Magnetic properties of two soil profiles from Yan’an, Shaanxi Province and their implications for paleorainfall reconstruction

Abstract

The physical and chemical properties of soils are closely controlled by the climate factors and thus are significant for paleoclimate reconstruction. In this study, two adjacent soil profiles (LP and LPM) with different slopes from Yan’an, Shaanxi Province, were investigated using magnetic methods to determine the impact of topography on magnetic properties of soil. Our results show that although LP and LPM have similar magnetic minerals and grain size distribution, both the average and maximum magnetic susceptibility (χ) of LP are almost doubled compared to those of LPM. In addition, the ratios of susceptibility enhancement to the background (E χ ) for LP and LPM are 2.27 and 2.04, respectively; the ratios of saturation isothermal remnant magnetization (SIRM) enhancement (E SIRM) for these two profiles are 1.80 and 1.86, respectively. The slopes of the linear regression trends between frequency-dependent susceptibility (χ FD) and “hard” isothermal remnant magnetization (HIRM) (χ FD/HIRM), Anhysteretic remnant magnetization (ARM) and HIRM (ARM/HIRM), are almost free from the effect of parent material. χ FD/HIRMs for LP and LPM are 28.7×10−5 and 28.9×10−5 A m−1, respectively; ARM/HIRMs are 0.35 and 0.33 for LP and LPM, respectively. These results demonstrate that parameters, χ FD/HIRM, ARM/HIRM, E χ and E SIRM, are affected less by parent material and topography, which are better than the χ for bulk samples to indicate the paleoclimatic conditions (e.g., the paleorainfall) in a large-scale region.