Geochemistry Characteristics Of The Dolomite From Dengying Formation In Xichuan,Southwest Henan:Implications For Paleoenvironment

Qinling orogen has been an active geological unit since Proterozoic,long-term geologic activity caused today's complex geological features,and the study about its evolution process has been a hot issue in geology.The evolution of the mode of Qinling orogen in late Precambrian haven't yet a unified understanding.At the same time,Dengying Formation developed in the southwest Xichuan area of Qinling orogen,the Neoproterozoic Dengying formation as the last strata in late Precambrian development has mainly dolomite and developes largely in the Yangtze platform margin,while the research is very weak in Xichuan,and the“Dolomite problem”still unsolved.The carbonate records the geological environmental evolution of Xichuan area during this period.In this paper,we report the trace and rare earth element,carbonate-oxygen isotope data of the dolomite from the Neoproterozoic Dengying Formation in Huwo and Daquangou section,Xichuan area,and attempt to discuss the petrology,geochemistry and sedimentary evolution of Dengying Formation in this area.Results show that:?1?The Dengying Formation mainly consists of dolomite,mainly including Micrite dolomite,argillaceous dolomite,fine dolomite,coarse crystalline dolomite and dolomite breccia type etc,and can be divided into three sedimentary facies,including subtidal slope zone,supratidal flat and intertidal zone.?2?Geochemical data indicate that the dolomite in Dengying Formation was mainly formed in a high-salinity,hot climate and low latitudes marine environment.Dengying Formation deposition of Xichuan area gradually changed from reducing environment to weak oxidation environment from the bottom to the top.The water changed from deep to shallow and deep,shallow.In the late Sinian period,most areas of the globe appear weak oxidation environment and expose the development characteristics of sediment.?¹³C values had significant negative bias.All shows an overall regression process.?3?The Dengying formation in Xichuan has a better consistency with other regions,and both of them were in shallow shelf environment in the edge of the Yangtze platform.Because of the same crystalline basement with,Xichuan area is considered to have a good affinity with the Yangtze plate during the Sinian Dengying stage,and be in back-arc rift environment in the edge of north Yangtze platform during the Neoproterozoic.This research have a great significance of“Deep time”geological events and The tectonic evolution process of Qinling orogenic belt during the Neoproterozoic.