Paléoenvironnement de l'Atlantique sud

A schematic model of the evolution of the South Atlantic paleoenvironment since the early Cretaceous is proposed. The reconstruction here proposed is based on all the data offered for the South Atlantic by the Deep-Sea Drilling Project. These data are integrated within the framework of Plate Tectonics. The emphasis is put on the methodology available to reconstruct the ocean crust morphology and its sedimentary cover throughout the opennig of the ocean. Paleobathymetric, paleocirculation and paleofacies maps are presented. The paleofacies maps are in great part based on a new paleo-CCD (paleo-calcite compensation depth) curve, which is tentatively proposed here for the South Atlantic. During the early Cretaceous the South Atlantic consisted of two narrow basins divided by the Rio Grande Rise-Walvis Ridge barrier. Free circulation between the South Atlantic and the Antarctic Ocean on one hand, the North Atlantic on the other hand, was respectively established during the early and the late Cretaceous. During the major part of the Cretaceous the south Atlantic had its own oceanographic characters. Its sedimentation, dominantly terrigenous, was marked by two important anoxic phases, characterized by the deposition of black shales and sapropels. In the late Cretaceous the South Atlantic became part of the world ocean system. The establishment of the deep antarctic circulation during Oligocene induced major changes in the sedimentary facies distribution and announced the establishment of the present oceanic environment in the South Atlantic. [NOT CONTROLLED OCR]