羌塘盆地昂达尔错地区油苗生物标志化合物特征及其指示意义

The oil seepages in theAngdar Lake area, Qiangtang Basin:The biomarkers and their indicative implications

关键词:  羌塘盆地  昂达尔错油苗  生物标志物  沉积环境  成熟度

Key words:  Qiangtang Basin  Angdar Lake  oil seepages  sedimentary environment  maturity

摘要:

本文以油苗抽提物的饱和烃色谱-质谱分析为基础,剖析了羌塘盆地昂达尔错地区油苗的生物标志化合物特征,探讨了其沉积环境和成熟度指示意义。昂达尔错油苗含有丰富的正构烷烃、类异戊二烯烃、萜类化合物和甾类化合物。正构烷烃轻烃组分含量较高,无明显的奇偶优势。Pr/Ph比小于1,显示一定的植烷优势。萜类化合物中五环三萜烷相对含量最高,四环萜烷含量最少,并有一定的伽马蜡烷和升藿烷分布。规则甾烷相对含量为C₂₇ > C₂₉ > C₂₈,呈不对称"V"字形分布,异构化成熟度参数值较高,且4-甲基甾烷化合物普遍存在。昂达尔错油苗母源岩沉积于具有较高盐度的还原环境,以藻类、菌类等海相有机质输入为主,油苗有机质处于成熟阶段。

Abstract:

Based on the analysis of chromatograms-mass spectrograms for the saturated hydrocarbons in the oil seepages extracts, the present paper deals with the biomarkers and their indicative implications for the sedimentary environments and maturity of the oil seepages in the Angdar Lake area, Qiangtang Basin. The results of research show that abundant biomarkers including n-alkanes, isoprenoids, terpanes and steranes are detected in the oil seepages in the Angdar Lake area. The n-alkanes show higher contents of light hydrocarbon components with no remarked odd-even predominance. The Pr/Ph ratios are less than 1, showing the phytane predominance. The terpanes have the highest contents of pentacyclic traterpane, and lowest contents of tetracyclic terpane. The gammacerane and homohopane occur in a certain amount in the oil seepages. The steranes have the relative contents of C₂₇ > C₂₉ > C₂₈, and show an asymmetric V-shaped distribution. The maturity parameters of steranes isomerization have higher values, and 4-methylsteranes are also detected. The source rocks of the oil seepages in the Angdar Lake area are interpreted to be deposited in reducing environments with higher salinity and abundant marine organic matter including algae and funguses. At present, the organic matter in the oil seepages is now in the mature stages.