Origin of desert loess from some experimental observations

Abstract

A longstanding problem of Quaternary geology has been the origin of the silty deposit known as loess. Of the many explanations for its formation and distribution^1,2, the most commonly accepted is that the silt is produced by subglacial grinding processes^1,3,4, followed by redistribution and deposition by the wind. The large expanses of loess in central Europe are therefore considered to be the consequence of Quaternary glaciation⁵. There is, however, a view^6,7 that loessic silt may also originate as the product of processes in hot deserts. Some proponents of the desert loess hypothesis consider that silt-size material is the product of weathering processes⁷ which may include salt weathering⁸ or weathering down incipient cracks⁹. An alternative mechanism is aeolian attrition of sand grains, although, probably as a result of the experimental work of Kuenen¹⁰, Smalley and Krinsley¹¹ consider that only fine silt (2–6 µm) is produced in large quantities by the abrasion of quartz grains. We have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts. The products of abrasion show that both coarse and fine silt sizes are produced. These findings suggest that desert aeolian processes can produce loess. We also suggest that much of this material from many deserts has been deposited in the sea but that the Chinese loess could have been produced in the Gobi desert. The finest particles produced by such attrition may be a source of silica for silcrete formation.