藏北羌塘盆地双湖地区下侏罗统油页岩的有机碳同位素异常和正构烷烃分布特征及大洋缺氧事件研究  

The Distribution of N-alkanes and Anomalies of Organic Carbon Isotopes and the Toarcian Oceanic Anoxic Events of the Lower Jurassic Oil Shales in Qiangtang Basin, North Tibet, China

作　　者：伊帆[1] 朱利东[2] 刘显凡[1] 伊海生[2,3] 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]成都理工大学沉积地质研究院,四川成都610059 [3]成都理工大学油气藏地质及开发工程国家重点实验室,四川成都610059

出　　处：《矿物学报》2016年第3期413-422,共10页Acta Mineralogica Sinica

摘　　要：针对世界性的大洋缺氧事件的成因机制问题,以藏北羌塘盆地双湖地区曲色组油页岩为例,根据野外地质观察与室内有机地球化学分析,探讨全球性的侏罗纪早Toarcian缺氧事件。有机地球化学分析表明,样品有机碳(TOC)变化范围为0.34%~15.28%,平均为6.85%,干酪根δ^(13)C_(org)值变化范围为-22.9‰^-27.2‰,平均值为-24.77‰,δ^(13)C_(org)值发生2次负偏移夹一次正偏移,最大偏移量达4.2‰,这种偏移模式指示所测剖面是一个国内罕见的较完整的Toarcian剖面。n(C)/n(N)原子比变化范围27.06~67.42,干酪根以Ⅱ型为主,正构烷烃碳数分布范围C_(13)-C_(35_之间,主峰碳多为n C_(16_或n C_(17_,OEP平均为0.97,碳优势指数CPI平均为1.02,TAR_(HC)值分布在0.13~0.79,有机质来源以藻类占优势,陆源植物持续输入,地层剖面上δ^(13)C_(org)值、n(C)/n(N)以及TAR_(HC)的变化趋势一致,分析认为藏北羌塘盆地双湖地区Toarcian缺氧事件受有机质组分变化控制。Mechanism of the global oceanic anoxic event has always been a controversial problem. This paper focus on the causation of the early Toarcian oceanic anoxic event in Shuanghu area of Qiangtang basin, northern Tibet, China, by organic chemistry analysis of the oil shales and geological observation. The result of organic chemistry analysis shows that TOC are0.34%-15.28% with an average of 6.85%. The δ^（13）C_（org） of kerogen fluctuates from-22.9‰--27.2‰ with an average of-24.77‰. The carbon isotope curve shows two positive excursions and one negative with the maximum excursion of 4.2‰, which is a rare and complete Toarcian section in China. The C/N atomic ratio fluctuates from 27.06-67.42, and the kerogen is mainly typeⅡ. The n-alkanes are characterized by the main peaks with the n C_（16_ or n C_（17_, with the carbon numbers of C_（13_-C_（35_, the OEP of an average of 0.97, and CPI of an average of 1.02. In addition, the TAR_（HC） fluctuates from 0.13 to 0.79, which indicates that the source of the organic matter is mainly algae with continuous terrestrial plants. The curve of C/N ratio and TAR_（HC） is consistent with that of the δ^（13）C_（org） of kerogen values. On the basis of organic geochemistry and according to the characters of the stratigraphic profile, it is suggested that the carbon isotope excursion is caused by the change of organic components in Shuanghu area of Qiangtang Basin, northern Tibet, China.

关 键 词：油页岩 Toarcian缺氧事件 有机碳同位素 正构烷烃 羌塘盆地 

分 类 号：P593[天文地球—地球化学] P597[天文地球—地质学]