Particle size contributions to bulk magnetic susceptibility in Chinese loess and paleosol |
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| Institution: | 1. School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon, 440-746, Republic of Korea;2. Korea Railroad Research Institute, 176 Cheoldo bangmulgwan-ro, Uiwang, Gyeonggi-do, 16105, Republic of Korea;1. Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan;2. Department of Surgery, Division of Medicine, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan;1. Laboratory of Nanostructure and Physics Properties and MOE Key Laboratory for Non-equilibrium Synthesis and Modulation of Condensed Matter, School of Science, Xi?an Jiaotong University, 710049 China;2. Department of Applied Physics, School of Science, Xi?an Jiaotong University, Shaanxi 710049 China;3. Lawrence Berkeley National Laboratory, Molecular Foundry, University of California, Berkeley 94704, USA;4. Department of Optical Information Science and Technology, School of Science, Xi?an Jiaotong University, 710049 China;1. Department of Chemistry, North University of China, Taiyuan, Shanxi 030051, China;2. Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, China;3. Materials Fabrication and Processing Division, Institute of Metal Research, Chinese Academy of Science, Shenyang 110016, China;1. Physical-Technical Institute UB RAS, 132 Kirov Street, 426000 Izhevsk, Russia;2. Institute for Theoretical and Applied Electromagnetics RAS, 13 Izhorskaya ul., 125412 Moscow, Russia;3. II Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany;4. St. Petersburg State University, 7/9 Universitetskaya nab., 199034 St.-Petersburg, Russia |
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| Abstract: | The magnetic enhancement of paleosol is observed in the Chinese loess. The origin of this magnetic enhancement is still very uncertain. It is, however, a key problem in correctly understanding the paleoclimatic significance of changes of magnetic susceptibility and in transferring the magnetic signals to paleoclimatic parameters. Two main models have been proposed to explain the mechanism of magnetic enhancement in paleosols: a depositional model and a pedogenic model. Together with composition and concentration, grain size distribution of magnetic minerals also plays an important role to the magnetic enhancement of paleosols. Systematic susceptibility measurements were carried out on the samples of the upper part (S0 to top of L2) of three loess sections from Jixian, Xifeng, and Xining, along an east–west transect in the loess plateau, China. The samples with the highest value of magnetic susceptibility in S1 and the lowest value in L2 of each section were selected as the representatives. These representatives were separated into different grain size fractions based on Stokes’ law for coarse grains and by centrifuge for fine grains. Measurements of magnetic susceptibility and mass have been carried out on these fractions. Results show that for the loesses magnetic susceptibility changes little in the fractions with different grain size and for the paleosols it increases with decreasing grain size. The magnitude of changes is bigger in the east (Jixian and Xifeng) than that in the west (Xining). The fraction with the finest particle size in paleosols does not show very high magnetic susceptibility values. A new approach is used to estimate the contribution of each fraction to total magnetic susceptibility. The contribution comes mainly from coarse grains (>10 μm) for loess samples. It reaches about 90%. The main contribution comes, however, from the particles with medium size (10–0.2 μm). The very fine grained particle (<0.3 μm), which is considered to be with the pedogenic origin, contributes little to the bulk magnetic susceptibility, no more than 3% because of their very little amount. This approach provides a sounder basis for the study of the origin of the magnetic susceptibility enhancement in paleosols and of the paleoclimatic significance of magnetic susceptibility of loess and paleosols. |
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