THE KEROGEN TYPE, DEPOSITIONAL ENVIRONMENT AND MATURITY, OF THE IRATI SHALE, UPPER PERMIAN OF PARANA BASIN, SOUTHERN BRAZIL

Two samples from the upper and lower horizons of the Irati oil shale of the Parana Basin, Brazil, were sampled in a single borehole and analyzed using organic petrography and geochemistry. The results are interpreted in terms of the kerogen type, maturity and depositional environment of the two horizons. Organic petrography shows the oil-shales to be composed of a mineral groundmass, mainly clay minerals, carbonate and pyrite, associated and sometimes impregnated with fluorescing organic material and disseminated phytoclasts. Humic material is fairly rare and mostly present as very small particles. A tentative interpretation of the extract and vitrinite reflectance data suggests a maximum paleo-burial of between 1. 3 and 2. 8 km for the analyzed section of the Irati Formation.