A grande elevação eustática do Mioceno e sua influência na origem do Grupo Barreiras

Abstract

The Barreiras Group is a lithostratigraphic unit, which crops out extensively along the Brazilian coast, from the state of Amapa (North Brazil) to the state of Rio de Janeiro (Southeast Brazil). It is characterized by its continuous occurrence and geomorphological regularity. Its origin has been the subject of much discussion and controversy. Traditionally, it has been considered as continental, but recent studies have shown an irrefutable marine influence, as indicated by paleontological and sedimentological evidence. The palynological dating and correlation of the Barreiras Group with coeval lithostratigraphic units in offshore basins of the Brazilian continental margin and elsewhere in the world permit new interpretations in the light of sequence stratigraphy concepts. This integrated analysis permits correlation of the origin of the Barreiras Group with the Miocene global eustatic rise, which reached its maximum from the Burdigalian to the Serravallian (12 - 20 Ma). Deposition of the Barreiras sensu lato was interrupted in the Tortonian (early Late Miocene), when a global eustatic fall exposed and eroded part of the Barreiras and led to formation of prograding wedges in the offshore portion of continental margin basins. Renewed eustatic rise in the Pliocene (Zanclean, 4 - 5 Ma) initiated a second depositional phase, represented by the upper part of the Barreiras Formation. Erosion and reworking of the Barreiras Group during the Quaternary have contributed to the present configuration of the continental shelf.