Evolution of the Sao Paulo Plateau (southeastern Brazilian margin) and implications for the early history of the South Atlantic

摘要

The São Paulo Plateau is a prominent marginal plateau in the southeastern Brazilian margin. Its surface displays a rough morphology either because of diapiric structures that have pierced and/or domed the overlying sediments or because of outcrops of igneous basement rocks. The plateau is bounded to the north and south by fracture zones and appears to be situated on oceanic crust created between Neocomian and Aptian time. At the end of Aptian, the segment of the initial spreading center that was bounded by the fracture zones that now form the northern and southern boundaries of the plateau shifted to the east. The newly created segment of the spreading center formed the eastern boundary of the plateau. The stratigraphy of the plateau has been inferred through correlation of seismic-reflection profiles with the drilling data from Deep Sea Drilling Project site 356, located on the southeastern corner of the plateau. We have attempted a comparison of the sedimentary facies of the plateau with those of the Santos Basin, a shelf basin located adjacent to the plateau. A continuous evaporitic layer of Aptian age extends from the basin to the plateau. In Albian time, shallow-platform limestone was deposited in the basin, while open-marine limestone was deposited on the plateau. Coarse conglomerates were deposited in the basin during Turonian-Coniacian time, whereas distal turbidites were contemporaneously deposited on the plateau. A major transgression in Maestrichtian time trapped the terrigenous sediments within the Santos Basin and halted terrigenous sedimentation on the plateau. Cenozoic sediments in both areas are open marine. The sedimentary history of the Santos Basin and the São Paulo Plateau thus suggests that the two regions have been structurally continuous at least since Late Cretaceous time. The region occupied by the plateau has acted as a depocenter and has evolved as a marginal plateau since the termination of evaporitic deposition in the South Atlantic.