LINKING COARSE SILT PRODUCTION IN ASIAN SAND DESERTS AND QUATERNARY ACCRETION OF THE CHINESE LOESS PLATEAU

In the search of the provenance of the well-defined Chinese Loess Plateau (CLP) we propose a genetic association between primary production of large amounts of coarse silt through aeolian abrasion of quartz sands and the buildup of the CLP. A field-scale experiment in the Gobi desert along sand streaks supports aeolian abrasion of sand as effective mechanism of grain-size comminution in central Asia. The genetic association between proximal immense sandy deserts and eolian abrasion of sand is compatible with a systematic NW-SE CLP depositional pattern where the grains gradually change from sandy loess to silty loess and to clay.

We suggest that whereas the fine-silt material in the CLP may be associated with variable sources, located even thousands of kilometers away, the coarse silt, a major component of the loess sequence, is derived by aeolian abrasion of the upwind proximal large sandy deserts, Mu Us, Tengger and Badain Jaran. Only these abraded coarse quartz grains can build up the mass of the loess sequence to form a massive and spatially well-defined loess plateau while the fine grain dust can be derived from everywhere. The more distal sandy deserts of Taklimakan, Qaidam, and Junggar cannot be major sources for the systematically deposited coarse silts and thinning trend (hundreds of meters in the north to several meters in the south) of the CLP. Long term persistent aeolian activity through time that both produce coarse silt quartz through abrasion of the immense Mu Us, Tengger and Badain Jaran dunes and delivers these abrasion products downwind, is a major process in forming the CLP.