Ostracodes cretácicos da Bacia de Barreirinhas: taxonomia, considerações bioestratigráficas e inferências paleoambientais

Abstract

The Barreirinhas Basin occupies the coastal and continental platform portion of the Brazilian equatorial margin of the Maranhão state, and contains a good marine ostracod fossil record, that haven’t so far been studied. The study of ostracods, in general, can contribute towards the better comprehension of the paleoenvironmental evolution and biostratigraphic discussions of the area. This work presents the result of the study made with ostracodes recovered from the wells 1-MAS-1, 1-MAS-3A, 1-MAS-4A and 1-MAS-14 of the Barreirinhas Basin, with the aim of expanding the knowledge about cretaceous ostracods of the Barreirinha Basin and, consequently, of the Brazilian equatorial margin. 147 samples were prepared and analysed, resulting in the recovery of 495 specimens, distributed between 40 species, 16 genera and nine families. The following genera were identified: Cytherella Jones, 1849, Bairdoppilata Coryell, Sample & Jennings, 1935, Argilloecia Sars, 1866, Paracypris Sars, 1866, Cythereis Jones, 1849, Ovocytheridea Grekoff, 1951, Sapucariella Puckett, 2016, Dumontina Deroo, 1966, Potiguarella Piovesan, Cabral & Colin, 2014, Sergipella Kroemmelbein, 1967, Krithe Brady, Crosskey & Robertson, 1874, Nigeroloxoconcha Reyment, 1960, Conchoecia? Dana, 1849, and Protocosta Bertels, 1969, as well as two unidentified genera belonging to unknown families. Based on the fauna found, three distinct paleoenvironments were defined: Marine 1, Marine 2A and Marine 2B, with an inner to outer neritic environment being attributed to Marine 1, a middle to outer neritic environment to Marine 2A, and an outer neritic one to Marine 2B. . Based on previously stablished biozones for the Sergipe basin, two biozones were identified: the Nigeroloxoconcha aff. Nigeroloxoconcha sp. GA A 22 Range Zone, of lower Cenomanian age; and the Brachycythere sapucariensis Interval Zone, of Turonian to middle Coniacian age.