SIMS U-Pb Zircon Geochronological and Carbon Isotope Chemostratigraphic Constraints on the Ediacaran-Cambrian Boundary Succession in the Three Gorges Area, South China  

作　　者：Taiyu Huangc Daizhao Chen Yi Ding Xiqiang Zhou Gongjing Zhang 

机构地区：[1]Key Laboratory of Petroleum Resources Research,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [2]University of Chinese Academy of Sciences,Beijing 100049,China [3]Institution of Earth Science,Chinese Academy of Sciences,Beijing 100029,China [4]Post-Doctoral Research Station of Geological Resource and Geological Engineering,Chengdu University of Technology,Chengdu 610059,China

出　　处：《Journal of Earth Science》2020年第1期69-78,共10页地球科学学刊（英文版）

基　　金：funded by the National Natural Science Foundation of China(Nos.41472089,91755210)

摘　　要：The Ediacaran–Cambrian succession in South China records dramatic biological,oceanic and geochemical changes,but it is not well constrained geochronologically.This study reports a new SIMS U-Pb date of 543.4±3.5 Ma(MSWD=1.2)from a tuffaceous layer in the Zhoujiaao Section,and carbonate C-O isotopes in both Zhoujiaao and Sixi sections,Three Gorges area.This tuffaceous layer is present in the Upper Dengying Formation(i.e.,the Baimatuo Member)which is characterized by a stableδ13Ccarb plateau and the beginning of a negativeδ13Ccarb shift near its upper boundary.In accordance with the existing biostratigraphic and chemostratigraphic data,this new date corroborates that the upper boundary of the Dengying Formation in South China is approximately equivalent to the Ediacaran-Cambrian boundary(ca.541 Ma).This age also provides the minimum age of the last appearance of the Shibantan biota in the Three Gorges area,indicating that the terminal Ediacaran index fossils(e.g.,Cloudina,Sinotubulites)are not reliable stratigraphic markers for further subdivision of the uppermost Ediacaran.The Ediacaran–Cambrian succession in South China records dramatic biological, oceanic and geochemical changes, but it is not well constrained geochronologically. This study reports a new SIMS U-Pb date of 543.4±3.5 Ma（MSWD=1.2） from a tuffaceous layer in the Zhoujiaao Section, and carbonate C-O isotopes in both Zhoujiaao and Sixi sections, Three Gorges area. This tuffaceous layer is present in the Upper Dengying Formation（i.e., the Baimatuo Member） which is characterized by a stable δ13 Ccarb plateau and the beginning of a negative δ13 Ccarb shift near its upper boundary. In accordance with the existing biostratigraphic and chemostratigraphic data, this new date corroborates that the upper boundary of the Dengying Formation in South China is approximately equivalent to the Ediacaran-Cambrian boundary（ca. 541 Ma）. This age also provides the minimum age of the last appearance of the Shibantan biota in the Three Gorges area, indicating that the terminal Ediacaran index fossils（e.g., Cloudina, Sinotubulites） are not reliable stratigraphic markers for further subdivision of the uppermost Ediacaran.

关 键 词：U-Pb dating carbon isotope chemostratigraphy Dengying Formation Ediacaran-Cambrian boundary Three Gorges area Shibantan biota geochemistry 

分 类 号：P597.3[天文地球—地球化学]