HR: 0830h
AN: GP41B-0045    [PDF]
TI: Determining of Grainsizes of Susceptibility and Anhysteretic Remanent Magnetization Carriers in Chinese Loess-Paleosol Ssequences
AU: * Liu, Q
EM: liux0272@tc.umn.edu
AF: Institute for Rock Magnetism, Department of Geology and Geophysics, University of Minnesota, Minneapolis, 55455 United States
AU: Banerjee, S K
EM: banerjee@tc.umn.edu
AF: Institute for Rock Magnetism, Department of Geology and Geophysics, University of Minnesota, Minneapolis, 55455 United States
AU: Jackson, M J
AF: Institute for Rock Magnetism, Department of Geology and Geophysics, University of Minnesota, Minneapolis, 55455 United States
AU: Maher, B A
EM: b.maher@lancaster.ac.uk
AF: CEMP, Lancaster Environment Center, Geography Department, Lancaster University, Lancaster, LA1 4YW United Kingdom
AU: Pan, Y
EM: yxpan@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Zhu, R
EM: rxzhu@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Deng, C
EM: cldeng@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Chen, F
EM: fhchen@lzu.edu.cn
AF: CAEP, College of Earth and Environment Science, University of Lanzhou, Lanzhou, 730000 China
AB: Detailed rock magnetic studies show that susceptibility (mass-specific $\chi$) and anhysteretic remanent magnetization (ARM) of the Chinese loess/paleosol sequences are carried by almost identical magnetic carriers. Therefore, the ratio $\Delta\chi$/$\chi$$_{ARM}$ (or equivalently $\chi$$_{ARM}$/$\Delta\chi$, where $\Delta\chi$ is background-corrected $\chi$, and $\chi$$_{ARM}$ is field normalized ARM) can be used to quantify the grainsize of $\chi$ and ARM carriers. By determining this ratio for three Chinese loess/paleosol profiles (Jiuzhoutai, Yuanbao, and Yichuan) characterized by different degrees of environmentally controlled pedogenesis and sedimentation rates, we show that the lower grainsize limit of aeolian magnetic particles in the less pedogenically-altered loess units is about 100-300 nm, in the finer-grained pseudo-single domain (PSD) grainsize range. In contrast, the grainsizes of pedogenically-produced magnetic particles for mature paleosols dominantly cover both the superparamagnetic (SP) and single-domain (SD) ranges. Based on plots of $\Delta\chi$/$\chi$$_{ARM}$ against $\Delta\chi$, the samples can be divided into four regions (I, II, II, and IV). Region I corresponds to the least pedogenically-altered primary loess samples, with $\Delta\chi$/$\chi$$_{ARM}$ of 0.165-0.24. Samples in region II, a transition zone between the least altered loess and the onset of development of paleosols, have $\chi$ values identical to those in region I, but have lower $\Delta\chi$/$\chi$$_{ARM}$ of 0.09-0.165. With increasing susceptibility in zone III, $\Delta\chi$/$\chi$$_{ARM}$ is positively correlated with $\chi$, indicating the gradually-increasing influence of SP particles. Finally, in zone IV with $\Delta\chi$ higher than ~6.5$\times$10$^{-7}$m$^{3}$kg$^{-1}$, $\Delta\chi$/$\chi$$_{ARM}$ is independent of the variations in $\Delta\chi$, suggesting that the $\Delta\chi$/$\chi$$_{ARM}$ is totally controlled by the pedogenic finest-grained particles, and the size distribution of these particles remains almost constant. The development of soils in the Chinese loess revealed by these three profiles from three sites can be clearly explained by a continuous process of pedogenesis, increasing from zone I to zone IV. Based on further comparison of our results with European loess records (Evans and Heller, 2003), we propose that the loess units of the European profile have a higher pedogenic degree than that of the Chinese loess, and correspond to Zones $(>)$ II. The definition of the pedogenic zones can help to improve our understanding of the underlying mechanisms and variability of pedogenesis, and thus could enable more successful and accurate separation of the authentic pedogenic signals from the background signal of the aeolian inputs at different loess sites worldwide.
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting