EXTRACTABLE AROMATIC-HYDROCARBONS IN A SHORT-TERM ORGANIC-CYCLE OF THE KIMMERIDGE CLAY FORMATION, YORKSHIRE (UK) - RELATIONSHIP TO PRIMARY PRODUCTION AND THERMAL MATURITY

Seven core samples from a 120 cm section of the Kimmeridge Clay format ion, Cleveland Basin, north-eastern England, comprising a short-term o rganic cycle were analyzed for extractable aromatic compounds. Yields and ring-class distributions of C-11+ aromatic hydrocarbon plus C-9+ a romatic sulphur compound fractions were determined by liquid chromatog raphy while distributions of benzohopanes, C-2-C-3 naphthalenes, C-0-C -2 phenanthrenes, C-1-C-3 benzo[b]thiophenes, and C-0-C-2 dibenzothiop henes were quantified by capillary gas chromatography. Early thermal e volution of the organic matter, corresponding to the top of the oil-ge neration window, was inferred from aromatic parameters (Methylphenanth rene index, methyldibenzothiophene ratio). It was verified by yields o f total methylphenanthrenes, C-1-C-3 benzo[b]thiophenes, and C-0-C-2 d ibenzothiophenes in the 30-40 mu g/g total organic carbon (TOC) range comparable to those in the Posidonia Shale (Toarcian) formation, weste rn Germany, at 0.5% vitrinite reflectance (R(r)). Variations in total aromatics yields are paralleled by TOC and Hydrogen Index variations w ith depth thus suggesting an origin of aromatics mostly from algal mat erial. Enhanced contributions of biological source materials other tha n algae to the sediments are indicated by elevated yields of benzohopa nes (C-32-C-35), alkylnaphthalenes, and alkylbenzo[b]thiophenes at the edges of the section investigated.