Upper Campanian calcareous nannofossils from the Core 2-RSS-1, Pelotas Basin, Brazil

Abstract

The deep wells drilled in the Pelotas Basin, located in the southernmost of Brazil, represent a rare opportunity to understand the geological evolution of the region during the Cretaceous. The biostratigraphic framework proposed for the basin used outdated data, demanding new studies for its improvement. The calcareous nannofossils of the core 2-RSS-1 (depth interval 4480.35 - 4487.70 meters), drilled by Petrobras in the offshore portion of the basin are reported here. Thirty species were recognized, the most important of them are Arkhangelskiella cymbiformis Vekshina, Broinsonia parca constricta (Stradner) Hattner, Wind and Wise, Calculites obscurus (Deflandre) Prins and Sissingh, Eiffellithus turriseiffelii (Deflandre) Reinhardt, Microrhabdulus decoratus Deflandre, Micula decussata Vekshina, Reinhardtites levis Prins and Sissingh, Retecapsa crenulata (Bramlette and Martini) Grün, Tranolithus orionatus (Reinhardt) Reinhardt, and Uniplanarius sissinghii Perch-Nielsen. The co-occurrence of Broinsonia parca constricta and Reinhardtites levis indicates that the studied rocks are included in the Standard biozones CC22b to CC23a. According to the Cretaceous Standard zonation used in the present work, the studied interval is deposited close to the Upper Campanian boundary. The present and forthcoming studies will contribute to the improvement of the biostratigraphic scheme previously proposed for the Cretaceous of the Pelotas Basin.