三峡地区岩家河埃迪卡拉系-寒武系界线剖面碳同位素地层学研究  

CARBON ISOTOPE STRATIGRAPHY OF YANJIAHE FORMATION ACROSS THE EDIACARAN-CAMBRIAN BOUNDARY IN THE AREA OF THREE GORGES

作　　者：王丹[1] 凌洪飞[1] 李达[1] 陈曦[1] 

机构地区：[1]南京大学地球科学与工程学院,南京大学内生金属矿床成矿机制研究国家重点实验室,江苏南京210093

出　　处：《地层学杂志》2012年第1期21-30,共10页Journal of Stratigraphy

基　　金：国家自然科学基金项目(No.40872025)资助

摘　　要：湖北宜昌三峡地区埃迪卡拉系-寒武系界线位置尚存争议,跨越这一界线的岩家河组地层的分段工作也缺乏统一的意见。对岩家河剖面开展岩相学和碳同位素地层学研究,揭示其碳同位素演化可与扬子板块内滇东北老林剖面和肖滩剖面对比,即自下而上在该界线附近存在一个大的δ13C负漂移、一个稍小的δ13C负漂移和一个大的δ13C正漂移。结合该剖面小壳化石首次出现的层位位于碳同位素大的负漂移之上的生物地层学证据,建议将埃迪卡拉系-寒武系界线置于δ13C大负漂移顶部和小壳化石出现层位的底部。埃迪卡拉系-寒武系界线附近的这一负漂移具有全球对比性,可作为三峡地区乃至全球范围内埃迪卡拉系-寒武系界线划分的标志之一。此外,根据碳同位素演化、岩石地层学和小壳化石资料以及与板块内滇东北地层剖面的对比,将岩家河剖面岩家河组划分为3段,它们分别相当于滇东北的朱家箐组的待补段、中谊村段和大海段。The precise placement of the Ediacaran-Cambrian boundary in the Three Gorges area at Yichang, Hubei has been in debate. The subdivision of the Yanjiahe Formation which spans the Ed-C boundary is also controversial. In this study we investigated the lithostratigraphy and carbon isotope chemostratigraphy of the Yanjiahe Formation at the Yanjihe section. Our δ13C curve is comparable to those from the Laolin section and the Xiaotan section in eastern Yunnan. They all contain a large negative carbon isotope excursion, a small negative excursion and a larger positive excursion in ascending order. Considering that small shelly fossils first appear above the large negative excursion, we suggest that the EdiacaranCambrian boundary be placed at the top of the large negative excursion, i.e. the bottom of the first appear- ance of small shelly fossils. This negative δ13c excursion itself can be a diagnostic indicator of the Ediacaran-Cambrian boundary not only in the Three Gorges area, but also around the world. Through correlations with the Meishucun, Laolin and Xiaotan sections in eastern Yunnan on the basis of biostratigraphic and carbon isotope chemostratigraphic, the Yanjiahe Formation is suggested to be divided into three members in upward sequence. These three members are correlated to the Daibu, Zhongyicun and Dahai members of the Zhujiaqing Formation in eastern Yunnan.

关 键 词：化学地层 碳同位素 岩石地层 埃迪卡拉系-寒武系界线 岩家河组 三峡 

分 类 号：P534.3[天文地球—古生物学与地层学]