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ABSTRACTS
Oral Communication: Domingos Rodrigues
RHODOLITH (“LARANJAS”) CONCENTRATIONS FROM CABEÇO DAS
LARANJAS (ILHÉU DE CIMA, PORTO SANTO, MADEIRA
ARCHIPELAGO). A PALEOPRODUCTIVITY SIGNAL?
Mário Cachão 1, Domingos Rodrigues 2 & Carlos M. Marques da Silva 1
1 Centre of Geology and Dep. Geology, Fac. Sciences, University of Lisbon, Edif. C6 Campo
Grande, 1749-016 Lisboa, Portugal, e-mail: mcachao@fc.ul.pt / Paleo.Carlos@fc.ul.pt; 2 CEM,
Centro de Estudos da Macaronésia, Univ. of Madeira, Caminho da Penteada, 9000-390 Funchal,
Madeira, Portugal, e-mail: domingos@uma.pt
A
bnormal concentrations of large
rhodolith are one of the main
features of the palaeontological
record of Porto Santo, in general, and
of Cabeço das Laranjas at its islet
Ilhéu de Cima, in particular. At this
locality the rhodolith beds may
achieve 6 meters thick and show
intercalations with volcanic derived
sediments with conspicuous sedimentary structures and bioturbation
levels. Previous studies based on
rhodolith morphometrics showed the
massive accumulations of Cabeço das
Laranjas are multi-modal and may
have been produced in place in contrast with other fossiliferous sections
(e.g. Pedra do Sol) in which these
macroalgae structures are one of the
components of a more diversified
assemblage containing in situ corals
and equinoderms (Clypeaster spp.)
(Cachão et al., 2000). Preliminary
studies disclosed the occurrence of
two species of Lithothamnium, rare
Lithophorella melobesioides, Peyssonneliacean algae, encrusting bryozoans,
serpulids and small corals. Further
studies are needed to complete the
total paleobiodiversity of these occurrences in order to understand paleoecological (paleoproductivity?) conditions that led to their massive
accumulations.
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Abnormal concentrations of large rhodolith are one of the main