Sedimentology, organic geochemistry, and petroleum potential of Jurassic Coal Measures; Tarim, Junggar, and Turpan basins, Northwest China

Source rock characterization of organic-rich shales interbedded in coal measures, as they outcrop at basin edges, shows dominance of type-III, terrestrial, higher-plant kerogen with oil-generation potential. Microscopic analysis shows that the kerogen macerals are vitrinite, exinite and inertinite except for a minor number of samples that contain amorphous macerals. Vitrinite reflectance, Ro, is generally in the oil window between 0.5 and 0.75, but the amorphous macerals sample is in the gas window at Ro 1.8. Rock-Eval parameters also show oil potential with hydrogen indices of 100-300 and oxygen indices generally < 10. Elemental H/C and O/C ratios are 0.4-0.9 and 0.05-0.6, respectively. Molecular fingerprints of extracts show some weak odd-over-even normal-alkane distributions, high pristane/phytane and high hopane/sterane ratios. Dominance of C29 sterane homologues, local abundance of diterperoid compounts, and low abundance of tricyclic terpanes. These extract characteristics correlate with four oils produced from these basins, but detailed biomarker differences suggest that the oil's source may be basinward lacustrine equivalents.