Study On Magnetic Spatial Differentiation Of Topsoil In Tianshan Mountains

Soil environmental magnetism is an important research method in soil environmental research to study the interaction between soil magnetism and environmental factors and explore the indicative significance of different magnetic parameters to the environment through rock magnetism.For aeolian topsoil in the Tianshan Mountains,magnetic minerals in soil are closely related to altitude,precipitation,windward and leeward conditions,provenance supply and other factors.Spatial differentiation of magnetic characteristics is the response of soil to deposition and soil formation processes in the complex mountain terrain.Research on its internal mechanism is of great significance for the study on soil environment and climate change.The loess is widely distributed in the Tianshan Mountains.There have been a lot of achievements on the paleoclimate evolution,stratigraphic age determination and the historical change of atmospheric circulation system in Central Asia,but there are relatively few studies on the modern topsoil,especially the spatial property differentiation of the topsoil.This paper selected aeolian topsoil from different regions of the Tianshan Mountains,and combined with the magnetic fabric parameters of the profile by experimental methods such as magnetism,particle size and diffuse reflection spectrum,so as to clarify the spatial differentiation of the properties of the mountain topsoil and explore the causes behind it.The preliminary conclusions of this study are as follows:(1)The dynamic conditions of the Tianshan Mountains are complicated and there are great differences between regions.Combining modern meteorological data and Anisotropy of Magnetic Susceptibility(AMS)parameters of Xinyuan(XY),Kansu(KS)and Baiyanghe(BYH)sections,it is found that the Ili Basin is mainly influenced by the Atlantic water vapor and the westerly wind.The southern Tianshan Mountains are mainly affected by the easterly jet stream from the Turpan Basin after crossing the Eastern Tianshan Mountains,while the northern Tianshan Mountains are mainly affected by the northerly wind and westerly wind due to the influence of the terrain.(2)The analysis of the magnetic parameters,particle size parameters and diffuse reflection spectral measurements of the topsoil in the Tianshan Mountains shows that the magnetic and particle size parameters of the surface soil in different regions are significantly different.The magnetic strength and the overall particle size frequency distribution characteristics of the topsoil in the Ili Basin and the northern foot of the Tianshan Mountains are in similarity,but the depositional patterns of the two regions may be different.The properties of the topsoil at the southern foot of the Tianshan Mountains differ greatly,but the zonal distribution is similar to the wind dynamic direction.(3)In terms of horizontal spatial differentiation of magnetic characteristics,the surface soil at the northern foot of the Tianshan Mountains is greatly affected by the fine magnetic minerals imported from aeolian sources in the middle and far regions,and the wind separation is better than that in other Tianshan Mountains regions,and the contribution of peel-forming to magnetic properties is limited.The magnetic properties of Ili Basin are greatly affected by the local topography,and the pedogenesis is also of distinguished significance.The significant property difference between the northern and southern slopes of the adjacent Daheshan Mountain in the west also indicates that the regional magnetic enhancement mechanism is the coupling result of the pedogenesis theory and the wind velocity theory.The topsoil at the southern foot of Tianshan Mountains is greatly affected by wind dynamics,and the magnetic properties of the topsoil are zonal,but the local topographic disturbance can also affect the properties of the topsoil.(4)In terms of vertical spatial differentiation,different regions show similar elevation characteristics of precipitation "inflection point".The elevation of "inflection point" at the north foot of Tianshan Mountain is about 2800m;the elevation of "inflection point" at the west of Ili Basin(north slope of Dasheshan Mountain)is higher than 3000m;and the elevation of "inflection point" at the east of Ili Basin and the south foot of Tianshan Mountain is higher than 2600 m.