Chemical Weathering Characteristics Of The Loess-paleosol Sequence In Harbin Huangshan Rock Core And Implication For Formation Environment Of The Paleosol

Loess is the product of wind-transported accumulation,which is unbedded yellow silty without secondary disturbance.It is a soil-like sediment rich in carbonate and with large pores.As a typical representative of Quaternary sediments,the continuity and extensity of its distribution is a good carrier to reveal the evolution information of Quaternary palesol-sedimentary environment.The chemical weathering characteristics of loess-palesol series are of great significance for understanding Asian inland aridity,East Asian monsoon evolution,and global carbon cycle.Harbin loess is located at the easternmost end of the Eurasian loess belt and at the leading edge of the easternmost advance of the Asian inland aridity process.The study on the chemical weathering characteristics of loess-palesol is helpful to interpret the climatic environment during the formation of loess and palesol in this region.The research system of weathering characteristics in southern China is relatively complete,the climate is hot and humid,the development environment is good,the distribution range is wide,the type is comprehensive.The hydrothermal disposition in northern China is not conducive to weathering and the degree of weathering is weak,which leads to less research on northern China.The chemical weathering characteristics of loess-paleosol sequence in Harbin are unknown,and the research system is not perfect.Element geochemistry,magnetic susceptibility and heavy mineral analysis of loess-palesol sequence from Harbin huangshan core.SiO₂(61.02%),Al₂O₃(19.51%),Fe₂O₃(4.19%)and K₂O(3.03%)are the main elements in Huangshan core loess layer,and the sum of the average contents of the four elements can reach 87.75%.Si O₂(65.85%),Al₂O₃(19.33%)and Fe₂O₃(4.23%)are the main elements in the palesol layer,and the sum of the three elements can reach 89.41%.The contents of hygrophilic elements(Sc,Cr,Co,Rb)in the ancient soil layer of Huangshan core are higher than those in the loess layer.Ancient like dry element content in the soil layer of zinc,the Sr is lower than China,V likes warm sex element,and Ba likes cold sex element content in the ancient soil layer and soil lager difference is small,due to the Harbin in high latitude,suggesting paleosol and China are the product of the cold climate,soil lager formation environment is relatively dry,paleosol formed relatively humid environment.The color of the palesols in Harbin is gray-brown to gray-black,which is different from the reddish brown of other regions.The CIA values of loess-palesol sequence ranged from 68 to 74(mean 72),indicating that the loess-palesol sequence of Huangshan cores in Harbin underwent moderate chemical weathering.However,compared with the loess layer,the paleosol layer showed no higher degree of chemical weathering,but similar to or even lower degree of chemical weathering than the loess layer.The CIA value of S1 and S3 palesol layer even reached the lowest value of loess-palesol sequence.On migration of chemical elements,characterization of the?^Alindex of element migration ability in the loess,palesol sequence in the sorting order?_Ca^Al(6.2)>?_Na^Al(2.8)>?_Sr^Al(2.0)>?_Fe^Al(1.53)>?_Mg^Al(1.51)>?_K^Al(1.46)>?_Ba^Al(1.28)>?_Rb^Al(1.23)>?_Ti^Al(0.91)>?_Cs^Al(0.75),showed that in the process of chemical weathering Ca,Na,Sr,Fe,Mg,K,Ba and relative loss of Rb element,Relative enrichment of Ti and Cs elements.The results of magnetic susceptibility and heavy minerals show that the magnetic susceptibility of palesol is obviously lower than that of loess,and the content of ferromagnetic minerals is obviously lower than that of loess,while the ferromagnetic minerals of loess are magnetite.Therefore,we believe that although the palesol of Harbin is the product of interglacial climate,the climatic conditions during the pedogenesis process were cold and wet,which led to the chemical weathering of the palesol layer even lower than that of the loess layer.The cold and wet pedogenic environment also reduced and decomposed the magnetite in the palesol layer,which resulted in a lower magnetic susceptibility of the palesol layer compared with the loess layer.The forming environment of Harbin paleosol is similar to that of the present Heilongjiang black soil,so it can be called palesol.