Evaluation of thermal effects of intrusive rocks on the kerogen present in the black shales of Irati Formation (Permian), Parana Basin, Brazil

Shale samples from outcrops of the Irati Formation (Permian), Parana Basin, Brazil were analyzed based on organic geochemistry, palynofacies, and stable carbon isotopes with the aim of evaluating thermal effects of igneous intrusions on the kerogen. The potential for hydrocarbon generation, the depositional paleoenvironment, and the input of the organic matter were also studied. Most samples have high total organic carbon content, excellent hydrocarbon source potential, and type I kerogen, except some samples which showed changes in their compositional characteristic due alteration in the depositional paleoenvironment and due to the high maturation caused by the heat of diabase intrusions. The composition and distribution of saturate and aromatic biomarkers and stable carbon isotopes provided evidence that the composition of organic matter in the shales is marine, except at the upper part of the outcrops where the shales have contribution of terrestrial organic matter. Saturate biomarkers results indicated thermal immaturity for hydrocarbon generation, except the samples that were influenced by the heat of intrusive rocks.