Abstract
Tectonic activity plays a significant role in fossil recovery within the Brejo das Freiras Sub-basin, Rio do Peixe Basin, influencing both fossil abundance and preservation state. In this study, lithological data from 203 cutting samples were used; 73 samples were analysed for calcareous microfossils. Additionally, 20 samples were selected for sedimentary organic matter analyses to support and refine the palaeoenvironmental interpretation. This research contributes to a better understanding of the palaeoenvironmental conditions of the Rio do Peixe Group (Lower Cretaceous) which comprises the Antenor Navarro, Sousa, and Rio Piranhas formations. Based on the integrated sedimentological and micropalaeontological data, the Antenor Navarro Formation is interpreted as representing a high-energy fluvial system. The Sousa Formation reflects a lacustrine environment with reduced energy conditions and increased stratification of the water column. The Rio Piranhas Formation indicates a return to higher energy depositional conditions, marking the final phase of lake sedimentation. Furthermore, the ostracod and palynomorph taxa support a Berriasian–Valanginian age for the Rio do Peixe Group. This age assignment is based on the stratigraphic ranges of Brasacypris ovum , Cypridea vulgaris , Cypridea vianai , Cypridea paraibensis and Cypridea miritiensis , as well as Dicheiropollis etruscus and Cicatricosisporites salardii , which correspond to the Rio da Serra Brazilian local Stage.