Petrological recognition of bituminous inertinite enriched coals of the Lower Silesian Coal Basin (Central Sudetes, SW Poland)

Abstract

Upper Carboniferous bituminous coals of the Lower Silesian Coal Basin occur in three main coal-bearing regions: the Wałbrzych region (in the N), the Nowa Ruda region (in the SE), and the Słupiec region (in the SSE). In contrast to the Wałbrzych region, coals representing Żacler Formation from the Nowa Ruda and Słupiec regions display elevated (up to 39.0% mmf) inertinite abundances. These coals were analyzed petrographically to determine what factors may have caused such inertinite-enriched coal formation and how these factors may have influenced the surrounding palaeoenvironment.The results of microscopic analyses show high amounts of vitrinite, relatively high content of inertinite, low quantities of liptinite, and low to high abundances of minerals. Values of random vitrinite reflectance are fairly constant (average 1.07% and 1.19% in the Słupiec and Nowa Ruda regions, respectively), and designate these coals as a medium volatile bituminous. The reflectance of inertinite varies significantly from 1.58% to 4.90%. This parameter has been used as a basis for further wildfire studies.The values of inertinite reflectance and studies of its distribution and morphology imply occurrence of diversified types of wildfires: ground, surface, and crown fires, though surface fires distinctly prevailed (estimated temperatures ranging from 405°C to 615°C). The evidences for ground and crown fires are scarce and suggest just occasional episodes of such wildfires or may indicate transport of charred material from another source area. Domination of microscopic charcoal may suggest transport by wind, but other transportation pathways (e.g. by water) cannot be excluded. Negative correlation of inertinite macerals and inorganic matter in some parts of studied profiles may reflect impact of wildfire on local erosional–depositional system, where increased share of mineral matter may suggest post-fire clastic-dominated input due to enhanced soil erosion.