Foraminíferos bentônicos da Formação Pirabas (Oligoceno-Mioceno), Plataforma Bragantina, nordeste do Estado do Pará, Brasil.

Abstract

The Bragantina platform occurs off the northern coast of Brazil and is delimited by the Bragança - Vizeu Basin to the east and the Guamá Arch to the south. The Pirabas Formation units of this platform as it has a rich fossiliferous content including vertebrates and invertebrates (especially foraminifera and ostracoda). This unit consists of carbonate and siliciclastic sediments deposited during transgressive and regressive episodes (Chattian-Burdigalian), intensely modifying the coastline in northern Brazil. In this study, benthic foraminifera were analyzed in 27 samples from core FPR-192, in the town of Primavera, northeast of the state of Pará, Brazil. Paleoenvironmental, paleoecological and paleobiogeographic conditions were inferred using multivariate and ratio (P/B) analyses, designating six biofacies, three associations, variations in paleoprofundity and six paleoecological variations from coastal or transitional zones (hypersaline to brackish lagoons, estuaries) to carbonate platforms (internal, middle and external). Local biozonation was proposed for the studied section based on benthic foraminiferal bioevents. These associations reflected three main ecozones according to paleoecological events related to sea level variations. These ecozones were defined and named five Partial Amplitude Zones (PAZ): Amphistegina lessonii, Heterolepa dutemplei, Elphidium crispum, Siphonina pulchra and Bolivina subcompressa; and one Concurrent Amplitude Zone: Buccella peruviana. The biochronostratigraphy of the section studied was based on the local appearance of A. lessonii and H. dutemplei (lower Oligocene, Rupelian) and the stratigraphic distribution of E. crispum, S. pulchra and B. subcompressa.