Biomarker and stable carbon isotope systematics of fossil wood from the second Lusatian lignite seam of the Lubstów deposit (Poland)

Decay of fossil wood (gelification) collected from the middle Miocene 2nd Lusatian lignite seam at the Lubstów open cast mine (Poland) is characterised by its maceral variety, fluorescence intensity and cellulose content. Cellulose decomposition leads to lower molar H/C ratio values of the organic matter as indicated by higher total organic carbon (TOC) content of samples characterised by low cellulose content. Biochemical formation of hydrocarbons in the wood due to enhanced microbial activity is evidenced by higher hydrocarbon content in the extracts. Higher relative proportions of n-alkanes and hopanoids are observed in the hydrocarbon fractions of wood remains characterised by low cellulose yield. The results provide evidence for the formation of these compounds during biogeochemical transformation of organic matter. Hopanoid contents are considered to reflect the activity of aerobic bacteria and/or fungi. Because of enhanced perylene content in the hydrocarbon fractions from gelified wood samples, fungi are considered as the major precursor carriers of this polycyclic aromatic hydrocarbon. The results provide evidence that biomarker composition of fossil wood can be used to trace biochemical transformation processes. Chemotaxonomical classification of fossil wood fragments as gymnosperms (most probably species of the coniferales families Taxodiaceae/Cupressaceae) are based on the molecular composition of terpenoid hydrocarbons and a mean δ13C value of −24.5‰. Depletion of gelified samples in 13C as compared to ungelified wood is caused by the effect of progressive decomposition of cellulose. The data indicate that cellulose δ13C data (mean δ13C = −20.8‰) are also affected by wood decomposition and so only samples with comparable cellulose content should be used for the reconstruction of environmental changes. Inter-species as well as intra-plant variation in carbon isotope differences and of decay resistance between cellulose and lignin have to be taken into account.