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

Abstract

Recent 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 lm 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 lm 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 lm) exhibits the minimum values of v, v ARM , and SIRM, demonstrating that the concentrations of ferrimagnetic grains are not positively correlated with the bulk particle size in the Central Asian loess deposits.

The relationship between environmental factors and magnetic susceptibility in the Ili loess, Tianshan Mountains, Central Asia

“…The MS of loess has been widely considered as a reliable proxy directly linked to the East Asian summer monsoon precipitation on the Chinese Loess Plateau (CLP; An, Kukla, Porter, & Xiao, ), because the fine‐grained ferrimagnetics produced in the weathering and pedogenesis are the main contributors to the magnetic enhancement of paleosols (Q. Liu et al, ; Zhou, Oldfield, Wintle, Robinson, & Wang, ). In contrast, coarse aeolian ferrimagnetic minerals appear to have provided the main control over the magnetic properties of loess in the Tarim Basin and Junggar Basin in ACA (Zan, Fang, Yang, Nie, & Li, ; Zan, Fang, Yang, & Yan, , ). However, the main factors controlling magnetic mineral concentration and the mechanism of its impact on the variations in Ili loess MS are still debated (Guo et al, ; Song et al, ; Song, Shi, et al, ; Wei et al, ).…”

“…The relationship between MS and pedogenesis in the Ili Valley is also not simply a linear correlation (Q. Chen et al, ). Recently, Zan et al () evaluated the relative contributions of pedogenic and detrital components in a loess‐paleosol sequence from the northern slope of the North Tianshan Mountains, Ili Valley, and the northern slope of the West Kunlun Mountains, and the results showed that the contribution of pedogenically produced superparamagnetic (SP) and stable single‐domain (SD) magnetic particles to the bulk magnetic properties is very limited. The relationships between the different grain size fractions and the MS in the Nilka (NLK) section which is located in the eastern Ili Basin, also indicated that the dominant contribution of coarse particles to the MS (Y. Li, Song, Fitzsimmons, et al, ).…”

Characterizing magnetic mineral assemblages of surface sediments from major Asian dust sources and implications for the Chinese loess magnetism

“…Previous studies have focused on dust signals recorded by terrestrial and marine sediments, e.g., from the Chinese Loess Plateau (CLP) , the Red Sea (Rohling et al 2008;Roberts et al 2011), the Indian Ocean (Bloemendal and deMenocal 1989), the North Pacific Ocean (Doh et al 1988;Yamazaki and Ioka 1997;Bailey et al 2011), and the North Atlantic Ocean (Bloemendal and deMenocal 1989;Itambi et al 2009Itambi et al , 2010a. Recently, a few studies have been conducted on surface sediments from dust source regions, e.g., the Asian interior (Maher et al 2009;Zan et al 2015) and North Africa (Lyons et al 2010(Lyons et al , 2012Oldfield et al 2014). Nevertheless, systematic environmental magnetic studies on material from broader dust source regions are still sparse.…”

A spectral mixing algorithm for quantifying suspended sediment concentration in the Yellow River: a simulation based on a controlled laboratory experiment

“…Wet sieving is applied for soil with a high clay content, because very fine powder (mostly <45) tends to agglomerate in the dry sieving process. The wet sieving method has been used often in soil physics studies (Zan et al 2015;Yan, Cheng-Hua, and Zhong-Jian. 2015).…”

“…2015). We applied a similar procedure as described by Zan et al (2015) but using a different series of sieves (2.0, 0.05, and 0.002 mm). Eight sediment types were generated (i.e.…”