Paleoenvironmental characterisation of the Campos Basin slope (SE Brazil) in front of Cape São Tomé based on benthic foraminiferal biofacies succession since MIS 5

Abstract

The distribution of benthic foraminifera and the assemblage dynamics were analysed on piston core GL-54 to understand the changes in paleoecology since Marine Isotopic Stage 5 (MIS 5). The core was drilled on the upper slope of the Campos Basin on the Rio de Janeiro (Brazil) coast. Benthic foraminifera biofacies, ecological indices, lithological facies, biostratigraphy, and isotopic analyses were undertaken to characterise the paleoenvironment in front of Cape of São Tomé. Two distinct biofacies were identified in the GL-54 sedimentary record since the Last Interglacial Period (MIS 5). These two biofacies point to seasonal organic matter and a well-oxygenated environment, however, Biofacies 2 can be differentiated from Biofacies 1 by the presence of significant bottom water currents. Biofacies 2 has the same species as Biofacies 1, except for Miliolinella subrotunda. Benthic foraminiferal species and biofacies from GL-54 were compared to the ones present in the upper portion of the GL-39 piston core, which was drilled from the middle slope of the same basin. Species such as Globocassidulina crassa, Islandiella norcrossi, Alabaminella weddellensis, Bolivina paula, M. subrotunda, Bulimina aculeata, Globocassidulina subglobosa, Rotorbinella lepida, and Uvigerina peregrina were found in both piston cores. The biofacies of both piston cores were correlated, pointing to similarities between the upper slope and the middle slope in the Campos Basin since MIS 5. In general, the upper and middle slopes of the Campos Basin are characterised as a well-oxygenated environment with variation in the deposition of organic matter. In addition to these environmental factors, there is evidence for a strong bottom current in MIS 2 at both sites, probably due to the displacement of Brazil Current and Intermediate Western Boundary Current.