Sedimentology, organic geochemistry, and petroleum potential of Jurassic coal measures: Tarim, Junggar, and Turpan Basins, Northwest China
- Stanford Univ., CA (United States)
- Univ. of Indiana, Bloomington, IN (United States)
- Exxon Production Research Co., Houston, TX (United States); and others
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 transacts 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 C{sub 29} 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. Pyrolysis-gas chromatography of selected Jurassic samples suggests that they possess potential for liquid hydrocarbon generation. Expulsion of C{sub 15+}, hydrocarbons from Jurassic source rocks appears likely, despite the traditional view that bituminous coals are incapable of expelling long-chain hydrocarbons.
- OSTI ID:
- 90870
- Journal Information:
- AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 7 Vol. 79; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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