COMBINED ISOTOPIC AND BIOMARKER INVESTIGATIONS OF TEMPERATURE-DEPENDENT AND FACIES-DEPENDENT VARIATIONS IN THE KUPFERSCHIEFER OF THE LOWER RHINE BASIN, NORTHWESTERN GERMANY

Organic material in selected Kupferschiefer samples from the Lower Rhine Basin of NW Germany has been studied using gas chromatography (GC), coupled gas chromatography-mass spectrometry (GC-MS) as well as C- and H-isotopic analyses of the organic matter. O- and C-isotope compositions of carbonates have also been investigated. The study area is located at the southwest shore of the ancient Zechstein ocean. The Permian Kupferschiefer was deposited here under anoxic, lagoonal conditions. Five closely-sampled profiles were analysed, covering a total depth range of 350-760 m in order to detect temperature-sensitive variations and compositional changes during Kupferschiefer deposition. Variations in isotopic and molecular compositions of organic material, as well as in calcite deltaC-13, within the Kupferschiefer section in proximity of the basic intrusion that forms the Krefeld High are the result of post-sedimentary thermal degradation of organic matter. Variations in the deltaO-18-values of carbonates are governed primarily by the mineralogical composition (CaO/MgO ratios). Outside this area the isotopic data point toward a slightly increasing salinity of the seawater during Kupferschiefer sedimentation. An input of terrigenous organic matter is indicated by the occurrence of the ring-A-degraded pentacyclic triterpenoid, des-A-arborene. The compound is thought to be generated from the related pentacyclic precursor by anaerobic bacteria. The significant decrease of the compound towards the top of the Kupferschiefer correlates with decreasing anoxic conditions during Kupferschiefer sedimentation.