CHARACTERIZATION OF ORGANIC-MATTER IN LATE CRETACEOUS BLACK SHALES OFTHE EASTERN ALPS (KAINACH GOSAU GROUP, AUSTRIA)

Bituminous marls occur at the base of the late Cretaceous Kainach Gosa u Basin, Eastern Alps. They interfinger with local coaly layers, and a re overlain by a turbiditic sequence. Forty outcrop samples with diffe rent lithologies were studied by Rock-Eval pyrolysis. Seven bituminous marls, one coaly sample, two siltstones from the turbiditic sequence and solid bitumen from the Paleozoic basement have been characterized in detail by organic geochemical and petrographic techniques. The orga nic matter from bituminous marls can be subdivided into allochthonous, terrigenous material (mainly recycled vitrinite), which is present in all samples in similar amounts, and autochthonous hydrogen-rich organ ic matter (alginite, liptodetrinite), which is most probably of lacust rine origin. Organic richness varies from 0.4 to 2.3% TOC. The amount of the autochthonous organic matter is controlled primarily by differe nt oxygen concentrations. Sedimentological (lack of bioturbation) and geochemical data (e.g. pristane/phytane ratios, homohopane indices, C- 30()/C-29 Ts ratios, distribution of phenol and alkylphenols in the p yrolyzate) suggest that the water column above the sediment surface wa s suboxic to dysoxic, but probably not anoxic. High energy events were responsible for short periods with enriched oxygen in the water colum n. The organic matter in the resulting sediments is of a residual type . Drift wood was transported from the nearby shore into the lake. Pale ontological evidence proves a temporary marine influence. Vitrinite re flectance and T-max indicate maturation levels ranging from the beginn ing to the peak stage of oil generation. Despite the fact that some hy drocarbons have already been generated, HI values of kerogens of bitum inous marls reach 605 mg HC/g TOC. Most analysed bituminous marls prod uce a high wax paraffinic oil during maturation and are good sources f or oil. Pyrolysis-gas chromatography and biomarker data indicate that changing wax contents of oils generated from bituminous marls might be a function of different oxygen concentrations in the water column. Co aly samples have a very good gas potential.