Lipid biomarker profile of the Permian organic-rich shales (Irati Formation) in the northernmost of Parana Basin, Brazil

The Irati Formation (Paran & aacute; Basin) is a mixed carbonate and organic-rich shale sequence intruded by Jurassic-Cretaceous basic rocks, featuring Brazil's most important oil shale deposits with different maturity levels. For the first time, the distribution of oil shale biomarkers from an outcrop section (quarry) of the Irati Formation in the northernmost Paran & aacute; Basin was analyzed by GC-MS and GC-MS/MS to determine the thermal evolution, organic matter origin and the depositional paleoenvironment. The organic-rich shale at the northernmost border of the basin has high similarity with the central and southernmost areas, indicating a primary control able to induce cyclic sedimentation in a broad (10 6 km 2 ) and restricted environment. PCA and HCA analysis of bulk and molecular parameters showed changes in the organic matter composition and paleoenvironmental conditions throughout the stratigraphic column. Nonetheless, there are significant differences compared to the central-eastern and southern areas of the basin. Contrasting with the southern region, the north, predominates biphytane, low and medium gammacerane index. Pr/ n-C 17 , Ph/ n-C 18 , HI and OI values suggest type II/III kerogen from marine organic matter with freshwater input. Among the steranes, those of stereochemistry alpha alpha alpha 20R predominate over alpha alpha alpha 20S, and the presence of beta Tm indicates the shales are less thermally evolved.