Types And Depositional Environment Of Microbial Dolomites In The Chigebulake Formation Of Sinian In Tarim Basin

Microbial carbonate reservoirs have attracted worldwide attention,and the in-depth study of microbial rocks has become a hot spot.The study of microbial rocks not only has high oil and gas value,but also has its unique significance in reconstructing paleoenvironment.However,there are few studies on the microbial dolomite of the Upper Sinian in the Tarim Basin,especially on its sedimentary environment.In order to have a systematic and comprehensive understanding of the microbial dolomite and its sedimentary environment of the Sinian in the Tarim Basin,this paper uses relevant data to study.In this paper,the types of microbial dolomite in the study area are classified by means of macro and micro methods combined with the outcrop characteristics of the profile,such as watch-book observation,thin section identification and CO isotope analysis.On this basis,the sedimentary environment of different types of microbial dolomite is interpreted,and the vertical environment of microbial dolomite in the Chigebrak Formation is performed.Finally,the characteristics of salinity and temperature of sea water are analyzed by using CO isotope data.The Xigou section and Shiairike section are described in detail,and the basic sedimentary characteristics of the Chigbrack formation are grasped.Based on this,the petrological characteristics of the microbial dolomite in the Chigebrak formation are studied,and the microbial dolomite in the group is classified into wavy/hill laminated dolomite,dome like laminated dolomite,columnar laminated dolomite,straight layered laminated dolomite,the foam layer dolomite,the clot dolomite and the algal bound sand debris cloud seven types.Based on previous research results and sedimentary characteristics of different types of microbial dolostones,the sedimentary environment of microbial dolostones,wavy/hill laminated dolomite,dome like laminated dolomite developed in intertidal zone,straight layered laminated dolomite can be deposit in supratidal,intertidal and subtidal zones.columnar laminated dolomite developed in the shallow subtidal-intertidal zone,clot dolomite,whether frothing or not,is developed in the subtidal zone.Algae?bound clastic dolomite developed in intertidal zone with high energy in water body.Sandy clastic dolomite is developed in intertidal zone with high energy in water body.Through longitudinal analysis of the types and characteristics of microbial rocks,it is pointed out that there are relatively abundant microbial rocks in the lower part of the Chigbrack formation,and seven subtypes of microbial rocks are all developed.The upward trend is characterized by foam crest dolomite and crock dolomite.Based on the longitudinal spatial variation trend of the accommodation space,it is pointed out that the Chigbrack group has the characteristics of deep seawater and deep continental retreat.Based on Carbon and oxygen isotope analysis,the trend of temperature rising and salinity decreasing in the vertical direction of the Cigebrak Formation is preliminarily clarified:corresponding to the decrease of microbial rock types in the vertical direction,the preliminary analysis shows that shallow water and high salinity are more conducive to microbial dolomite breeding.