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STRUCTURAL VARIATION AND PROVENANCE OF SULFUR-RICH ORGANIC MATTER IN NÖRDLINGEN POST-IMPACT SEDIMENTS

Summary The Nordlinger Ries crater in southern Germany was formed by a meteorite impact 14.6±0.2 Ma ago and contains a sequence of Miocene post-impact lacustrine sediments. A suite of bulk rock and kerogen samples from exploration well Nordlingen-1973 (18–260 m depth) has been analysed in terms of bulk geochemical composition, organic petrology, online Curie Point-pyrolysis gas chromatography-mass spectrometry and attenuated total reflectance Fourier-transform infrared spectroscopy for getting insights into the chemical composition and structural evolution of the kerogen up the sedimentary sequence in relation to sources for organic matter. The results show that hydrogen- and sulphur-rich kerogen prevails in the post-impact sediments, having abundant aliphatic and thiophenic constituents, which is proved by high H/C (1.6 on average), intensive aliphatic CH stretching vibration bands at 2700–3000 cm-1 in ATR FT-IR spectra, abundant aliphatic and thiophenic pyrolyzates. The OM mainly originates from algal and microbial material as suggested by prominent n-alkane/-alkene doublets and iso-alkanes. Type III kerogen occurs in the uppermost unit, containing more aromatic and phenolic constituents with abundant phenolic and aromatic pyrolyzates, in which OM is partly of higher land plant origin with ample vitrinite and inertinite particles.