Analysis Of Microfacies And Sedimentary Environment Of Ediacaran Of Luchi,Zhenba Area,South Shannxi

As a high-quality reservoir of the lower assemblage,The Dengying formation has been proved by the oil and gas exploration in Sichuan basin and its surrounding areas in recent years.However,the details of reservoir distribution in Dengying formation remain controversial,which in some extent restricts the exploration of oil and gas in Dengying formation.Based on the outcrop of Doushantuo Formation and Dengying formation at Luchi section,southern Shaanxi province,this paper carried out a detailed study of Ediacaran sedimentary microfacies.Furthermore,combined with microscopic characteristics,the sedimentary characteristics and genesis of types of rocks are sorted out and explained.As for Doushantuo Formation,these rock types included silty shale,argillaceous siltstoue,debris quartz sandstone and micritic dolostones.As for Dengying Formation,these rock types included micritic dolostones,(residual)dolarenite,stromatolite dolostones,thrombolite dolostones,microbe-bonded dolarenite,argillaceous siltstone,argillaceous dolostones and(dolomite-bearing)siliceous rock.Shore-shelf deposition developed in the early period of Doushantuo Formation in the study area,which was characterized by continuous rise of relative sea level.In the late period of Doushantuo Formation,the study area was featured with a slow regressive deposit in the context of highstand systems tract,and the development of slope deposits of mud shale and with interbedded dolomites.The sedimentary environment of Dengying formation in the study area is open carbonate platform,which had experienced two transgression-regressive cycles.The crbon and oxygen isotope and trace element data indicate that the sedimentary paleoenvironment during deposition of Dengying Formation changed dramatically.In the whole,the deposition period of the Dengying Formation is roughly featured with the decreasement of seawater salinity,increasement of seawater temperature and gradual increasement of oxygen content,but the environmental fluctuations may exist.