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Oil reservoirs have been discovered in the Mesoproterozoic strata in the Liaoxi Depression, NE China. In order to determine the source of oil shows of the Mesoproterozoic Gaoyuzhuang Formation and their organic geochemical characteristics, eight source rocks and reservoir cores from the Mesoproterozoic Gaoyuzhuang Formation and four source rocks from the overlying Middle Jurassic Haifanggou Formation were geochemically analysed. The distribution patterns of normal alkanes, acyclic isoprenoids, hopanes, steranes and triaromatic steroids of the Mesoproterozoic hydrocarbons from Well N-1 are consistent with those of source rock extracts from the Mesoproterozoic Gaoyuzhuang Formation in the Well L-1. The molecular marker compositions of source rock extracts from the overlying Middle Jurassic Haifanggou Formation are distinctively different from those of the Mesoproterozoic hydrocarbons. The results suggest that the Mesoproterozoic source rocks have significant petroleum generation potential. The Mesoproterozoic paleo-reservoir may be prospecting exploration targets in the Liaoxi Depression, NE China.

In this study, the Linxia Basin, northeastern margin of Qinghai Tibet Plateau, China was taking as an example to study the relationship of branched chain alkanes and climate change. In which, the pseudohomologous series of odd carbon numbered 5,5-diethylalkanes (series A), C21-C37 5-butyl, 5-ethyl-alkanes (series C), and even carbon numbered C20-C26 6,6-diethylalkanes (series B) associated with a biosynthetic origin in Middle Miocene to Early Pliocene (13-4.3 Ma) lacustrine sediments (Maogou section) in the Linxia Basin were identified using gas chromatography-mass spectrometry. Each series displays strong odd or even carbon number preferences, which clearly indicates a possible source organisms of prokaryotes that favour environments under warm and wet climate conditions. Thus, the molecular distributions of BAQCs exhibit good agreement with the temporal distributions of climate. By comparing the distribution patterns of branched alkanes in 20 samples, it was found that the low A23-27/(nC22+nC24+nC26) ratios, B20-26/(nC19+nC21+nC23+nC25) ratios, and C23-27/(nC22+nC24+nC26) ratios at -10.77 Ma, -8.72 Ma, -7.17 Ma, and -6.45 Ma indicated a dry climate. At -9.42 Ma, -7.87 Ma, -6.92 Ma, and -6.27 Ma, the high A23-27/(nC22+nC24+nC26) ratios, B20-26/(nC19+nC21+nC23+nC25) ratios, and C23-27/(nC22+nC24+nC26) ratios indicated a wet climate. [ABSTRACT FROM AUTHOR]

Oil shales from the Yamalikeshan (YML), Shuimogou (SMG) and Sangonghe (SGH) sections of the Lucaogou Formation in the southeastern Junggar Basin, Northwest China are rich in organic matter and have high hydro­carbon generation potential, as shown by bulk Rock-Eval and chloro­form extract analyses. The contrast in organic composition between the oil shales implies that Sangonghe is the richest hydrocarbon source rock section in the studied area in the Junggar Basin. The distribution of biomarkers and organic carbon isotope parameters indicate that oil shales of the Lucaogou Formation were deposited in a cool and humid paleoclimate and that some layers were partly subjected to microbial modification. In addition, the Sangonghe oil shale suggested a strongly reducing depositional environment, deeper and higher-salinity lake waters and a higher input of lower aquatic organisms compared with oil shales of the other two sections. Therefore we conclude that brackish reducing deep lakes were favourable for the develop­ment of petroleum source rocks. Ketones and aldehydes were identified in two Yamalikeshan oil shale samples, while ketones and fatty acid methyl esters (FAMEs) were found in the other two samples from the same section. In none of the samples the co-existence of all three compounds was established. The unique occurrence of aldehydes and fatty acid methyl esters may imply the varying depositional environment of the Yamalikeshan section. [ABSTRACT FROM AUTHOR]