塔里木北缘震旦纪——寒武纪转折期碳同位素漂移事件及成因机制  

Carbon isotope excursion and its genetic mechanism during the Sinian to Cambrian transition in the northern Tarim Basin

作　　者：樊奇 樊太亮[2] 李清平 张岩 谷雨 商雅欣 FAN Qi;FAN Tailiang;LI Qingping;ZHANG Yan;GU Yu;SHANG Yaxin(State Key Laboratory of Natural Gas Hydrates,CNOOC Research Institute Co.,Ltd.,Beijing 100028,China;Ministry of Education Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Enrichment Mechanism,China University of Geo-sciences(Beijing),Beijing 100083,China;North Branch of the 1st Construction Engineering Co.,Ltd.of the 3rd Bureau,CSCEC,Beijing 100097,China)

机构地区：[1]中海油研究总院有限责任公司天然气水合物国家重点实验室,北京100028 [2]中国地质大学(北京)海相储层演化与油气富集机理教育部重点实验室,北京100083 [3]中建三局第一建设工程有限责任公司北方公司,北京100097

出　　处：《地学前缘》2021年第5期436-447,共12页Earth Science Frontiers

基　　金：国家科技重大专项(2017ZX05005,2017ZX05009);国家重点研发计划项目(2016YFC030400,2019YFC0312301);国家自然科学基金项目(51574208,41102087,U19B2005);中国科学院A类战略性先导科技专项(XDA1401020102);中国海油重点实验室前瞻基础研究项目。

摘　　要：震旦纪—寒武纪转折期是地球演化的关键节点,这一时期的碳氧同位素记录在塔里木保留完整却关注较少。选取苏盖特布拉克露头震旦系与寒武系交界地层实测采样,并开展了古生物、镜下鉴定、碳同位素漂移事件的综合分析,探讨了N1(BACE)、P1(ZHUCE)等碳同位素漂移事件的成因机制。样品的δ13Ccarb和δ18Ocarb相关系数(R2=0.05)、δ18Ocarb和Mn/Sr相关系数(R2=0.09)及岩石学特征表明,后期成岩改造并未导致碳氧同位素的显著分馏,原始碳同位素特征得以基本保留。由下至上,在该剖面识别出P-1事件(δ13Ccarb峰值1.9‰~2.4‰)、N1事件(-6.8‰~-10.3‰)、P1事件(1.4‰~4.1‰)、N2a c事件(-0.4‰~-2.8‰)、P2a c事件(0.2‰~0.6‰)和N3事件(-3.4‰)。综合碳同位素演化特征与古生物、年代学数据,确认了玉尔吐斯组底部硅质页岩与奇格布拉克组顶部藻云岩的分界面为塔里木震旦系与寒武系的分界线,并实现了该露头与老林、肖滩、三峡、西伯利亚、阿曼和摩洛哥剖面的地层对比。分析认为,塔里木北缘震旦纪—寒武纪转折期的碳漂移事件,更多受控于古海洋氧气含量变化引起的固碳率forg的波动。玉尔吐斯组早期海侵背景下的大规模缺氧事件导致的初级生产力和固碳率降低,是N1负漂移事件(BACE)的主因;随后海退中氧气含量的增加引起生产力重建和固碳率增加,形成了P1正漂移事件(ZHUCE)。这一成果性认识有助于塔里木盆地寒武纪古环境研究与深层超深层油气远景资源评价。The Sinian to Cambrian transition is a time node for the Earth evolution,yet carbon and oxygen isotopes,which are well preserved in the Tarim Basin during this period,are barely studied.Here,based on the measurements of the Sugaitebulake outcrop,a comprehensive analysis of paleontology,microscopic identification,and carbon isotope excursions is carried out,and the genetic mechanism of the N1(BACE)and P1(ZHUCE)excursion events is explained.The correlation coefficient betweenδ13Ccarb andδ18Ocarb(R^(2)=0.05)orδ18Ocarb and Mn/Sr(R2=0.09),as well as microscopic characteristics,shows that the later diagenesis did not lead to fractionation of carbon and oxygen isotopes significantly,and the original carbon isotopic characteristics are basically preserved.Six carbon excursions were detected from the bottom to the top of the formation,which comprise,respectively,excursions P-1 withδ13Ccarb between 1.9‰ and 2.4‰,N1 withδ13Ccarb between-6.8‰and-10.3‰,P1 withδ13Ccarb between 1.4‰ and 4.1‰,N2a c withδ13Ccarb between-0.4‰ and-2.8‰,P2a c withδ13Ccarb between 0.2‰ and 0.6‰,and N3 withδ13Ccarb peaked at-3.4‰.Together with paleontological and chronological constraints,the interface between silica-phosphorus shale of the bottom Yuertusi Formation and algal-dolomite of the top Qigebulake Formation is confirmed as the boundary of the Sinian to Cambrian of the northern Tarim Basin.Also completed is a structural correlation framework comparing the northern Tarim with Tabei,Laolin,Xiaotan,Three Gorges,Siberia,Oman,and Morocco plates.It reveals the carbon isotope excursions during the Sinian to Cambrian transition in northern Tarim are more controlled by the fluctuation of carbon fixation rate(forg)due to paleo-marine redox changes.The decreased productivity and carbon fixation,caused by large-scale anoxic events in the transgression of the Yuertusi Formation,is the main reason for the N1 excursion;then the recovered productivity and carbon fixation from oxygen increase during regression forms the P1 excurs

关 键 词：塔里木 震旦纪 寒武纪 碳同位素 漂移 固碳率 

分 类 号：P539.6[天文地球—古生物学与地层学] P597.2[天文地球—地质学]