Middle Cretaceous calcareous nannofossils from the cored well UFRJ-2-LRJ-01-SE, Sergipe-Alagoas Basin, Brazil: New biostratigraphy and paleobiogeographic inferences

This paper presents new biostratigraphic data and paleobiogeographic inferences obtained from the nannofossil content of the cored well UFRJ-2-LRJ-01-SE, drilled in the Sergipe-Alagoas Basin, Brazil. This material represents one of the best and most complete recovered sections of the mid-Cretaceous in the whole South America. Quantitative analyzes of calcareous nannofossils were performed on 78 samples and a total of 127 nannofossil taxa were identified. Eleven biostratigraphic intervals (BC26-UC7) were recognized, allowing to assign a late Albian-early Turonian age for the section. The absence of marker-taxa in the lower part of the Zone UC1 (early Cenomanian) associated with the indication of tectonic activity (fault) suggests a stratigraphic break/unconformity within the section. Nannofossil taxa with known stratigraphic distribution restricted to the Aptian (e.g., Nannoconus quadriangulus and Nannoconus troelsenii) were considered reworking. Nannofossil assemblages showed an abundance of nannofossil taxa with cosmopolitan and Tethyan affinities. However, the occurrence of Sollasites horticus, species with Boreal affinity, seems to be related to an increase in the effectiveness of the ocean circulation pattern coming from northern part of South Atlantic between the latest Albian and the late Cenomanian. The decrease in the abundance of Tethyan-affinity taxa recorded from the upper Cenomanian to the top of the section may be related to the development of more open oceanic condition. The absence of Austral taxa in the studied samples may be related to a low efficiency of ocean circulation pattern coming from the southern part of the South Atlantic, probably due to influence of geological barriers (e.g., Rio Grande Rise-Walvis Ridge) until the latest early Turonian. This study establishes the first bio-chronostratigraphic framework for the well UFRJ-2-LRJ-01-SE, providing the context and basis for further research that will contribute to a better understanding of the evolution of the South Atlantic during the middle Cretaceous. (C) 2019 Elsevier Ltd. All rights reserved.