(
Cicncias da Terra (UNL)
Lisboa
N.o 14
pp. 183-190
4 Figs.
2000
)
High resolution stratigraphy and miocene facies correlation in Lisbon and
Setuba l Peninsula (Lower Tagus ba sin, Portugal)
M. Telles Antunes'!', P. Legolnh a'" , P. Proenea C un ha'» & J . Pa ts'"
Work su ppo rted by "Praxis XXI 2!2.1!CTA/ I06J94" and by " POCTV32 34SICTN2000 Proj ects ( FCI).
1 - Acade mia das Ctencus de Lisboa , Centro de Estudos Geol6gicos (JNICT), Faculdade de creocies e Tecnologia, Quinta da Torre,
P·282S·114 Caparica, Portugal; mla@maiL fct.unl.pt;
2 • Centrode EstudosGeologicos(INICT), Faculdade de Ciencus e Tecnologia, Quintada Torre, P-Z825-11 4 Capanca, Portugal; [email protected],pt;
3 - Centrede Geocier cias. Departamentode Cienciasda Terra, Faculdade de ciences e Tecnologia, Largo Marques de Pombal, Coimbra; cunha@c Luc.pt;
4. Centro deEstudos GeoI6gicos(JNICT), Faculdadede Ciencias eTecnologia,Quinta da Torre, P·2825-l14Caparica, Portugal; [email protected]
ABSTRACT
K ey words: Sequencial stratigraphy; Miocene; Lower Tagus Basin; Lisbon; Setu bal Peninsula; Portugal.
Correlation between facies associations (marine, estuarine and distal fluviatile environments) and disconformities, observed
between Foz da Fonte (SW of'Sctubal Peninsula) andSantaIria daAz6ia (NE of Lisbon) are presented, The precise definition of the
marine-continental facies relationships improved very much the chronology of the depositional sequence boundaries, Tectonic and
eustatic controlsare discussed on the basis of subsidence rates' variation,
RESUl\10
Palavras chave: Estrangrafia sequencial; Miocenicc; Bacia do Baixo Tejo; Lisboa; Peninsula de Setlibal; Portugal.
Apresenta-se correlacgo entre assoctacees de facies (ambientes marinhos, estuarinos e fJu viais distais) e deseontinuidades
scdimentares desde Foz da Fonte (a SW da Peninsula de Setilbal) ate Santa Iria de Azcia (a NE de Lisboa). A defini"ao precise da
interdig jtacjlu entre facies marinhase continentais permitiu precisar a cronclogia dos limites das sequenctas deposicionais. Discutese a influencia dos controlos tectonico e eustatico na geracao de espaco de acomodacao com base na analise das veoecees da
subsidencia.
INTRODUCTION
The Lower Tagus basin is situated in the western margin of the Iberian plate, It pres ents an NE-SW alignment.
Its almost siliciclastic neogene infilling shows several sedimentary unconformities. The most important are angular
unconformities related to tec tonic events assoc iated to
the geod inamic evolution of the Iberian plate.
The Lisbon and Setubal Pe ninsula areas belong to the
distal part of the Lower Tagus basin where the predominant estuarine sedimentation passes westwards to an oceanic one (Antunes et al.. 1987; Cunha , 1992a; Cunha
1992b; Pena dos Reis et al., 1992; Barbosa, 1995).
The Miocene (Aquit anian to Early Tortonian) succession is bounded by angular unconformities. It reflects a
compressive context related to the Betic collision . Basin's
depocen ter is placed in the Setubal Peninsula whe re
thickness attains about 900 m.
Several logs allow high resolution correlations between
marine and continental levels dated by planktic forams,
mammals, and/or isotopic ages (KlAr - glauconites; Sr isotopes). Small and large mammals give precise datation
for flu via l/estuar ine beds. Pal aeontologi e wea lth dinoflagellates, palino fossils , nannoplancton, algae, plant
macroremains, fora ms, ostracods and other crustaceans,
molluscs, echinoderms, fish. reptiles, mammals - as well
183
10 Ccngresso sobre 0 Cenoz6ico de Portugal
as Oxygen and Carbon isotopic studies provide a huge
amo un t of informa ti on o n pa la eo ge og raph ic an d
palaeobiogeographic recons tructions.
Antunes et al, (1973) defined sedimentary cycles in
the Lisbon region based on the sucessive unit' s transgressive/regressive character. Antunes & Pais (1993) made
correlati ons with Almada (Setubal Peninsula) and with the
inland part of the basin (Ribatejo); seven transgressiveevents
alternating with six regressi ve ones were recognized.
Research on the Setubal Penins ula (Scn er al., 1992;
Legoinha, 1993;A ntunes et al., 1995;Antunes et al. , 1996)
improved the biostratigrafic knowledge ofsome units (presenting correlation difficulties because of facies differences
from Lisbon region).
T he integration of all lithologic, biostratigraphic (first
and last occurrence of significant groups/species of forams
and mammals) and isotope (KiAr e ~1S rfl6Sr) dating allowed the chronostratigraph ic framework from Lower
Tagus basin Miocene series, as well as the characterization
o f eight depositiona l sequences (Antunes et al. , 1999 ).
Analysis and interpretation of outcrops and boreholes
(Fig. l ) from the Lisbon-Sctubal Peninsula area (Cotter,
1950; Choffat, 1956;Antunes & Torquato, 1969; Antunes
et al.; 1996a; 1996b; 199 8; 1999 ; Sen et aI., 1992) are
presented . Taking into account the previously defined
depositional seque nces, we present a detailed correlation
scheme between facies and discontinuities, as well as a
palaeoenvironmental interpretation. Lateral and vertical
thickness changes are discussed.
FAC IES ASSOCIATIONS
Lithology, sedimentary structures, palaeontologie contents and sedimentary d iscontinui ties were used to characterize facies (marine, estuarine and fluviatile). Correlations from Foz da Fonte (SW, in the Sctubal Peninsula) to
Santa Iria da Az6ia (NE, Lisbon) are shown (Figs 2 and
3).
Vertical and lateral facies' shifts were used to interpret
the see level changes and 10 characterize transgressiveregressi ve cycles of different scale order. The eustatic
changes could be registered because of the continuous
regional subsidence.
The thickness of the Miocene successio n increases
from Foz da Fontc-Ribeir a da Lage sector (about 85m) to
Charneca (more than 494m). It diminishes from there to
Santa Iria da Az6ia (about 162m; Choffat , 1956). In the
southwestern and centra l sectors of the concerned area an
altemance between marly limestones and marls predominates. In the NE sector detrital sedimentation predominates in result of the fluviatile influx.
Fig. I - t ccettzacsc dos cortesgeol6gicos, das sondagens e do perfil interpretativo.
184
Ciencias da Te"a (UNL), 14
SO- SI , 0 7 - 15,3 Ma;
Facies associations and sedi mentary environments are
as follows:
SO-S2, 0 8 - 12,7 Ma;
So-T!, D9 - 11,6 Ma;
An - infralittoral to circalittoral (conglomera tes!
gla uco n ite sands and san dy marls with
plankt ic forams) ;
Af2 - Iirtoral to estuarine, infratidal (biocalcarenires
and marls, with mo lluscs);
AO - tid al flats (silts, often with abundant organic
matter);
Af4 - delta/e stuary chann els and bars (bi oclastic,
fine to middle san dston es);
Af5 - dista l fluvial (c oarse to middle grained
sandstone s and clays, with plant and mammal remain s).
DEP OS ITI O NA L SEQUEN CES AN D T il E C II RO :\,O LOGY OF Dl SC O:"'TI :"'UITI ES
For each log, sea-level changes were intrepreted on
sedi mentological chara cteristics and palaeontologie contents. Trans gressive/regr essive cycles were correlat ed between all the studied stratigraphic columns . Ten ma in cycles have been recognized and named by depositiona l sequences (SO). As the result of better correlation data obtained no w, the previous sequence SO-A is divi ded in SOAI and SO-A2 as we ll as the SOoT in SO-Tl and So-TI.
Th e last two have not been sufficiently characterized be ·
cause ofme poor expo sition and the scarce biostrati graph ic
mark ers (Figs 3 and 4).
Integra ting all the avail ab le data , and the ir precise
stratigraphic position in each sequence, discontinuities
between depositional sequences are dated as follows:
SD·A I, 0 1 - 23 Ma;
SO-A2, 0 2 - 21 Ma;
SO-BO, 0 3 - 20 Ma ;
SO. B l, D4 - 19 Ma ;
SD-B2, D5 - 17,8 Ma ;
SO-L1, 0 6 · 17 Ma;
SO-12, 01 0 - 9,5 Ma.
A correspondence with 3'" order eusta tic cyc les (Haq
1987) is presented (Table I ). Sequences SO AI,
A1, 8 2, L1, S I and Tl see m to correspond to 3rd order
eustatic cycles. Sequences SO-BO, ,S O-B I concern the
sa me eustatic cycle (T Bl . I), while SO ·S2 corresponds to
. two (T B 2 .5 and TB2 .6 ) cycles . In some seq uences
(SO .L1 , SO-5 1 and SO-52) lower order cycl es can be
recognized.
As Antunes et 01. ( 1996) had referred, discrepancies
between the basin 's max imum floodi ng event s and the
eustatic maxima (Haq el 01., 1987) may be rela ted to loca l
changes on subsiden ce (and/or inaccurate corre lati on
bet ween different chrono and biostra tigrap hic scales).
et
at.,
S UBS IDEl'"CE ANALYSIS
A ready aproac b to the subsidency rat e (Table 2) for
each depositional sequence was obtained by divid ing
thickness by the age span between the upper and lower
discontinu ity boundaries . B a ckstrippi ng wa s no t
calcula ted ; th is was regarded as irrelevant due to the
succession's weak burial.
Sedi mentation begins in the Lisbon area . Th is area is
the only one where the SO·A I sequence has been recognized. Subsidence rate increases everywhere till BI
(Fig.4). After a general decr ease during SD.B2 , subsidence
inc re ases be tween C orroi o s and Li sbon (SD-L 1).
Subsidence rate increases again in the Ribeira da LageChamcca region (SO-S2).
.
T he thickness of depositional sequences changes laterally very much . Mi gration ofthe depocenter also is significant. The A2, BOand B I sequences depocenters are in
Almada and Charneca . The 82 dcpocenter is confined to
C harn eca. In se quences LI and S I the depocenrer is
located at Co rroio s, in sequence 52 it returns to Chameca.
JO o r d . Cy cl es
Depcs, Seq .
T2?
B urdig a li an
TB 3.2
TB3 .1
TB2 .6
TB2.s
TB2 .4
TB2 .3
TB2.2
TB 2.1
Aq uitania n
TB U
TB l.4
C h r o nos t ra tig ra phy
T ortonian
S erra vallian
Lana h ian
TI
S2
SI
LI
B2
BI
BO
A2
AI
Table I • 3'"order cycles (Haq et al., 1987) and depositional sequences in the distal part of the LowerTagus Basin.
185
I' Ccngressc scbre 0 Cenoz6ico de Portugal
Dep.Seq
FF-RL
CH-AC8
Corr·AC2
AL
Al
0
0
12
0
38
48
0
18
30
0
46
37
25,8
93,3
45,7
34 ,S
32,3
70 ,9
15,2
83,3
27,1
56 ,4
46,2
38,2
92,5
21,4
13,6
13,8
12,7
10,5
53,3
19,3
32,7
12,3
10,9
17,1
26
32
A2
BO
Bl
B2
Ll
51
52
T1
T2
7,1
0
1,2
29
8,6
15,2
51A
0
6
14
1I
19,5
17
20
43 ,3
11,4
25,5
6,9
10,9
7,6
Table 2 - Subsidence rate (mlMa) for each deposicional sequence on studied logs (FF- Foz da Fonte; RL · Ribeira da Lagc: CHChameca; AC8 - Corrcios; AL - Almada; Li - Lisboa; Am - Ameixocira; SIA- Santa lriada Azoia). Darkbluecolour stresses the
greatest subsidence rate for eachdepositional sequence.
100
90
80
!..
,
70
+---_
_
4 \\
---1+-
/1 \\
II 1 \ \
60
" 50
~
~
]
,"
•
/\
40
/
/ \
\
/
30
20
~/
/
10
Al
A2
BO
B1
B2
L1
51
52
T1
T2
De pos ilio na l seq ue nce
Fig. 4 _ Subsidence rate (mlMa) for the studied logs(FF. Foz da Fonte; RL· Ribeirada Lagc; CH - Chameca; AC8 · Corroios;
AL · Almada; Li - Lisboa; Am- Ameixoeira; SIA · Santa Iriada Azoia).
Tl and T2 sequences (T2 restricted to a narrow area
between Fonte da Telha and Lisb oa) show greater
subsidence rate in Lisbon.
In a regional compressive context between the area to
the North of Lisbon and the Arrabida chain (defining a
large syncline with continuous subsidence) depocenter
migration results from block's tectonics. Northwards migration of the depocentcr between 82 and L I is a consequence of a tectonic event (about 17 Ma). This event originatedan angular unconformitythat may be seen at Portinho
da Arrabida (Pais et al., 1991; Antunes et at., 1995).
186
CONCL USIONS
• Correlation of facies associations and deposicional
sequences in several Miocene logs (outcrops and
boreholes) from Lisbon and Senlbal Peninsula has
been achieved.
• Vertical and lateral facies changes of the Aquitanian
to Tortonian depositional sequences have been characterized in detail. Redefinition of the previous SDA and SD·T sequences is proposed.
Cu nctas da Terra (UNL), 14
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187
1°Congresso sobre 0 Cenoz6ico de Portugal
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Cunctas da Terra (UNL), 14
• A chr onostr atigraphic framework of the facies,
deposi tional sequences and co rr es po nd in g
boundaries is presented. Sequence depositional (SO)
boundaries (0 ) are aged (Ma) as follows:
- Aquitanian: 01 - 23 Ma (beginning of Miocene
sedimentation);
- Aquitanian: 0 2 - 21 Ma (SDA1-SDA2);
- Burdigalian: 03 - 20 Ma (SDA2-SDBO);
- Burdigalian: 0 4 - 19 Ma (SOBO-SDB I);
- Burdigalian: D5 - 17,8 Ma (SDB I-SDB2);
• BurdigalianlLangh ian : 0 6 - 16,4 Ma (SDB2-SD
Ll);
• Langhian: 0 7 - 15,3 Ma (SOLl -SDSl);
- Serravallian: 0 8 - 12,7 Ma (SOS I-SDS2);
- Serravallian: 0 9 - 11,6 Ma (SDS2-S0T1);
- Tortonien: 0 10 - 9,5 Ma SDn -SOT2).
• Local subsidence rates have been quantified in the
Foz da Fonte - Ribeira da Lage, Chamec a, Corrolos,
Almada, Lisboa.Ameixoeira and Santa Iria daAzoia
sectors.
• Analysis of the sedimentary and palaeontological
contents and isotopic dating provides an improved
assessment of the influence of tectonics, eustatism
and sedimentary supply in the generation of the
accomodation space.
• In a regio nal NW-SE comp ressive con text, the
Albufeira syncline had continuous subsidence; that
allowed eustatic changes of d iverse ord er to be
recognized.
• Oepocenter migration and facies changes suggest
that tectonic blocks subside d at different rates.
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