The Stratigraphic Characteristic And Corelation Of Ediacaran-Cambrian Interval In Eastern Yunnan

After the "Snowball Event",the early life presents a multi-level,massive explosion.South China has more records of fossil than any other country during Precambrian-Cambrian interval.This provides important fossil evidence to explain the continuous process of animal origin to the Cambrian Explosion,and also provides a great convenience for our researcher to explore the development and evolution of multi-cell.Main research of this paper is the stratigraphic division and comparison of the Ediacaran-Cambrian,also some advices about its index fossil.We were surveyed the Qingshuigou Section,the Piantoushan Section and the Meishucun Section in eastern Yunnan,analysed output layers and zonality of the small shell fossil in every formation.There are three small shell fossil assemblage zone: 1.Anabarites--Circotheca;2.Paragloborilus--Siphogonuchites;3.Sinosachites--Eonovita-tus.The assemblage zone could be correlated with the same horizon of Southwest Sichuan,Central Guizhou,Eastern Yangtze Gorges and South Shaanxi,it could also identify the basic stratigraphic framework in Ediacaran-Cambrian interval.However,there are still great differences in the division of the most important geological boundaries,Precambrian-Cambrian stratotype section and point(?Golden Nail?,GSSP).Treptichnus pedum as a marker fossil of the GSSP has been questioned constantly in the global biostratigraphic division(especially in Siberia an South China),and trace fossils remains as a symbol also has certain defects.The ribbon Shaanxilithe-like which in the top of Xiaowaitoushan Member,Dengying Formation and the bottom of the Zhongyicun Member,Yuhucun Formation in Eastern Yunnan has a steady output layer,short biological extension and could be compared in region.In this paper,by studying the stratigraphic distribution and geographical distribution characteristics and the evolutional significance of the system are analyzed.The potentials of Shaanxilithe-like as markers of Cambrian bottom are further studied,and they are put forward a more ideal standard in order to determine the Precambrian-Cambrian boundary.Through the research in this paper,there are three conclusions.1.The biozonation of the small shell fossil of the Meishucun section in Eastern Yunnan have similar characteristics in Southern China.The strata of the Ediacaran-Cambrian interval in Southwest Sichuan,Central Guizhou,Eastern Yangtze Gorges and South Shaanxi could be correlation with layer of Eastern Yunnan.2.The ribbon Shaanxilithe-like fossils are widely distributed under phosphate rock in the bottom of the Cambrian,easy to identify with,suddenly extinct in Cambrian and short biological extension.Therefore,it could be used as index fossil in the Ediacaran-Cambrian boundary.3.The ribbon Shaanxilithe-like fossil which is stable outputed in the bottom of Cambrian could be compared with other region.Its extinction layer(LAD)is a clear boundary,therefore,the Xiaowaitoushan Member could be classed in Dengying Formation.