LATE PERMIAN GEOCHEMICAL CHARACTERISTICS AND PALEOENVIR-ONMENT OF SOUTHEASTERN ORDOS BASIN:A CASE STUDY OF THE SHIQIANFENG FORMATION IN THE XUEFENGCHUAN SECTION,HANCHENG
Previous studies on the paleoclimate inferred from the relatively continuous deposition of Per-mian marine strata in the Ordos Basin are well-developed.However,research on the continental strata de-posited during the same period remains limited and lacks systematic exploration,requiring further en-hancement to comprehensively understand the sedimentary characteristics and environmental conditions of the region during this crucial phase of global climate change in the late Permian.Through meticulous ob-servation,precise measurement,and systematic sampling of the geological sections of the Shiqianfeng For-mation in the Xuefengchuan area southeast of the basin,coupled with systematic petrological and elemen-tal geochemical analyses,this study aims to investigate the paleoclimate,paleosalinity,and paleoenviron-mental characteristics of the Shiqianfeng Formation's sedimentary period.The goal is to elucidate its evo-lutionary patterns and contribute to a deeper understanding of this transitional period in Earth's history.The study results indicate the following key findings:1.The chemical alteration index(CIA)ranges from 15.35 to 78.28,with most samples falling between 65 to 85,suggesting a moderate degree of weathering.The carbon isotope deviation(3.47‰)reflects abrupt climate shifts from semi-humid to semi-arid condi-tions,indicating increased aridity during certain periods.2.Correlation analysis of carbon and oxygen iso-topes,along with Z and S values calculations,reveal a trend of increasing paleosalinity from bottom to top.The Z and S values in the upper layers are 119.98‰ and 31.36‰ respectively,indicating a transition to a brackish water environment.3.Paleoredox indices(U/Th,Ni/Co,V/(V+Ni)ratios ranging from 0.15 to 1.00,1.35 to 2.43,and 0.73 to 0.88,respectively)indicate a strongly oxidizing sedimentary en-vironment throughout the area during the deposition period.4.Additionally,the presence of calcareous nodules,silty limestone,and purplish red sand mudstone in the upper part of the Shiqianfeng Formation suggests an evolving sedimentary environment towards aridity during the Permian period.In summary,comprehensive analysis reveals significant changes in geochemical elements and sedimentary facies in the southeastern part of the basin during the Late Permian.These changes indicate a shift to hotter and drier climates and an increase in salinity,highlighting notable shifts in paleoclimate and paleoenvironment.
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