- 期刊
The Early Jurassic Oil Shales in the Qiangtang Basin, Northern Tibet: Biomarkers and Toarcian Oceanic Anoxic Events
並列摘要
In the Qiangtang Basin, northern Tibet, the most complete and extensive marine sedimentary strata outcropped in the Shuanghu-Sewa-Amdo area during the Jurassic, especially the Early Jurassic. The organic-rich marine sediments-commonly referred to as black shales-were deposited in the Early Jurassic, therefore, many petroleum geologists have been focusing on them for many years. Although achievements in geological investigations and petroleum resource assessments during recent years have been remarkable, the environmental conditions, mechanics, and process that resulted in the deposition of high-organic sediments during the Early Toarcian (183-176.5 Ma, Early Jurassic) Oceanic Anoxic Event are still a matter of discussions. In this paper, we deal with the biomarker distributions of Lower Jurassic oil shales in the Biluo Co section, Shuanghu area of northern Tibet. The oil shales are characterized by a marked predominance of short chain nalkanes with a maxiumun at C16 or C17, nC17/nC31 ratio values between 9.4 and 17.8, and low Pr/Ph ratios. Furthermore, a series of C27 and C29-C35 hopanes with minor amounts of gammacerane are present in all samples, as indicated by gammacerane/C30-17α-hopane values from 0.06 to 0.12 and the steranes C27/C29 ratios higher than 1 in the three samples. The abovementioned parameters indicate that the organic matter source is attributed to an algal/bacterial contribution. According to maturity parameters, all the homohopane 22S/(22S+22R) values in this study are ＞ 0.58 and the sterane 20S/(20S+20R) values are all between 0.48 and 0.59, which is consistent with a higher level of thermal maturity. Widespread anoxia led to the deposition of organic-rich sediments that removed isotopically light carbon from the oceans and drove carbon-isotope ratios to higher values with a positive excursion close to 2.17 per mille. From biomarker distributions, the differences in δ^13C(subscript kerogen) are related to the difference in δ^13C of CO2 in the photic zone rather than the organic matter compositions.
延伸閱讀
- Fu, X. G., Wang, J., Zeng, Y. H., Tan, F. W., Chen, W. B., & Feng, X. L. (2010). Geochemistry of Rare Earth Elements in Marine oil Shale-A Case Study from the Bilong Co Area, Northern Tibet, China. Oil Shale, 27(3), 194-208. https://www.airitilibrary.com/Article/Detail?DocID=17367492-201009-201010290110-201010290110-194-208
- Gong, Z. (2012). Application of optical dating to late quaternary uplift and thrust activity in the northern piedmont of Tian Shan, China [doctoral dissertation, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-0511201300009009
- 林宜臻（2007）。Geochemical Constraints on the Petrogenesis of Cretaceous to Paleocene Granitoids and Volcanic Rocks from SE Tibet〔碩士論文，國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342/NTU.2007.01999
- Chan, S. L. (2006). Paleocene deep-marine sediments in southern central Tibet [master's thesis, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-1812201200013090
- MENG, Q., LIU, Z., SUN, P., XU, Y., LI, F., BAI, Y., XIE, W., DENG, S., SONG, S., WANG, K., & XU, C. (2018). CHARACTERISTICS AND ACCUMULATION OF MIDDLE JURASSIC OIL SHALE IN THE YUQIA AREA, NORTHERN QAIDAM BASIN, NORTHWEST CHINA. Oil Shale, 35(1), 1-25. https://doi.org/10.3176/oil.2018.1.01