Generation potential of the Zechstein Main Dolomite (Ca2) carbonates in the Gorzów Wielkopolski–Międzychód–Lubiatów area: geological and geochemical approach to microbial-algal source rock

Abstract

A b s t r a c t . Source rocks of microbial-algal origin commonly occur in the Main Dolomite strata in the Gorzów Wielkopolski–Międzychód–Lubiatów area on carbonate platform slopes and on carbonate platforms. Oil-prone type II kerogen dominates with occasional amounts of type III or type I kerogens. Hydrocarbon generation processes followed two pathways. In the first pathway, generation was a single-stage process with full generation of hydrocarbon mass in a continuous progression of organic matter transformation, in late Triassic time. In the second pathway, the generation took place in two stages. Eighty to ninety percent of hydrocarbon mass was generated from kerogen by the end of the Jurassic period and the remaining generation was completed during post-Cretaceous time. As a consequence, oil accumulated in traps at the turn of the Triassic- Jurassic periods, and gas saturation of oil accumulations took place by late Jurassic time, with the final gas generation in the Paleogene or Neogene time. Hydrocarbons migrated only a few kilometres from source rocks to reservoir rocks within the Main Dolomite strata.