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Geochemical and organic petrological characterization of the organic matter of lacustrine Eocene oil shales (Prinz von Hessen,Germany): reconstruction of the depositional environment
Authors:Email author" target="_blank">Peter?HofmannEmail author  Martina?Duckensell  Arkadi?Chpitsglous  Lorenz?Schwark
Institution:(1) Department of Geology, University of Cologne, Zülpicher Str. 49a, 50674 Cologne, Germany
Abstract:Optical and geochemical techniques were applied to sedimentary organic matter from the profundal area of the Eocene Lake Prinz von Hessen, which formed in a pull-apart basin on the Sprendlinger Horst, near Darmstadt, Germany. Variations in total sulphur content (S tot) and total organic carbon content (TOC), hydrogen index (HI), oxygen index (OI) and delta13C values of the organic matter were used to reconstruct the lakersquos filling history. Following an initial rapid deepening phase, open lake conditions developed with HI reaching more than 500 mg HC/g TOC and TOC values up to 40%. The productivity of the lake was probably high and organic matter preservation was enhanced by a stratified water column. As the lake began to fill with sediment and became shallower, TOC and HI values declined, as the lake water was better oxygenated and preservation conditions declined. delta13C values between –31 and –27permil are controlled by the mixing of aquatic (algae and microbial mats) and terrigenous organic matter (wood, spores, pollen and cuticles). Following a rapid drop in lake level, shallow lake conditions alternated with swamp deposits (lignites) in the basin center. The organic matter preserved during this stage is strictly terrigenous in nature and experienced oxic degradation (HI sim 100 mg HC/g TOC). delta13C values between –26 and –24permil are typical for Eocene terrigenous matter. The inferred lake level fluctuations are interpreted to have been controlled by tectonic as well as climatic processes.
Keywords:Eocene  Isotopes  Lake  Oil shale  Organic carbon  Productivity
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