An Attempt to Recover a Paleomonsoon Signal in the Chinese Loess Plateau Using Anisotropy of Magnetic Susceptibility

Feng Xian,Rui Zhang

doi:10.3389/feart.2020.569072

Abstract

The paleowind direction in the Chinese Loess Plateau (CLP) was studied using anisotropy of magnetic susceptibility (AMS) data. Magnetic fabrics were examined for the last glacial loess (L1) and last inter-glacial paleosol (S1) in the southern and central CLP along a present day precipitation zone of 600 mm per year. Statistical analyses of the orientations of AMS ellipsoids indicate that strong rainwater events may cause random distributions for the AMS azimuth of maximum axis and no deviation from the vertical plane for the average minimum axis. As high rainfall can distort paleowind analyses, it is challenging to conduct paleowind studies on the southern CLP - a topography of high precipitation density. Future studies could focus on the western and northern CLP, where there is less rainfall, making it more suitable for paleowind analysis by AMS.

Highlights

The Chinese Loess Plateau (CLP) has the best preserved and most continuous sequence of eolian deposits in the world (Liu, 1985) (Figure 1)
After removing 1 m thick coverage, this was accomplished for the XY (11 m collected) and LC (10 m collected) sections, due to local weathering and erosion, we were limited to a portion of L1 and no S1 for the LY section (5 m collected)
Each sample was rotated through three orthogonal planes, and the susceptibility ellipsoid was calculated by the least-squares method

Summary

Introduction

The Chinese Loess Plateau (CLP) has the best preserved and most continuous sequence of eolian deposits in the world (Liu, 1985) (Figure 1). A number of studies of Chinese loess have established reliable chronologies, described their pedogenesis, and examined relationships to the uplift of the Tibetan Plateau (e.g., Ding et al, 1994; Porter and An, 1995). Dust flux and grain size have been shown to reflect winter monsoon intensity; and a variety of chemical indicators, as well as magnetic susceptibility, have been shown to be related to weathering and summer monsoon intensity. Such studies have revealed variations in the ancient monsoon in northern China since at least 8 Ma (An et al, 2001; An, 2014). Methods of determining paleowind directions in different portions of the CLP remain scarce and controversial

Results

Discussion

Conclusion