Magnetic fabric from red clay sediments in the Chinese Loess Plateau.

Hujun Gong,Yunxiang Zhang,Leping Yue,Jianxing Li,Rui Zhang

doi:10.1038/srep09706

Abstract

Well-distributed eolian red clay in a wide area of northern China is believed to imply the onset of an ancient East Asian monsoon system since Late Miocene. Two continuous red clay sequences spanning the time interval 7–2.6 Ma and 11–2.6 Ma in the Chinese Loess Plateau was investigated to determine the magnetic orientation and grain alignment in the primary fabric of eolian sediments. The north-westerly orientation of the AMS of the eolian red clay sequences parallels the material transportation direction, which differs from the model that suggests that airborne dust from overlying loess-paleosol sequences were transported by the East Asian winter monsoon and fixed by the East Asian summer monsoon. Our results further reveal that present-day climate and air circulation patterns differ from those of the pre-Quaternary, and may provide evidence of a prevailing wind during deposition of the red clay.

Highlights

Well-distributed eolian red clay in a wide area of northern China is believed to imply the onset of an ancient East Asian monsoon system since Late Miocene
The north-westerly orientation of the anisotropy of magnetic susceptibility (AMS) of the eolian red clay sequences parallels the material transportation direction, which differs from the model that suggests that airborne dust from overlying loess-paleosol sequences were transported by the East Asian winter monsoon and fixed by the East Asian summer monsoon
In the present study we investigated two continuous red clay sequences from Lingtai and Shilou in the Chinese Loess Plateau to evaluate its magnetic properties and grain alignment and describe the primary eolian www.nature.com/scientificreports and water-lain sediment fabric

Summary

Introduction

The latest studies of binary source of the loess and paleosol on the Chinese Loess Plateau (CLP) revealed by Nd-Sr isotopic and U-Pb ages of Zircon[33,34,35,36] suggests that both NTP and Gobi Altay Mountains (GAMs) contribute to the dust transported to CLP It seems from those results, the binary source of eolian dust on CLP or North China craton shift between the Qiliang Mountains (QLMs) and GAMs keeps all the way back from early Miocene to present day. In the present study we investigated two continuous red clay sequences from Lingtai and Shilou in the Chinese Loess Plateau to evaluate its magnetic properties and grain alignment and describe the primary eolian www.nature.com/scientificreports and water-lain sediment fabric. About 77 oriented samples were taken from the fossiliferous horizons to verify their transport by water flow Another 11-Myr eolian red clay profile was reported by Xu et al.[41] for the Shilou profile in Shanxi Province, eastern Loess Plateau. The AMS of each sample was measured by a KappaBridge KLY-4S magnetic susceptibility meter coupled with automated sample handling system, and AniSoft software using the statistical method of Constable and Tauxe[42]

Results

Discussion

Conclusion