Paleoenvironmental reconstruction based on palynological and palynofacies analyses of the Aptian-Albian succession in the Sergipe Basin, northeastern Brazil

Palynological and palynofacies analyses were carried out on samples from two wells in the Sergipe Basin with the aim of reconstruction the paleoenvironments of the upper Aptian-middle Albian interval. Altogether 19 species of spores, 31 species of pollen grains, 20 species of dinocysts were identified. Moreover, one genus of Acritarcha and one genus of fresh-water algae were recorded. The sections are clearly dominated by the pollen group, in particular gymnosperms, which is by far the most abundant group in the two wells studied. In well GTP-17-SE the second most abundant group is the spores. Well GTP-24-SE is characterized by high abundance of marine. One zone and two sub-zones and one zone of middle Albian were recognized. The absence of the three sub-zones and one zone of the uppermost Aptian to lower middle Albian indicates a possible hiatus. Four clusters, which represent different palynological assemblages. The stratigraphic distribution of these Four assemblages allowed the definition of seven ecophases. The relative abundance of spores and the genus Classopollis indicates for a predominantly arid paleoclimate. However, these conditions tend to decrease upwards in sequence, changing to tropical climates. 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. The increase in abundance of amorphous organic matter (AOM) and palynomorph groups indicates a transgression or a decreasing terrestrial influx. The palynological and palynofacies analyses of the successions studied allowed detailed environmental reconstruction. Six depositional environments were recognized: a brackish lagoonal; lagoonal coastal plain environment; intertidal-nearshore, shallow-neritic shallow marine and middle-neritic. The paleoenvironmental evolution reflects the progressively increasing marine influence into the area