Organic Geochemistry and Biomarker Characterization of Eocene Coal from the Burgas Basin

Abstract

This study presents new data on the organic geochemistry of sub-bituminous coals from two previously uninvestigated mine galleries (301 and 109) in the Burgas Basin (Bulgaria). The samples are characterized by low thermal maturity, as indicated by vitrinite reflectance, high volatile matter contents and biomarker compositions. Abundant hopanoids, moderate, uniform ash yields and high sulphur contents suggest deposition in a marine/brackish influenced low-lying mire with a stable water level. n-Alkane distributions show a pronounced predominance of long-chain odd-numbered homologues, with maximum at n-C31, indicating a significant contribution of leaf waxes from higher terrestrial plants and warm climate. Pristane/phytane ratios suggest deposition under slightly fluctuating redox conditions. Terpenoid assemblages indicate mixed vegetation input, with a substantial contribution from coniferous plants (particularly in gallery 301) and a very variable angiosperm proportions in gallery 109. Hopanoid distributions reflect low thermal maturity and enhanced microbial activity. The obtained results extend existing knowledge by providing data from previously unstudied galleries in the Burgas Basin and allow for a more detailed characterization of origin and depositional environment of organic matter.