羌塘盆地胜利河油页岩有机地球化学特征及意义

通过对藏北羌塘盆地胜利河地区2008年新发现的油页岩剖面进行系统采样和GC—MS分析，结果显示该地区油页岩具有较高C29ααα20S/ααα(20S+20R)（0.38~0.44）、C29αββ/(ααα+αββ)（0.37~0.47）和C3122S/(22S+22R)（0.52~0.59）比值，表明其有机质已进入生油阶段。分析的油页岩样品具有较高的C27甾烷含量（32.82%~43.6%）和较高4 甲基甾烷/规则甾烷（0.04~0.22）、甾/藿（0.80~1.04）比值，显示浮游植物为主的生物母源对油页岩的贡献。此外，油页岩具有较高的γ 蜡烷指数（0.34~0.50）、C35升藿烷指数（0.076~0.102）和较低的Pr/Ph比值（0.32~0.49），表明胜利河地区油页岩沉积期水体处于相对闭塞还原和盐度较高的沉积环境。

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

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.