Jürgen Rullkötter

Geochemistry and Petrography of Organic Matter in Northwest African Continental Margin Sediments: Quantity, Provenance, Depositional Environment and Temperature History

This report synthesises the results of organic geochemical and organic petrographic analyses of sediments fron deep sea drilling sites on the Northwest African continental nargin. The investigation of the quantity, type, and composition of the organic matter and of the depositional environment leads to the recognition of a number of organofacies. Based on the organofacies, the sediments can be classified according to their differing hydrocarbon potentials, although the organic matter in all the sediments encountered has been determined to be iirmature, the onset of thermal hydrocarbon generation having not been reached at present burial depths.

A synthesis of organic petrographic and geochemical results from DSDP sites in the eastern central North Atlantic

Abstract A synthesis of organic analyses of deep sea drilling sites off Western Sahara, Morocco and Northern Iberia (Sites 397, 415/416 and 398) is attempted. Paleogeography and lithology are related to organic carbon contents, carbon normalized extract values, normal and branched/cyclic alkane distributions, odd/even carbon preference indices (CPI), pristane/phytane and sterane/triterpane relative abundances, hydrogen/carbon atomic ratios, stable carbon isotope compositions, and the kerogen type determined by microscopy. In the Tertiary at Site 397, allochthonous deposits orginally accumulated within a midwater oxygen minimum layer are contrasted with contiguous hemi-pelagic sediments. Higher and fluctuating organic carbon contents, bimodal n -alkane distributions, a dominance of steroidal hydrocarbons, and mixed terrestrial and aquatic liptinites in the former, and well rounded, fine vitrinite/inertinite-dominated kerogens in the latter characterize these 2 organofacies. Terrigenous organic matter dominates the Lower Cretaceous shales. The origin of these laminated (nonbioturbated) organic rich mudstones is ascribed to an oxygen deficit generated by the influx of major quantities of terrestrial plant debris from Wealden deltas and its subsequent (partial) oxidation. This oxygen deficit mechanism for black shale formations is identified by reinterpreting abnormally broad and multimodal vitrinite reflectance histograms as representing the remnants of oxidation. A ratio of altered to unaltered vitrinite particles at Site 398 is a measure of the degree of oxidation, and may be related to distance of transport or availability of oxygen during transport. Broad multimodal spreads in histograms of vitrinite reflectance values are the key character of this organofacies, though extract yields, H/C ratios and CPIs also seem to be influenced.

Oil-oil and oil-condensate correlation by low eV GC-MS measurements of aromatic hydrocarbons

Abstract Molecular ion distributions obtained by low voltage GC-MS measurements of aromatic hydrocarbon fractions are used for oil-oil and oil-condensate correlation in cases where the concentration of tetra- and pentacyclic biological marker compounds in the saturated hydrocarbon fractions is insufficient (e.g. most condensates, old and very mature oils). Correlation is performed by comparing distribution curves of homologous molecular ion series or, for large sample numbers in regional basin studies, by cluster analysis of up to 70 most significant molecular ions. Examples show that positive correlations can be achieved, even where there is a large vertical separation of genetically related hydrocarbons. Furthermore, it is demonstrated that the method can be applied, with some limitations, to biodegraded oils.