| The Mesoproterozoic has long been regarded as a period of environmental and biological stagnation in Earth’s history,also known as the "dry billion years".With the progress of science and technology,as well as the research on the fossils of multi-nucleated eukaryotes,many transient Marine oxidation events occurred in the Mesoproterozoic.The discovery and suggestion of these phenomena means that this is not a "dull billion years".Scholars at home and abroad have also turned their eyes to jixian section in North China,Tianjin,which has been highly studied in the Middle Proterozoic.The lithology of jixian section is mainly carbonate rock,especially in Gaoozhuang Formation and Wumishan Formation,there are large areas of sedimentary Marine and continental carbonate rocks.Therefore,using the original geochemical information of carbonate rocks(especially Li and Sr elements)can effectively reflect the REDOX characteristics of the sedimentary environment during the Mesoproterozoic period,thus indicating the sedimentary environment at that time.In order to make effective use of the original geochemical information of carbonate rocks,it is necessary to exclude the influence of non-carbonate components(such as clay minerals,phosphate,iron and manganese oxides and sulfides).Carbonate rocks contain carbonate minerals,non-carbonate minerals,such as clay minerals.A comprehensive analysis of calcium carbonate includes not only calcium carbonate but also calcium from other sources,such as clay minerals and calcium sulfate.When only carbonate minerals need to be analyzed,carbonate minerals need to be separated from non-carbonate minerals.The non-carbonate portion is called insoluble residue and is formed by geological processes,sedimentation,or weathering.For example,carbonate rocks in seawater,fresh water or salt water contain this residue.Therefore,the study of carbonate minerals must take into account the existence of insoluble residues and the relationship between various elements in carbonate rocks.In this paper,through summarizing predecessors did study,choose different acid,acid concentration,the dissolving time to dissolution of carbonate rock samples,through the analysis of carbonate leaching liquid of Li,Sr elements and rare earth elements and carbonate the correlation of main elements and the influencing factors of leaching liquid to get ideal leaching conditions.Tianjin jixian section is s $in the ancient world section,is typical of China’s most complete and continuous ancient neritic facies sedimentary profile,one of neritic facies sedimentary formation of jixian profile slight metamorphic deformation,good preserve its original geochemical information,the study of jixian above zhuang and mist fan hill group formation to systematically study,through the analysis of the main and trace elements,Element anomaly and sedimentary environment indicator element ratio were analyzed by means of methods and methods,and the following results were obtained:(1)Different acids,different acid concentrations and different dissolution times were selected to dissolve carbonate rocks,and the correlation and influencing factors of elements in the leaching solution were analyzed.The results show that Li and Sr elements mainly occur in carbonate rocks,while rare earth elements mainly come from terrigenous clays such as clay minerals.Using 0.5mol/L acetic acid to dissolve carbonate samples can effectively avoid the influence of non-carbonate components.Different concentrations of acetic acid dissolve different carbonate samples,and the element content of the leached solution is related to the proportion of clay minerals or other impurities in the whole carbonate rock.The purer the carbonate rock,the more information about the carbonate rock that is less polluted by non-carbonate components can be obtained.Different dissolution time has little influence on carbonate karst dissolution.Analyzing the element correlation of carbonate leaching solution,it is found that in order to ensure sufficient information of Li and Sr leaching,the dissolution time is recommended to be 3-5 hours.In conclusion,it is suggested to use 0.5mol/L acetic acid and dissolve it for 3h to obtain the content of Li and Sr elements required for later testing,reduce the influence of non-carbonate components,and further promote the subsequent more effective analysis of Li and Sr elements and isotopes.(2)the carbonate leaching experiment conclusion of this article analysis the experimental conditions,apply to tianjin jixian section samples,through the analysis of the leaching solution of acetic acid dissolving reaction after the correlation of the geochemical elements,trace elements and the main characteristics,elements,anomaly,sedimentary environment indicate element ratios,the results show that higher than the group of three,zhuang REDOX sensitive elements trend is consistent,In addition,Fe and Mn tended to be enriched.Combined with Ce/Ce* anomalies and other indicators,the element enrichment in this period was caused by oxidation.Mist fan mountain group mainly for deep-water environment,sedimentary environment and sedimentary environment have depth conversion,reflect the corresponding partial drought and partial short wet climate transformation,and higher than the group of sedimentary water depth than mist fan zhuang mountain group of sedimentary water depth,but the ancient climate change for partial damp climate characteristics,shows characteristics of climatic variation in group is higher than the zhuang is relatively complex,The REDOX characteristics of sedimentary water environment are not obvious. |
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