High-precision Determination Of Iron Isotope And Preliminary Study On The Case Study Of Sedimentary Carbonate In Chaohu Area

Based on the establishment of a high-precision Fe measurement method,this paper combines the C-O isotopes of the whole rock,the Fe isotopes of the whole rock and carbonate components,and other geochemical indicators to study and explore the significance of paleo-ocean environment indicators.Based on previous research,established a high recovery rate,low background and simplified process,the Fe isotope geological sample processing method and the high-precision Fe isotope MC-ICP-MS analysis method.The sample test results and accuracy are consistent with other laboratories,and it also enriches the Fe isotope database in the natural system.On this basis,we analyzed the Fe isotopic composition of carbonate rocks in the west of Pingdingshan and the south section of Majiashan in the Chaohu area,and the results were used to explore the significance of Fe isotopes in the paleo-ocean environment,and then to constrain the early Triassic ocean environment,and obtained the following results and understanding:1.High precision Establishment of Fe Isotope Analysis MethodEstablished a high-precision Fe isotope analysis method,including chemical separation process and MC-ICP-MS Fe isotope composition determination,and evaluated a number of factors that may affect the accuracy of Fe isotope testing,including allotropic interfering elements Cr,Ni,polyatomic ion interference elements Cu,Co,Zn,and acidity/concentration matching of sample and standard.Through long-term repeated determination of geological standard samples(BCR-2,AGV-2),the Fe isotopic composition is consistent with international reports.The long-term external accuracy of the whole process of ?56Fe is better than 0.05‰(2SD).2.Early Triassic Fe isotopic composition of Chaohu section and its significance in paleo-ocean environmentA series of major geological and biological evolution events occurred at the turn of the Permian-Triassic interval(251.9±0.02Ma),which was a period of major changes in the evolution of the epigenetic environment and the biosphere in the history of the earth.The Early Triassic,which experienced the greatest extinction of Phanerozoic organisms and drastic global changes at the turn of the Paleo-Mesozoic era,was a special period in the history of the earth's development.Not only did the earth's biological world gradually recover from the extreme crisis,the earth's environment also experienced a comprehensive restructuring.This paper systematically analyzed the composition of major trace elements and Fe isotopes in the west of Pingdingshan and the south section of Majiashan in Chaohu area,Anhui Province,and explored the significance of Fe isotopes in the paleo-ocean environment.Studies have shown that Fe isotopic composition and other geochemical indicators show systematic changes.The Fe isotopic composition of the whole carbonate rocks in the Chaohu area of the Early Triassic was relatively uniform,but some samples had certain changes,with the variation range of ?56Fe ranging from-0.65‰ to 0.29‰.The Fe isotopic composition of the carbonate component fluctuates greatly,and the variation range of ?56Fe is from-3.74‰ to-0.7‰,indicating that there were several fluctuations in the oxygen content of the ocean under the overall hypoxia condition.The paleo-ocean sedimentary environment in the early Triassic was characterized by ocean circulation decline,low primary productivity,and a quiet sea environment with hypoxia.Preliminary studies have shown that the Fe isotopic composition of the carbonate phase has the potential to trace paleo-ocean chemical conditions.