Sedimentary Geochemistry And Paleoenvironment Reconstruction Of Cambrian Canglangpu Formation In Southwest Margin Of Upper Yangtze Area

The Canglangpu Formation in the southwest margin of the Yangtze area is taken as the research object,and the petrological and sedimentary characteristics are studied by means of sedimentology,sedimentary petrology and element geochemistry.Mineralogy and sedimentology of Canglangpu Formation are analyzed based on the detailed observation and description of field outcrop lithology,color and sedimentary structure,together with thin section,mineralogy and element geochemistry.The main achievements are as follows.The petrological characteristics show that the rocks are mainly quartz sandstone and lithic quartz sandstone in Hongjingshao Member,Canglangpu Formation.The rock debris in the sample is mainly quartz,with content more than 85%in most sections.The clastic rock of Wulongqing Member,Canglangpu Formation is composed of shale and argillaceous siltstone,with a small amount of quartz sandstone.The mineral content show that the average content of quartz with average content 70.14%in Hongjingshao Member is highest,followed by dolomite,orthoclase,clay minerals and muscovite,with the average content of 11.55%,10.87%,4.13%and 2.81%respectively.The average content of quartz in Wulongqing Member is 43.60%,followed by dolomite,orthoclase,clay minerals,muscovite and calcite,with an average content of 25.13%,14.94%,7.41%,7.94%and 0.88%respectively.The content of major elements in Hongjingshao Member is mainly SiO₂,with an average content of 77.75%,and the rest are Al₂O₃,TFe₂O₃,K₂O,MgO and Cao in turn.The content of major elements in Wulongqing Member is mainly SiO₂,with an average content of62.16%,and the rest are Al₂O₃,TFe₂O₃,K₂O,MgO and Cao in turn.Li,Co,Y and W in Hongjingshao Member are enriched relative to North American Shale,while Be,Cr,Pb and Hf are relatively depleted.Li,Y and W in Wulongqing Member are enriched relative to North American Shale,while Be,Ni,Sr and Pb are relatively depleted.The sedimentary facies of Hongjingshao Member are mainly shore,shelf and delta facies.The subfacies are composed of foreshore,shallow water shelf and delta front.The sedimentary facies of Wulongqing Member are mainly shore and shelf facies.Paleoenvironment reconstruction shows a warm and humid climatic conditions during the sedimentary period of Canglangpu Formation.The source rocks of Canglangpu Formation in the study area are mainly sedimentary rocks and felsic volcanic rocks.