oa Origin, Depositional Environment and Maturity of Coal from the Late Miocene Karlovo Basin (Bulgaria)

The present study focuses on coal from the late Miocene Karlovo Basin which is the easternmost basin within the Sofia coal province. So far, some boreholes from the Karlovo coal Basin have been studied in terms of organic petrography and mineralogy, distribution of major elements, and palynology (pollen and spores). However, a detailed organic geochemical study has not yet been performed. Therefore, the goal of the current paper is to evaluate the sources, depositional environment and maturity of organic matter (OM) of the Late Miocene Karlovo coal. For that purpose, bulk organic geochemistry, Rock-Eval data and detailed biomarkers analysis of are used. Conifers are the main precursors of OM, associated with variable, but generally upward decreasing contributions of angiosperms. Input of ferns and fungi is also evident. The composition of the diterpenoid biomarkers argues for the predominance of species from Pinaceae family, whereas Cupressaceae played a subordinate role. Non-hopanoid triterpenoid patterns indicate an angiosperm mesophytic flora and temperate climatic conditions. The peat formation occurred in the wet forest swamp, with certain variations in water level, caused by seasonal changes. The OM is immature and corresponds to lignite rank. The obtained results are consistent with findings from organic petrography and palynology.