Carbonate Microfacies and Sedimentary Facies of Middle Cambrian Formation at Xiaweidian Profile in Western Hills,Beijing,China

By means of microfacies analysis,this paper studies in detail the grain composition,the types and texture of the matrix,the microfacies characteristics of the carbonate rocks of Middle Cambrian of Xiaweidian profile in Western Hills,Beijing.The Middle Cambrian carbonate rocks in the studied profile can be mainly divided into eight microfacies types,including microbreccia bioclastic-lithoclastic packstone,allochthonous bioclastic packstone and wackstone,packstone and wackstone with coated micrite ooids and abraded bioclastic,grainstone with coated micrite ooids,crinoids packstone,ooid grainstone with concentric ooids,grainstone and packstone with micrite ooids,grainstone and packstone with radial ooids.Analysis of all the microfacies reveals that the Middle Cambrian of the studied profile had experienced two sedimentary facies sequences of sea level rise.One of the sedimentary facies sequences starts from an open marine facies of the lower part of Xuzhuang Formation,and gradually evolves upwards to a slope facies of the shoal front of the upper part of Xuzhuang Formation.The others develop from an open marine facies of the lower part of Zhangxia Formation to a slope facies of the shoal front of the upper part of Zhangxia Formation.