地质学报（英文版）2005，Vol.79Issue(3)：392-397,6.
Organic Geochemistry of the Early Jurassic Oil Shale from the Shuanghu Area in Northern Tibet and the Early Toarcian Oceanic Anoxic Event
Organic Geochemistry of the Early Jurassic Oil Shale from the Shuanghu Area in Northern Tibet and the Early Toarcian Oceanic Anoxic Event
摘要
Abstract
This paper presents new geological and geochemical data from the Shuanghu area in northern Tibet, which recorded the Early Toarcian Oceanic Anoxic Event. The stratigraphic succession in the Shuanghu area consists mostly of grey to dark-colored alternating oil shales, marls and mudstones. Ammonite beds are found at the top of the Shuanghu oil shale section, which are principally of early Toarcian age, roughly within the Harplocearasfalciferrum Zone. Therefore,the oil shale strata at Shuanghu can be correlated with early Toarcian black shales distributing extensively in the European epicontinental seas that contain the records of an Oceanic Anoxic Event. Sedimentary organic matter of laminated shale anomalously rich in organic carbon across the Shuanghu area is characterized by high organic carbon contents, ranging from 1.8 % to 26.1%. The carbon isotope curve displays the δ13C values of the kerogen (δ 13Ckerogen) fluctuating from -26.22to -23.53‰ PDB with a positive excursion close to 2.17‰, which, albeit significantly smaller, may also have been associated with other Early Toarcian Oceanic Anoxic Events (OAEs) in Europe. The organic atomic C/N ratios range between 6 and 43, and the curve of C/N ratios is consistent with that of the δ13Ckerogen values. The biological assemblage,characterized by scarcity of benthic organisms and bloom of calcareous nannofossils (coccoliths), reveals high biological productivity in the surface water and an unfavorable environment for the benthic fauna in the bottom water during the Oceanic Anoxic Event. On the basis of organic geochemistry and characteristics of the biological assemblage, this study suggests that the carbon-isotope excursion is caused by the changes of sea level and productivity, and that the black shale deposition, especially oil shales, is related to the bloom and high productivity of coccoliths.关键词
oil shales/Early Toarcian/organic carbon isotope/organic atomic C/N ratios/Oceanic Anoxic Events/northern TibetKey words
oil shales/Early Toarcian/organic carbon isotope/organic atomic C/N ratios/Oceanic Anoxic Events/northern Tibet分类
天文与地球科学引用本文复制引用
CHEN Lan,YI Haisheng,HU Ruizhong,ZHONG Hong,ZOU Yanrong..Organic Geochemistry of the Early Jurassic Oil Shale from the Shuanghu Area in Northern Tibet and the Early Toarcian Oceanic Anoxic Event[J].地质学报（英文版）,2005,79(3):392-397,6.基金项目
This study was funded by grants from the Major State Basic Research Program of the People's Republic of China (G1998040801-5), Regional Geological Reconnaissance in Ulan U1 Lake on the scale of 1:250,000 (200013000147) and is also a contribution to the State Key Laboratory of Organic Geochemistry Program of the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (OGL-9703). （G1998040801-5）
