Integration of Structural Analysis and 2D Gravity Modeling of the Ultra-Thin Sergipe-Alagoas Rifted-Passive Margin, Northeastern Brazil

Authors: Hualing Zhang (presenter), Paul Mann, Dale E. Bird, University of Houston

The Sergipe-Alagoas Basin is a Cretaceous rifted-passive margin basin located along the northeastern Brazilian margin of the South Atlantic Ocean that is a conjugate of the Gabon basin of west Africa. The structural framework is controlled by normal fault systems striking NE-SW and subsidiary transfer faults trending E-W and NW-SE. We investigate the crustal architecture and the nature of the continental-oceanic boundary (COB) of the Sergipe basin by building two regional gravity models (AA’ and BB’) that are aligned with two ION seismic lines recorded to a sub-crustal depth of 30 km. Wells logs and refraction stations were added to better constrain the gravity models. Onshore gravity and magnetic data were integrated with seismic control in order to extend the models eastward across the Reconcavo–Tucano–Jatoba failed rift system. Gravity model A-A’ is oriented NW-SE through the central Sergipe Basin and crosses the Aptian Bahia Seamounts to the southeast, which exhibits a 22-km-deep root into the upper mantle. The rifted continental crust is thicker compared to that seen on gravity model B-B’ with its large seamount influence. Model B-B’, oriented NW-SE through the southern edge of the Sergipe Basin, shows a 3-25-km thick, ultrathin continental crust with a distinct COB. Modeling results suggest that the crust thins abruptly over a distance of 3.5 km from the shelf to the deepwater region. Both gravity models show seaward-dipping reflectors that fill the area separating the continental-edge, marginal rift, and the oceanic crust. These new observations provide important constraints on the crustal and upper mantle framework of the Sergipe Basin that relates to hydrocarbon accumulation, the amount of crustal thickening influenced by Cretaceous-Eocene volcanism, and a tectonic reconstruction of its conjugate margin in Gabon.

Bio:

Hualing Zhang, University of Houston

Hualing is a PhD student at the University of Houston. She is a member of AAPG and AGU.