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Paleodictyon maximum: forma típica da Icnofácies de Nereites em ambiente de rampa carbonatada do Jurássico Médio da Praia da Mareta (Bacia do Algarve, Portugal)
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Advisor(s)
Abstract(s)
O presente trabalho descreve a ocorrência de um exemplar de
Paleodictyon maximum proveniente de ambientes de rampa carbonatada
do Jurássico Médio (Bajociano superior) da Bacia do Algarve e discute as
suas implicações para a compreensão do ambiente deposicional da
sequência da Praia da Mareta, bem como para o comportamento do
organismo produtor. Forma arquetípica da Icnosubfacies de Paleodictyon
de ambientes marinhos profundos turbidíticos, mostra no Mesozoico, pelo
menos, ser uma relíquia ecofenotípica do Paleozoico e ocorre, com uma
relativamente ampla distribuição paleogeográfica, em ambientes de
plataforma associados a eventos de sedimentação (tempestíticos,
turbidíticos). Níveis de sedimentação elevados terão possibilitado a
preservação deste Paleodictyon ao limitar a bioturbação subsequente. O
exemplo de P. maximum da Praia da Mareta serve ainda para mostrar que,
para a identificação das icnofácies e correspondentes interpretações
paleoambientais e batimétricas, é fundamental identificar associações de
icnofósseis ou icnocenoses recorrentes e não apenas icnofósseis
individuais, integrando a informação sedimentológica e icnológica, para
além de enquadrá-las no contexto paleoecológico evolutivo para o
período cronoestratigráfico que representam.
This work describes the occurrence of one specimen of Paleodictyon maximum from the Middle Jurassic (upper Bajocian) carbonate succession of Mareta Beach, Algarve Basin. It discusses its implications for the carbonate ramp environments of the Mareta Beach sequence, as well as the behaviour of its producer. Archetypal trace fossils from the Paleodictyon Ichnosubfacies, associated with deep-sea turbidite environments that occur in the Mesozoic, are interpreted to be an ecophenotypical relict from the Paleozoic Evolutionary Fauna. It occurs with relatively wide paleogeographical distribution in shelfal environments associated with event beds (tempestites, prodelta turbidites). High sedimentation rates may have allowed the preservation of this Paleodictyon, by limiting subsequent bioturbation. The example of P. maximum from Mareta Beach section helps to show that, for the determination of ichnofacies and correspondent paleoenvironmental and bathymetric interpretations, the best method is to identify recurring ichnocoenoses and not relying only in individual trace fossils. The integration of sedimentological and ichnological information, together with the inclusion of this data within the evolutionary paleoecology of trace fossils for the chronostratigraphic time under analysis proved to be a powerful tool in basin analysis.
This work describes the occurrence of one specimen of Paleodictyon maximum from the Middle Jurassic (upper Bajocian) carbonate succession of Mareta Beach, Algarve Basin. It discusses its implications for the carbonate ramp environments of the Mareta Beach sequence, as well as the behaviour of its producer. Archetypal trace fossils from the Paleodictyon Ichnosubfacies, associated with deep-sea turbidite environments that occur in the Mesozoic, are interpreted to be an ecophenotypical relict from the Paleozoic Evolutionary Fauna. It occurs with relatively wide paleogeographical distribution in shelfal environments associated with event beds (tempestites, prodelta turbidites). High sedimentation rates may have allowed the preservation of this Paleodictyon, by limiting subsequent bioturbation. The example of P. maximum from Mareta Beach section helps to show that, for the determination of ichnofacies and correspondent paleoenvironmental and bathymetric interpretations, the best method is to identify recurring ichnocoenoses and not relying only in individual trace fossils. The integration of sedimentological and ichnological information, together with the inclusion of this data within the evolutionary paleoecology of trace fossils for the chronostratigraphic time under analysis proved to be a powerful tool in basin analysis.
Description
Keywords
Paleodictyon maximum Icnoassociação Ambientes deposicionais Rampa média Jurássico Médio Bacia do Algarve Ichnoassemblage Depositional environments Mid-ramp Middle Jurassic Algarve Basin
Citation
Carvalho et al. 2020, ‘Paleodictyon maximum: forma típica da icnofácies de Nereites em ambiente de rampa carbonatada do Jurássico médio da praia da Mareta (bacia do Algarve, Portugal)’, Comunicações Geológicas, vol. 107, nº 1, pp. 13-20.
Publisher
LNEG - Laboratório Nacional de Energia e Geologia