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华南上扬子区桐梓组为下奥陶统最底部的岩石地层单位之一。通过贵州习水吼滩剖面桐梓组的系统分析,并结合上扬子区多个相关剖面的资料,确定桐梓组以中厚层白云岩、白云质灰岩、页岩为主,偶夹薄层生屑灰岩。桐梓组主要形成于浅潮下带至深潮下带环境,其沉积厚度具由西向东逐渐增大的趋势,白云岩所占比例由西向东逐渐减少。通过对白云岩岩石学特征分析,初步得出桐梓组白云岩成因:在台地浅滩附近以混合水白云岩化为主,在台地内部以回流渗透作用为主。整个桐梓组自下而上可以建立5个牙形石带,分别是Cordylodus angulatus带、Glyptoconus quadraplicatus-Scolopodus?pseudoplanus带、Paltodus deltifer-Triangulodus proteus带、Triangulodus bifidus带、Serratognatus divers带。桐梓组上下界线均为穿时界线,底界由西向东向上穿时,顶界向下穿时。
The Tongzi Formation in the upwelling sub-region of South China is one of the rock formations at the bottom of the Lower Ordovician. Based on the systematic analysis of the Tongzi Formation in Xiushoutan section of Xishui, Guizhou Province, and combining with the data of multiple related sections in the upwelling subregion, it is determined that the Tongzi Formation is dominated by medium-thick dolomite, dolomitic limestone and shale, Limestone. The Tongzi Formation mainly formed in the shallow-tidal zone to the deep-tide environment. The sedimentary thickness tended to increase gradually from west to east, and the proportion of dolomite gradually decreased from west to east. Based on the petrologic characteristics of dolomite, the genesis of the dolomite in the Tongzi Formation is initially obtained: dolomitization of mixed water is dominant near the platform shoal, and the infiltration and infiltration are dominant in the interior of the platform. There are five conodont zones in the Tongzi Formation, which are Cordylodus angulatus, Glyptoconus quadraplicatus-Scolopodus pseudoplanus, Paltodus deltifer-Triangulodus proteus, Triangulodus bifidus and Serratognatus divers. Tongzi group upper and lower boundaries are worn when the line boundary, the bottom boundary from west to east wear, top down when worn.