Aeolian abrasion and modes of fine particle production from natural red dune sands: an experimental study

A series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles (< 125 mum) by (1) the release of resident fines; (2) spalling, chipping and breakage of particles; and (3) the removal of grain surface coatings. Parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass 'test tube' chamber for up to 120 h. The fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle-size analyses using a Coulter Multisizer. The abrasion of untreated parent samples produced fine particles in one of two main size classes, < 10 mum and > 50 mum, but when the parent sample was sieved to exclude particles < 250 mum, relatively more material in the range 10-50 mum was produced. For unsieved parent samples, the size range associated with the dominant mode varied according to the length of the abrasion time. The coarsest mode (> 63 mum) was dominant during the first 16 h of abrasion, then became less significant and is thought to be associated with the release of resident fines into suspension. The finest mode (< 10 mum) was absent or very weak during the first 16 h of abrasion, then became more significant and, in some instances, dominated the distribution as abrasion continued. Removal of grain surface coatings is the main source of fine material < 10 mum, and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles. By comparison with previous studies of aeolian particle abrasion, these natural dune sands produced very low quantities of fine material (by weight), but their spatial extent makes them potentially a significant source of dust-sized particles at the global scale.