COMPOUND-SPECIFIC HYDROGEN ISOTOPES OF BIOMARKERS AS PALEOCLIMATIC, PALEOENVIRONMENTAL AND BIOSYNTHETIC PROXY IN LATE PALEOZOIC SEDIMENTS

The primary hydrogen isotope ratio (D/H) of source water is established by the regional and global climatic conditions. In different climatic regions, temperature-dependent processes during evaporation and precipitation modify the D/H of the source water. Reconstruction of former climate conditions can be based on D/H of hydrocarbons in the organic biomass of recent sediments. However, changes in D/H that occur during the transformations of organic hydrogen in hydrocarbons during maturation of the sediments are not well known and may impede the use of hydrogen isotope ratios as a proxy for paleoclimate and paleoenvironment.

Here we demonstrate for the first time that the D/H values of alkanes and acyclic isoprenoids from two sediment sections (Posidonienschiefer, Early Toarcian; Kupferschiefer, Early Zechstein) positively correlate with maturation indices. Additionally, the absence of fractionation of D/H between normal alkanes and acyclic isoprenoids in mature sediments can be explained by the larger D-enrichments of initially lighter acyclic isoprenoids during sustained maturation. These results enable D/H values from biomarkers from sediments of known maturity to be corrected back to their initial values, allowing them to be used for to make climatic and biosynthetic reconstructions at the time of sedimentations.

D/H of alkanes are used here for the first time to reconstruct paleoclimatic and paleoenvironmental conditions in the Permo-Carboniferous icehouse and in the intermittent warming phases during the Stephanian conditions which controlled biomass sedimentation in tropical European paleolakes from the Late Carboniferous to the Early Permian.