Paleoenvironmental reconstruction based on palynofacies analysis of the Aptian–Albian succession of the Sergipe Basin, Northeastern Brazil

Abstract

Palynofacies analyses were carried out on 272 core samples from two wells (GTP-17-SE and GTP-24-SE) in the Sergipe Basin, with the aim of reconstructing the paleoenvironments of the upper Aptian–middle Albian. For the palynofacies analysis the kerogen categories were counted and subjected to cluster analyses. For detailed environmental analysis, kerogen distribution trends and parameters were applied, based on percentages of kerogen categories. Total organic carbon analysis was also used. The stratigraphic distribution of palynofacies associations that defined eight palynofacies units in well GTP-17-SE and ten in well GTP-24- SE reflects a continuous terrestrial influx throughout the succession. Amorphous organic matter (AOM) and palynomorph groups show moderate to high percentages, especially in well GTP-24-SE. The increase in relative abundance of these groups suggests that a long-term a transgression and/or a decreasing terrestrial influx occurred in the area. From the bottom to top six depositional environments were identified in wells GTP-17-SE and GTP-24, respectively, and they reflect the progressive increase in marine influence as the basin evolved. Brackish lagoon conditions changed to more open marine conditions as sea level changed during the separation of South America from Africa.