The Disappearance of Coal Seams Recorded in Associated Gangue Rocks in the SW Part of the Upper Silesian Coal Basin, Poland

Coal seams in the Upper Silesian Coal Basin vanish within the Carboniferous Upper Silesian Sandstone Series and below an unconformity marking the Carboniferous top surface. Changes in the geochemical, mineralogical, petrological and palynological characteristics of gangue rocks associated with the vanished seams record what happened. The observed changes could have been caused by (1) coal-seam paleofire, (2) peat combustion, (3) igneous intrusion, (4) metasomatism and/or (5) weathering. Multifaceted research on samples collected at the Jas-Mos mining area, a part of the operating Jastrzębie-Bzie Coal Mine that are representative of different geological settings in the northern and southern parts of the mining area, point to intra-deposit paleofire as the most plausible reason for the disappearance. Biomarkers enabled recognition of differences in heating duration and oxygen access. Coal seams in the south burned quickly with abundant oxygen supply. Seams in the north pyrolyzed for an extended time under conditions of limited oxygen. Though other methods used proved less sensitive, all confirmed low (100–150 °C) paleotemperature heating. Overall, the reason for the local disappearance of the coal seams, making their exploitation difficult and unprofitable, can be assigned to a variety of different processes in a complex overlapping history of variable weathering, heating due to local endogenic fires and, probably, earlier peat combustion