Biomarkers and aromatic hydrocarbons in bituminous coals of Upper Silesian Coal Basin: Example from 405 coal seam of the Zaleskie Beds (Poland)

Abstract

This paper presents the geochemical characteristics of hard coals from the 405 coal seam found in several mines in the Upper Silesian Coal Basin (Poland). The coals, classifying as of medial coalification, types D and C, and as para- and orthobituminous coals, show variable technical, chemical and petrographic properties. Vitrinite reflectance values range from 0.65 to 1.24%, Cdaf from 79.2 to 88.3wt.%, and Vdaf from 23.7 to 37.4wt.%. Maceral composition in all of the coals studied is dominated by vitrinite macerals (43.5–74.0%). Gas chromatography–mass spectrometry was applied to assess organic-matter sources and ranks, using several biomarker- and aromatic-hydrocarbon parameters. Distributions of n-alkanes, acyclic isoprenoids, diterpenoids, steranes and triaromatic steroids indicate that the organic matter in the coals analysed is derived mostly from terrestrial vascular plants. The biogenic organic matter was deposited mostly in an estuarine/deltaic environment with a normal- to low water level. In a few cases, a marine/lagoonal- or paludal environment is possible. Tetracyclic diterpanes such as phyllocladanes and kauranes, indicators of the Podocarpaceae and Araucariceae families, are explained by proposing input of organic matter deriving from Voltziales plants which may have been able to synthesise these compounds. Biomarker and aromatic-hydrocarbon parameters of thermal maturity in the coals show a clear correlation to vitrinite reflectance values and carbon content, indicating degrees of thermal maturity in the range from early- to advanced catagenesis. Frictional heat related to the Klodnica fault movement caused aberrations in values of aromatic-hydrocarbon maturity parameters in coals sampled <0.5m from the fault plane. In this last context, unchanged reflectance values testify to the more sensitive response of the geochemical parameters when compared to that of commonly applied petrographic parameters.