
plataforma continental adyacente a las Rías Baixas. El análisis de estos sedimentos se ha abordado
desde un punto de vista multidisciplinar, que incluye aspectos estratigráficos, sedimentológicos,
micropaleontológicos y geoquímicos.
Sedimentación pre-Holoceno
En diferentes puntos de la costa occidental gallega afloran entre 0,5 y 2 metros por encima del
nivel del mar actual depósitos de playas y dunas fósiles cuya edad todavía no ha sido establecida,
aunque probablemente correspondan al último interglacial. No se ha constatado la presencia de
sedimentos más recientes hasta los atribuidos al Último Máximo Glacial. Durante este periodo, tanto en
sondeos de la plataforma interna como de La Ramallosa, se registra un depósito de gravas
granodecrecientes, polimígticas, constituidas por clastos de cuarzo, granito y esquisto en una matriz
arenosa muy gruesa. En general son depósitos azoicos, si bien en La Ramallosa se han reconocido
algunos gasterópodos terrestres hacia el techo de este tramo. Se interpretan como sedimentos fluviales
generados con un nivel del mar al menos 70 metros más bajo que el actual.
Evolución holocena
Depósitos transgresivos
Sobre los depósitos fluviales anteriormente citados comienzan a registrarse sedimentos con
influencia marina, cuya base es diacrónica dependiendo del paleorrelieve. La datación más antigua de la
que se tiene constancia es de 9400 cal BP, en un sondeo de la plataforma interna frente a la Ría de Vigo,
a 73 metros de profundidad. Se trata de sedimentos de tamaño arena media, compuestos por granos de
cuarzo y glauconita, con bajas proporciones de carbono orgánico (0,5%) y abundantes foraminíferos,
mayoritariamente epifaunales. Se interpreta como un sedimento de plataforma interna depositado en un
fondo sometido a un régimen energético relativamente alto. En La Ramallosa el inicio de la
sedimentación marina se ha establecido en 8200 cal BP. Se trata de arenas siliciclásticas de tamaño
medio-grueso, con abundantes restos de vegetales de origen continental y fragmentos de conchas de
moluscos. Estos sedimentos corresponden a facies de desembocadura fluvial con influencia marina, en
condiciones probablemente intermareales. En la zona externa de la Ría de Muros los sedimentos
claramente marinos más antiguos recuperados, corresponden a 8000 cal BP, mientras que hacia la zona
media-interna comienzan a registrarse a 6000 cal BP. En el resto de localidades estudiadas no se
encuentran depósitos con influencia marina hasta, al menos, 4500 cal BP.
En torno a 7500 cal BP, se registra un cambio en las condiciones de sedimentación como
consecuencia del rápido ascenso del nivel del mar. En La Ramallosa comienzan a depositarse fangos
intercalados con capas ricas en turba y con niveles de arena de grano fino a medio. Hacia el techo van
despareciendo los niveles de turba y aumenta progresivamente la presencia de moluscos. Sus
características indican que se trata de facies de lagoon y marisma costera. En la Ría de Muros y en la
plataforma continental interna este cambio se manifiesta por una brusca disminución de la influencia
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terrígena, una leve disminución del tamaño de grano, un ligero aumento del contenido en carbono
orgánico y un cambio en las asociaciones de foraminíferos, tanto planctónicos como bentónicos.
Depósitos de alto nivel del mar
El mantenimiento de la subida del nivel del mar provocó la máxima inundación de las
desembocaduras fluviales entre 6000 y 5500 cal BP, permitiendo el depósito de sedimentos marinos en
sectores previamente emergidos. Tanto en La Ramallosa como en Moaña se instalan condiciones de
estuario-bahía protegida, con una lámina de agua entre 8 y 14 m. En la plataforma se registra un máximo
de la productividad biológica durante este periodo. A pesar del alto nivel del mar, en las Islas Cies se
desarrolla una ambiente pantanoso de agua dulce entre 6000 y 4000 cal BP, que da lugar a la formación
de una turba que se apoya directamente sobre el zócalo granítico. También se encuentran sedimentos de
turba similares en la Playa de Patos, cuyo techo se ha datado en 4600 cal BP. Para la formación de estos
depósitos se requiere el desarrollo de barreras arenosas que protejan a estas zonas costeras de la
influencia marina.
El evento más importante que se registra en esta región durante el Holoceno tuvo lugar a 4000 cal
BP. En las zonas costeras de La Ramallosa y Moaña la sedimentación agradante que ha caracterizado a
las fases descritas, pasa a ser progradante. En estas localidades se instala un ambiente de llanura
intermareal, donde se depositaron arenas gruesas, gránulos y gravas siliciclásticas con abundates restos
de moluscos y con estructuras lenticular, flaser y laminación paralela. Sobre los niveles de turba, en las
Islas Cíes se desarrolla un lagoon y en Patos se forma una playa. En la Ría de Muros se registra un
cambio abrupto tanto en el registro isotópico del oxígeno como en las asociaciones de foraminíferos
bentónicos, en las cuales comienzan a aparecen especies que previamente no estaban presentes. El
mecanismo de este cambio probablemente esté relacionado con causas climáticas e hidrográficas. Una
modificación en la posición de los frentes, particularmente del Frente de Finisterre, reforzó la influencia de
aguas subpolares y de los procesos de afloramiento en el Norte de la zona estudiada. Estos reajustes
dieron lugar a una fase de inestabilidad climática que potenció la sedimentación arenosa en la plataforma
continental, como consecuencia de una mayor incidencia del régimen de tormentas hasta 3000 cal BP. A
esta edad comienza a desarrollarse la lengua de fangos en la plataforma media, aumentan los procesos
de mezcla en la columna de agua, fenómeno que favorece la productividad primaria y el enriquecimiento
del sedimento en ópalo y carbono orgánico. En este momento se inicia un periodo de relativa estabilidad
ambiental que no supone cambios destacables en el régimen de sedimentación hasta 500 cal BP, cuando
las playas y barreras arenosas retrogradan hasta alcanzar su posición actual. A esta misma edad
comienza a registrarse una influencia progresivamente mayor de la actividad antrópica.
Agradecimientos
Trabajo parcialmente financiado por los proyectos REN2003-09394/MAR, PGIDIT04PXIC31204PN, EVK2-CT-2000-00060,
BTE2000-0877. Se agradece al Ministerio de Educación, Cultura y Deportes, a la Xunta de Galicia y a la Universidad de Vigo las
becas concedidas a varios de los autores. A la Cofradía de Pescadores La Anunciada de Baiona por las facilidades brindadas para
el trabajo de campo.
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OSCILACIONES CLIMÁTICAS MILENARIAS EN EL ATLÁNTICO NORTE DURANTE
EL HOLOCENO: TELECONEXIONES ENTRE ALTAS Y BAJAS LATITUDES (TALK)
L.D. Pena1, Guilhermo Francês 2, P. Diz 2, 3, Miguel Angel Nombela 2 & Irene Alejo2
1
Universitat de Barcelona. GRC Geociències Marines, Dpto. Estratigrafía, Paleontología i Geociències Marines. C/ Martí i Franqués,
s/n, E-08028 Barcelona, España; [email protected]
2
Universidad de Vigo. Dpto. Geociencias Marinas y O.T. Fac. Ciencias del Mar. As Lagoas-Marcosende, s/n, E-36200 Pontevedra,
España; [email protected]
3
Cardiff University. School of Earth, Ocean and Planetary Sciences. Main Building,Park Place Cardiff CF10 3YE, Cardiff, U.K;
[email protected]
Durante los últimos años diversos trabajos han documentado la existencia en el Atlántico Norte de
una serie de eventos climáticos relativamente fríos durante el Holoceno, que se caracterizan por
presentar una recurrencia temporal a escala milenaria (Bond et al., 1997, 2001; Bianchi y McCave, 1999;
Keigwin y Boyle, 2000; Marchitto y deMenocal, 2003). Estos cambios abruptos han sido igualmente
registrados en otras regiones como, por ejemplo, el Atlántico subtropical (deMenocal et al., 2000a, b). La
característica más distintiva de estos eventos es presentar una recurrencia temporal cíclica en torno a
1500±500 años (Bond et al., 1997; Bianchi y McCave, 1999). A pesar de que todavía existen
discrepancias en torno a la cronología, periodicidad (Schulz y Paul, 2002) y el origen de estos eventos
(Bond et al., 2001), hay un gran número de evidencias que apuntan hacia estos ciclos cuasi periódicos
como uno de los componentes más significativos de la variabilidad climática de nuestro planeta durante el
Holoceno. Por tanto, partimos de la hipótesis de que estos eventos pueden haber quedado registrados
también en otras zonas con especialidad sensibilidad climática de latitudes medias.
Para este estudio hemos utilizado un testigo de gravedad (EUGC-3B, 42º45’N; 9º02’W; 40 m
profundidad) recogido en la zona externa de la Ría de Muros (NW de la Península Ibérica) y que registra
los últimos 8200 años (el modelo de edad se ha establecido mediante 7 dataciones de radiocarbono).
Esta zona se caracteriza por la presencia de un frente hidrográfico sub-superficial entre dos masas de
agua: la Eastern North Atlantic Central Water subpolar (ENACWsp), al norte del frente y la Eastern North
Atlantic Central Water subtropical (ENACWst), al sur del frente. Además, los eventos de afloramiento
estacionales causan que, dependiendo de la posición del frente subsuperfical, pueda aflorar una u otra
masa de agua. Álvarez-Salgado et al. (1993) han constatado que la posición del frente hidrográfico puede
oscilar en función de los factores climáticos y oceanográficos que afectan a la región, migrando hacia el
Norte o hacia el Sur en periodos relativamente cortos de tiempo. Una oscilación semejante ha podido
ocurrir también a escalas más largas de tiempo (Holoceno). Con el objetivo de detectar estos cambios
hemos analizado los isótopos estables de oxígeno y carbono (δ18O y δ13C) en el foraminífero bentónico
Nonion commune (D’Orb.), ya que se trata de una especie infaunal somera que es abundante a lo largo
de todo el registro. Todos los análisis fueron realizados en un espectrómetro de masas FINNIGAN MAT
251 (Universidad de Bremen, Alemania), obteniéndose una precisión analítica de ±0.07‰ para δ18O y de
±0.05‰ para δ13C, respectivamente, siendo todos ellos normalizados al estándar V-PDB.
Los valores de δ13C se encuentran comprendidos entre -0.70‰ y -4.45‰, obteniéndose un valor
promedio para el registro completo en torno a -3.13‰. En el caso del δ18O, los valores oscilan entre
1.60‰ y 2.15‰, y el valor promedio se sitúa en torno a 1.82‰. Los datos obtenidos muestran la
presencia de una serie de eventos isotópicos significativos en el registro de δ13C, mientras que en el
registro de δ18O esta variabilidad es mucho menor. Los eventos registrados en los valores de δ13C se
caracterizan por rápidos incrementos y decrementos en los valores de δ13C. Los incrementos se
interpretan como una mayor presencia de la ENACWsp en la Ría de Muros durante periodos de
afloramientos más intensos y circulación más vigorosa. Por el contrario, los periodos con valores más
negativos de δ13C se corresponderían con una mayor influencia de la ENACWst, afloramientos menos
intensos y circulación ralentizada.
Los diversos métodos de análisis espectrales aplicados a este registro muestran una periodicidad
muy significativa en torno a 1500 años a lo largo de todo el Holoceno. A modo de comparación, hemos
seleccionado dos registros marinos en los que también se ha puesto de manifiesto una alta variabilidad
climática durante el Holoceno. El testigo VM 29-191 (Bond et al., 1997), en el Atlántico Norte (W de
Irlanda), y el ODP Hole 658C (deMenocal et al., 2000a), en el Atlántico subtropical (NW de África),
presentan sendos registros cíclicos con periodos de 1500 años durante el Holoceno. Es factible entonces
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que, sea cual sea el origen de esta serie de eventos durante el Holoceno, estos hayan caracterizado el
clima y la oceanografía de estas tres áreas, y, por tanto, se podrían establecer correlaciones entre estas
tres regiones tan distantes cuyas características estarían gobernadas, al menos en parte, por los mismos
mecanismos.
Una vez llevada a cabo la correlación entre los tres registros aludidos, se pone de manifiesto que la
mayor similitud (r2=0.812) se produce entre la curva isotópica del carbono obtenida en la ría de Muros
(EUGC-3B) y la curva de anomalías de la temperatura superficial calculadas para el noroeste africano
(Hole 658C; deMenocal et al., 2000). Así pues, los momentos durante los cuales la ría de Muros recibe
una mayor influencia de ENACWsp (afloramientos intensificados) coinciden con anomalías relativamente
frías en las temperaturas superficiales del océano al oeste de Cabo Blanco. Dichas anomalías han sido
interpretadas como una probable advección de aguas subpolares relativamente más frías y/o como una
intensificación de los grandes eventos de afloramiento característicos de esta región africana (deMenocal
et al., 2000b). La concordancia entre ambos fenómenos es justificable porque, tanto las aguas de
latitudes medias como de latitudes subtropicales del Atlántico Noroccidental, forman parte del mismo
sistema de corrientes (Portugal-Canarias). Por tanto, cualquier alteración de este macro sistema de
corrientes, como una intensificación de los vientos de componente norte o una migración hacia el sur de
los frentes hidrográficos, debería ser registrada de manera similar en ambas áreas. Un segundo punto a
favor de esta interpretación es la conexión propuesta entre los eventos fríos subtropicales y una serie de
eventos de enfriamiento que caracterizaron las latitudes altas del Atlántico Norte durante el Holoceno
(Bond et al., 1997; Bianchi y McCave, 1999). Estos eventos fríos en latitudes más altas se caracterizan
porque los sedimentos marinos presentan un mayor contenido de partículas transportadas por los
icebergs (IRDs). Esto implicaría que durante el Holoceno ha habido una serie de enfriamientos periódicos
en latitudes altas que provocaron importantes cambios hidrográficos en el Atlántico Norte, entre los
cuales cabe destacar la migración hacia el Sur de los frentes y los reajustes de los sistemas regionales
de corrientes y vientos.
Bibliografía
Álvarez-Salgado, X.A., Rosón, G., Pérez, F.F. & Pazos, Y. 1993. Hydrographic variability off the Rías Baixas (NW Spain) during the
upwelling season. Journal of Geophysical Research, 98(C8): 14447-14455.
Bianchi, G.G. & McCave, I.N. 1999. Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland. Nature, 397:
515-517.
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. & Bonani, G.
2001. Persistent Solar Influence on North Atlantic Climate during the Holocene. Science, 294: 2130-2136.
Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I. & Bonani, G. 1997. A
pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science, 278: 1257-1266.
deMenocal, P., Ortiz, J., Guilderson, T., Adkins, J., Sarnthein, M., Baker, L. & Yarusinsky, M. 2000). Abrupt onset and termination of
the African Humid Period: rapid climate responses to gradual insolation forcing. Quaternary Science Reviews, 19: 347-361.
deMenocal, P., Ortiz, J., Guilderson, T. & Sarnthein, M. 2000b. Coherent high- and low-latitude climate variability during the
Holocene warm period. Science, 288: 2198-2202.
Keigwin, L. D. & Boyle, E.A. 2000. Detecting Holocene changes in thermohaline circulation. PNAS, 97(4): 1343-1346.
Marchitto, T. M. & deMenocal, P. 2003. Late Holocene variability of upper North Atlantic Deep Water temperature and salinity.
Geochemistry, Geophysics and Geosystems, 4(12): 1100.
Schulz, M. and A. Paul 2002. Holocene Climate Variability on Centennial-to-Millennial Time Scales: 1. Climate Records from the
North-Atlantic Realm. In: G. Wefer, W.H. Berger, K.E. Behre and E. Jansen (Eds.): Climate Development and History of the North
Atlantic Realm. Springer-Verlag. Berlin. 41-54 p.
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LONG AND SHORT TERM DENUDATION RATE CALCULATIONS FOR THE “RÍA DE
VIGO” (SPAIN): AFTD, DEM-BASED ANALYSIS, RIVER LOADS AND SEDIMENT
VOLUME (TALK)
Marta Pérez-Arlucea1, A. Carter2, F. Clemente1, Miguel Angel Nombela1 & D. González1
1
Dpto. Xeociencias Mariñas y O.T. Facultade de Ciencias, Universidade de Vigo. 36.200 Vigo, Spain; [email protected],
[email protected], [email protected]
2
School of Earth Sciences.University and Birkbeck College, Gower Street, London, WC1E 6BT, UK.
A comparative study of denudation rates obtained by 5 different methods is been accomplished: 1)
Apatite Fission Track Dating (AFTD) thermochronology; 2) potential denudation calculations based on
theoretical equations derived from digital elevation models; 3) Landscape degradation by rock volume
loss; 4) sediment volume evaluation in the beach barrier-lagoon complex (A Ramallosa), and 5) fluvial
sediment loads. Techniques 1, 2 and 3 allow calculations of long-term denudation rates (on the order of
106 years), whereas 4 permits calculation of short-medium rates (from late Holocene to modern, order of
102 years) and finally 5, modern sediment fluxes and denudation rates. Long term calculations are
highlighted and compared with those based on river loads and sediment volume, the latter discussed in
more detail in Pérez Arlucea et al. (2005). Additional data corresponding to extreme storm events are
included for load calculations. Two river catchments have been studied in the Ría de Vigo, the Miñor and
the Lagares. The geology of the source area is dominated by igneous (alkaline and calc-alkaline granites)
and metamorphic rocks (schist and gneiss) of Precambrian to Palaeozoic age. Rare Quaternary rocks and
recent fluvial-estuarine and coastal sediments are located chiefly on the coast. The Lagares catchment
has higher proportions of metamorphic rocks, whilst the Miñor’s has a predominance of granites.
Weathering is quite intense and mass wasting is common on natural slopes and road cuts.
AFTD data analysis was carried out in 5 samples collected in a granitic outcrop at different
elevations (intervals of 100 to 200 m). Methods 2 and 3 are based on digital elevation model (DEM)
databases (25 m resolution). Sediment distribution and facies analysis for volume calculations (method 4)
were estimated by coring (TESS-1 suction corer Méndez et al., 2003). Up to 4.0 m boreholes were
sampled every 0.10 - 0.20 m for grain size analysis by mechanic sieving and Sedigraph. Marine shells
and wood fragments were dated by 14C, enabling calculation of sediment accumulation and denudation
rates. Age determinations were calibrated by the University of Washington Quaternary isotope lab
Radiocarbon Calibration Program Rev. 4.3 (Stuiver & Reimer, 1993). Denudation rates by river load data
(method 5) were calculated in two rivers from May 1997 to July 1998 and from May 2000 to May 2001and
water samples were collected for suspended and dissolved loads. Denudation rates (DR) obtained by all
methods are summarized in table 1. All long-term denudation rates give values from 12 to 26 mm/kyr,
which are slightly lower but similar to the typical denudation rates obtained in granite terrains, usually
comprised between 20 and 40 mm/kyr (Riebe et al., 2001; Gunell, 1998). AFTD data indicate cooling
throughout the Mesozoic at a steady rate of ~0.4°C/Myr. Geothermal gradients were below global mean
values of ~30°C/km. Although the precise geothermal gradient cannot be established, the FT data help
place upper limits for an estimate of the maximum amount of section lost to denudation in the Mesozoic.
Based on a maximum geothermal gradient value of 30°C/km, the modelled FT data records 60°C of
cooling over a 150 Myr, i.e. 2000 m over 150 Myr, which is equivalent to a denudation rate of 13 mm/kyr.
Short term denudation rates are variable depending on weather conditions and anthropogenic influence.
River loads give short-term mechanical denudation rates (MDR) of 10-100 m/Myr and chemical
denudation rates (QDR) 40-90 mm/kyr, unusually high in proportion when compared to present day rivers.
Sedimentation rates from compaction-corrected cores and 14C sediment ages generally indicate values of
3.3-4.4 mm/yr, with 1.1 mm/yr for the oldest sediments. Mass accumulation rates are 1.1 mm/yr for the
older dated interval (1517 years) and average 3.7 mm/yr for the younger interval (484 years). These allow
calculation of denudation rates for average rock density of 2.7 ton/m3 of 10.1 mm/kyr for the older interval
and 33.4 mm/kyr for the younger.
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Core data indicates that 90-95% of the total sediment volume is bed-load, thus providing a method
to estimate bed-load derived material. Data shows that 74-90% of mud from the fluvial suspended load is
exported to the Ría during normal weather conditions. This estimate can be 3 times higher in extreme
rainfall situations or storms. If we assume that bedload and suspended load give values of total
mechanical denudation rates, the result are quite high, although they cannot be extrapolated too far back
into the Holocene due to the lack of uniformity in controlling parameters affecting vegetation cover by
human impact such as deforestation,
cultivation and construction activities leading
enudation rates (mm/kyr)
to soil exposure and degradation. In fact,
Miñor R.
Lagares R.
sediment yields can even be two orders of
Long Term
magnitude higher for areas subjected to road
AFTD
13
works and building. It is remarkable that the
Potential (from relief)
26.5
21.7
Lagares River catchment, with a smaller area
Potential (from elevation)
16
12
and lower slopes than the Miñor shows higher
Landscape volume loss:
21.7
21.7
concentrations for river load, and a
denudation rate four times higher. Differences
Short Term:
in lithology play a roll in the observed results,
From River loads:
as the Lagares catchment area has a higher
MDR:
9.5
40.5
1997/98
proportion of metamorphic rocks than
2000/01
59.8
55.6
granites, but the Lagares is also influenced
QDR:
more by human activities as it contains the
44.3
74.6
1997/98
urban area of Vigo city and has a higher
2000/01
97.1
58.2
overall population density. Considering total
From sediment volume
denudation from different sources (bedload,
2001 to 484 yr. BP:
suspended and dissolved loads), is possible
484 yr. BP to Present:
to conclude that denudation rates are higher
10.1
for the short-term scale than those obtained
33.4
for long-term denudation rates and that there
is an increase in denudation from the last 500
Table 1- Summary of denudation rates obtained by all different methods.
years approximately. Major increases in
sedimentation rates from the first interval
(2001 yr. BP to 484 yr. BP) to the second (484 yr. BP to present) may also be interpreted in terms of
progressively more restricted conditions accompanying evolution of the spit in the Ramallosa Complex,
along with an superimposed human influence. Pollen data suggest that climatic changes during the last
2500 years are not significant and vegetation changes are due mostly to human influence (Tornqvist et al.,
1989).
Acknowledgements
Grants from OMA (U. Vigo) and projects: PGIDT00MAR30103PR, PGIDT00PX-130105PR, CICYT REN2000-1102MAR, Xunta de
Galicia y REN2003-09394/MAR (MCYT).
References
Gunnell, Y. 1998. Present, past and potential denudation rates: is there a link? Geomorphol., 25: 135-153.
Méndez, G., Pérez-Arlucea, M., Stouthamer, E. & Berendsen, H. 2003. The TESS-1 suction corer: a new device to extract wet,
uncompacted sediments. Journal of Sedimentary Research, 373: 1078-1081.
Pérez-Arlucea, M., Méndez, G., Clemente, F., Nombela, M., Rubio B. & Filgueira M. 2005. Hydrology, sediment yield, erosion and
sedimentation rates in the estuarine environment of the Ria de Vigo, Galicia, Spain. Journal of Marine Systems, Spec. vol. 54:
209-226.
Riebe, C.S., Kirchner, J.W., Granger, D.E. & Finkel, R.C. 2001. Minimal climatic control on erosion rates in the Sierra Nevada,
California. Geology, 29 (5): 447-450.
Stuiver, M., Reimer, P.J. 1993. Extended 14C database and revised CALIB radiocarbon calibration program. Radiocarbon, 35: 215230.
Tornqvist, T.E., Janssen, C.R. & Pérez-Alberti, A. 1989. Degradación antropogénica de la vegetación en el noroeste de Galicia
durante los últimos 2500 años. Cuadernos de estudios Gallegos, 38: 175-198.
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MULTI-PROXY DESCRIPTION OF MAJOR SEDIMENTARY ENVIRONMENTS IN
MORBIHAN’S GULF (NW FRANCE) (TALK)
L. Pérez-Belmonte1 & E. Goubert2
1
Université Bretagne Sud (LEMEL) - Géosciences Rennes, Campus Tohannic, CER « Yves Coppens », BP 573, 56017 Vannes
Cedex, France ; [email protected]
2
Université Bretagne Sud (LEMEL) - Géosciences Rennes, Campus Tohannic, CER « Yves Coppens », BP 573, 56017 Vannes
Cedex, France; [email protected]
Three different estuarine environments and their transition facies have been described from
geophysical (VHR seismic and lateral sonar), sedimentological (grab samples) and paleoenvironmental
(foraminifera) data. Their spatial distribution follows a linear transition from the east point to the west point
of Morbihan’s Gulf agreeing with hydrodynamic conditions but often truncated by topographic accidents.
At the eastern area supra and intertidal environments were recognized as it follows: marshes and
salt meadows in the highest part and intertidal mudflats with associated channels in the lowest part.
Foraminifera assemblages are quite homogeneous in this area, but some differences can be recognized
between Zostera marina area and channels axes, where surface sediment is very reduced.
At the central area the subtidal environment is characterized by the confluence of small tidal
channels to give larger ones. 80% of total foraminifera preserved in channel sediments is constituted by
exotic species transported from the sea. Different stages of sedimentary filling can be recognized in these
large tidal channels from the seismic data, as well as a major erosive surface which can be correlated
among channels. The origin of this surface is still uncertain, but it could be either related to some different
transgressive pulses or generated by some catastrofic local events.
The western area is influenced by very violent flood and ebb currents in the strait mouth of the Gulf
(4.5 m/s). In this zone prevails the absence of sediments except in the beaches vicinity where active
dunes can be observed.
Current spatial distribution of these environments seems to be controlled by three main factors: tidal
currents, depth and coastal morphology.
Acknowledgements
This work is funded by COTARMOR project under research grant of Brittany’s government. Geophysical survey was made with the
logistic and human help of Geosciences Rennes and UMR 6143 « Morphodynamique Continentale et Côtière», at Caen’s University.
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THE LAST 200 YEARS OF SEDIMENTATION IN SANTO ANDRÉ LAGOON (SW
PORTUGUESE COAST) – RESULTS FROM SEDIMENTOLOGICAL AND
GEOCHEMICAL PROXIES (TALK)
Rute Ramos1, Anabela Cruces1, Maria da Conceição Freitas1, César Andrade1 Maria de Fátima Araújo2 &
Jean-Marie Jouanneau3
1
Laboratório de Processos Costeiros, Centro e Departamento de Geologia da Faculdade de Ciências da Universidade de Lisboa.
Edifício C6, 3º Piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected], [email protected], [email protected],
[email protected]
2
Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal; [email protected]
3
Dép. Géologie et Océanographie, UMR 5805, CNRS, Univ. Bordeaux I, Av. des Facultés, 33405, Talence Cedex, France ;
[email protected]
Introduction
Santo André lagoon is located in Tróia-Sines coastal bay, 80km S of Lisbon and exhibits a complex
morphology: it is formed by a main lagoonal body with maximum dimensions of 2 x 1.5km along N-S and
E-W, respectively; it extends southward throughout two elongated bodies aligned N-S (locally named
“Poços”), that are connected with the main body by narrow and shallow channels (Fig. 1).This is a shallow
lagoonal system with average depth of 2m, although in periods of maximum flood depths can reach 4-5m.
Maximum water surface changes seasonally, mean values being circa 2.5km2 but reaching 3.7km2 in
exceptionally rainy winters.
The lagoon is isolated from the sea by a welded sand barrier where an artificial inlet is annually
opened, allowing exchanges between the lagoonal space and the ocean; complete silting up of the inlet is
promoted by tides and waves in a time interval varying from few days to weeks. During open-inlet periods
marine sediments are input via tidal channel and complete renewal of the lagoonal water is achieved,
which becomes similar to ocean water, with salinity of 35‰. When the lagoon is isolated from the ocean,
water becomes brackish to fresh and anoxic conditions may develop near bottom; in this stage the lagoon
collects fluvial inputs of water and sediment from a drainage basin with 145km2. Most of the bed load is
entrapped in alluvial fans, while suspended sediment added by autochthonous organic matter eventually
settle in the central main basin.
N
¿
c
da
ábi
r
r
A
N
n
hai
Tróia
Sado
estuary
11
Espichel cape
0
8
100km
Atlant
ic
Ocean
100
7
Santo André
lagoon
Sampling site
Sines
5
0
10
A B
20km
0
LSA
1 km
Figure 1 - A – Location of Santo André lagoon in the coastal arc of Tróia-Sines; B – Sampling sites of “short” cores LSA7, LSA8 and
LSA11 and “long” core LSA (Ordinance survey map 505, 1/25000, 2000 – IGeoE).
Methods
This study relies upon the analysis of three gravity cores collected in the lagoonal central basin. In
all sites, two replicates have been taken for sedimentology and geochemistry: LSA8a and LSA8b, 57 and
81cm long, respectively, were cored in May 1998; LSA7a – 100cm and LSA7b – 103cm, LSA11a – 86cm
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and LSA11b – 92cm, have been taken in February 2003 (Fig. 1B). Compaction during sampling was
considered negligible in all cases. Cores LSA8a and b were sub-sampled at each 1cm; LSA7a and
LSA11a were sub-sampled at each 2cm for sedimentological analysis; 15 and 12 sub-samples 2.0 to
2.5cm-thick have been taken in the upper 30cm of cores LSA7b and LSA11b, and 7 and 6 sub-samples
(thick between 1 - 2.5cm) in the remaining of the same cores, for geochemistry, respectively.
Sedimentological studies included: texture (classified following Flemming, 2000), sediment pH determined using the electrometric method according to LNEC (1967a) and classified following Pratolongo
(in Costa, 1999), organic matter (OM) - determined through oxidation with K-dichromate followed by
titration using Fe-sulphate (LNEC, 1967b) and CaCO3 content - using an Eijkelkamp calcimeter (except in
LSA8a, where it was determined by weight difference before and after digestion with diluted hydrochloric
acid).
Geochemical analysis have been performed by Atomic Absorption Spectrophotometry (AAS) in
core LSA8b and the total content in Mg, Al, Si, Ca, Mn, Fe, Ni, Cu, Zn, Cd and Pb (total sample procedure by Rantala & Loring, 1977) has been determined; Energy Dispersive X-ray Fluorescence
(EDXRF) was used to obtain 21 elements (Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr,
Y, Zr, Nb and Pb) in <2mm fraction (Araújo et al., 2002) in LSA7b and LSA11b cores. In the latter,
natural excess of 210Pb and 137Cs were determined by gamma spectrometry and used as chronometric
tracers to estimate sedimentation rates.
The background concentrations for heavy metals (Cr, Ni, Cu, Zn and Pb) were obtained in
Holocene “Fossil Lagoonal Deposits” (FLD) found in core LSA (Fig. 1B) (Freitas et al., 2003). Values of
Average Shale (AS) were also used for the same intent.
Results and Discussion
Sedimentology
In all cores no evidence of erosional surfaces was found and the high resolution of sedimentological
analysis, allowed the definition of three main Units (Unit I, II and III) (Fig. 2) in spite of macroscopic
textural homogeneity. The bottom and top units are enriched in coarse material, mainly composed of
carbonate and few quartz particles.
Depth (cm)
0
0
LSA 7
8 16
0
LSA 8
8 16
0
Depth (cm)
0
0
LSA 7
20 40
0
20
40
26 cm
26 cm
30
30
40
40
43 cm
46 cm
46 cm
43 cm
50
50
60
60
70 cm
70
70 cm
70
80
80
100
LSA 11
0
20
20
90
LSA 8
20 40
11 cm
10
11 cm
10
LSA 11
8 16
90
94 cm
A
100
94 cm
B
Figure 2 – Sedimentological depth profiles: A - organic matter content; (%); B – >63µm fraction (%).Unit I (100-94cm, LSA7a; 5743cm, LSA8a; 86-70cm, LSA11a) – is dominated by sandy mud to slightly sandy mud (<63µm fraction > 67%), subalkaline (pH 8.28.4), with low OM (maximum 7.2%) and high carbonate (maximum 29%) contents.
Unit II (94-46cm, LSA7a; 43-11cm, LSA8a; 70-26cm, LSA11a) – consists of mud and slightly sandy
mud (<63µm fraction > 84%), subalkaline (pH 8.2-8.5) with OM content similar to the underlying unit (4.18.7%), but lower in carbonate (maximum 12%).
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Unit III (46-0cm, LSA7a; 11-0cm, LSA8a; 26-0cm, LSA11a) – is dominated by slightly sandy mud
(<63µm fraction >76%). Although subalkaline, the sediment shows the lowest values of pH (pH 7.5-8.2)
and maximum contents in OM and carbonate, reaching 15% and 26%, respectively.
Geochemistry
The main purpose of the geochemical study was to determine the beginning of anthropogenic
influence in the system and, if possible, to quantify it.
The concentration in Si and Al mirrors sediment mineralogy and, indirectly, the texture; vertical
variation in these elements shows, in general, some depletion in bottom and top sections in consequence
of Ca and Sr enrichment, which is in agreement with sedimentology (Fig. 3).
The profiles of concentration in Br and Cl follow a pattern similar to the one of water content,
suggesting a decrease with increasing depth; this variation, although not completely understood, may be
an artefact induced by loss of interstitial water during compaction.
In general, the concentrations values in Cr, Ni, Cu, Zn e Pb show little variations along the cores;
however Zn and Pb increase slightly to the surface. Comparing the values of all metals with FLD and AS,
only Zn and Pb show some enrichment (Fig. 4) with absolute concentration values of 183 and 77mg/kg,
respectively; these values are not very high, when compared with those found in other Portuguese
estuarine/lagoonal environments.
LSA 7
Depth (cm)
Si (%)
LSA 11
LSA 8
Si (%)
Ca (%)
Al (%)
Ca (%)
Si (%)
Al (%)
Ca (%)
10
5
0
10
7
4
28
22
16
10
5
0
10
7
4
28
22
16
10
5
0
10
7
4
28
22
16
0
Al (%)
III
10
III
20
Figure 3 – Geochemical depht
profiles of Si, Al and Ca.
III
II
30
40
50
II
60
I
70
II
80
I
90
I
LSA 7
LSA 8
LSA 11
5
LSA 7
LSA 8
LSA 11
Average Shale
Lagunar Fóssil - IIA
Lagunar Fóssil - IIB
70
200
180
160
140
120
100
80
60
40
20
0
6
7
8
Al (%)
9
10
LSA 7
LSA 8
LSA 11
5
6
7
8
Al (%)
9
10
50
40
30
20
LSA 7
LSA 8
LSA 11
Average Shale
Lagunar Fóssil - IIA
Lagunar Fóssil - IIB
0
5
100
90
80
70
60
50
40
30
20
10
0
Average Shale
Lagunar Fóssil - IIA
Lagunar Fóssil - IIB
60
10
6
7
LSA 7
LSA 8
LSA 11
8
Al (%)
9
10
Average Shale
Lagunar Fóssil - IIA
Lagunar Fóssil - IIB
5
6
7
8
Al (%)
108
9
5
6
7
Al (%)
8
9
10
Figure 4 - Relationship of concentration values
Metal versus Al of cores LSA7, LSA8, LSA11
(recent sediments) and LSA (“Fossil Lagoonal
Deposits” and Average Shale.
Pb (mg/kg)
Zn (mg/kg)
80
100
90
80
70
60
50
40
30
20
10
0
Average Shale
Lagunar Fóssil - IIA
Lagunar Fóssil - IIB
Cu (mg/kg)
200
180
160
140
120
100
80
60
40
20
0
Ni (mg/kg)
Cr (mg/kg)
100
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In core LSA11b, the vertical plot of 210Pb follows a linear trend in the first 20cm and no signs of near
surface disturbances induced by sediment mixing have been found. The linear regression of the data
indicates a sedimentation rate of 2.8mm/year. The first appearance of 137Cs in lagoonal sediments has
been detected at 20-22.5cm and assumed to represent the earliest release of this radionuclide in the
Northern Hemisphere, in 1954 (Delaune et al., 1978, in Cearreta et al., 2000), thus implying an inferred
sedimentation rate of 4.3mm/year for the last sixty years. Thus, assuming a constant sedimentation rate,
this column may represent the last 200 - 300 years of accumulation.
Conclusions
The study of the top 1m of bottom sediments collected in three different sampling points in the main
body of Santo André lagoon, allowed to recognize changes that took place in the last 200 years in this
system. Three main sedimentary sequences were recognized, where textural variability associates with
contents in sand-sized bioclasts, less abundant in the middle section. Geochemistry of major elements are
in agreement with sedimentological results and among the analysed heavy metals only Zn and Pb show
some enrichment in topmost layers that may be a consequence of anthropogenic influence. However, the
concentrations values of 183 and 77mg/kg, respectively, are not very high, when compared with other
Portuguese systems.
Acknowledgements
This work was funded by FCT project «Global vs Local Forcing Factors and Paleoenvironmental Changes of Estuaries and Lagoons
of SW Portugal Since the Lateglacial » (POCTI/MAR/15231/99). The authors thank Ana Vidal, Director of the “Reserva Natural da
Lagoas de Santo André e da Sancha” for facilities during field work and José Matos and Bruno Bastardo for help in coring. Carlos
Vale (IPIMAR) performed geochemistry of core LSA8; Pedro Valério and Catarina Corredeira (ITN), are thanked for EDXRF
analytical facilities.
References
Araújo, M.F., Jouanneau, J.-M., Valério, P., Barbosa, T., Gouveia, A., Weber, O., Oliveira, A., Rodrigues, A. & Dias, J.M.A. 2002.
Geochemical Tracers of Northern Portuguese Estuarine Sediments on the Shelf. Progress in Oceanography, 52: 277-297.
Cearreta, A., Irabien, M.J., Leorri, E., Yusta, I., Croudace, I.W. & Cundy, A.B. 2000. Recent anthropogenic impacts on the Bilbao
Estuary, northern spain: geochemical and microfaunal. Estuarine, Coastal and Shelf Science, 50: 571-592.
Costa, J.B. 1999. Caracterização e constituição do solo. Fund. Cal. Gulbenkian. 4ª ed., 527p.
Flemming, B.W., 2000. A revised textural classification of gravel-free muddy sediments on the basis of ternary diagrams. Continental
Shelf Research 20: 1125-1137.
Freitas, M.C., Andrade, C., Rocha, F., Tassinari, C., Munhá, J.M., Cruces, A., Vidinha, J. & Silva, C.M. 2003. Lateglacial and
Holocene environmental changes in Portuguese coastal lagoons: 1. The sedimentological and geochemical records of the Santo
André coastal area (SW Portugal). The Holocene, 13, 3: 433-446.
L.N.E.C. – Laboratório Nacional de Engenharia Civil 1967a. Especificação E 203, Solos – Determinação do pH. Documentação
normativa, Outubro de 1967. 2p.
L.N.E.C. – Laboratório Nacional de Engenharia Civil 1967b. Especificação E 201, Solos – Determinação do teor em matéria
orgânica. Documentação normativa, Outubro de 1967. 3 p.
Rantala, R.T.T. & Loring, D.H. 1977. A rapid determination of 10 elements in marine suspended particulate matter by atomic
absortion, At. Absorpt. Newsl., 16: 51-52.
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EVOLUTION OF THE TRÓIA PENINSULA: THE FOREDUNES RECORD (TALK)
Luís P. Rebêlo 1, Pedro O. Brito 1, Pedro G. Terrinha 2 & Hipólito C. Monteiro 3
1
Coastal and Marine Geology Department, INETI; [email protected], [email protected]
Geology Department, FCUL; [email protected]
3
Coastal and Marine Geology Department, INETI; [email protected]
2
The Tróia Peninsula is located on the west Portuguese coast, 50 km south of Lisbon, near
Setúbal, at the southwest end of the Sado estuary (Fig. 1). The peninsula consists of a sand spit
approximately 14 km long by 1.5 km wide, covered by sand dunes.
Since Roman times to recent days, written and geographical testimonies (aerial photography,
historical and recent maps) show that the northern part of the peninsula has been very active. Roman
settlement ruins (dated 1st to 5th century AD) are strong evidence of local coastal change, since, today,
some of their facilities are underwater while some others are deeply covered by aeolian sand.
Furthermore, the Roman settlement has been described as sitting on an island, named Acála (Étienne et
al., 1994) that no longer exists.
The main purpose of this work is to contribute to the understanding of the coastline evolution of
the Tróia Peninsula and to relate these changes with the enclosure of the Sado estuary in the Holocene,
based on foredune analysis.
Mapping of the Tróia dune crestlines (Fig. 1) relied upon detailed study of morphological features
and their spatial distribution, in USAF 1958 aerial photographs. These photographs were particularly
relevant, since human occupation was incipient in 1958, and therefore different dune types and
generations could be traced. Recent evolution was studied using 1995 orthofotomaps and published
studies on the area (Gomes et al., 2002).
Foredunes are indicators of shoreline position since they grow and evolve on the upper part of the
beach. Foredunes accreting in a growing beach are different from foredunes accreting in an eroding
beach (Psuty, 1992). Thus, analysis of dune morphology and of dune crests makes it possible, not only to
establish past positions of the coastline but also to find out whether the dunes were built during periods of
coastal progradation or retreat.
The study of the Tróia peninsula evolution, in terms of dune morphology analysis, has been
previously addressed (Psuty, 1992; Gomes 1992; Quevauviller, 1984). However, the larger scale used in
this work allowed a different interpretation of both the evolution of the peninsula’s morphology and
associated aeolian processes. Although various types of dunes were found, this paper will focus only on
foredunes.
Detailed morphological analysis of dunes in the northern part of the peninsula showed that
foredune ridges are very well preserved (Fig. 1). Seventeen sedimentary episodes, corresponding to
beach accretion or erosion, were recognized, according to dune morphology and spatial relation criteria.
Other aeolian features, typical of blowouts and larger-scale transgressive events, were also found.
Foredune interpretation shows that the recent evolution of the peninsula changed several times from
accretion to erosion. Accretion episodes usually comprise several sub-parallel dune crests, forming a
“sedimentary package”. Altough absolute dating has not yet been attempted, spatial relations between
crests and “sedimentary packages” are good evidences of how the coastline and the peninsula
morphology have evolved.
Three major evolution events can be recognized, regarding foredune crests orientation and
geographical position (Fig. 1): Unit 1 – Dunes probably contemporaneous with the enclosure of the
estuary, trending NNW-SSE: Unit 2 – Dunes built during a major event of offshore shift of the shoreline
with an orientation close to NW-SE; Unit 3 – Dunes contemporaneous with the northern part of the
peninsula growth episode. This unit is responsible for the formation of the Caldeira.
The interpretation of the Tróia Peninsula foredunes indicates that the spit has shifted seawards
while it was growing northwards. The Tróia Caldeira was probably formed during the development of the
northern part of the peninsula, by means of a detached sand spit that joined the farmost northern part of
the peninsula, Foredunes interpretation also allows to determine paleo-coastlines, probably since Acála
times to recent days, i.e. from approximately the 1st century Ad to Present.
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Figure 1 – Northern part of Tóia Peninsula. Dune crests representation obtained from 1958 USAF aerial photos and complemented
by 1995 orhtorectified aerial photo. Inset showing Tróia peninsula location. Coordinates Hayford-Gauss, Datum Lisboa, in meters
and underwater morphology represented by 10m interval contours. 1,2 and 3: Major evolutionary events.
References
Gomes, N., Andrade, C., Carapuço, M. & Morgado N. 2002. Estudo de Impacte Ambiental da Marina e novo Cais dos “ferries” do
Troiaresort – Anexos: Dinâmica Costeira. Sonae Turismo: Imoareia. 83-136.
Étienne, R., Makaroun, Y. & Mayet, F. 1994. Un Grand Complex Industriel a Tróia (Portugal). Diffusion E. De Boccard, Paris. 189p.
Psuty, N.P. 1992. Spatial variation in coastal foredune development. In: Coastal Dunes. Carter, Curtis & Sheehy-Skeffington, 3-13.
Gomes, N. 1992. Dinâmica Dunar no Arco Litoral de Tróia-Sines (Portugal). Dissertação apresentada à Universidade de Lisboa para
obtenção de grau de Mestre em Geologia Económica e Aplicada. 121p.
Quevauviller, P. 1985. Estuário do Sado – Costa da Galé: Análise Geomorfológica e Estudo de Alguns Aspectos Sedimentares,
Trabalho realizado ao abrigo de uma colaboração entre o Instituto de geologia da Bacia da Aquitânia e a Direcção Geral do
Ordenamento. Direcção Geral do Ordenamento. 85p.
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COCCOLITHOPHORES FROM THE RIA DE AVEIRO LAGOON (NW PORTUGAL).
IMPLICATION FOR THE CIRCULATION PATTERN OF MARINE WATERS (TALK)
Maria de Jesus Ribeiro1, Mário Cachão1, 2, I.Abrantes3 & Fernando Rocha4
1
Centre of Geology, Univ. Lisbon, C6 Campo Grande, 1749-016 Lisboa, Portugal; [email protected].
Department Geology, Fac. Sciences, Univ. Lisbon, C6 Campo Grande, 1749-016 Lisboa, Portugal; [email protected]
3
Escola Superior Educação Viseu, Rua Maximiano Aragão, 3504 - 501 Viseu, Portugal; [email protected]
4
Geosciences, Univ. Aveiro, 3810-193 Aveiro, Portugal; [email protected]
2
Coccolithophores is mainly an oceanic dwelling phytoplankton group although certain taxa may be
common on neritic environments, both as cells (coccospheres) as well as parts of their carbonate cell
cover (coccoliths). Their record can be used as a tracer of the marine circulation inside coastal systems
(Ramalho, 2003; Ribeiro et al., subm.).
Ria de Aveiro lagoon is a shallow well-mixed estuary-coastal lagoon, in the transition between the
Vouga river (NW of Portugal) basin and the Atlantic Ocean, strongly influenced by marine and fluvial
processes (Abrantes, 2004).
The concentration of coccolithophores in the water column (both coccospheres and coccoliths)
was studied during two tidal cycles [a Summer neap tidal cycle (September 11th 2001) and a Winter neap
tidal cycle (February 20th 2002)] and relate the ecological conditions that allow certain taxa to survive
inside transitional environments as Ria de Aveiro lagoon.
Our results show that the passive transport of coccolithophores changes from summer to winter and from
neap flood to neap ebb tide. The occurrence of coccospheres during Winter is mainly restricted to station
1 (inlet), while during Summer the values are more distributed inside the lagoon, namely the S. Jacinto
channel, being more pronounced during the flood tide than during the ebb tide.
Dispersed coccoliths in the water column are normally more abundant than the coccospheres and
more distributed along the entire lagoon, particularly during summer neap flood tide.
Four complete tidal cycles were analyzed on station 1 (located at the lagoon permanently open
mouth): summer neap tide; summer spring tide, winter neap tide and winter spring tide. Results for
summer indicate that there is an inflow of coccospheres (namely Coronosphaera mediterranea) and
coccoliths (one to two orders of magnitude higher), particularly during spring tide, at surface and middle
water column.
During winter an outflow of coccoliths was registered at both spring and neap tides. In what
concerns coccospheres results show mainly outflow at spring tide. However, there is a significantly high
inflow of coccospheres of Helicosphaera carteri, Emiliania huxleyi and Gephyrocapsa ericsonii during
winter neap tide.
Key words: Coccolithophores, Aveiro lagoon, marine circulation, coastal production.
Acknowledgements
This work was funded by the project «Canal» (POCTI/PAL/32724/2000).
References
Abrantes, I., Dias, J.M. & Rocha, F. in press. Spatial and Temporal Variability of Suspended sediments concentration in Ria de
Aveiro Lagoon and Fluxes between the Lagoon and the Ocean. Journal of CoastalResearch, 39.
Ramalho, M. J. 2003. Aplicação do Nanoplâncton Calcário em Interpretação (Paleo)ambiental de Regiões Costeiras: o caso das
Lagunas de Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 127p. (unpublished)
Ribeiro, M. J., Cachão, M., Freitas, M. C. & Cruces, A. submited. The coastal record of Calcareous Nannoplankton inside the
Lagoons of Melides and Santo André (SW Portugal). Journal of Nannoplankton Research.
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NANNOLITHS AS A TRACER OF MARINE INFLUENCE INSIDE COASTAL
LAGOONS: THE CASES OF MELIDES AND SANTO ANDRÉ (TALK)
Maria de Jesus Ribeiro1, Mário Cachão1, 2, Maria da Conceição Freitas1, 2 & Anabela Cruces1
1
Centre of Geology of the Univ. Lisbon, C6, 3º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected],
[email protected]
2
Department of Geology, Fac. Sciences, Univ. Lisbon, C6, 4º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected],
[email protected]
The lagoonal environments of Melides and Santo André are located on Southwest Portugal, circa
80 km south of Lisbon, in the Southern half of the Tróia-Sines arc. In both of these lagoons a drift-aligned
sand barrier separates the lagoon from the sea.
The Melides lagoon is elongated obliquely to the coast (trending NE–SW). It occupies a flooded
surface of 0.4 km2 and has an average depth of about 2 m, with maximum depths of 6 m in the main
channel (Cruces, 2001).
The Santo André lagoon has a more complex morphology. It consists of one shallow main body
from which several confined and dead-end channels emanate, trending north-south. Its flooded surface
occupies a maximum 2.5 km2 with 256 m long. It has maximum depths of 5 m in the main channel and
between 3 and 4 m in the confined channels (Cruces, 2001).
Nannoliths are biogenic calcite complex structures that cover calcareous nannoplankton, namely
the coccolithophore cells. These constitute one of the most important groups of phytoplankton algi that
can be found in the open ocean domain but also in neritic environments.
The purpose of this work is to show that lagoonal environments such as Melides and Santo André
are places of nannolith sedimentation. The present study involves 390 surface samples, 89 from Melides
and 301 from Santo André. Field work was carried out from January 23rd 2000 to November 2000 (8
surveys) inside the Melides lagoon and from January 23rd 1998 to April 27th 2001 (18 surveys) inside
Santo André lagoon (Ribeiro 2003; Ribeiro et al., subm.).
Variations on nannolith abundance on present day sediments reflect factors associated with the
lagoonal dynamic such as (1) distance to the inlet, (2) the degree of confinement and (3) the
hydrodynamics inside these lagoonal bodies (Ribeiro 2003; Ribeiro et al., subm.).
Key words: Nannoliths, Coccolithophores, Lagoonal environments, Melides lagoon, Santo André lagoon, sedimentation,
Quaternary.
Acknowledgements
This work was funded by the FCT projects «Global vs local forcing factors and paleoenvironmental changes of estuaries and lagoons
of SW Portugal since the Late Glacial» (POCTI/MAR/15231/1999) and «Canal» (POCTI/PAL/32724/2000).
References
Cruces, A. 2001. Estudo a Micro e Meso-Escala Temporal de Sistemas Lagunares do SW Alentejano (Portugal): As Lagunas de
Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 228 pp. (unpublished)
Ramalho, M. J. 2003. Aplicação do Nanoplâncton Calcário em Interpretação (Paleo)ambiental de Regiões Costeiras: o caso das
Lagunas de Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 127 pp. (unpublished)
Ribeiro, M. J.; Cachão, M.; Freitas, M. C. & Cruces, A. subm., 2005. The coastal record of Calcareous Nannoplankton inside the
Lagoons of Melides and Santo André (SW Portugal). Journal of Nannoplankton Research.
113
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NANNOLITHS AS AN IMPORTANT TOOL TO MESOSCALE (CENTENNIAL)
PALEOENVIRONMENTAL INTERPRETATION – SANTO ANDRÉ LAGOON.
PRELIMINARY DATA (TALK)
Maria de Jesus Ribeiro1, Mário Cachão1, 2, Maria da Conceição Freitas1, 2 & Anabela Cruces1
1
Centre of Geology of the Univ. Lisbon, C6, 3º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected],
[email protected]
2
Department of Geology, Fac. Sciences, Univ. Lisbon, C6, 4º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected],
[email protected]
The purpose of this work is to show that nannoliths can be used as an important proxy of marine
influenced sedimentation in coastal environments at mesoscale (centennial) from high resolution sediment
cores retrieved from coastal lagoons.The present work is based on a high-resolution study (82 onecentimetre thick sample set) of a core (S8) recovered from the main body of the Santo André lagoon. This
core retrieved a continuous sedimentary sequence with an estimated age of 160 years (Cruces, 2001).
The predominant species of nannoliths is Emiliania huxleyi (max. 34 CAI - coccoliths per 30 mm column of
the smearslide – at 38 cm depth), with the occasional occurrence of Gephyrocapsa oceanica (max. 8 CAI,
at 74 cm depth), Gephyrocapsa muellerae (max. 5 CAI, at 52 cm depth) and Gephyrocapsa ericsonii
(max. 4 CAI, at 47 and 51 cm depth) (Ramalho, 2003; Ribeiro et al., subm).Variations on the total
nannolith content show a strong oscillatory behavior from high frequency peaks to lower frequency
fluctuations, disclosing trends of increase alternating with others of decrease of the marine influence. The
registered high frequency oscillations are interpreted as directly related to the efficiency (duration and
width) of the inlet. Based on present day observations this efficiency is greatly influenced by the water
level inside the lagoon previously to its opening, which in turn is determined by pluvial winter intensity
(Cruces, 2001). Nannolith abundance inside the lagoon can thus be indirectly related, at least in a part, to
winter meteorological conditions. However, the circulation pattern inside this shallow lagoonal system can
also be a decisive factor that influences nannolith abundance by favoring or restricting marine water
circulation on a particular sector of the lagoonal water body. New cores will be analyzed with the same
resolution to bring additional information and help clarify which of the above factors are determinant on the
registered pattern.
Key words: Coccolithophores, Santo André lagoon, marine circulation, coastal production
Acknowledgements
This work was funded by FCT projects «Global vs local forcing factors and paleoenvironmental changes of estuaries and lagoons of
SW Portugal since the Late Glacia » (POCTI/MAR/15231/1999) and «Canal» (PDCTI/PAL/32724/2000).
References
Cruces, A. 2001. Estudo a Micro e Meso-Escala Temporal de Sistemas Lagunares do SW Alentejano (Portugal): As Lagunas de
Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 228p. (unpublished).
Ramalho, M.J. 2003. Aplicação do Nanoplâncton Calcário em Interpretação (Paleo)ambiental de Regiões Costeiras: o caso das
Lagunas de Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 127p. (unpublished).
Ribeiro, M.J., Cachão, M., Freitas, M.C. & Cruces, A. submitted. The coastal record of Calcareous Nannoplankton inside the
Lagoons of Melides and Santo André (SW Portugal). Journal of Nannoplankton Research.
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NANNOLITHS AS AN IMPORTANT TOOL TO MACROSCALE (MILLENNIAL)
PALEOENVIRONMENTAL INTERPRETATION: THE CASE OF
MELIDES AND SANTO ANDRÉ LAGOONS (TALK)
Maria de Jesus Ribeiro1, Mário Cachão1, 2, Maria da Conceição Freitas1, 2 & Anabela Cruces1
1
Centre Geology of the Univ. Lisbon, C6, 3º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected], [email protected]
Department of Geology, Fac. Sciences, Univ. Lisbon, C6, 4º piso, Campo Grande, 1749-016 Lisboa, Portugal; [email protected],
[email protected]
2
The purpose of this work is to show that nannoliths can be used as an important proxy for marine
influenced sedimentation in coastal environments at macroscale (millennial) from high resolution sediment
cores retrieved from coastal lagoons.The present work is based on the study of two long cores, one made
in Melides lagoon barrier flat (MB: 39.85 m long) and other on the alluvial plain of Santo André lagoon
(LSA: 25.45 m long), retrieved during June 1998. 32 and 69 samples were studied from each of these
cores, respectively (Ramalho, 2003).
The nannolith assemblages registered on both cores are composed of eight species: Emiliania
huxleyi, Gephyrocapsa oceanica, Gephyrocapsa muellerae, Gephyrocapsa ericsoni, Syracosphaera sp,
Calcidiscus leptoporus, Helicosphaera carteri and Braarudosphaera bigelowii, with a vestigial reworked
component (Ribeiro et al., subm).
Core MB shows considerable variation of the nannolith abundances from barren to more than 800
CAI - coccoliths per 30 mm smear column - (sample – 16.27 meters above mean sea level - MSL). This
variation allows us to consider three intervals, from the base to the top: interval A, a barren section
between -32 and -20.85 m (MSL); interval B, between -20.61 and -16.27 m (MSL) with significant
nannolith content, suggesting strong input of marine driven sediments. Sample -16.27 (MSL) depicted
nannoliths in such quantity and diversity that suggests sedimentation in inner to middle shelf conditions;
interval C, represented by samples between -16.03 and 0.3 m (MSL), disclosed a low and intermittent
nannolith content, reflecting a paralic sedimentation with occasional marine influence. The number and
diversity of nannoliths found in this last sector are similar to those found in present day aqueous body
(Ribeiro et al., subm). Core LSA shows nannolith abundances varying along a more or less similar pattern
than the earlier core, with values ranging from null to more than 1000 CAI (-12.6 m MSL). The variation of
nannoliths content throughout the sedimentary column enables to consider four intervals: interval A,
between -21.35 and -14.26 m (MSL) in which no nannolith was observed; interval B, between -14.18 and 12.23 m (MSL), two main episodes can be considered (from -12.61 to -12.63 m and from 13.86 and 13.98
m) where frequent and diverse nannoliths are observed; interval C, between -12.19 and -2.69 m MSL) has
same samples (not continuous) with a relatively high abundance of nannoliths, although there is no
significant diversity; interval D, between -2.50 and +1.70 m (MSL) is practically barren with just a single
species (Emiliania huxleyi) rarely occurring (Ribeiro et al., subm). So, the variation pattern of nannolith
abundances along the sedimentary columns of MB and LSA allows to subdivide them into several zones,
each corresponding to a distinct (paleo) environment. The complete sequences are interpreted as
changing from fluvial, estuarine, ria (open bay by flooding of a fluvial valley), lagoonal to fluvial conditions
again (Cearreta et al., 2003; Ribeiro et al. subm.; Guerreiro et al. subm.).
Key words: macroscale, nannoliths, (paleo) environments, Melides Lagoon, Santo André Lagoon
Acknowledgements
This work was funded by FCT projects «Global vs local forcing factors and paleoenvironmental changes of estuaries and lagoons of
SW Portugal since the Late Glacial» (POCTI/MAR/15231/1999) and «Canal» (POCTI/PAL/32724/2000).
References
Cearreta, A., Cachão, M., Cabral, M.C., Bao, R. & Ramalho, M.J. 2003. Late Glacial and Holocene Environmental Changes in
Portuguese coastal lagoons: - The Santo André coastal area (SW Portugal) during the last 14 000 years based on
micropaleontological multiproxy evidence. Holocene 13 (3): 447-458.
Guerreiro, C., Cachão, M. & Drago, T. submitted. Calcareous Nannoplankton in coastal sediments, NW of Portugal, over the last 14
000 BP. Journal of Nannoplankton Research.
Ramalho, M. J. 2003. Aplicação do Nanoplâncton Calcário em Interpretação (Paleo)ambiental de Regiões Costeiras: o caso das
Lagunas de Melides e Santo André. Master thesis Dep. Geology Faculty Sciences Univ. Lisbon, 127p. (unpublished).
Ribeiro, M. J., Cachão, M., Freitas, M. C. & Cruces, A. submitted. The coastal record of Calcareous Nannoplankton inside the
Lagoons of Melides and Santo André (SW Portugal). Journal of Nannoplankton Research.
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VARIAÇÕES AMBIENTAIS HOLOCÉNICAS NO ESTUÁRIO DO MINHO (NW
PORTUGAL) – ABORDAGEM MINERALÓGICA (TALK)
Fernando Rocha1, Teresa Drago2 & Paula Gonçalves1
1
MIA, Dep. Geociências, Univ. Aveiro, 3810-193 Aveiro, Portugal; [email protected]
Instituto Nacional de Investigação Agrária e das Pescas-IPIMAR; [email protected]
2
Introdução
O estuário do Minho localizado no norte de Portugal, com uma orientação NNE-SSW, é
caracterizado na sua margem sul, por uma planície costeira que se desenvolve a partir de uma
paleoarriba com 200-400m de altura e que termina por uma barreira arenosa bastante larga coberta por
pinheiros - Pinhal do Camarido.
Neste estudo foram colhidos 2 cores na barreira arenosa acima mencionada, pelo método de
perfuração mecânica - core 1 e core 2. Ambas as sondagens estão alinhadas perpendicularmente à linha
de costa e separadas entre elas de 200m. Apresenta-se a seguir os resultados da mineralogia das
fracções fina e argilosa do core 1 (localizado mais perto do canal do rio) com o objectivo de contribuir
para o modelo de evolução paleoambiental deste estuário.
O core 1 é constituído da base (-29.90m) para o topo (3.44m) por blocos de granito alterado, que
corresponderá ao “soco”, (até aos -29.45m), seguido por um nível de areia e intercalações de cascalho e
areia cascalhenta até aos -27.88m. O nível de areia cascalhenta apresenta alguns bioclastos, e clastos
de quartzito. Seguem-se depois várias intercalações de níveis de areia e areia ligeiramente lodosa de
espessura variável apresentando por vezes alguns bioclastos disseminados. Ao longo desta intercalação
de fácies ocorrem alguns níveis de espessura centimétrica de lodo arenoso (-14.77m) e de areia
ligeiramente lodosa (-26.11m, -21.13m, -19.71m e -18.31m). Entre -7.77 e -6.75m ocorrem alguns níveis
de areia cascalhenta. A partir de -4.94m e até à superfície aparece um espesso nível de areia com
intercalações de areia ligeiramente lodosa (-4.03m), lodo ligeiramente arenoso e areia lodosa (-2.74m, 3.73m), lodo arenoso (-2.65m), cascalho (-2.34m) e areia cascalhenta (-0.23m; -1.47m, -2.31m).
Materiais e Métodos
Foram analisadas 120 amostras de sedimentos provenientes deste core do estuário do Rio Minho.
Os estudos texturais, mineralógicos e químicos foram levados a efeito em ambas as fracções
granulométricas separadas, fracção fina (<63 µm, obtida por crivagem por via húmida) e fracção argilosa
(<2 µm, obtida por sedimentação e de acordo com a Lei de Stokes). As análises texturais foram
efectuadas por um Granulómetro (“Grain Size Analyser”) por Absorção de Raios X (Sedigraph 8100),
tendo-se obtido para cada amostra a curva de distribuição cumulativa, os teores das fracções argilosas
(<2 µm) e o parâmetro φ50 das fracções finas.
Nas análises mineralógicas semiquantitativas efectuadas por DRX adoptaram-se os critérios
recomendados por Schultz (1964) e Thorez (1976).
Três
índices
mineralógicos
foram
calculados:
filossilicatos/(quartzo+feldspatos),
carbonatos/filossilicatos e carbonatos/(filossilicatos+quartzo+feldspatos) para cada amostra. O índice
filossilicatos/(quartzo+ feldspatos) está relacionado com o transporte de materiais detríticos (os valores
mais elevados indicam baixo hidrodinamismo). Os índices carbonatos/filossilicatos e
filossilicatos/(quartzo+feldspatos) expressam a dicotomia entre o transporte detrítico e a componente
biogénica (os valores mais altos indicam baixa contribuição de materiais detríticos). Os resultados obtidos
permitiram a elaboração de “logs” e seu confronto com a zonografia previamente estabelecida.
Resultados e Discussão
Com base nos parâmetros sedimentológicos já determinados, nos logs elaborados e na análise
composicional, distinguiram-se as seguintes unidades litoestatigráficas (Drago et al., 2004):
Unidade I – tem cerca de 0.5-1m de espessura e é constituída por balastros de quartzito numa
matriz fina, variável em abundância; regista-se uma predominância de quartzo e feldspatos na fracção
fina, enquanto que na fracção argilosa se verifica um predomínio de ilite acompanhada por clorite e
caulinite; ambas as associações são típicas de forte acarreio detrítico.
Unidade II – é constituída essencialmente por areia e areia ligeiramente lodosa com alguns níveis
finos de areia lodosa e lodo arenoso; os sedimentos desta unidade são mais finos e em geral mais ricos
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em carbonatos e lodo relativamente às unidades sub- e suprajacentes, I e III; a componente biogénica da
areia está melhor representada sendo constituída por moluscos, foraminíferos bentónicos e
equinodermes; na mineralogia das fracções finas verifica-se um incremento dos carbonatos e dos
filossilicatos à custa de um decréscimo acentuado do quartzo e, em menor grau, dos feldspatos,
enquanto que na fracção argilosa se verifica um incremento de esmectite e ilite-esmectite face a um
decréscimo de clorite, a par de um discreto enriquecimento de caulinite face à ilite; todas estas evoluções
são típicas de uma evolução para ambientes marinhos
Unidade III – constituído por níveis alternados de areia e areia ligeiramente lodosa; os níveis de
areia cascalhenta e cascalho estão relacionados com a existência de bioclastos e restos de plantas; para
o topo, a componente terrígena torna-se mais importante, enquanto que a componente biogénica
desaparece; na mineralogia das fracções finas verifica-se um acentuado incremento, da base para o
topo, do quartzo e dos feldspatos, à custa de um decréscimo acentuado dos carbonatos e, em menor
grau, dos filossilicatos enquanto que na fracção argilosa se verifica um acentuado decréscimo de
esmectite e ilite-esmectite face a um discreto enriquecimento de clorite e de ilite face à caulinite,
denunciando uma discreta mas contínua evolução para ambientes mais energéticos, com acarreios
fluviais mais intensos.
Unidade IV – está representada por aproximadamente 5m de areia média; na mineralogia das
fracções finas verifica-se um incremento, da base para o topo, dos filossilicatos à custa de um novo
decréscimo dos carbonatos, com o quartzo e os feldspatos a manterem-se estáveis, enquanto que na
fracção argilosa se verifica um acentuado incremento de ilite face a todos os demais minerais argilosos,
com um notório decréscimo de clorite e quase total desaparecimento de esmectite e ilite-esmectite; este
predomínio absoluto de ilite indicia processos de elevada selectividade como os eólicos; a ilite é
geralmente o mineral argiloso predominante nos aerosóis atlânticos (Chamley, 1989).
A análise das unidade litoestatigráficas sugerem que estes sedimentos registam a primeira
influência da transgressão Holocénica na transição das unidades I e II. A expressão do sinal marinho está
presente através de toda a unidade II e é bastante provável que nesta altura a zona de sondagem fizesse
parte de um golfo aberto à influência marinha (incremento dos carbonatos e dos filossilicatos, e nas
argilas, de esmectite, ilite-esmectite e caulinite, face a um decréscimo de clorite e ilite). A Unidade III
representa o estádio inicial da acrecção do planície costeira do Camarido, com episódios ocasionais de
influência marinha nas cristas dunares. A Unidade IV corresponde a areias éolicas que cobrem as cristas
dunares. Enquanto a Unidade basal I indica uma paleotopografia bastante inclinada (favorecendo o forte
acarreio detrítico, rico em quartzo, feldspatos, ilite e clorite), os limites das unidades subsequentes com
inclinações <1% sugerem que não existe uma continuidade lateral constante; o que por sua vez pode
indicar que a acrecção da planície costeira pode ter acontecido por crescimento de corpos dunares
lineares em direcção ao mar.
Conclusões
Os resultados obtidos permitiram iniciar um ensaio de zonografia do core em estudo, assim como
tecer considerações preliminares de natureza paleoambiental e paleogeográfica.
Importa prosseguir com as análises destes resultados e compará-los com os obtidos por outras
metodologias, possibilitando avanços significativos nas reconstituições paleoambientais, paleoclimáticas
e de proveniência dos sedimentos.
Agradecimentos
Os autores expressam os seus agradecimentos a Sílvia Serina e Selma Gabriel pela colaboração prestada na gestão das
sondagens e respectiva amostragem.
Este trabalho foi realizado no âmbito do projecto ENVI-CHANGES-PLE/12/00 financiado pela Fundação para a Ciência e
Tecnologia (FCT).
Bibliografia
Chamley, H. 1989. Clay Sedimentology. Springer-Verlag, Berlin, 623p.
Drago, T., Freitas, M.C., Rocha, F., Moreno, J., Cachão, M., Naughton, F., Fradique, C., Araújo, F., Silveira, T., Oliveira, A.,
Cascalho, J. & Fatela, F. 2004. Paleoenvironmental evolution of estuarine systems during the last 14000 years – the case of
Douro estuary (NW Portugal). Journal of Coastal Research, Special Issue 39.
Schultz, L.G. 1964. Quantitative interpretation of mineralogical composition from X-ray and chemical data for the Pierre Shale.
United States Geological Survey Professional Paper 391-C: 1-31.
Thorez, J. 1976. Practical identification of clay minerals. G. Lelotte. Bruxelles. 99p.
117
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LATE HOLOCENE PALAEOECOLOGICAL EVOLUTION OF FORAMINIFERAL
ASSEMBLAGES FROM THE NW PORTUGUESE SHELF OFF THE DOURO RIVER
(POSTER)
Francisca Rosa1, Francisco Fatela1, Selma Gabriel2, Silvia Serina2 & Teresa Drago2
1
2
Dep. e Centro de Geologia, Univ. Lisboa, C6 Campo Grande, 1749-016 Lisboa, Portugal; [email protected]
IPIMAR (Inst. Inv. das Pescas e do Mar), Av. 5 de Outubro, 8700 Olhão, Portugal.
Introduction
The present study concerns small timescale fluctuations of the foraminiferal record in the core POS
287, which covers 370cm of the Mud Deposits located on the middle shelf, close to the head of the Oporto
Canyon. The main sediment source of this deposit is the fluvial discharge from the Douro River [1]. The
foraminiferal data, combined with organic matter, carbonates and sediments texture, were used to perform
a high resolution palaeoenvironmental analysis of this section of the NW Portuguese margin during the
last 1400yr.
The sensitivity of coastal environments and adjacent shelf to climatic and oceanographic changes
along the late Holocene [2], motivated several studies about the short time variability in the NW Iberian
Margin [3, 4, 5, 6]. The micropalaeontological analyses performed on core POS 287 revealed that benthic
foraminiferal assemblages established on the shelf during the last 1400 years follow the signal imposed
by the climatic changes that have characterized the Holocene times.
Methods and Materials
Gravity core POS 287 was recovered at 81m depth. It consists of very fine sediments, mostly mud,
except between 330 and 370cm where sand presence is significative. Core bottom sample (370cm) was
dated by 14C AMS at Beta Analytic Inc. (USA). The sampling was made every 10cm for foraminiferal
analysis, every 5cm for carbonate and organic matter contents and every cm to sediment texture. A split
of 300 individuals, from the >63 µm fraction, was concentrated with tricloroethilene for benthic
foraminiferal analyses. Classification up to genus level followed systematic reviewed by [7].
Results and Discussion
Radiocarbon age of the bottom sample is approximately 1380-1270 cal yr BP, thus allowing a
sedimentation rate estimation of circa 2.8mm/yr for this core.
Stainforthia fusiformis is always the most abundant species amongst benthic foraminifera, showing
a dominant or co-dominant behaviour throughout the core. This probably reveals both continuous and
abundant organic matter supply providing an organically enriched but oxygen depleted environment [8].
Bolivina and Brizalina species, also opportunistic under such conditions [3, 9, 10] are the co-dominant
taxa. Nevertheless, the analysis of the benthic assemblages and parameters highlighted in figures 1 and 2
allow to distinguish three main zones that can be related with the climate events of late Holocene age.
Figure 1 - Plot of <63 µm
fraction and planktonic
foraminifera from core
POS 287.
depth (cm)
0
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90
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f ine f r act ion
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75
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0
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10
12
fi (%)
f i (%)
organic matter
carbonates
plankt onic f oram.
118
Figure 2 - Plot of
organic matter and
carbonate content from
core POS 287.
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
Zone 1) From 370 to 320cm Bolivina dilatata is co-dominant. Planorbulina mediterranensis and
Bulimina elongata occur associated with coarser sediments, higher carbonate and lower organic matter
contents. Rectuvigerina phlegeri, a species from the inner shelf, is also significant in this assemblage. An
increase of freshwater input seems to be identified around 1230-1200 cal yr BP [6], probably related with
a climate decline during the glacier advances of the Dark Ages (450-950 AD). If so, shelf areas within the
range of fluvial discharges would receive coarser sediments and benefit from better oxygenation in bottom
sediments during this time.
Zone 2) Between 320 and 190-200cm, upwelling related Brizalina pseudopunctata and Brizalina
spathulata [11] become co-dominant with S. fusiformis. The former species related with coarse sediments
are rare. In fact the fine fraction makes up more than 90% of the deposits, reflecting a reduction of the
Douro run-off. The organic matter also reaches its highest values under these new hydrodynamic
conditions that favoured its preservation. A possible increase of oceanic productivity in the Iberian Margin
between 1060 and 670 cal yr BP [12] fits with this section of the core which will correspond to the
Medieval Warm Period.
Zone 3) From 200cm to the core top B. pseudopunctata and B. spathulata are overrun by B.
dilatata together with main S. fusiformis. Rectuvigerina phlegeri that was practically absent during the
warm period of zone 2, is present again. These data associated to the decrease of organic matter content
suggests a possible variation in food supply, probably associated to the climatic and oceanographic
changes of the Little Ice Age (1300-1850 AD), as both organic matter and foraminifera seem to suggest.
Concerning the general tendency of the planktonic foraminifera on this shelf domain, it does not
seem to follow the trend of upwelling intensity. In fact, their higher abundance at zone 1 is associated to
the lowest organic matter content. On the other hand, high organic content implies a low presence of
planktonic foraminifera in the sediment that could result from shell dissolution under low pH conditions.
Acknowledgments
This paper is a contribution of the FCT project – Envichanges (PLE/12/00).
References
[1] Drago, T. 1995. La vasière Ouest-Douro sur la plateforme continentale Nord Portugaise. Rôle, fonctionnement, évolution. Thèse
de Doctorat, Univ. Bordeaux I, Bordeaux.
[2] Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I. & Bonani, G. 1997. A
pervasive millenial-scale cycle in North Atlantic Holocene and glacial climates. Science, 278: 1257-1266.
[3] Diz, P., Francés, G., Pelejero, C., Grimalt, J. & Vilas, F. 2002. The last 3000 years in the Ría de Vigo (NW Iberian Margin):
climatic and hydrographic signals. The Holocene, 12: 459-468.
[4] Desprat, S., Goñi, M. & Loutre, M. 2003. Revealing climatic variability of the last three millennia in northwestern Iberia using
pollen influx data. Earth and Planetary Science Letters, 213: 63-78.
[5] Drago, T., Naughton, F., Moreno, J., Rocha, F., Cachão, M., Goñi, M., Oliveira, A., Cascalho, J., Fatela, F., Freitas & C.,
Andrade, C. 2002. Geological record of environmental changes in the Douro Estuary (NW Portugal since the late Glacial.
Proceedings of the Littoral 2002, Conference, 341-346.
[6] Moreno, J. & Fatela, F. 2005. Palaeoenvironmental evolution over the last 10 kyr BP at Caminha tidal marsh (NW of Portugal) :
Foraminiferal evidences. This issue.
[7] Loeblich, A. & Tappan, H. 1988. Foraminiferal Genera and their classification. Van Nostrand Reinhold Company, New York.
[8] Gooday, A. & Alve, E. 2001. Morphological and ecological pararells between sublittoral and abyssal foraminiferal species in the
NE Atlantic: a comparison of Stainforthia fusiformis and Stainforthia sp. Progress in Oceanography, 50: 261-283.
[9] Schmiedl, G., Mackensen, A. & Müller, P. 1997. Recent benthic foraminifera from the eastern South Atlantic Ocean : dependence
on food supply and water masses. Marine Micropaleontology, 32: 249-287.
[10] Stefanelli, S., Capotondi, L. & Ciaranfi, N. 2005. Foraminiferal record and environmental changes during the deposition of the
Early-Middle Pleistocene sapropels in southern Italy. Palaeogeography, Palaeoclimatology, Palaeoecology, 216: 27-52.
[11] Mathieu, R. 1988. Foraminiféres actuels et ressurgences cotiéres sur la Marge Continentale Atlantique du Maroc. Revue de
Paléobiologie, vol. spéc. 2: 845-850.
[12] Soares, A. 2004. Identificação e caracterização de eventos climáticos na costa portuguesa entre o final do Pleistocénico e os
tempos históricos: o papel do radiocarbono. In Actas “Evolução Geohistórica do Litoral Português e Fenómenos Correlativos”,
Universidade Aberta, 171-199.
119
IBERIAN COASTAL HOLOCENE PALEOENVIRONMENTAL EVOLUTION – COASTAL HOPE 2005 - PROCEEDINGS
PALEOTEMPERATURE AND PALEOPRODUCTIVITY OFF THE NORTHWESTERN
IBERIA MARGIN DURING THE LAST 140 KY (TALK)
Emilia Salgueiro1,3, A. Voelker1, L. de Abreu1, 2, Fátima Abrantes1, H. Meggers3, G. Wefer3 & C. Lopes1,4
1
Instituto Nacional de Engenharia, Tecnologia e Inovação I.P., Dept. Geologia Marinha e Costeira, Alfragide, Portugal
Godwin Laboratory, University of Cambridge, Pembroke Street – New Museums Site, Cambridge CB2 3SA, United Kingdom.
FB Geowissenschaften, University of Bremen, Bremen, Germany
4
College of Oceanic and atmospheric Sciences, Ocean Administration Building 104, Oregon State University, Corvalis, OR 973315503, USA; [email protected]
2
3
Paleoceanographic conditions of the northwestern Iberian margin during the last 140 ky were
investigated through a multi-proxy approach (planktonic and benthic foraminifera stable isotopes, grain
size analysis, carbonate content, planktonic foraminiferal assemblages and detrital grain counts) along
core SU92-03 (3005 m water depth) off Cape Finisterra. Planktonic foraminifera census counting was
used to reconstruct Sea Surface Temperature (SST) and Productivity with the modern analog technique
SIMMAX 28 (Pflaumann et al., 1996, 2003), using as reference the Portuguese margin database
(Salgueiro et al., submitted) added to the surface samples data from the North Atlantic used by the
MARGO project (Kucera et al., 2005). Modern SSTs for 10 m water depth were taken from the World
Ocean Atlas 1998 and the modern oceanic primary productivity is based on satellite measurements of
Antoine et al. (1996).
Present day hydrographic conditions at the study area are characterized by seasonal (May to
September) intense and persistent upwelling of cold and nutrient-rich North Atlantic Central Waters
(NACW). Filaments of upwelled water penetrate about 200 km offshore from the Finisterra Cape (Fiúza et
al., 1998). The site is bathed by North Atlantic Deep Water (NADW), below which Antarctic Bottom Water
(AABW) occurs.
δ18O of planktonic and benthic foraminifera preliminary results allow the identification of the last two
deglaciations, interglacial and glacial periods back to Marine Isotope Stage (MIS) 6. The six youngest
Heinrich events (H) and respective Bond cycles are also clearly marked by the deposition of large sized
detritic grains (>2 mm) and an increase in smaller size lithic grains, both of which are interpreted as Ice
Rafted Debris (IRD). Furthermore, abundance of N. pachyderma (sinistral) reaches more than 70%, and
summer temperature and productivity drop by 11-14ºC and 50–80 gC/m2/y, respectively. Heinrich event
H2 is an exception, with N. pachyderma (sinistral) abundance around 30%, and temperature and
productivity drops of 8ºC and 30 gC/m2/y, respectively.
Carbonate content shows typical Milankovitch cycles with maxima in MIS 5e, 5c, 5a, and MIS 1.
Low benthic foraminifera δ13C values (<0.4‰) during MIS 6 reflect less ventilated waters and indicate the
replacement of NADW by AABW.
Higher percentage of the upwelling species, like G. bulloides, are contemporary with increases in
organic carbon content, and transfer-function-estimated productivity maxima clearly indicate periods of
high productivity.
References
Antoine, D., André, J.-M. & Morel, A. 1996. Oceanic primary production. 2. Estimation at global scale from satellite (coastal zone
color scanner) chlorophyll. Global Biogeochemical Cycles 10: 57-69.
Kucera, M., Weinelt, M., Kiefer, T., Pflaumann, U., Hayes, A., Weinelt, M, Min-Te Chen, M-T., Mix, A., Barrows, T., Cortijo, E.,
Duprat, J., Juggins, S. & Waelbroeck, C. in press. Reconstruction of sea-surface temperatures from assemblages of planktonic
foraminifera: multi-technique approach based on geographically constrained calibration data sets and its application to glacial
Atlantic and Pacific Oceans. Quaternary Science Reviews.
Fiúza, A.F.G., Hamann, M., Ambar, I., del Rio, G. D., González, N. & Cabanas, J. 1998. Water masses and their circulation off
western Iberia during May 1993. Deep-Sea Research I, 45: 1127-1160.
Pflaumann, U., Duprat, J., Pujol, C. & Labeyrie, L. 1996. SIMMAX: A modern analog technique to deduce Atlantic sea surface
temperatures from planktonic foraminifera in deep-sea sediments. Paleoceanography 11: 15-35.
Pflaumann, U., Sarnthein, M., Chapman, M., de Abreu, L., Funnell, B., Huels, M., Kiefer, T., Maslin, M., Schulz, H., Swallow, J., van
Kreveld, S., Vautravers, M., Vogelsang, E. & Weinelt, M. 2003. Glacial North Atlantic: Sea-surface conditions reconstructed by
GLAMAP-2000. Paleoceanography 18: 1065, doi: 10.1029/2002PA000774
Salgueiro, E., Abrantes, F., Meggers, H., Pflaumann, U., Voelker, A., Loncaric N., Oliveira, P., Bartels-Jónsdóttir, H.B., Moreno, J. &
Wefer, G. submitted. Planktonic Foraminifera from Modern Sediments Reflect Upwelling Patterns off Portugal: Insights from a
Regional Transfer Function. Quaternary Science Reviews.
120
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EVOLUÇÃO HOLOCÉNICA DO LITORAL EM REGIME TRANSGRESSIVO: O CASO
DA COSTA DE QUARTEIRA (ALGARVE, PORTUGAL) (TALK)
Sebastião Braz Teixeira
Comissão de Coordenação e Desenvolvimento Regional do Algarve, Rua José de Matos 13, 8000-503 Faro, Portugal;
[email protected]
Introdução
O litoral de Quarteira é constituído por uma série de troços de arribas arenosas, separadas por
barreiras arenosas que isolam lagoas costeiras holocénicas. A informação histórica e arqueológica,
disponível sobre este troço costeiro, denuncia uma evolução relativamente rápida, traduzida na
colmatação das zonas vestibulares das linhas de água que afluem ao litoral e na migração da costa,
associada à erosão das arribas (Teixeira, 2004). Os sítios romanos de Loulé-Velho e do Cerro da Vila
(Fig. 1), além de tanques de salga (cetárias), contêm, respectivamente, concheiros de bivalves
característicos de ambientes estuarinos e infra-estruturas portuárias (Matos, 1996), comprovando a
franca penetração da maré coeva nos estuários em cujas margens estes sítios foram edificados. Diversos
indícios permitem recuar no tempo o processo de erosão do litoral. No século XX, ruíram os fortes
construídos no litoral de Quarteira, que haviam sobrevivido ao Terramoto de Lisboa de 1755: o Forte
Novo tombou sobre a praia com o mesmo nome, no final da década de setenta e os últimos vestígios no
Forte do Valongo (ou Val Longo) ainda eram visíveis no topo da arriba, no final da década de 1940
(Marques, 1997). Dois sítios arqueológicos romanos comprovam a persistência temporal da migração do
litoral: a) o sítio de Loulé Velho, construído no interflúvio Almargem-Carcavai (Fig. 1) cujos vestígios são
sucessivamente expostos na face da arriba e destruídos com o recuo da mesma e que se estendem para
o largo, até à profundidade de 5m, a 250m da praia (Teixeira, 2004); b) as ruínas de Quarteira Submersa
identificadas em 1998 (Simplício & Barros, 1999/2000), actualmente a 600m ao largo do litoral, a 9 m de
profundidade, assentando sobre lodos depositados em ambiente estuarino, com idades radiocarbono de
5720±200BP (Teixeira, 1999/2000). Em 1999, foram exumados na praia do Forte Novo, vestígios de
ocupação neolítica, com cerâmica e estruturas de combustão (Rocha & Barros, 1999/2000), em que
foram datados fragmentos de carvão, com idades radiocarbono de 4150-4570BP (Soares et al., 2003).
Datações que incidiram sobre troncos de pinheiro (Pinus pinea) na envolvente deste sítio arqueológico,
identificados na praia na zona entre-marés, sem relação óbvia com o sítio, apontam para idades da
ordem de 5-6 kaBP (Soares et al., 2003), demostrando que, durante esse período, o enquadramento
geomorfológico era bem diferente do actual, correspondendo a uma zona de características continentais,
sem relação directa com o mar.
Aqui apresenta-se uma súmula da informação geológica holocénica e uma proposta de
reconstituição da evolução do litoral de Quarteira nos últimos nove milénios, baseada em dados
recolhidos nas sequências sedimentares acumuladas nas zonas terminais dos vales e nos depósitos
exumados na zona submarina, em consequência da erosão costeira.
Resultados e discussão
A consulta de cerca de meia centena de relatórios de furos de sondagens, executados nas últimas
décadas na planície de inundação actual da ribeira de Quarteira (Fig. 1), revela um preenchimento
sedimentar holocénico com uma espessura que pode atingir 20m, disposto numa sequência tipicamente
transgressiva: a unidade superior, composta dos sedimentos fluviais essencialmente constituídos por
argilas vermelhas e calhaus de calcário, com uma espessura da ordem de 2 a 5m, assenta sobre uma
unidade de sedimentos lodosos com conchas, cuja espessura varia em função da sua localização
relativamente ao eixo do vale, onde atinge 12m. A base dos lodos com conchas cobre uma unidade de
argilas negras a castanhas com níveis de cascalheiras, que assentam sobre o substrato plio-plistocénico.
Sondagens de pequena profundidade (2 a 4m), executadas nas planícies de inundação das ribeiras do
Almargem e Carcavai, revelaram o mesmo tipo de sequência, com uma unidade superior de
características fluviais (lodos negros e argilas vermelhas) e uma unidade de lodos contendo conchas de
bivalves característicos da franja entre-marés, em posição de vida (Scrobicularia plana, Ruditapes
decussata, e Cerastoderma edule). A datação destas conchas revelou idades compreendidas entre 1.0 e
3.5ka calBP (Teixeira, 2004; Teixeira et al., 2005).
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Figura 1 – Síntese da informação recolhida no litoral de Quarteira. Batimetria referida ao nível médio do mar. Sítios arqueológicos:
Cerro da Vila (C); Forte Novo (F); Loulé-Velho (L); praia do Forte Novo (P); Quarteira submersa (Q); Forte do Valongo (V). A figura 2
contém o corte do perfil p1.
Em mergulhos exploratórios na zona submarina Teixeira et al. (1998) identificaram afloramentos
dispersos da plataforma de abrasão, talhados em arenitos argilosos vermelhos, na continuidade dos
troços de arriba, e de sedimentos lodosos nos enfiamentos das fozes das ribeiras, interpretados como os
resíduos morfológicos do litoral em erosão. As zonas em que afloram arenitos argilosos vermelhos (caso
das ruínas submersas de Loulé Velho) correspondem a interflúvios arrasados e os locais onde afloram
lodos coincidem com as áreas anteriormente ocupadas por ambientes estuarino-lagunares. No sentido de
obter uma cobertura espacial do substrato subaflorante da zona submarina, foram executados mais de
sessenta mergulhos ao largo da área de estudo. Nalguns locais foi possível aceder directamente aos
afloramentos, por se encontrarem expostos. Na maior parte dos casos, porém, o acesso ao substrato foi
assegurado mediante sondagens manuais de pequena profundidade (0.2-0.4m). A informação recolhida
permitiu reconstituir o traçado do sistema fluvial Quarteira-Almargem-Carcavai, até à batimética dos 16m
(abaixo do actual nível médio do mar), conforme ilustrado na figura 1. O traçado segue genericamente a
versão preliminar proposta por Teixeira (1999) e confirma a hipótese da manutenção da direcção da
ribeira de Quarteira ao largo, condicionada pela falha de S. Marcos-Quarteira, inferida através da análise
dos traçadores naturais (Teixeira & Pinto, 2002). Os resultados evidenciam que as ribeiras de Almargem
e Carcavai foram afluentes da ribeira de Quarteira, individualizadas no decurso do processo de recuo do
litoral. O núcleo dos afloramentos rochosos plio-plistocénicos submersos das Barrocas corresponde ao
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resíduo das margens da ribeira de Quarteira e constituiu condicionante morfológica temporária do
encaixe daquela linha de água. A continuidade espacial da unidade de arenitos argilosos vermelhos,
desde as Barrocas às arribas actuais de Vale de Lobo, comprova a existência de obstáculo real entre o
litoral de Quarteira e o sistema de ilhas-barreira da Ria Formosa. Estes dados sugerem que os dois
sistemas funcionaram de forma independente, sem continuidade espacial, pelo menos, desde que o nível
médio do mar ultrapassou a actual batimétrica dos 15m (ca 9ka BP, Teixeira et al., 2005), quando a foz
da ribeira de Quarteira se localizava ao largo de Vale de Lobo.
Figura
2
–
Corte
representativo da geologia
da
zona
submarina
(localização na fig. 1). A
profundidade refere-se ao
nível médio do mar. As
datações
referem-se
a
idades calibradas e foram
obtidas em conchas de
bivalves característicos de
ambientes entre-marés, em
posição de vida (v. Teixeira
et al., 2005).
Figura 3 – Proposta de reconstituição da evolução do litoral de Quarteira.
Proposta de reconstituição da evolução do litoral
A proposta de reconstituição da evolução do litoral (Fig. 3) assenta sobre o conjunto de informação
histórica, arqueológica e geológica recolhida, integrada com a curva de evolução do nível médio do mar
nos últimos nove milénios do litoral de Quarteira, traçada por Teixeira et al. (2005). A evolução é
caracterizada pela migração sistemática do litoral, com taxas de recuo da ordem de 1-2m/ano, quando o
nível do mar subiu a taxas de 0.6-0.7m/século (9-7kaBP) e valores mais baixos, da ordem de 0.30.5m/ano, no período subsequente. Face à litologia das formações em que as arribas são talhadas, a
123
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erosão destas vertentes deverá ter produzido a carga sedimentar suficiente para manter saturada a
capacidade de transporte da ondulação, permitindo a permanência de praias e barreiras ao longo dos
nove milénios. Esta disponibilidade sedimentar e a fraca resistência das arribas terão facilitado a
construção de um litoral de traçado linear em planta, temporária e localmente interrompido na área onde
actualmente afloram os resíduos resistentes do substrato plio-plistocénico (Pedras das Barrocas, Fig. 1).
Nas zonas vestibulares das linhas de água, a evolução segue padrão transgressivo típico, com a
progressiva inundação dos vales associada à subida do nível médio do mar, acompanhada pela
deposição de sequências contínuas de sedimentos lodosos (Fig. 2).
Durante o período romano, as zonas vestibulares das linhas de água, protegidas pela acção
directa das ondas e periodicamente inundadas pela maré, reuniam as condições favoráveis ao
crescimento de bivalves, que sustentaram as indústrias de garum do Cerro da Vila (Quarteira) e Loulé
Velho (Almargem e Carcavai). O estuário da ribeira de Quarteira, ainda largo e aberto, ofereceria
navegação segura e uma área portuária natural de excelentes condições, provavelmente com restrições
de manobra na barra em condições de baixa-mar. A sedimentação no interior das lagunas costeiras terá
reduzido progressivamente o espaço disponível para inundação da maré, de que terá resultado
incremento dos episódios de encerramento das barras e subsequente diminuição da influência marinha,
acompanhado pelo incremento da deposição de sedimentos de origem fluvial, que construíram
progressivamente as várzeas que hoje conhecemos. As datas do encerramento definitivo das lagunas
são desconhecidas, mas previsivelmente terão sido mais precoces nas pequenas linhas de água
(Almargem) e mais tardias nas ribeiras de Carcavai e Quarteira. Nos séculos I a III DC ainda se
formavam sapais na laguna do Almargem (Teixeira, 2004) e quatro séculos depois ainda se acumulava
este tipo de depósitos na laguna do Carcavai. O estuário da ribeira de Quarteira foi aquele em que a
influência marinha se estendeu por mais tempo; ainda se produzia sal em Quarteira em meados do
século XVIII, quando a barra permitia a entrada de pequenas embarcações na preia-mar (Magalhães,
1993).
Agradecimentos
O autor agradece aos companheiros de mergulho Marcos Rosa, Vasco Pinhol, Salvador Rocha, Celso Pinto, Fernando Macedo,
António Contreiras, Erika Kopernaes e José Felizardo e a Ana Poeiras o processamento das imagens. O presente trabalho foi
parcialmente financiado pela União Europeia, ao abrigo dos projectos MARIM (45.03.16.fdr 00019 ProAlgarve) e RISCO
(45.03.16.fdr 00030 ProAlgarve).
Referências
Magalhães, J.R. 1993. O Algarve económico 1600-1773. Editorial Estampa, Lisboa, 452p.
Marques F.M.S.F. 1997. As arribas do litoral do Algarve. Dinâmica, Processos e Mecanismos. Dissertação de Doutoramento,
Universidade de Lisboa, 556p.
Matos, J.L. 1996. Cerro da Vila. Al-Ulyã, nº 5, Loulé, 23-28.
Rocha, L. & Barros, P. 1999/2000. Escavações de emergência no povoado da Praia do Forte Novo, Quarteira (Loulé). Al-Ulyã, nº 7,
Loulé, 19-25.
Simplício, M. C & Barros, P. 1999/2000. “Quarteira submersa”: resultados da campanha de 1998. Al- Ulyã nº 7, Loulé, 55-76.
Soares, A.M., Barros, P. Queiroz, P., Dias, J.M.A., Rocha, L. & Leewaarden, W.V. 2003. Lagoonar deposits eastward of Quarteira
(Algarve) – preliminary results. Thalassas nº 19 (2b), Vigo, 180-183.
Teixeira, S.B. 1999. Contribuição para o conhecimento da evolução do litoral entre Olhos de Água e Ancão: prospecção de ruínas
submersas ao largo de Quarteira (Algarve-Portugal). Direcção Regional do Ambiente do Algarve, 34p. (relatório não publicado).
Teixeira, S.B. 1999/2000. Contribuição para o conhecimento da evolução do litoral de Quarteira (Algarve-Portugal) nos últimos
8.000 anos. Al-Ulyã, nº 7, Loulé, 27-53.
Teixeira, S.B. 2004. Evolução do litoral de Quarteira (Portugal). Actas do Seminário de Valorização Turística do Património
Arqueológico Submerso de Quarteira, 22-57.
Teixeira, S.B., Gaspar, M. & Furtado, A. 1998. Avaliação do impacte da alimentação artificial da praia de Vale do Lobo nas
comunidades de bivalves (Algarve-Portugal). Com. Sem. Eurocoast. Dragados, Dragagens e Ambientes Costeiros, Lisboa, 79-89.
Teixeira, S.B., Gaspar, P. & Rosa, M. 2005. Holocene sea-level index points on the Quarteira Coast, (Algarve, Portugal) (este
volume).
Teixeira, S.B. & Pinto, C.A. 2002. Submarine evidences of Holocene shoreline migration on Quarteira Coast (Southern AlgarvePortugal). Litoral 2002, The Changing Coast, Eurocoast/EUCC, Porto, Portugal, Ed. EUROCOAST-Portugal, Vol.III, 411-416.
124
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HOLOCENE SEA-LEVEL INDEX POINTS ON THE QUARTEIRA COAST
(ALGARVE, PORTUGAL) (TALK)
Sebastião Braz Teixeira, Paula Gaspar & Marcos Rosa
Comissão de Coordenação e Desenvolvimento Regional do Algarve, Rua José de Matos 13, 8000-503 Faro, Portugal;
[email protected], [email protected], [email protected]
Introduction
Biological indicators of former sea-levels must satisfy two cumulative conditions: a) the fossil
organism should be buried in place (rooted tree stumps satisfy this condition but unpaired valves do not,
e.g. Kearney, 2001); b) their habitats should be restricted to within a very narrow fringe with respect to
coeval mean sea-level. Here, we present a series of sea-level index points inferred from radiocarbon
dates of articulated bivalves collected in lagoonal/estuarine sediments, at depths from 0 to -13m (relative
to present mean sea-level) on the Quarteira Coast, Algarve, Portugal (Fig. 1).
Figure 2 - Underwater collection
of articulated bivalves (photo
Vasco Pinhol).
Figure 1 - Location of study area and sampling sites (adapted from Teixeira, 2005). Depth Figure 3 - A trench in the beach
(barrier of Carcavai)
in meters below mean sea-level.
Methods and Results
We collected samples of estuarine/lagoonal muds and sandy muds on the Quarteira Coast (Fig. 1),
where mean tidal range is 2m and spring-tide range is 3m. In the submarine area sample collection was
performed by scubadiving either directly in outcrops of muddy sediments (Fig. 2) or by means of
superficial boreholes (0.2-0.4m depth). In the continental area, samples were gathered through manual
coring (maximum depth 0.5m) or in trenches (maximum depth 4m), in the beach (Fig. 3) and in the flood
plains of the coastal streams (Quarteira, Almargem and Carcavai, Fig. 1). In several sample sites it was
possible to gather bivalves with articulate valves of one species to a maximum of six different species
(Table I). On land, levelling of boreholes and trenches was established with an electronic total station tied
to the National Geodetic Survey network. At the underwater sample sites, absolute depth was deduced
from relative depth measured with a depth gauge (precision 0.1m) and the height of the tide at the time of
sample collection. Underwater site coordinates were obtained using a portable GPS gauge (mean error
125
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less than 10m). Coordinates of the underwater sites were crosschecked to a recent (2002) hydrographical
survey (scale 1/10,000). Deviation between the relative depth calculated from in situ measurements and
the depth determined from the hydrographical survey never exceeded 0.2m.
We selected fourteen samples of articulated bivalves (in life position) for radiocarbon dating. In
each sample, the dated species was typically the most abundant. We also dated two individuals of
different species in one site (QM91, Table I) to confirm that individuals of different species gathered in the
same sample were contemporaneous. Radiocarbon dating was carried out by means of AMS at Beta
Analytic, Inc. and dates were calibrated with CALIB 5.0 (Stuiver & Reimer, 1993) and the Marine 04
database (Hughen et al., 2004).
Table I – Database of 14C samples and results
Laboratory
code
Beta-195967
Beta-198135
Beta-204554
Beta-200317
Beta-198136
Beta-195969
Beta-195970
Beta-195972
Beta-195472
Beta-195971
Beta-204555
Beta-196238
Beta-200318
Beta-204558
Beta-196239
Dated species
S. plana
S. plana
C.edule
S. plana
S. plana
S. plana
G. fragilis
G. fragilis
R. decussata
G. fragilis
P.aurea
G. fragilis
C. glaucum
S. plana
S. plana
δ 13C/12C
‰
-2.5
-4.6
0.0
-3.9
-1.6
-4.1
-0.3
+0.6
-0.5
+0.8
-0.9
-0.1
+0.5
-3.1
-3.1
14
C Convenc. age
(yBP)
3550±40
1520±40
2220±40
3260±40
5320±40
6480±40
6730±40
6760±40
6690±40
6920±40
6790±40
7380±40
7810±50
8070±50
8040±40
calib. BP age
(2 sigma)
3340-3550
1300-1500
1710-1920
2930-3250
5580-5800
6870-7130
7160-7360
7200-7400
7140-7310
7320-7530
7240-7410
7740-7940
8170-8370
8410-8630
8400-8590
sample code
(location)*
VLM (QRT)
C1 (CRC)
C20 (CRC)
C10 (CRC)
QM156 (CRC)
QM90 (ALM)
QM89 (ALM)
QM93 (ALM)
QM79 (CRC)
QM91a (CRC)
QM91b (CRC)
QM94 (CRC)
QM150 (CRC)
QM134 (QRT)
QM140 (QRT)
n species
®- roots
1®
1®
2®
1
1
2
5
3
3
5
5
6
4
1
1
Depth
(m-MSL)
-0.1±0.2
-0.5
-0.5
-1.2
-2.0
-3.2±0.2
-4.4±0.2
-5.3±0.2
-5.5±0.2
-7.1±0.2
-7.1±0.2
-8.3±0.2
-10.8±0.2
-11.5±0.2
-13.0±0.2
(*)ALM- Almargem; CRC- Carcavai; QRT- Quarteira;
Discussion and conclusions
Sample potential as bioindicators of former sea level was assessed through the intersection of the
altitudinal and tidal distribution of the taxa identified, as showed in figure 4. Samples where individuals
with articulated valves of intertidal taxa (e.g. Gastrana fragilis, Scrobicularia plana, Cerastoderma edule or
Ruditapes decussata) and individuals of infra-littoral taxa (e.g. Dosinia exoleta, Nucula nucleus or Loripes
lacteus) with articulated valves coexist, were used as relative sea level index points since that association
typically occurs at the narrow fringe (0.5m high) between minimum low tide and medium low spring tide.
At sites where only Scrobicularia plana individuals were identified the associated tidal habitat
embraces the range between mean tide level and minimum low tide level. Whenever S. plana and vertical
roots coexist (suggesting vertical proximity to the low marsh) the range was reduced to its upper half.
2
1
Mean high spring tide
high
marsh
Mean high neap tide
low marsh
Mean sea-level
-1
Mean low tide
Mean low spring tide
Minimum low tide
Dosinia exoleta
Cerastod. glaucum
Nucula nucleus
Loripes lacteus
Abra pelucida
Parvicardium exiguum
Paphia aurea
-6
Cerastoderma edule
-5
Ostrea stentina
-4
Ruditapes
decussata
-3
Gastrana fragilis
-2
Scrobicularia plana
altitude (m-MSL)
0
-7
126
Figure 4 – Altitudinal (relative to
mean sea-level) and related tidal
ranges of habitats of marine
bivalves.
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A conservative error of ±0.2m was added to the altitudinal (vertical) ranges of sea level index points,
in order to account for the uncertainty in the assessment of absolute depth in the underwater samples and
to the vertical uncertainty of the sample collection depth in trenches.
Assuming that ocean tidal amplitude has suffered no significant changes for the last 9ky, (as
suggested by Thomas & Sundermann, 1999) and taking into consideration the systematic presence of
marine species in the sediments of the study area (i.e. assuming that paleotides were similar to the
present coastal tides), sea level index points were used to define the relative mean sea-level (RMSL)
evolution on the Quarteira Coast, for the last 9cal kyBP (Fig. 5).
Collectively the sea-level index points data set is time and depth consistent; dates of underwater
samples collected at the same depth in different locations are almost contemporaneous. The error boxes
form an envelope with an altitudinal medium error of about ±1m. The RMSL curve is characterized by a
generally smooth trend; our data shows no evidence of abrupt rises or stillstands of relative mean sea
level. The curve shows a fast rise between 9 and 7cal kyBP (6-7mm/year), a deceleration period between
7 and 5cal kyBP, and a stable trend after 5 cal kyBP, when mean sea level reached its present position.
No highstand above the present MSL, higher than the maximum range of the box errors (1m), can be
inferred from our sea level index points.
altitude (m - MSL)
0
-3
-6
-9
land samples
underwater samples
-12
RMSL curve
-15
0
1
2
3
4
5
6
7
8
9
age (cal kyBP)
10
Figure 5 - Holocene relative mean
sea-level curve on the Quarteira
Coast, inferred from the sea-level
index points. Each error box
represents
one
sample;
the
horizontal side gives the statistical
uncertainty of the calibrated age (2σ
- 95% probability); the vertical side
takes into account both the
altitudinal range of taxa distribution
and the error band of uncertainty of
sampling depth.
Acknowledgements
The authors wish to express their thanks to diving partners Vasco Pinhol, Celso Pinto, Salvador Rocha and António Contreiras and
to Luís Santos and Ricardo Almeida for their assistance in fieldwork. César Andrade and A. Monge Soares are acknowledged for
their useful discussions. Miguel Gaspar and Carlos Marques da Silva assisted in species identification. This work was co-funded by
the European Union under the projects MARIM- 45.03.16. FDR 00019 and RISCO- 45.03.16. FDR 00030 ProAlgarve.
References
Kearney, M.S. 2001. Late Holocene Sea Level Variation. In Douglas, S., Kearney, M. S. and Leatherman, S. P. (eds) Sea level rise,
History and consequences. Academic. Press, 13-36.
Stuiver, M. & Reimer, P.J. 1993. Extended 14C database and revised CALIB radiocarbon calibration program, Radiocarbon 35: 215230.
Hughen, K.A. et al. (27 co-authors) 2004. Marine04 Marine radiocarbon age calibration, 26 - 0 ka BP. Radiocarbon 46: 1059-1086.
Teixeira, S.B. 2005. Evolução holocénica do litoral em regime transgressivo: o caso da Costa de Quarteira (Algarve, Portugal). This
volume.
Thomas, M, & Sundermann, J. 1999. Tides and tidal torques of the world ocean since the last glacial maximum. Journ. Geophys.
Research, Vol. 104, nº 2:. 3154-3183.
127
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PROBLEMAS Y AMENAZAS PARA LA CONSERVACIÓN DE LAS ZONAS
HÚMEDAS MEDITERRÁNEAS (TALK)
María José Viñals
Universidad Politécnica de Valencia
La región mediterránea es una zona de transición biogeográfica entre tres continentes que se
caracteriza por albergar ecosistemas con alta biodiversidad, tener una ocupación humana intensa y
poseer humedales hidrogeomorfológicamente singulares, de entre los cuales hay aproximadamente 150
sitios incluidos en la lista de la Convención Ramsar sobre humedales de importancia internacional.
Los humedales del Mediterráneo son de diferentes tipologías morfológicas: fluviales de cuenca
baja (llanos de inundación, deltas...), llanos costeros (lagunas, albuferas,...), depresiones endorreicas y
aquellos humedales artificializados y artificiales (salinas, arrozales, etc.).
Al ser zonas de intensa ocupación humana, albergan diferentes actividades que impactan sobre
sus recursos: agua, geoformas, suelo, fauna, vegetación y paisaje, y generan una serie de efectos sobre
el ecosistema que requieren medidas correctoras. Sin embargo, debemos tener presente que su
degradación también tiene su origen en las políticas económicas, administrativas y sociales que guían el
desarrollo de las últimas décadas. Los conflictos derivados de la gestión de estos tres sectores, se han
materializado en una serie de consecuencias ambientales negativas para los humedales como
consecuencia de las presiones y amenazas a los que se ven sometidos por la acción humana.
El estado de conservación de los humedales mediterráneos es delicado, particularmente en
algunas áreas de la cuenca. La clave para su mejora y conservación a largo plazo es identificar las
amenazas, emprender acciones preventivas necesarias para mitigar sus efectos y concienciar a los
decisores sobre la necesidad de una gestión sostenible.
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FINE SCALE SEDIMENTARY SEQUENCES OF DOURO MUDDY COMPLEX
(NORTHERN PORTUGUESE CONTINENTAL SHELF) (POSTER)
Olivier Weber1, Teresa Drago2, Filipa Naughton1,2,3, Jean-Marie Jouanneau1, Selma Gabriel2 & Sílvia
Serina2
1
2
3
DGO, UMR-CNRS EPOC 5805, Bordeaux 1 University, 33405 Talence, France; [email protected]
INIAP, IPIMAR, CRIPSUL, Instituto Nacional de Investigação Agrária e Pescas, Av. 5 de Outubro, 8700-305 Olhão, Portugal
Departamento de Geologia -Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
Introduction
The Douro muddy complex is located 20-30km offshore Douro estuary. It is constituted essentially
by terrigenous particles, mainly sourced from Douro river (Vitorino et al., 2002). It is an active
sedimentation zone, tectonically depressed and thus making an efficient sediment trap, partly limited by
reliefs of different magnitude (Drago et al., 1999). This sedimentary body is therefore an excellent feature
for studying the sedimentary pattern in the continental shelf throughout the last millennia.
Methods
A gravity core (POS27-13-2G) 3.70m long was taken at 81m depth in the central part of Douro
muddy complex. One half of the core was sub-sampled for several analyses: sedimentological (water
content, grain-size - laser difractometry, carbonates, organic matter), palynological, foraminiferal and
nannoplankton studies (the latter two are subject of separate papers in this Conference). 14C AMS dating
and excess of 210Pb were determined in four selected levels. In the symmetric half a 1cm – thick slab was
sampled along the whole core length and X-radiographied using Scopix system (Migeon et al., 1999). The
study of X-ray imagery supported definition of sedimentary sequences, and using systematic
determination of grey levels, profiles of mean-grain size and carbonates have been obtained. Sediment
classification followed Flemming (2000) criteria.
Results
Four sedimentological units can be distinguished, according to sedimentological parameters, with
boundaries at 3.20m and 1.80m and 0.3m below sediment-water interface. The sedimentary sequences
found within each unit contrast in thickness and number and follow those limits; in general, they are made
of 2-3 sub-units showing fining-upward trend.
The lowermost unit consists of muddy sand and develops between circa cal AD 650 and cal AD
1010. Mean grain-size has a modal value of about 80µm but can reach 126µm. It is the coarsest unit in
the core. Carbonate contents shows the highest values suggesting that the sediments are predominantly
biogenic; inversely, organic matter has the lowest values. Five sedimentary sequences, 2-19cm thick
(average 8cm) were defined in this unit. Taking into account the ages and number of sequences, it was
found that, on average, one sequence formed every 45 years.
The intermediate unit has an age between cal AD 1010 and cal AD 1625, this last one interpolated.
The monotonous character of the slightly sandy mud that constitutes this unit is only interrupted in the top
by an 8cm thick muddy layer. The mean grain size is in general smaller than 40µm, carbonates content
are <4% and organic matter is usually about 10%. Sedimentary sequences present a higher frequency
than in the lower unit; about 23 sequences were defined, which thickness varying between 2 and 12cm
(average ~ 6cm). Using the same criterium one sequence formed on average in this unit every 27 years.
The following unit corresponds with the interpolated ages of cal AD 1625 and cal AD 1937. Mean
grain-size is higher than in the underlying unit, close to 40µm, but frequently exceeding this value. The
content in carbonates is also slightly higher. Sediments are represented slightly sandy mud. Sedimentary
sequences defined in this unit are much thicker, presenting a mean of 11cm (3 to 33cm). From the base to
the top of this unit 15 sequences were identified (rate of emplacement estimated in 20 years).
Finally, the top unit is characterized by a mean grain size that becomes coarser towards the
surface, reaching 60µm, which is accompanied by increasing carbonate content. Sedimentary sequences
present again a high frequency with an average thickness of 4cm. In this unit, the excess in 210Pb yielded
a sedimentation rate of 0.24cm/year.
129
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Discussion
Sediments transport in continental shelf is intimately related with hydrodynamic regime. In the case
of Douro muddy complex, sediment seems to be essentially sourced in the Douro river,
contemporaneously to storms episodes, when downwelling processes combine with northwards currents
to produce a resulting transport trend towards NW (Drago et al., 1999; Vitorino et al., 2002). This idea
implies that the sedimentary sequences defined are the expression of the short-term sediment availability
(related with precipitation, floods) and/or with the energy of the carrying hydrodynamic episode (storms).
As observed, sedimentological units are also typified by differences in the character of sedimentary
sequences, and this must have an environmental significance.
The time interval recorded in this core is comprehended between cal AD 650 and the year of core
sampling (AD 2002). Contemporaneous environmental conditions include mesoscale climatic changes
such as the Medieval Warm Period (MWP) and the Litlle Ice Age (LIA). Pollen analysis indicates a time
period for the MWP between circa 1010 and 1500 AD, and for LIA, between 1500 and 1850 AD. Earlier
than MWP, the time period between 850 AD and 600-750 AD is characterized by the advance of alpines
glaciers, characterized by strong inundations and storms (Lamb, 1997). The thick sedimentary sequences
of the basal unit, constituted by coarser sediment may correspond to this time period. However, the
sediments are mainly biogenic and may represent open shelf sedimentation before the emplacement of
the muddy patch.
Upwards, between circa 1010 and (interpolated) 1630 AD, sedimentary sequences become thinner.
This set of sequences may be the expression of frequent sediment input, probably related with the humid
conditions of the MWP climatic event (Lamb, 1997), from 1000 AD to 1500 AD. This set, accumulated until
the lower half of LIA (1500-1800AD); the high frequency of sediment arrival at the muddy patch may be
related with the persistency of humid conditions along this period; during the last half of this climatic stage
and part of the “recent warming” period - until 1937 AD, sedimentary sequences are thicker. This might
be the expression, at least in LIA, of retreat of highland glaciers and consequent high sediment supply into
the shelf. From 1909 onwards, the known history of floods of the Douro may bear some relationship with
the defined sedimentary sequences, a hypothesis at present being investigated.
Acknowledgments
This work was undertaken as a part of the ENVI-CHANGES project (PLE/12/00) funded by FCT (Portugal). Gravity core was
collected in mission Poseidon 287, in the scope of collaboration with the INETI Marine Geology team (many thanks to Fátima
Abrantes). Thanks also to Saint-Paul of Bordeaux University for slabbing and X-ray processing and finally, to my colleague Francisco
Fatela and César de Andrade for the results discussion and the carefully revision of this paper.
References
Drago, T., Oliveira, A., Magalhães, F., Cascalho, J.P., Jouanneau, J.-M. & Vitorino, J. 1998. Some evidences of northward fine
sediment transport in the norterh portuguese continental shelf. Oceanologica Acta, 21(2): 223-231.
Drago, T., Araújo, F., Valério, P., Weber, O. &. Jouanneau, J.M. 1999. Geomorphological control of fine sedimentation on the
northern portuguese shelf. Proc. 2nd Symposium on the Atlantic Iberian Continental Margin, Cadiz, Publicação Especial do
Instituto Español de Oceanografia.
Flemming, B.W. 2000. A revised textural classification of gravel-free muddy sediments on the basis of ternary diagrams. Cont. Shelf
Res., 20: 1125-1137.
Lamb, H.H. 1997. Climate History and the Modern World. London and New York, Routledge, 433p.
Migeon, S., Weber, O., Faugères, J.C. & Saint-Paul, J. 1999. SCOPIX : a new X-Ray imaging system for core analysis . Geo-Mar
Letters, 18: 251-253.
Vitorino, J., Oliveira, A., Jouanneau, J.M. & Drago, T. 2002. Winter dynamics and the transport of fine sediments on the northern
portuguese shelf. Part I - physical processes. Progress in Oceanography. 52, issues 2-4: 129-153.
130
COASTAL HOPE 2005 - Lisboa, Portugal
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Fundaçao Calouste
Gulbenkian
ISBN: 972-99694-0-X
FCUL-DG