Lower and Middle Jurassic coal-bearing strata occur widely throughout central Asia and are well developed in northwestern China, where their thicknesses in the southern Junggar, northern Tarim, and Turpan basins exceed 2500, 2300, and 1500 m, respectively. Examination of these strata along 13 transects across basin margin outcrop belts indicates that they are entirely nonmarine meandering fluvial deposits with local development of braided fluvial and lacustrine deltaic facies. Chinese subsurface data suggest that regional Jurassic lacustrine facies are present down depositional dip, consistent with predictions from global circulation modeling of Early and Middle Jurassic monsoonal precipitation.

Laboratory analyses of coals and organic-rich shales show a dominance of terrestrial, higher plant components. Visual kerogen analysis indicates that vitrinite, inertinite, and exinite are the dominant macerals, and elemental analysis characterizes most kerogens as type III. Rock-Eval analyses yield moderate hydrogen index values (50-300) and very low oxygen index values (<20). Jurassic source rock extracts are characterized by odd-over-even normal alkane distributions, high pristane/phytane and high hopane/sterane ratios, dominance of C29 sterane homologs, local abundance of diterpenoid compounds, and low abundance of tricyclic terpanes.

Geochemical correlation with four petroleums from the Junggar, Tarim, and Turpan basins strongly suggests that the Jurassic coaly deposits and their lacustrine equivalents downdip are petroleum source rocks. Sterane and hopane distributions of petroleums and extracts of their putative Jurassic source rock are similar and can be easily distinguished from published distributions of these compounds in other source rock layers. Additional correlation parameters include high pristane/phytane; low abundance or lack of tricyclic terpanes, but similar distributions where present; and lack of gammacerane (with one exception) and carotanes, compounds that characterize Permian and Ordovician source rocks and their respective petroleums. Pyrolysis-gas chromatography of selected Jurassic samples suggests that they possess potential for liquid hydrocarbon generation. Expulsion of C15+ hydrocarbons from Jurassic source rocks appears likely, despite the traditional view that bituminous coals are incapable of expelling long-chain hydrocarbons.

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