Organic petrography, geochemistry, and sulfur speciation of a new potential Mesozoic source rock in western Greece

Summary A new potential source rock formation was discovered in Ionian Zone, Epirus region, western Greece and its organic petrographic and organic geochemical characteristics were investigated. The formation lies between the overlying lower Liassic “Pantokrator Limestones” and the underlying Rhaetian “Pantokrator Dolomites”. It consists of alternating organic-rich black shale and less organic-rich gray dolomite/dolomitic sandstone beds. The organic geochemical results suggest high amounts (up to 35,56 wt.% TOC) of Type I and II/IIS organic matter, with a Hydrogen Index up to 790 mg HC/g rock and a high remaining generation potential (S2) of 237,4 mg HC/g rock. Based on the mean Tmax of 422⁰C and on %VRo-eq from solid bitumens, formation hasn’t entered the oil window in this part of the basin. Nevertheless, presence of Type IIS kerogen in some samples, indicate that certain intervals of the formation may already have entered oil window and produced liquid hydrocarbons. Relatively high clastic input may be indicative of a climatic shift towards seasonably controlled wetter conditions, as it is inferred from adjacent areas. This study suggests that the stratigraphic position and the geochemical characteristics are comparable to intervals in Albania and Italy, possibly indicating a source rock interval with regional significance.