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In order to find out the element geochemical characteristics of Silurian Longmaxi Formation shale in Yanjin area,southwestern Sichuan Basin,as well as the material source and structural background of shale formation,the petromineralogy and geochemistry of 19 shale samples from Niuzhai section of Yanjin area were tested and analyzed. Combined with the previous research results and adjacent areas,the rare earth elements were mainly applied to discuss the sedimentary environment, the accumulation rate,material source and tectonic setting of the Longmaxi Formation shale in the study area. The results show that the mineral composition of the Longmaxi Formation in Niuzhai section of Yanjin is mainly quartz,carbonate minerals and clay minerals. The mineral triangle diagram shows that the Longmaxi Formation shale is mainly a combination of clay shale and mixed shale. The normalized partition pattern of rare earth elements is characterized by Ce deficit and weak Eu enrichment. The δCe values,Ni/Co and V/Cr values of the samples indicate that the paleo-water depth increases suddenly in the early stage and becomes shallow gradually in the later stage. Oxygen content gradually changes from anoxic reduction state in the early stage to weak oxidation state in the later stage. LaN/YbN values show that the shale deposition rate increases firstly and then decreases under the influence of sea level and terrigenous debris input. Provenance analysis shows that the source rocks area are mainly felsic igneous rocks and intermediate-acid geological bodies of granitoids. The La-Th-Sc diagram and tectonic setting characteristics show that the main tectonic setting of the source rocks is passive continental margin. Combined with previous studies and tectonic setting,it is inferred that the main source of the Longmaxi Formation shale is formed in the Passive continental margin of hypoxia,and the provenance is mainly from the Kang-Dian ancient land to the west of the study area,followed by the Central Guizhou uplift. 相似文献
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