Structural evolution of the Sergipe-Alagoas Basin, Brazil
Castro, Augusto Canellas Monteiro de, Jr
Bally, Albert W.
Doctor of Philosophy
The evolution of the Sergipe-Alagoas Basin started during the Early Cretaceous, as part of the rift system that initiated the separation between the South American and African plates. The direction of propagation of the rift was controlled by preexisting basement fabric, and the Sergipe-Alagoas Basin developed as a rift bounded by N-S oriented normal faults, formed by crustal extension oriented obliquely to the direction of propagation of the rift. Different rates of crustal attenuation along the basin, due to the heterogeneous nature of the continental crust, were accommodated by transfer faults which divided the basin in three separate Domains. Crustal extension was substantially less in the Northern Domain than in the Central and Southern Domains. The first marine incursions in the basin occurred during the Aptian, after the end of the rifting phase, and the period is marked by the deposition of large amounts of evaporites. From the Albian to the Santonian, the basin was covered by a shallow but permanent sea, and great thickness of carbonates were stacked on high proximal areas, whereas in the distal portions of the basin only a thin, condensed section was deposited. Open oceanic conditions were installed towards the end of the Cretaceous, during the Campanian, and a prograding clastic wedge started to be deposited. The distribution of the post-rift sediments, as evidenced by isopach maps, indicates that the Northern Domain remained essentially stable throughout the post-rift evolution of the basin, and that the post-rift subsidence was mostly concentrated in the Southern and Central Domains. Structures formed after the rifting phase are restricted to those associated with sediment mobilization (especially evaporites), but the distribution of both structures and sediments in the post-rift phase was strongly controlled by the tectonic framework created during the rifting phase.