Geochemistry and Significance of Oil Seepages in the Zaring Area of the  Southern Qiangtang Depression, Northern Tibet

Key words: 
• biomarkers /
• carbon isotopic composition of individual nalkanes /
• oil/source correlation /
• southern Qaingtang depression

Abstract: Located on the southern margin of the southern Qaingtang depression, the Zaring area is a “gap area” for hydrocarbon investigation. Detailed reconnaissance of 1∶〖KG-*2〗50,000 petroleum geological structures was carried out in the Zaring block of the Qaingtang Basin, and according to the reconnaissance results the authors analyze biomarkers and molecular carbon isotopic composition of oil seepages in this area, and the oil/source correlation was also discussed in this paper. The data indicate that the oilforming matrixes are algae and higher plants, especially with an important contribution of algae to the formation. The crude oils were formed under weak reductionreduction and salt water environment. The crude oils are mature. The biomarkers of crude oils are closely correlated to those of the Xiali Formation hydrocarbon source rocks, reflecting that crude oils were mainly originated from the Xiali Formation. However, compound specific Cisotope composition exists some differences between crude oils and Xiali Formation hydrocarbon source rocks, indicating a mixture of sources.