Mesozoic biochronostratigraphy and paleoenvironment of the South Atlantic: A revised framework based on 20 DSDP and ODP deep-water sites

Abstract

The South American and West African margins of the South Atlantic and the Southern Ocean are characterized by Mesozoic black shales that serve as source rocks of known and unknown petroleum systems. The knowledge of regional chronostratigraphy and paleoenvironment enables the prediction of the stratigraphic and geographic distribution of black shales with precision, as well as the understanding of local heterogeneity in regional- or global-scale oceanographic changes, such as oceanic anoxic events. Through sample re-analyses, this study provides a high-resolution Mesozoic chronostratigraphic and paleoenvironmental framework with the help of new micropaleontological data generated from 17 DSDP and ODP sites (out of 20 study sites), ranging from the Equatorial South Atlantic to the Southern South Atlantic. A series of eight regional Mesozoic unconformities are proposed and correlated to previously known unconformities or seismic reflectors. The regional paleoenvironmental interpretation, which utilizes the standardized chronostratigraphic framework, is herein accomplished for four time-horizons, namely, Middle Jurassic–Valanginian, Hauterivian–Albian, Cenomanian–Turonian, and Coniacian–Maastrichtian. Chronostratigraphic cross-sections and reconstruction maps for the time-horizons show that significant changes in paleoenvironmental parameters, such as bottom-water oxygenation and allochthonous sedimentation, were governed by the tectonic evolution of the South Atlantic margins.