Characteristics of elemental geochemistry of the Cambrian carbonate rocks and their palaeoenvironmental implication in western margin of Qinshui Basin, Shanxi Province
Guo Xiao-Qiang1, Li Hao-Bin1, Wei Rong-Zhu2, Dong Ai-Guan2, Du Yan-Wei2, Yang Jun-Cai2
1 Mining Engineering Institute,Taiyuan University of Technology,Taiyuan 030024,China; 2 Shanxi Institute of Geological Survey,Taiyuan 030006,China
Abstract：A set of significant Cambrian carbonate rocks are found in Qinshui Basin of Shanxi Province. On the basis of field investigation,the petrology and element geochemical composition of Cambrian rocks in the western margin of Qinshui Basin are studied. The results show that the Cambrian carbonate rocks are mainly composed of limestone from the Zhangxia and Gushan Formations, and dolostone from the lower part of Sanshanzi Formation. They are mainly shallow platform facies deposits which can be divided into three types: Restricted platform,open platform and platform margin reef and ramp. There are large variation ranges for the authigenic elements(CaO,MgO)and terrestrial elements(SiO2,Al2O3 and Fe2O3). They have two vertical upward and downward cycles,reflecting the sedimentary environment with high turbulence. The content of K2O is high,but the contents of Na2O and Sr are relatively low. The contents of ΣREE+Y are relatively high and vary widely,and the LREE are much richer than the HREE. A slight negative anomaly of Ce and Eu is found. The normalized curves show a slightly leftward-flat trend,which conforms to the characteristics of the typical marine sediments. The δ13C value is in the range of -1.96‰~0.41‰,showing an overall change of initial increase and then decrease trend. The δ18O value ranges from -9.96‰~-5.33‰,showing a ladder-like upward trend from bottom to top. Related geochemical parameters indicate that the study area was a saltwater marine environment. The paleo-seawater temperature belonged to a warm subtropical climate environment,generally changing from warm to hot and then to cold trends. The paleoclimate experienced a transition of relative humidity-relative dry and heat environmen-relative humidity. The paleo-water depth underwent a variation of shallow-deep-shallow. The ancient sea level experienced a large-scale transgression-regression process. A good coupling relationship between different palaeoenvironment elements is found,showing a certain restriction on the types of sedimentary facies. The results in this paper are very significant for the studies of Cambrian lithofacies palaeogeography and petroleum exploration in the Qinshui Basin and the adjacent regions. It provides a significant theory and practical guidance in the reconstruction of Cambrian palaeoenvironment,palaeotology and palaeoecology evolution of the North China Craton.
Guo Xiao-Qiang,Li Hao-Bin,Wei Rong-Zhu et al. Characteristics of elemental geochemistry of the Cambrian carbonate rocks and their palaeoenvironmental implication in western margin of Qinshui Basin, Shanxi Province[J]. JOPC, 2020, 22(2): 349-366.
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