Sergipe-Alagoas Basin, Northeast Brazil: A reference basin for studies on the early history of the South Atlantic Ocean

Abstract

Early Cretaceous sedimentary basins on the South Atlantic continental margins of South America and Africa are closely related with the Gondwana break-up, and record coeval paleoceanographic, paleoclimatic, and biotic changes during the late Barremian–Albian. The Sergipe-Alagoas Basin of northeastern Brazil contains one of the most complete Lower Cretaceous stratigraphic successions of the South Atlantic Ocean, including sedimentary and paleontological records nearly absent in nearby basins on the African/Brazilian continental margins. Fossil-rich sedimentary successions from the Sergipe-Alagoas Basin have allowed to assess: (i) evolutionary stages of the early South Atlantic Ocean; (ii) paleobiogeography of marine incursions (Austral and/or North Atlantic/Tethyan influences); and (iii) local signatures of global-scale paleoceanographic, paleoclimatic, and biotic events. Here we provide an overview on fossil-based biostratigraphic and paleoenvironmental studies of the Sergipe-Alagoas Basin, from the first marine incursions in a continental setting, to fully open-marine conditions. Based on eight fossil groups (ammonites, calcareous nannofossils, echinoids, planktonic and benthonic foraminifera, ostracods, palynomorphs, and radiolarians) from 107 sites, we observed that the marine biota shows strong affinity with Tethyan Realm in the Aptian–Albian interval, and provincialism/endemism is likely tied to the early-stage development of the South Atlantic Ocean. Based on late Barremian–late Albian lithological, paleontological, and geochemical data, we suggest three Sergipe-Alagoas Paleoenvironmental Stages (SAPSs): (i) continental conditions with possible episodic marine incursions (SAPS-1); (ii) transitional system, from continental to restricted-marine conditions (SAPS-2); (iii) transition from restricted- to open-marine conditions (SAPS-3). These local-scale evolutionary stages are correlated with early phases of the South Atlantic Ocean and major late Early Cretaceous paleoceanographic and paleoclimatic events. Moreover, we provide new approaches on the response of low-latitude biota to changing ocean circulation patterns in a hot, ice-free “greenhouse” world.