The potential of biomarkers to distinguish Lower and Middle Miocene lignites from the coal-mining district of Lusatia

Abstract

The organic geochemical study of Lower and Middle Miocene lignites from the coal-mining district of Lusatia in eastern Germany has been performed. Since the samples showed a uniform and low degree of maturity (0.32-0.37 %Rr), it can be considered that maturity has no significant impact on biomarker distributions. Therefore, the objective of the study is to examine the potential of biomarkers to distinguish Lower and Middle Miocene lignites in relation to sources and depositional environment of organic matter (OM). The biomarker patterns show relatively similar compositions in studied lignites, indicating no significant change in palaeclimate from Lower to Middle Miocene. Middle Miocene lignites are characterized by more pronounced variations of biomarker signatures due to the more pronounced fluctuation of water-level and/or palaeo-wildfires. Peatification was performed under stable water-level. The main differences between Middle and Lower Miocene coals are expressed by higher dehydroicetexane content, Paq index, the tetracyclic/tricyclic diterpanes ratio and non-hopanoid triterpenoids content, as well as by lower content of hopenes and fernenes in the latter one. Mentioned results indicate decreasing contribution of Cupressaceae and emergent macrophytes, associated with increased input of Pinaceae, angiosperms and ferns to the precursor OM of Middle Miocene samples in comparison to Lower Miocene samples.