Aeolian microtextures in silica spheres induced in a wind tunnel experiment: Comparison with aeolian quartz

Abstract

Microtextures in quartz attributed to aeolian transport, principally bulbous edges and abrasion fatigue have seldom been tested in the laboratory under controlled conditions. A wind tunnel experiment was conducted, using glass spheres (>70% SiO2) as a proxy for quartz, with the objective of determining the extent of mechanical damage to silica/glass transported in a mixture with quartz beach sand. The microspheres were microscopically imaged prior to transport in a wind tunnel, subjected at velocities ranging from 4 to 13 m/s in sequential runs of 10 min. The range in velocity is capable of lifting grains into the air column or saltating quartz grains and silica/glass spheres to produce mechanical impact, i.e. abrasion commonly experienced in aeolian transport. With increasing velocity silica/glass spheres, which displayed minor imperfections prior to transport, began to show significant grain damage exhibiting increasing depth into the silica/glass fabric – a result of mechanical contact – as well as increasing frequency of craters, dislodged plates and abrasion fatigue. While pits appear earlier in the experiment (8 m/s), dislodged plates and abrasion fatigue need a threshold velocity of near 10 m/s to become more frequent. Bulbous edges on the grain surface, often considered the hallmark of aeolian transport, are not seen in the grain population analyzed, possibly because of the initial near-perfect sphericity of the silica/glass spheres. The experiment proved that aeolian transport throughout short distances and during a relatively short period of time is enough to imprint significant abrasion marks in microspheres. In fact, the microtextures produced were fresh surfaces, fractures and abrasion that imprinted areas of different sizes. A comparison of microtextural imprints on silica/glass spheres relative to coastal dune sands was made to better understand energy thresholds required to achieve grain damage. © 2012 Elsevier B.V. All rights reserved