In sedimentology, winnowing is the natural removal of fine material from a coarser

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

by wind or flowing water. Once a sediment has been deposited, subsequent changes in the speed or direction of wind or water flowing over it can agitate the grains in the sediment and allow the preferential removal of the finer grains. This action can improve the sorting and increase the mean grain size of a sediment after it has been deposited.Compton, R. R., 1962, Manual of field geology, John Wiley & Sons, 378 p. The term ''winnowing'' is from the analogous process for the agricultural separation of wheat from chaff.

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{{Wiktionary-inline, winnowing Sedimentology Separation processes