Publication: Moluscos bivalves da Formação de Água de Madeiros
(Sinemuriano superior) da Bacia Lusitânica (Portugal)
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2013
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Instituto Geológico e Mineiro (Lisboa)
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Abstract
Apresenta-se a distribuição estratigráfica dos taxa de moluscos bivalves ao longo da Formação de Água de Madeiros (Sinemuriano superior–extrema base do Pliensbaquiano) na Bacia Lusitânica. Estudaram-se as secções de S. Pedro de Moel e Peniche, por serem as mais completas e representativas do ponto de vista do registo paleontológico e seu significado biostratigráfico. Esta análise estratigráfica de alta resolução baseia-se em 2691 espécimes recolhidos em 180 estratos, o que permitiu um acréscimo significativo (31%) de novos taxa reconhecidos na bacia neste intervalo. Evidencia-se uma variação vertical na composição taxonómica das associações faunísticas com o surgimento de espécies oportunistas interpretadas como facultativamente pseudoplânctónicas. Este registo é observado na transição entre as cronozonas Oxynotum e Raricostatum, interpretando-se como tendo sido favorecido por mudanças na deposição, de que resultaram condições pelo menos disóxicas. O surgimento de formas de Pseudomytiloides e de Oxytoma durante o Sinemuriano terminal da bacia aponta para que estas ocorrências sejam as primeiras no contexto do Jurássico NO europeu.
The stratigraphic distribution of bivalve molluscs throughout the Água de Madeiros Formation (Upper Sinemurian– lowermost Pliensbachian) at the Lusitanian Basin is present here. The work was carried out on the sections of S. Pedro de Moel and Peniche. This high-resolution stratigraphic analysis is based on 180 sampled beds and 2691 bivalve specimens. This new collection allows a significant improvement (31%) of the number of taxa already known for the basin, during this interval. The occurrence of a faunal turnover that allowed the spanning of opportunistic species, here interpreted as representative of a pseudoplanktonic habitat, is also shown. This record is noted around the Oxynotum–Raricostatum chronozone transition and inferred to have resulted from depositional changes linked with dysoxic conditions near the water-substrate interface. The appearance of Pseudomytilodes and Oxytoma forms in the Lusitanian Basin seems to be the earliest in the NO European Lower Jurassic province
The stratigraphic distribution of bivalve molluscs throughout the Água de Madeiros Formation (Upper Sinemurian– lowermost Pliensbachian) at the Lusitanian Basin is present here. The work was carried out on the sections of S. Pedro de Moel and Peniche. This high-resolution stratigraphic analysis is based on 180 sampled beds and 2691 bivalve specimens. This new collection allows a significant improvement (31%) of the number of taxa already known for the basin, during this interval. The occurrence of a faunal turnover that allowed the spanning of opportunistic species, here interpreted as representative of a pseudoplanktonic habitat, is also shown. This record is noted around the Oxynotum–Raricostatum chronozone transition and inferred to have resulted from depositional changes linked with dysoxic conditions near the water-substrate interface. The appearance of Pseudomytilodes and Oxytoma forms in the Lusitanian Basin seems to be the earliest in the NO European Lower Jurassic province