Abstract:

The Dengyingxia Stage (Late Precambrian) in South China is a marine carbonate sedimentary stage with extensively developed dolostones. The primary dolostones precipitated directly from sea water are developed in the middle unit of Dengying Formation and their primary texture are reserved well. The δ¹³C and δ¹⁸O values have been determined from 40 samples of primary dolomites (dolostones): 13C=3.64‰ and δ¹⁸O=-1.17‰ (n=6) for micrite dolomites; δ¹³C=3.52‰ and δ¹⁸O=-1.86‰ (n=15) for algae dolostones; δ¹³C=2.90‰ and δ¹⁸O=-2.65‰ (n=8) for fibrous dolomite cements; δ¹³C=2.96‰ and δ¹⁸O=-2.41‰ (n=8) for bladed dolomite cements; δ¹³C=2.79‰ and δ¹⁸O=-3.13‰ (n=3) for micrite lamella and fibrous dolomite cements.  The average  δ¹³C and δ¹⁸O values of all 40 samples are 3.25‰±0.44‰ and -2.12‰±0.98‰ respectively (PDB standard). The heaviest δ¹³C and  δ¹⁸O values in overlap ping area of the values of the primary dolomite sediments and the cements in diagram, δ¹³C=4.43‰ [JP](PDB) and δ¹⁸O=-0.62‰ (PDB), has been determined as the primary carbon and oxygen isotope composition of the Dengyingxia marine carbonate. The δ¹⁸O value of sea water of Dengyingxia Age is 2.90‰(SMOW) calculated based on the salinity of the inclusion in primary dolomite cement. The temperature of sea water at that time is 40.8 ℃ calculated on the basis of the primary δ¹⁸O value. It indicates that hot climate and high temperature existed in Dengyingxia Age in South China.

摘要：

中国南方灯影峡期(晚前寒武纪)是白云岩广泛发育的海洋碳酸盐沉积时期，在灯影组中部发育从海水直接沉积沉淀的原生白云岩，目前仍保留其原始组构特征。从40个原生白云石(岩)中测得:泥晶白云石的δ¹³C值为3.64‰,δ¹⁸O值为-1.17‰(n=6);白云岩的13C值为3.52‰，δ¹⁸O值为-1.86‰(n=15);海水纤状白云石胶结物δ¹³C值为2.90‰，δ¹⁸O值2.65‰(n=8)；海水刃状白云石胶结物的δ¹³C值为2.96‰,δ¹⁸O值为-2.41‰(n=8);晶纹层和海水纤状白云石胶结物的δ¹³C值为2.79‰，δ¹⁸O值为-3.13‰。40个岩样的δ¹³C平均值为3.25‰±0.44‰,δ¹⁸O平均值为-2.12‰±0.98‰(均以PDB标准)。对于灯影峡期海相云岩的原始δ¹³C和δ¹⁸O值，不采用所有样品的平均值，而是采用原生白云石沉积物与海水白云石结物δ¹³C值和δ¹⁸O值两个图示分布区重叠部分的最重同位素值，即：δ¹C值为4.43‰(PDB标准),δ¹⁸O值为-0.62‰(PDB标准),将其作为灯影峡期海洋碳酸盐岩的原始同位素组成。对海水原生白云石胶结物包裹体盐度进行了测定，海水δ¹⁸O计算值为2.90(SMOW标准)，用原始δ¹⁸O值计算的原生白云石形成时的海水温度为40.8 ℃。这说明中国南方灯影峡的海洋为炎热的较高的海水温度环境。