YI Fan1, ZHU LI-dong2*, LIU Xian-fan1, YI Hai-sheng2,3
(1. Institute of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China;
2. State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation, Chengdu 610059, China)
Abstract：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 δ13Corg 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 nC16 or nC17, with the carbon numbers of C13-C35, the OEP of an average of 0.97, and CPI of an average of 1.02. In addition, the TARHC 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 TARHC is consistent with that of the δ13Corg 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.
Keywords：oil shale; early Toarcian oceanic anoxic event;organic carbon isotope; n-alkanes; Qiangtang Basin
E-mail：zhuld33@gmail.com
ACTA MINERALOGICA SINICA Vol. 36, No. 3, 2016, Page 413-422
