Geology and thermal maturity of Namurian deposits in the Němčičky Sub-basin as the South-eastern continuation of the Upper Silesian Coal Basin (Czech Republic)

Abstract

The southernmost documented occurrences of Namurian coal-bearing strata can be found in the Němčičky area, SE Moravia, that is considered to be the southern continuation of the Upper Silesian Coal Basin. Since the south-eastern Moravia belongs to the most prospective areas in terms of hydrocarbon exploration and production in the Czech Republic and Namurian deposits are considered to be one of the potential source rocks, there was a systematic evaluation of the southernmost occurrence of coal-bearing Carboniferous deposits in the Czech Republic during the hydrocarbon exploration within the area with regard to the regional geological setting and thermal maturity. 2D and high-quality 3D seismic surveys were used for a detailed thermal maturation analysis and a determination of the regional situation of heavily faulted/eroded Namurian strata. Cores and cuttings of coal and siltstones were used from 8 boreholes to investigate and measure the vitrinite reflectance; the lithology and petrography definition was also done based on thin sections. All new measurements were compared with archived data and older studies. In the Němčičky Sub-basin, the complete sedimentary succession occurs as part of typical cyclic development, starting with basal conglomerates and followed by sandstones alternating with claystones, siltstones and coal seams of marine and transitional origin. Samples from the Nikolčice-Kurdějov ridge are showing significantly lower vitrinitte reflectance values with respect to their depths than those from the Nesvačilka graben; this fact is supporting the distinctive lateral movement along the western Nesvačilka fault as presumed from the seismic interpretation. Dominant source from “immature” orogen is combined with the source from the “mature” continetal block i.e. opposite margin of the basin. The seismic interpretation shows that the thicknesses of Namurian deposits are not decreasing at all towards the recently deeper positions; accordingly, it is suggested that it is right within this erosionally untouched accommodational space of the Němčičky Sub-basin where we can find the interconnection to the USCB in the north.