Geochemical characteristics, thermal maturity and source rock potential of the Oligocene Šitbořice Member of the Menilite Formation in the Ždánice Unit (Czech Republic)

Abstract

Rocks deposited in the Oligocene Paratethys are recognized as one of the most important source rocks in the Flysch Carpathians. The Sitbořice Member (uppermost NP23 to lowermost NP25 zone) represents the upper part of the Menilite Formation in the Outer Flysch Carpathians of the Czech Republic. This paper presents results of bulk geochemical analysis, Rock-Eval pyrolysis and organic petrography. The geochemical evaluation, source rock potential, kerogen type and thermal maturity were studied using borehole cores. Based on the classification of Peters (1986), the evaluated Sitbořice Member is mostly classified as a “very good” source rock according to TOC and variable, mostly “poor” to “good” according to the petroleum potential. However, the average petroleum potential value assigned the member to “good” source rock which is in accordance with the TOC classification if the “live” TOC is used. A comparable distribution between kerogen type II and III has been indicated by HI. Unlike this, the organic petrography observations show the organic matter belongs to the kerogen type II which corresponds to the relationship of residual hydrocarbon potential versus TOC and HI calculated based on “live” organic carbon. Presumed immaturity was confirmed by Rr and Rock-Eval T max . Oxygen-restricted conditions or a dysoxic environment have been indicated by the TOC/TS ratio