The Study Of Micro-area Geochemical Characteristics And Genesis Of Reticulated Red Clay In Xiangyang Xuancheng Profile

The origin of southern reticulated red clay has always been a major concern in the academic community.By clarifying the formation process of reticulated red clay,and extracting the recorded information of the origin of reticulated red clay,it can be used to understand the quaternary environmental change process in eastern China.Micro-area analysis is a technology that directly performs component analysis,micro-area morphology,micro-area structure and other physical and chemical properties on the surface of the sample to be measured or the analysis depth within 1?m.With the advantages of micro-quantity,in-situ,non-destructive and accurate,the content information of multiple elements can be obtained at one time.This technique can effectively avoid the disadvantages of difficult selection and large artificial interference factors in the process of separating matrix and texture of the reticulated laterite sample,and improve the accuracy of the data obtained.In this paper,the red matrix and white texture of the reticulated red clay in Xiangyang Xuancheng profile,in the middle and lower reaches of the Yangtze River are selected as the research objects.On the basis of in-situ sampling without destroying the original characteristics of the sample,the line analysis method in XRF micro-analysis technology.The geochemistry of red matrix and white reticulate of the reticulated layer was systematically and quantitatively analyzed,and relevant conclusions on the formation of reticulated red clay were obtained.Research indicates:?1?The geochemical distribution of the red matrix and white texture are characterized by a higher content of SiO₂,K₂O and Ti in the white texture than that of the red matrix.From the core of the texture to the core of the matrix,the content of SiO₂,K₂O and Ti decreases trend.The distribution characteristics of Fe₂O₃ and Mn contents show that the content of the red matrix is higher than that of the white texture.From the texture core to the matrix core,the content of Fe₂O₃ and Mn shows an upward trend.Compared with these elements,the content of Al₂O₃,MgO,CaO,NaO and Zr fluctuates more gently in most cases,and the difference between the red and white components is small.SiO₂,Fe2O3,K2O,Mn and Ti all appeared obvious content abrupt changes in the red-white transition region,indicating that the formation of reticulated red clay has a certain relationship with element migration.?2?The red matrix and white texture of the textured layer both show strong silicon-aluminum-iron-rich features.The average order of the main element oxide content of the textured layer is SiO₂>Al₂O₃>Fe₂O₃>K₂O>CaO?MgO>Na₂O.The content of Mn and Ti are higher in trace elements,and the content of Zr,Rb and Sr are less.The difference between the main element oxides of the red matrix and the white texture is reflected in the differences in SiO₂ and Fe₂O₃ content,and the differences in trace elements are reflected in the differences in Mn and Ti content.The characteristics of the geochemical changes of the red matrix and the white texture layer are that the content differences between the SiO₂,Fe₂O₃,Mn and Ti,red matrix and the white texture are obvious.The sharp fluctuation of the content indicates the important influence of the above elements in the process of the separation of red and white components.Weathering parameter index feedback the texture layer as a whole shows strong weathering characteristics,and the weathering degree gradually decreases from bottom to top.The overall weathering difference between red matrix and white texture is not large,but the matrix is higher than the texture and the cycle phenomenon in some depths.It is not very effective to use the ferrosilicon coefficient to directly indicate the weathering degree of reticulated red clay.?3?The results of the change rates of the red matrix and white texture elements indicate that most of the elements in the red matrix except MnO and Si O2 are enriched relative to TiO₂ during chemical weathering,most of the elements in the white texture except MgO are relatively TiO₂ migrates out during chemical weathering,and the degree of enrichment and migration gradually decreases from bottom to top.The concentration or migration of Fe₂O₃ and Mn in the matrix and texture is most obvious.?4?Studies on the particle size characteristics of the ratios of the two characteristic elements of Ti/Zr and Ti/Al2O3 have shown that there may be differences in the material sources of the red matrix and white texture.?5?Ca,Na,K,and Mg are absorbed by plants as important nutrients needed for plant growth.The distribution of K2O in red and white components is very different from CaO,Na2O and MgO.The reason may be related to the source and element's ability to dissolve water.The decomposition of clay minerals and silicate aggregates,and the accumulation of some elements.The effect of plant roots plays a more important role in the formation of reticulation.Under the action of plant roots,the laterite is destroyed to form holes,which accelerates the migration of elements and the decomposition of minerals,The lighter substance in the upper part is poured into the hole to form the netting and the intuitive difference in Fe content,particle size and color of the matrix and the matrix produces the netting phenomenon resulting in reticulation.Holes provide a channel for groundwater circulation.Groundwater action has become the main driving force for accelerating deirization of laterite.After the reticulation stage ends,the leaching and migration of soluble elements such as Ca,Na,Mg,and K continue to occur,and deironization activities still surround the holes Occurred nearby,Si,Fe,Mn,Ti and other relatively stable elements are preserved,and finally present significant features such as the formation of the texture in a small area,the most intuitive color differentiation between the matrix and texture,and the distribution of some elements.?6?The study of the reticulated section further confirmed the existence of holes in the reticulated pattern.The existence of the elongated reticulated pattern and the preservation of the small dot-shaped pores indicate that the formation of the reticulated pattern is related to the root system of the plant.Therefore,from the perspective of reticulated morphology,the theory of reticulated plants is supported.