Paleodictyon maximum: Typical trace fossil of the ne-reites ichnofacies in carbonate ramp environment from the middle jurassic of mareta beach (Algarve basin, Portugal)

摘要

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 paleo-environmental 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.