Evolution of lignite seams within the South Moravian Lignite Coalfield based on certain qualitative data

Abstract

This paper focuses on evolution of lignite seams (the Pannonian) in the South Moravian Lignite Coalfield (SMLC). It is based on data analysis (seam geometry, ash yield, sulfur content, and lithology) from more than 3300 boreholes and many channel samples. The results show that the Vienna Basin in the Pannonian period gradually developed into a freshwater bay. In the Early Pannonian the sedimentary environment was tectonically calm. The salinity of the sedimentary environment was changing as a consequence of recurring transgressions. The studied area was under the influence of rivers flowing into the region from the west, north, and northeast. In the upper part of zone B (Papp's classification of the Pannonian sediments), especially in the northern areas of the SMLC, suitable conditions for coal-bearing sedimentation (the Kyjov seam) occurred. Zones C–F were characterized by simple or incomplete cyclic sedimentation processes. The Vienna Basin opened and the subsidence between the Steinberg fault zone and Lužice–Lanžhot fault zone (interconnected with the Polešovice fault zone) took place in the SMLC. At the beginning of zone F the swamp areas suitable for Dubňany seam formation developed in the SMLC. The coal-forming conditions were repeatedly restored. The sedimentary cycles with the coal-bearing deposits occurred also in zone G, however only in the central and southern parts of the SMLC. The increasing thickness of the deposits in zone G and the increasing number of cycles with lignitic layers in the southern part of the SMLC indicate a shift of the suitable conditions for swamps towards the south and into the overlying rocks. A distinct tectonic deformation of the lignite seam in the SMLC started only in the Pliocene, when due to the change of the stress field in the Vienna Basin the rejuvenation of the tectonic zones of the pull-apart system took place towards the NE–SW and NW–SE to NNW–SSE.