Biostratigraphy and Paleoenvironmental Characterization of the Lower Cretaceous Codó and Itapecuru Formations (Aptian–Albian, Parnaíba Basin, Brazil)

The Parnaíba Basin is a Brazilian intracratonic basin located in the North and Northeastern regions of the country. Its Cretaceous succession holds significant scientific and economic importance, as it is correlated with the Aptian Pre-Salt deposits of Brazil and contains early records of marine incursions associated with the opening of the South Atlantic Ocean. This study aims to identify ostracods and organic matter constituents recovered from samples of a fully cored geological section recently drilled in the Parnaíba Basin (2-CO-1-MA borehole, within the interval corresponding to the Codó and Itapecuru formations). The objectives are to establish an ostracod-based biostratigraphic framework for this section, and to infer paleoenvironmental conditions through the integrated analysis of ostracods and palynofacies. Species of the ostracod genera Damonella and Pattersoncypris were identified, alongside megaspores, termite coprolites, fish fragments, gastropoda and foraminifera, characterizing a low diversity fauna and flora assemblage. In addition, the palynofacies revealed the presence of phytoclasts, amorphous organic matter, and palynomorphs within the studied samples. Four microfossil associations and three palynofacies were identified in the studied section, which is constrained to the upper Aptian. The evolution of the sedimentary succession is marked by a range of paleoenvironments, including lacustrine, brackish lacustrine, evaporitic-sabkha, fluvial, lagoonal, and fluvio-deltaic settings.