Organic geochemistry of the Grodziec beds (Upper Carboniferous) : Upper Silesian Coal Basin, Poland

Five lithologically different rock samples from the "Niwka" brickyard exposure, including one coal sample, were geochemically characterized as regards their mineral composition and sedimentary organic matter present in them. Various methods, including: X-ray diffraction, solvent extraction, group separation by preparative thin layer chromatography, infra-red spectroscopy for assessment of the content of different functional groups in total rock extracts and their separated polar compound fractions, and capillary gas chromatography for analysis of aliphatic hydrocarbon fractions. It was found that the "Niwka" brickyard rocks are rich in organic material present as the plant detritus (cane-break) or as compounds adsorbed on clay and carbonaceous minerals. Yields of bitumen extraction, group composition of extracts and content of various functional groups assessed by infra-red spectra seem to be related to mineral composition of the host rocks and type of kerogen present. Higher contents of clay minerals, especially chlorite, enriches both extracts and their polar compound fractions in aliphatic structures while the organic matter of both sandstones analysed contains more condensed aromatic structures and functional oxygen groups. Generally the organic matter of the host rocks was deposited in an oxic environment and belongs to type III kerogen with a dominant terrestrial biogenic source or to type II kerogen of bacterial/terrestrial origin of primary biogenic matter. Its thermal maturity stage can be estimated as end-diagenetic or early catagenetic. The highest maturity is shown by the organic matter in the basal sandstone (the S2 sandstone) and probably is caused by imput of older migrating bitumen. Biodegradation of organic matter seems to be influenced by the mineral composition of the host rock, with a high content of clay minerals giving protection.