Caracterização e significado paleoambiental da fauna de ostracodes da Formação Codó (Neoaptiano), leste da bacia de Grajaú, MA, Brasil

Abstract

The study of ostracods from sedimentary successions exposed in the east portion of the Grajau Basin, Maranhao State, related to Codo Formation, revealed a Neoaptian lacustrine fauna characterized exclusively by Harbinia and Candona represented by the species Candona sp., Harbinia micropapillosa (Bate), Harbinia angulata (Krommelbein & Weber), Harbinia sinuata (Krommelbein & Weber), Harbinia sp. aff. H. symmetrica (Krommelbein & Weber), Harbinia salitrensis (Krommelbein & Weber) and Harbinia sp. The stratigraphical distribution patterns of the ostracod palaeocommunities in the studied sections confirmed the occurrence of a cyclic depositional lacustrine environment, as assumed by previous faciological studies. These cycles are associated with events of expansion and contraction of the lake, characterized mainly as hipersaline, with shallow-water and very low oxygen levels. The sudden environmental changes caused by these events produced a monospecific occurrence of some resilient species, followed by a mass death.