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Yuan F.,CAS Guangzhou Institute of Geochemistry | Yuan F.,University of Chinese Academy of Sciences | Liao Y.,CAS Guangzhou Institute of Geochemistry | Fang Y.,CAS Guangzhou Institute of Geochemistry | And 2 more authors.
Acta Geochimica | Year: 2016

There are abundant bitumens and oil seepages stored in vugs in a Lower-Triassic Daye formation (T1d) marlite in Ni’erguan village in the Southern Guizhou Depression. However, the source of those oil seepages has not been determined to date. Multiple suites of source rocks of different ages exist in the depression. Both the oil seepages and potential source rocks have undergone complicated secondary alterations, which have added to the difficulty of an oil-source correlation. For example, the main source rock, a Lower-Cambrian Niutitang Formation (Є1n) mudstone, is over mature, and other potential source rocks, both from the Permian and the Triassic, are still in the oil window. In addition, the T1d oil seepages underwent a large amount of biodegradation. To minimize the influence of biodegradation and thermal maturation, special methods were employed in this oil-source correlation study. These methods included catalytic hydropyrolysis, to release covalently bound biomarkers from the over mature kerogen of Є1n mudstone, sequential extraction, to obtain chloroform bitumen A and chloroform bitumen C from the T1d marlite, and anhydrous pyrolysis, to release pyrolysates from the kerogen of T1d marlite. Using the methods above, the biomarkers and n-alkanes released from the oil samples and source rocks were analysed by GC–MS and GC-C-IRMS. The oil-source correlation indicated that the T1d oil seepage primarily originated from the Є1n mudstone and was partially mixed with oil generated from the T1d marlite. Furthermore, the seepage also demonstrated that the above methods were effective for the complicated oil-source correlation in the Southern Guizhou Depression. © 2015, Science Press, Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg.

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