Abstract

A barchan dune was constructed of quartz sand, to which had been added either magnetite grains or maghemite-coated quartz grains, blown down a macadam roadway, and the fabric allowed to develop. The anisotropy of magnetic susceptibility, indicative of magnetic fabric, was measured for 75 samples, representing 13 sites within the dune. The results show that the dominant fabric is controlled by simple gravitational settling but that long axis alignment is developed obliquely to the wind direction on the windward side of the dune and normal to the crest of the dune on the lee slope. Long axes of grains are imbricated in the wind direction. These data show that grain motion is controlled by wind on windward-sloping dune faces, whereas lee-slope alignments are produced by avalanche flow. No difference in fabric is observed between magnetite samples and maghemite-coated samples.

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