Bulk particle size distribution and magnetic properties of particle‐sized fractions from loess and paleosol samples in Central Asia

Abstract

AbstractRecent studies demonstrate that particle size separation based on gravitational settling and detailed rock magnetic measurements of the resulting fractionated samples constitutes an effective approach to evaluating the relative contributions of pedogenic and detrital components in the loess and paleosol sequences on the Chinese Loess Plateau. So far, however, similar work has not been undertaken on the loess deposits in Central Asia. In this paper, 17 loess and paleosol samples from three representative loess sections in Central Asia were separated into four grain size fractions, and then systematic rock magnetic measurements were made on the fractions. Our results demonstrate that the content of the <4 μm fraction in the Central Asian loess deposits is relatively low and that the samples generally have a unimodal particle distribution with a peak in the medium‐coarse silt range. We find no significant difference between the particle size distributions obtained by the laser diffraction and the pipette and wet sieving methods. Rock magnetic studies further demonstrate that the medium‐coarse silt fraction (e.g., the 20–75 μm fraction) provides the main control on the magnetic properties of the loess and paleosol samples in Central Asia. The contribution of pedogenically produced superparamagnetic (SP) and stable single‐domain (SD) magnetic particles to the bulk magnetic properties is very limited. In addition, the coarsest fraction (>75 μm) exhibits the minimum values of χ, χARM, and SIRM, demonstrating that the concentrations of ferrimagnetic grains are not positively correlated with the bulk particle size in the Central Asian loess deposits.