Facies and rank of the Permian Kupferschiefer from the lower Rhine basin and NW Germany

Abstract

The Kupferschiefer of the Lower Rhine Basin and of NW Germany is a typical black shale containing C org values between 0.5 and 9.1%. On average it contains 4% C org. In coal petrographic terms the organic matter of the Kupferschiefer is characterized by well preserved liptinite as sporinite - especially derived from the pollen grains of conifers - in the area of the Lower Rhine Basin and as alginite towards the centre of the Kupferschiefer sea. The high content of bituminite in all of the samples shows that the main source of organic matter is derived from plancton and bacteria. Vitrinite and inertinite are rare. The rank of the organic matter in the sediment varies between the lignite stage (Lower Rhine Basin) and the bituminous coal stage (NW Germany). Geochemical investigations have shown that residual heat from the Krefeld High was active until the lower Zechstein. This has caused a change in the chemical composition of the organic matter but did not express itself in the optical parameters. Inhomogeneities of the organic matter in low-rank and bituminization in higher-rank materials influence the vitrinite reflectance. Fluorescence measurements are more sensitive in sapropelic sediments and oil shales than vitrinite reflectance. It is evident that the red/green ration is more reliable in view of diagenesis studies than the lambda max of the fluorescence spectra. Geochemical parameters are partly much more sensitive towards thermal stress as compared to vitrinite reflectance, e.g. metalloporphyrin concentrations decrease with increasing temperatures. The parameter covers a temperature range from ca. 40°C to 80°C. The weighted average mass of the vanadyl-cycloalkano-porphyrins is suitable to characterize the influence of temperature on the Kupferschiefer between ca. 40°C and 150°C. Summing up, the Kupferschiefer of the Lower Rhine Basin in NW Germany is a sidiment very well suited for parallel petrographic and organic-geochemical research. The results of this might be also of interest in the field of oil prospecting.