Geochemical Characteristics and Geological Significance of Shengli River Oil Shale in Qiangtang Basin, Northern Tibet, China

Key words: 
• Qiangtang Basin

Abstract: Marine oil shale from the Shengli River oil shale section discovered in 2008 in the Qiangtang basin, northern Tibet, China, was collected systematically and analyzed by means of GCMS. The results indicate that the oil shales from Shengli River area exhibit relatively high values of C31steranes 22S/(22S+22R) \[0.38~0.44\], C29steranes αββ/(ααα+αββ) \[0.37~0.47\] and C31steranes 22S/(22S+22R) \[0.52~0.59\] ratios. These results indicate that the thermal evolutionary phase of organic matter in oil shale has reached oilgenerating window. The relatively high concentrations of C27steranes\[32.82%~43.6%\] and relatively high values of 4methyl sterane to regular sterane ratios\[0.04~0.22\], sterane to hopane ratios\[0.80~1.04\] unanimously indicate that the biological sources of organic matter in oil shale are phytoplankton and bacteria, especially with an important contribution of phytoplankton. The relatively high values of gammacerane index\[0.34~0.50\], homohopane index \[0.076~0.102\] and low pristine to phytane ratios\[0.320.49\]indicate the occlusive water environments are anoxic and relatively hypersaline in the Shengli River area during oil shale deposition.