Early Cretaceous marine microbiofacies from the South Atlantic Ocean (Sergipe–Alagoas Basin, Brazil): palaeobiogeographical and palaeoceanographical inferences

During the Early Cretaceous, several extensive carbonate shelves were developed in the sedimentary basins located on the Central Segment of the South Atlantic Ocean. These marine successions are characterized by mixed carbonate and siliciclastic sediments with a diverse fossil content, deposited during the late Aptian–Albian interval. The microbiofacies content of two continuous cores (SER-01 and SER-03), each approximately 200 m deep, drilled in the onshore region of the Sergipe–Alagoas Basin, north-eastern Brazil consists of mudstones, wackestones, packstones, grainstones, rudstones, marls, claystone, shales and sandstones in Core SER-01, whereas those from Core SER-03 are essentially fine-grained lithologies such as mudstones, wackestones, claystone and shales. Two low-frequency sedimentation cycles are identified, with SER-01 being characterized by restricted and shallow-marine facies that grade up in a transgressive trend, which is also present throughout Core SER-03. Six microfacies are recognized, indicating deposition in a high-energy shallow-marine environment with a sand-bar system, which later evolved into a low-energy deeper-marine environment (outer shelf). The microfossil content includes planktic and benthic foraminifera, which are dominant in both cores, as well as macrofossils such as echinoderms and molluscs. Cadosinids, green algae, microcrinoids and inoceramids occur locally in both cores. In addition, Core SER-01 is characterized by abundant microbial units. The fossil content shows palaeogeographic affinities with the Tethyan Realm. These records suggest water connections between the South Atlantic and the North Atlantic/West Tethys Sea since the late Aptian interval.