We investigated early diagenetic processes of the extractable organic matter from the Miocene freshwater sequence, which consists of coal fragments in clays, sandstones and shales alternating with continuous brown coal layers. We examined eight coals, thirteen sediments and three non-coaly underground layers. The molecular assemblages of the identified aliphatic hydrocarbons in the Krepoljin Basin reflect the abundance of plant taxa as precursors or participants in the early diagenetic stage. The data provide insight into the conditions prevailing in the lakes and bogs during early diagenesis. The dominance of diterpanes indicates that the prevalent of the organic matter was of gymnosperous origin. The hopanoid contents are considered to reflect microbial activity. That the organic matter in the Miocene Krepoljin Coal Basin is immature was confirmed by the presence of biolipids such as beta beta-hopanes, C-27 17 beta (H)-trisnorhopane. Saturated and aromatized abietanes, pimaranes and phyllocladanes, the most abundant compounds in all samples, indicate a predominantly higher plant input related to the Coniferous group, but identification of the individual plant families was not possible. beta-Amyrin and other triterpenoid-derived triaromatic and triaromatic C-ring cleaved hydrocarbons with triterpenoid structures are thought to be characteristic for angiosperms. Unsaturated compounds, Delta(2)-triterpanes, early intermediaries in the diagenetic transformation of angiosperms also indicate a low degree of sediment maturity. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.