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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。
Aiming at the genesis mechanism of the worldwide oceanic hypoxia event, taking the oil formation of the Songshu Formation in the Shuanghu area of the Qiangtang basin in northern Tibet as an example, this paper discusses the global Jurassic early according to the field geological observation and indoor organic geochemical analysis Toarcian anoxic event. Organic geochemical analysis showed that the TOC ranged from 0.34% to 15.28% with an average of 6.85%. The δ ~ (13) C_ (org) value of kerogen ranged from -22.9 ‰ to -27.2 ‰, with an average of Value of -24.77 ‰, δ ~ (13) C_ (org) value of two negative offset folder a positive offset, the maximum offset of 4.2 ‰, this offset mode indicates that the measured profile is a rare domestic More complete Toarcian profile. The atomic ratio of n (C) / n (N) varied from 27.06 to 67.42, while the kerogen was dominated by type Ⅱ. The carbon number distribution of n-alkanes was between C_ (13) -C_ (35_) (16_ or n C_ (17_), the OEP average is 0.97, the average CPI of carbon is 1.02, and the distribution of TAR_ (HC) is 0.13 ~ 0.79. The source of organic matter is dominated by algae and the terrestrial plants are continuously input. (13) The values of C_ (org), n (C) / n (N) and TAR_ (HC) showed the same trend. The analysis of Toarcian hypoxia in Shuanghu area of Qiangtang basin in northern Tibet was controlled by the change of organic matter composition.