Characteristics And Genesis Of Stromatolite Dolomite Geochemistry Of The Dengying Formation In Ediacaran,Western Zhejiang

The problem of Ediacaran dolomite has always been the focus of scholars.This paper focuses on the mineralogical,petrological and geochemical characteristics of stromatolite dolomite in the Dengying Formation of the Ediacaran system in Jiangshan,Zhejiang Province.Starting from the genetic analysis of dolomite,the following conclusions are drawn:The stromatolite dolomite of the Dengying Formation in western Zhejiang is divided into micrite dolomite,fine crystal dolomite,algal mass dolomite,and breccia dolomite.The lower part of the micrite-silty dolomite is more common in the laminated stromatolite,and the fine-grained dolomite is mainly developed in the columnar stromatolite and breccia dolomite.The ordered degree of dolomite crystal in the study area is concentrated in 0.36-0.63,which is obviously in inverse proportion to the molar content of Ca CO₃.The characteristics of order degree indicate that the samples of Dengying Formation have the characteristics of quasi contemporaneous dolomitization and buried dolomitization.If the degree of order of some crystals is less than 0.5,it is speculated that they have experienced in-situ rapid burial.The geochemical characteristics of the sample show that the value of ?¹³C is between 1.21‰and 4.56‰,which is a low positive value as a whole;the value of?¹⁸O is between-6.27‰and-1.52‰,and the medium negative and low negative values are distributed.The seawater temperature calculated according to?¹⁸O,It fluctuates between13.62? and 57.13?.The sample's?Eu appears as a weak negative anomaly or a weak positive anomaly,and?Ce shows a negative anomaly.The comprehensive analysis of the research area during the Dengying period is a dry and hot ancient climate,which belongs to the high salinity tide plate Sedimentary facies,seawater is the main source of dolomite chemical fluids.Combining the mineralogy,petrology,geochemistry and other characteristics of the Dengying Formation dolomite,the diagenetic stage can be divided into three stages:syngenetic dolomitization,quasi-syngenetic dolomitization,and buried dolomitization.The syngenetic dolomitization is closely related to the algal microbial action in the Dengying stage of Ediacaran;the quasi syngenetic dolomitization is affected by the characteristics of seawater fluid,temperature and pressure in the Dengying stage;the post burial dolomitization is related to the burial depth and pore fluid temperature.In summary,the formation of the Ediacaran Dengying Formation dolomite in the western part of Zhejiang is mainly controlled by the sedimentary environment.The main laminated stromatolite is composed of micrite dolomite and silty dolomite,which is of syngenetic quasi syngenetic origin.The fine-grained dolomite around the columnar stromatolite is affected by the late burial diagenesis.