Loess‐Like Dust Appearance at 40 Ma in Central China

Niels Meijer,Carina Hoorn,Natasha Barbolini,Norbert Nowaczyk,Guillaume Dupont‐Nivet,Michael Dietze,Amber Woutersen,Christoff Andermann,Alexis Licht,Hemmo A Abels,Rik Tjallingii,Alexander Rohrmann,Yang Zhang,Xiang‐Jun Liu

doi:10.1029/2020pa003993

Abstract

AbstractAsian mineral dust has been studied extensively for its role in affecting regional‐to global‐scale climate and for its deposits, which enable reconstructing Asian atmospheric circulation in the past. However, the timing and origin of the dust deposits remain debated. Numerous loess records have been reported across the Asian continent with ages varying from the Miocene to the Eocene and linked to various mechanisms including global cooling, Tibetan Plateau uplift and retreat of the inland proto‐Paratethys Sea. Here, we study the Eocene terrestrial mudrocks of the Xining Basin in central China and use nonparametric end‐member analysis of grain‐size distributions to identify a loess‐like dust component appearing in the record at 40 Ma. This is coeval with the onset of high‐latitude orbital cycles and a shift to predominant steppe‐desert vegetation as recognized by previous studies in the same record. Furthermore, we derive wind directions from eolian dune deposits which suggest northwesterly winds, similar to the modern‐day winter monsoon which is driven by a high pressure system developing over Siberia. We propose that the observed shifts at 40 Ma reflect the onset of the Siberian High interacting with westerly derived moisture at obliquity timescales and promoting dust storms and aridification in central China. The timing suggests that the onset may have been triggered by increased continentality due to the retreating proto‐Paratethys Sea.

Highlights

During wintertime, the Asian continent is characterized by a high atmospheric pressure system developing over southern Siberia and Mongolia
We propose that the observed shifts at 40 Ma reflect the onset of the Siberian High interacting with westerly derived moisture at obliquity timescales and promoting dust storms and aridification in central China
We identified the appearance of a loess-like dust component in the terrestrial record of the Xining Basin at 40 Ma, coeval with the onset of obliquity cycles and a shift to dominance of steppe-desert vegetation previously identified by Bosboom et al (2014)

Summary

Introduction

The Asian continent is characterized by a high atmospheric pressure system developing over southern Siberia and Mongolia. The Siberian High creates a strong meridional temperature contrast between cold air in the north and warmer air in the lower mid-latitudes that can result in frequent dust storms (Roe, 2009). These storms transport silt-sized material (with median grain-sizes of 20–60 μm) from the arid upwind areas to the Chinese Loess Plateau located downwind The transported mineral dust plays an important role in cooling the atmosphere by scattering solar radiation, promoting cloud formation and providing nutrients to the Pacific Ocean (Jickells et al, 2005; Martin, 1990; Shaffer & Lambert, 2018)

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