Integrated Organic Geochemistry and Palynofacies Analysis of Organic Matter in the Pirara Formation, Tacutu Basin

The Tacutu Basin developed during the Mesozoic from an intracontinental rift related to a triple junction formed in the Jurassic. It is located on the border between the state of Roraima, Brazil, and the Upper Takutu-Upper Essequibo district, Guyana. The Pirara Formation, the focus of this research, represents the rift phase of this basin and is composed of evaporitic, carbonate, and pelitic rocks. The age and depositional environment of this unit remain unclear, generating debate regarding its origin. This study is unique as it’s the first time that these samples from the Pirara Formation, a non-outcrop unit in the Brazilian portion of the Tacutu Basin, are analyzed and integrated in public domain. This material originated from two shallow core wells, approximately 40 m deep, drilled in the border region between Brazil and Guyana. The methodology employed involves organic geochemistry (TOC and Rock-Eval Pyrolysis) and palynofacies. Organic geochemistry data revealed high total organic carbon (TOC) levels, ranging from 2% to 8%, indicating a well-preserved organic matter content and significant hydrocarbon-generating potential. Hydrogen Index (HI) and Oxygen Index (OI) values indicate the presence of Type II, III, and IV kerogens, suggesting continental organic matter that has undergone varying degrees of oxidation and thermal maturation. The palynofacies indicate a predominance of organic matter of terrestrial origin, corroborated by the absence of marine palynological components. These results suggest significant variations in the paleoenvironmental conditions and the deposition and preservation processes of the Pirara Formation.