Biomarker and carbon isotope variation in coal and fossil wood of central Europe through the Cenozoic

Biomarker and carbon isotope systematic in coal and fossil wood are expected to provide valuable information for the reconstruction of floral assemblages and paleoenvironmental changes during the Cenozoic. Carbon isotope analyses of terrigenous organic matter have been used to reconstruct changes in the isotopic composition of upper ocean and atmospheric carbon reservoirs. Carbon isotope values of cellulose from tree-rings and fossil wood have also been related to climatic change via water-use efficiency of land plants.
Coal, resinites, woody macrofossils, and extracted cellulose obtained from lignite deposits of Central Europe covering the time interval from Early Eocene to Pliocene were investigated.. The concentration of diterpenoid hydrocarbons, characteristic for gymnosperms, relative to the sum of land plant-derived terpenoid biomarkers (diterpenoids plus triterpenoid hydrocarbons, the latter typical for angiosperms) are used as proxies for the contribution of gymnosperms versus angiosperms to peat formation. Bulk organic matter of coal and coaly sediments is influenced by varying contributions of angiosperms and gymnosperms, by different isotopic composition of land plant tissue (e.g. leafs, wood, bark), as well as by microbial activity. The ratios of terpenoid biomarkers indicate the predominance of angiosperms in the peat-forming vegetation during Eocene and Early Ologocene, whereas Late Oligocene to Pliocene coals are derived from gymnosperm-dominated (i.e. coniferous) sources. The results are in general agreement with paleobotanical records and demonstrate the potential of biomarker analyses in paleoecological studies.
The δ¹³C variations found in resinites, fossil wood and wood cellulose support their capability to trace paleoenvironmental conditions. In contrast to fossil wood, δ¹³C values of cellulose from woody macrofossils are only negligible influenced during decomposition. The carbon isotope analyses demonstrate isotopic trends of land plants parallel to the marine record during the Tertiary. Co-variations of δ¹³C of coals, fossil wood from gymnosperms, and wood cellulose with climatic changes (i.e. mean annual temperature, mean annual precipitation) reconstructed from paleobotanical data from eastern Germany are noticed. We propose that the observed patterns were primarily produced by variations of the isotope ratios of oceanic and atmospheric carbon reservoirs, and additionally modified by climatic changes due to their influence on plant physiology. Thus, the terrestrial carbon isotope record indicates changing δ¹³C values of atmospheric CO₂ associated with atmospheric pCO₂ and paleoclimate.