24 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: [email protected] / [email protected]; 2 CEM, Centro de Estudos da Macaronésia, Univ. of Madeira, Caminho da Penteada, 9000-390 Funchal, Madeira, Portugal, e-mail: [email protected] 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.