The Brazilian Equatorial Margin from Rift to Drift: Faulting, Deposition, and Deformation in the Offshore Barreirinhas Basin

The Equatorial South Atlantic contains elements of an oblique-rifted margin and a sheared margin. The Barreirinhas Basin is a basin on the Brazilian coast located north of the shoreward limit of the Romanche Fracture Zone and south of the shoreward limit of the Saint Paul’s Fracture Zone. The main characteristic of the Barreirinhas Basin is an abrupt transition zone between oceanic and continental crust as a result of being located on a transform margin with, consequently, a very narrow and steep continental slope. This study focuses on the rift to drift evolution of the Barreirinhas Basin and the Barreirinhas Basin deep-water fold-belt, and is the first detailed published local study of the tectonic evolution of the Brazilian Equatorial margin. Complementary structural work over most of the Brazilian Equatorial margin provided a framework in which to place the tectonic history of the Barreirinhas Basin. Regional seismic reflection profiles across the Barreirinhas Basin on the Brazilian Equatorial margin reveal two major deep-water fold and thrust belts linked landward to extensional fault systems. Thrust faults are interpreted to be products of shortening caused by gravity-driven extension on the continental margin that involve rocks at both the shelf and the slope. Two main deformation events during the Cretaceous (99.6 to 83.5 Ma) and the Cenozoic (65.5 to 0 Ma) were distinguished. The Cretaceous deformation affected only a one kilometer thick section but the Cenozoic structural episodes involved a thicker (over 4 km) sedimentary sequence of Turonian to Miocene age, and cross-cut the pre-existing Cretaceous deformed sequence. Normal faults connect to the thrust faults at depth, forming two discrete bowl-shaped fault systems, linked at depth at different stratigraphic levels. Plots of displacement versus time show normal and thrust fault movements at the same time intervals, indicating close linkage between extension on the continental shelf and shortening on the slope. Deformation has increased dramatically during the past ten million years, with movement on all earlier and some newly formed faults. The increased deformation coincided with regional paleogeographic changes in northern South America in the Late Miocene that led to an increase in the sediment supply to the Barreirinhas Basin.Earth and Atmospheric Sciences, Department o