Evolution of the Paraíba do Sul Deltaic Complex (SE Brazil) based on benthic foraminiferal biofacies succession

Abstract

Benthic foraminiferal assemblage distribution and paleoecology were analyzed in two previously studied well-cores (2-MU-1-RJ—ranging from 64.35 to 1.85 m; 2-BG-1-RJ—from 40.50 to 10.50 m) drilled in the central sector of Paraiba do Sul Deltaic Complex (PSDC), RJ, SE Brazil. The assemblages allowed to identify periods of higher and lower marine/continental influence in the study area and to infer events of marine ingressions or regressions during the late Pleistocene, associated with the penultimate marine transgression (123,000 years before the Present). Foraminifera were found in the upper part of both well-cores but they are more abundant in one of the studied well-core. Based on biofacies, the paleoenvironmental conditions and the complex dynamic estuarine evolution were analyzed. Seven foraminiferal biofacies associated with sea-level oscillations were determined throughout cluster analysis, as well as dominant and indicator species in the two well-cores. In the well-core (2-MU-1-RJ) with a higher abundance of foraminifera was identified the following environmental succession: (i) an inner shelf evolving to an estuarine environment; (ii) a return to marine shelf conditions; (iii) followed by the establishment of a lagoon system towards the well-core top. On the other well-core (2-BG-1-RJ), it can be observed the change of estuarine environment under the strong fluvial influence at the bottom of the studied interval; followed by an increase of marine influence from the middle toward the upper part of the well-core. The benthic foraminiferal absence in the samples at the top of the well-cores suggests an abrupt change from marine to the non-marine environment. The two well-cores were compared and the results contribute to the understanding of the estuarine complex dynamics of PSDC in late Pleistocene based on benthic foraminifera biofacies and their paleoecology in marine sediments of the upper portion of the well-cores. It recognized different environments due to the different location of the analyzed cores in the estuary and the neotectonic movements.