Coalified bitumens from the Kłodawa salt structure (central Poland) as evidence of migration of hydrothermal fluids in Zechstein (Upper Permian) deposits

Abstract

The paper presents the results of petrographic and geo chemical studies of coaly matter occur ring in Stinking Shale and Main Dolomite (PZ2, Upper Permian) de pos its in the Kłodawa Salt Structure in central Po land. The coaly matter is both dispersed in the PZ2 shales and carbonates and concentrated in veins which cross cut these deposits and, depending on the location, depicts contrasting maceralcom position and the rank of coal. The veins are built of colotellinite and micrinite, showing a mean random reflectance of coal in the range of 1.38–1.40%, whereas the dispersed organic matter is com posed mostly of semifusinite and fusinite with minor vitrinite, showing a mean random reflectance of 0.82%. It is interpreted that the heterogeneous com position and rank of coal result from mi gration of hot flu ids within a fracture sys tem developed in the PZ2 shale and car bon ate beds. The in flux of hot flu ids into the organic matter-rich beds led to the generation of bitumen which catagenetically altered along the hot fluid conduits. The coalification of bitumens took place at an early stage of tectonic deformation of the Zechstein salt series, initiated by regional extension and nor mal displacement on a basement fault, most probably in the Late Permian–Early Tri as sic.