Susceptibility variations of multiple origins of loess from the Ily Basin(NW China)  

作　　者：CHEN Qu LIU XiuMing HELLER F HIRT Ann M LU Bin GUO XueLian MAO XueGang ZHAO GuoYong FENG Hua GUO Hui 

机构地区：[1]Key Laboratory of Western China's Environmental Systems,Lanzhou University,Lanzhou 730000,China [2]Institute of Geophysics,ETHZ,CH-8092,Switzerland [3]School of Geographical Sciences,Fujian Normal University,Fuzhou 350007,China [4]Department of Environment and Geography,Macquarie University,Sydney NSW 2109,Australia

出　　处：《Chinese Science Bulletin》2012年第15期1844-1855,共12页

基　　金：supported by the National Natural Science Foundation of China (40830105,40772109,40721061);the China Scholarship Council

摘　　要：The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.The magnetic susceptibility of loess from the Ily Basin, northwestern China shows maximum values in SO paleosols but minimum values in other paleosols, the mechanism of which has been well debated. In this work, systematic magnetic measurements were made on a representative section from Neleke county. The results show that the loess horizons （L1, L2 and L3） have multi-domain magnetite grains of aeolian origin, SO is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals, and the other paleosols （S 1, $2, and $3） are characterized by the formation of nonferrimagnetic minerals associated with waterlogging. The correlation between the low concentration of ferrimagnets, high paramagnetic content, high magnetic coercivity remanence, fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols. Pedogenetic depletion dominates and is responsible for the low susceptibility. Changes in magnetic grain size distribution occur during pedogenetic depletion. The susceptibility variations are of multiple origins in the loess of the Ily Basin. Pedogenetic enhancement, pedogenetic depletion, and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters.

关 键 词：中国西北地区 磁化率 黄土 盆地 铁磁性矿物 颗粒尺寸分布 成土作用 土壤发生学 

分 类 号：P318[天文地球—固体地球物理学]