Palaeoenvironment of the Eocene Eckfeld Maar lake (Germany): implications from geochemical analysis of the oil shale sequence

Drill core samples from the depth interval between 19.4 and 32.0m of the laminated central lake facies of the Eocene Eckfeld Maar were investigated for biomarker and stable isotope composition. Bulk organic geochemical parameters (C/N, HI) and the molecular composition of the soluble organic matter indicate a dominance of particulate organic matter from land plants and microbially derived lipids in the lower part of the sedimentary succession. An angiosperm-dominated vegetation is indicated from the terpenoid biomarker composition. Abundant 4-methylsteroids in the 25.6–30.8m section of the oil shale sequence reflect a contribution of algal-derived biomass. Samples with high concentrations of methylsteroids are characterized by low amounts of triterpenoids related to the arborane skeleton, and vice versa. This pattern is interpreted as reflecting differences in autochthonous organic matter production vs. microbial activity.