Depositional regimes at the Brazilian Equatorial Margin during the Cenozoic

The Brazilian Equatorial Margin (BEM) is a passive margin located at equatorial latitudes for the last 100 million years. For that reason, its Cenozoic sediments recorded the changes and evolution of climate and oceanography of Equatorial Atlantic. Using new data available for the basins of the BEM, it was possible to unravel some new evidence of how the oceanographic and climate conditions of its basins evolved through the Cenozoic. Working with high-resolution 2D and 3D seismic data and well information (gamma-ray, density, sonic, and lithology), distinct depositional phases were identified for the Cenozoic, showing very different Paleogene and Neogene sedimentation. A backstripping model was produced from well data from the Ceará Basin and a seismic facies analysis from 2D and 3D data resulted in 5 chronostratigraphic-tied seismic horizons, interpreted across the central BEM. As a result of different oceanographic and climate conditions, the deposition at the BEM evolved though the Cenozoic from a condition with less-intense/nor-existent bottom-current activity during the Paleogene to conditions of intense shallow and deep-water circulation with the North Brazil Current (NBC) and the Deep Western Boundary Current (DWBC). This prepare the conditions to understand the evolution of the relation between the NBC, DWBC and the Atlantic Meridional Overturning Circulation (AMOC).This development in circulation produced changes in sediment deposition and accumulation.The backstripping model showed that from ~70 Ma, subsidence was mostly constant, which points to stronger climate and oceanography component on thickness variation and distribution across the BEM. Modern deposition in the central and eastern BEM presents evidence of clear depression trails, formed by upslope-migrating sediment waves that evolve into cyclic steps. Those depression trails are very effective not only in shaping the submarine landscape and controlling sediment delivery to the basin but also in creating syn-depositional pathways for vertical fluid migration.