Petrogeochemical Characteristics Of Carboniferous Carbonate Rocks In Dongshan Area,Mengzi

The Mengzi Dongshan area is located in the critical area of the three major units of the central Yunnan-Guizhou Plateau,Yunnan-Guangxi mountain and hills and Western Yunnan mountain.It is located on the west side of the thrust nappe belt in Southeast Yunnan.It belongs to the forward part of the thrust nappe tectonic belt,the north side is adjacent to the Nanpan River craton basin,and the west side is the Red river fault.On the basis of comprehensive collection of relevant data in the study area,the geochemical characteristics of Carboniferous carbonate rocks in the study area are analyzed by means of rock ore identification and geochemical analysis,and the rock types of Carboniferous carbonate rocks in the study area are discussed on the basis of detailed field investigation and detailed field investigation,combined with measured profile data,rock ore identification and geochemical analysis and the diagenesis environment and sedimentary environment.Through field investigation and analysis of sedimentary facies and sedimentary facies,it is believed that the Carboniferous system of the study area is mainly deposited in the open platform facies marine carbonate rocks,the main lithology of which is bioclastic limestone and muddy grained limestone,a small amount of dolomite and dolomitic limestone.The content of elements,CaO,MgO,Al₂O₃,TiO₂,Th and U and other elements were used to discriminate the degree of influence of main sediments and terrigenous clasts in the study area;Sr content,Y/Ho ratio,REE element distribution mode and Eu anomaly characteristics are used to distinguish source index of diagenetic fluid;the ratios of Na and Rb,K/Na,Na/Ca,Sr/Ba and Sr/Ca are indicators of paleo salinity in sedimentary waters;Ti,Mn,P and other elements eliminate the amount of terrigenous detritus,and then calculate the enrichment factor as an indicator of paleoenvironment and climate;Cd content,Th/U ratio,V/Cr ratio and Ce anomaly characteristics were used to study the change of redox state in paleoenvironment;In this study,the REE research was compared with the standardization of North America shale and seawater REE,the results showed that seawater standardization had higher Eu anomaly than that of North America shale.Comprehensive analysis shows that the diagenetic fluid of Carboniferous carbonate in the study area is mainly seawater,with a certain participation in atmospheric precipitation,part of the phosphorous rich hydrothermal fluid and the hydrothermal fluid rich in iron and manganese oxides.The diagenetic environment has a high salinity seawater environment,climate has the characteristics of drought and heat,deposition is above the redox interface,oxidation characteristics are dominant and have certain reduction characteristics.