Evaluation of source, environments of deposition and diagenesis of some israeli “oil shales” — N-Alkanes, fatty acids, tetrapyrroles and kerogen

Abstract

The distribution of n-alkanes and fatty acids, the composition of the kerogen and the content of tetrapyrrole pigments of the bituminous chalks of the Campanian—Maastrichtian Ghareb Formation in Israel differ in the Horon, Nebi Musa, Ef'e and Ein Boqeq basins. The degree of diagenesis is sufficiently low to permit identification of terrestrial and marine-derived organic matter. n-Alkane distribution patterns, both of those extractable from the total sample and of those associated with either carbonate or silicate minerals, differ considerably in various samples. These differences are attributed to the source and are compatible with conclusions based on carbon-isotope composition. These may be used to retrace the sedimentation processes of detrital and autochthonous minerals and of the organic matter. The range of tetrapyrrole pigments — chlorins, porphyrins of DPEP etio- and rhodo-type series and bile pigments — reflects a variety of chlorophyll precursors, which underwent degradation reactions under mild reducing conditions. The occurrence of p and e chlorins and etio porphyrins suggests a degradation series alternative to that of DPEP conversion to etio. The ratio of Ni and VO porphyrins shows a regional pattern which corresponds to that of the Ni/V ratio in the respective kerogens, but is independent of the Ni and V concentrations in the mineral fractions, indicating a relation between Ni and V complexation in tetrapyrrole pigments and kerogen.