Chemical Weathering Intensity and Terrigenous Flux in South China during the Last 90,000 Years—Evidence from Magnetic Signals in Marine Sediments

Xiaoqiang Yang,Xiaoke Qiang,Xuechao Peng,Yuejun Wang,Niu Li,Qixian Zhou

doi:10.3389/feart.2016.00047

Abstract

The level of chemical weathering is strongly affected by climate. We presented magnetic properties associated with element ratios from the northern part of the South China Sea to denote links between chemical weathering intensity and monsoon changes in the previous 90,000 years. The magnetic parameter IRMAF80mT/SIRM, representing the variations of high coercivity minerals in marine sediments accompanied with the Al2O3/TiO2 and the Chemical Index of Alteration (CIA), demonstrates strong chemical and physical weathering processes during the last 84-40 kyr when intensified Asian monsoon and warm climate occurred. High susceptibility, TiO2 content, and relatively coarser magnetic mineral grain (relatively low ARM/SIRM ratio) also suggest more terrigenous clastic flux resulting from intensified physical erosion and river transport ability. During the 40-15 kyr period, a low IRMAF80mT/SIRM as well as chemical proxies indicate weak weathering as the climate cooled and precipitation decreased.

Highlights

Weathering intensity and continental erosion determine the geological progression in near-surface spaces, and these are related to tectonic uplift and climate change (Clift and Giosan, 2014; Zhao and Zheng, 2015)
On the basis of the chronology of integrating the paleointensity and oxygen isotope, magnetic properties of marine sediments provide a good record of the chemical weathering intensity and clastic flux processes in Southern China
All authors listed, have made substantial, direct, and intellectual contribution to the work, and approved it for publication

Summary

INTRODUCTION

Weathering intensity and continental erosion determine the geological progression in near-surface spaces, and these are related to tectonic uplift and climate change (Clift and Giosan, 2014; Zhao and Zheng, 2015). Magnetic properties IRMAF80mT (Saturation Isothermal Remanent Magnetization after 80 mT alternation field demagnetization) associated with the element ratios Al2O3/TiO2 and the Chemical Index of Alteration (CIA) were used as the chemical weathering proxies while volume susceptibility, TiO2 content and ARM/SIRM represent clastic flux which was related to the physical erosion. The grain size proxies of ARM(20–60 mT)/SIRM(20–60 mT), ARM/κ and SIRM/κ all show obvious variations down core (Figure 4) Their values display four segments: two lows from 0 to 50 cm and 170 to 360 cm suggest relative coarse magnetic. SIRM, ARM, volume susceptibility, and IRMAF80mT/SIRM of samples varied within one order of magnitude These properties met the requirements for reconstructing relative paleointensity using the normalized NRM (King et al, 1983; Tauxe and Wu, 1990).

DISCUSSION

SUMMARY