Study On The Geochemical Features And Weathering Intensity Of Topsoil In Qiantang Rvier Basin

The study of soil geochemical characteristics is important to reveal the soil formation process,environmental evolution and weathering effect.Qiantang River Basin is located in the southeast coastal areas of China,which is an important area of social and economic developent in Zhejiang Province.And Qiantang River Basin is ideal study area where appeal to many scholars beacause of complex soil and diverse natural resources which ware made by subtropical monsoon climate,complex the landform and dense water network.But with the development of social economy,the region land utilization unreasonable phenomenon,waste of resources and land degradation problems emerge in endlessly,soil characteristics research remains to be further strengthened.In this paper,the surface soils of the Qiantang River basin are used as the research object,and the geochemical characteristics,clay mineral assemblage and spatial distribution of the topsoil elements in the study area are analyzed by means of elemental geochemistry and clay minerals.The relationship between clay minerals and elements will be discussed.And at last it will summarize the assemblage of clay minerals under different weathering conditions.Which can provide the basic data and the theory basis to further understand the different soil characteristics of the Qiantang River Basin and the rational utilization of the land resources.Specific conclusions are as follows:?1?The surface soil of the Qiantang River is mainly SiO₂,Al₂O₃ and TFe₂O₃ are the second,the content of K₂O is slightly higher than that of MgO,TiO2 and CaO,and the content of Na₂O is the lowest in constant element.Compared with the average chemical composition of the upper continental crust,the relative enrichment of Al₂O₃,TFe₂O₃ and TiO2 in the watershed is relatively depleted,K₂O,MgO,CaO and Na₂O are relative losses,and the content of SiO₂ is equivalent to that of UCC.Compared with the soil in the middle latitude,the contents of Al₂O₃ and TFe₂O₃ in the Qiantang River Basin are relatively high and the SiO₂ content is relatively small.?2?The chemical weathering effect of the Qiantang River Basin is more intense;and the CIA is between 70.67 and 99.65,with an average value of 87.87.By analyzing the chemical weathering characteristics and A-CN-K chemical weathering trend in different areas of Qiantang River Basin,it can be seen that the Fenshui River Basin with higher latitude is medium chemical weathering and chemical weathering in the rest are strong.?3?The clay minerals in the Qiantang River Basin are mainly illite,kaolinite,1.4nm clay minerals?mainly 1.4nm mixed layer minerals,followed by vermiculite,and contain very small amount of chlorite?,accompanied by a small amount of smectite.The average content of illite is 48.9%,kaolinite 28.0%,1.4nm clay mineral 20.0%,smectite 3.1%.Clay mineral assemblage is illite-kaolinite-1.4nm clay mineral?-smectite?.?4?The difference of soil factors not only affects the distribution of clay minerals,but also affects the clay mineral assemblage characteristics in soil.The difference of climatic conditions makes the illite mainly distributed in the northern part of the basin,and the kaolinite is mainly distributed in the south of the basin.The difference of lithology on both sides of the Jiangshan-Shaoxing fault and the geomorphic form of the basin make the smectite mainly distributed in the Cao'e River area.Different weathering of the study area makes the 1.4nm mixed layer minerals mainly distributed in the southeastern,the vermiculite mainly distributes in the northeastern region,and the chlorite mainly distributes where the terrain is high and the chemical weathering is relatively weak.In addition,red soils and slope deposit which with higher development level had higher kaolinite?>30%?,and 1.4nm clay minerals were mainly 1.4nm mixed layer minerals.Purple soil and limestone soil which with low development level had higher illite?>78%?;coarse soil and paddy soil had more smectite?>7%?.?5?The relationship between the clay minerals and the constant elements and the CIA values in the Qiantang River Basin shows that the smectite and illite are positively correlated with the soluble elements and have a negative correlation with the insoluble elements.The kaolinite and the 1.4nm mixed layer minerals are contrast.So,it is showed that smectite and illite indicate a weak chemical weathering effect,kaolinite and 1.4nm mixed layer minerals are indicative of strong chemical weathering.Therefore,the clay mineral assemblage of Qantang River Basin where chemical weathering strong is illite?low?-kaolinite?high?-1.4nm clay minerals?high,mainly to HIV?;where chemical weathering slightly strong is illite?slightly lower?-kaolinite?micro high?-1.4nm clay minerals?slightly high,mainly V-?_smectite?high?;and where chemical weathering medium is mainly illite?high?-kaolinite?low?-1.4nm clay mineral?low?-smectite?micro high?.