Non-marine ostracods from the Hauterivian, Recôncavo Basin, northeast Brazil

The Recôncavo Basin is located in the State of Bahia, in Northeastern Brazil. It is part of the Recôncavo-Tucano-Jatobá Rift System and was the first onshore basin to be explored for hydrocarbons in the country. The genesis of the Recôncavo Basin is related to the distensional efforts that culminated in the fragmentation of the Gondwana Supercontinent and the establishment of the South Atlantic Ocean. Sedimentary rocks from this basin have been useful in establishing biozonation based on non-marine ostracods, and a key tool in dating strata based on these microfossils. The present study analyzed samples collected from wells 9-FBA-65-BA and 9-FBA-79-BA drilled in Aramari City (Bahia State). Both cores record the contact between the Marizal Formation (Aptian) and the Ilhas Group (Valanginian–Barremian) to the top. A total of 133 samples of fine- to medium-grained sandstones and shales from the Ilhas Group were collected. The fauna consist of 6701 ostracod specimens is mainly composed of the genera Paracypridea Swain, Cypridea Bosquet, Reconcavona Krömmelbein, Theriosynoecum Branson, and Alicenula Rossetti and Martens. The biochronostratigraphic position in the Aratu Local Stage (Hauterivian–Barremian) was based on the occurrence of the index species Paracypridea obovata obovata (Biozone OST-005). Some carapaces were recrystallized, and others were replaced by pyrite. In both wells, internal and external ostracod molds were the most common type of preservation. The faunistic ostracod association was interpreted as typical of a lacustrine environment, presenting moderate abundance and richness.