Palaeoclimatic imprint, distribution and genesis of Zechstein Main Dolomite (Upper Permian) petroleum source rocks in Poland: Sedimentological and geochemical rationales

Abstract

AbstractArid palaeoclimatic conditions and marine current circulation influenced organic matter productivity and its distribution and preservation in the Upper Permian (Zechstein) Main Dolomite (Ca2) source rocks in Poland. The gaseous and liquid hydrocarbons occurring within the Main Dolomite show distinctive geochemical characteristics which distinguish them from those derived from Carboniferous or other Permian strata and indicate that the main type of organic matter from which they were derived was of microbial origin. It is suggested here that the majority of the Ca2 hydrocarbons come from in situ organic matter (intraformational deposits). The lagoonal and slope zones are enriched in total organic carbon (TOC) compared to both the oolite shoal and basinal facies. These sedimentary settings were dominated by various biolaminated microbialite facies. The basinal areas, previously believed to be the location of the main source rocks for hydrocarbons found in the Main Dolomite, appear to have little source rock potential. Geochemical and geological features such as high organic productivity in lagoonal and slope zones of the Main Dolomite indicate that at least some of the hydrocarbons may have been generated from in situ deposited and degraded organic matter. This conclusion may improve prediction of the occurrence of hydrocarbon deposits in the Ca2.