Geochemical Characteristics and Paleoenvironmental Analysis of Carbonate Rocks of the Lower Cretaceous Langshan Formation in Asodong Area,Nyima County,Xizang
Based on the section measurement and collection of 23 carbonate rock samples from the Langshan Forma-tion in the Asodong area of Nyima County,the paleo-marine sedimentary environment of the carbonate rocks formed in the Langshan Formation was analyzed and discussed through the microscopic rock features,element component content and related element ratio characteristics data.Through the analysis of the major and trace elements and their ratios in carbonate rocks,the following conclusions were drawn:(1)The contents of SiO2,Al2O3,K2O,Fe2O3 and TiO2 were basically the same,and they werenegatively correlated with CaO,and their contents increased significant-ly with the decrease of CaO content.(2)The ratio of Sr,Mn/Fe,and Mg-Al(m*)decreased from the first section to the third section of the Langshan Formation,indicating that the sedimentary water body became shallower upward.(3)The paleoclimate and paleoenvironment of the Langshan Formation during deposition were analyzed according to the characteristics of V/Ni,Mg/Ca,Mn/Fe,Mg-Al ratio(m*),Sr,V/(V+Ni),Ce anomaly(Ce/Ce*),and Eu anomaly(Eu/Eu*)values.The results show that the Langshan Formation is generally an oxygen-rich and oxygen-poor oxida-tion environment under humid-hot and slightly-humid-hot climatic conditions,formed in the sedimentary tectonic en-vironment of the passive continental margin,and shows a trend of sea retreat.
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