Abstract

Loess deposits in the Cypress Hills were derived from a single, local source located adjacent to the southwestern margin of the plateau. The distributions of sand, clay, and heavy minerals, the changes in thickness of the deposits, and the orientation of the clasts all indicate that the direction of transport was from southwest to northeast. The changes in the textural composition of the loess are reflected in variations in the sorting, with the best sorted material being located in intermediate positions. The loess is depleted in feldspar relative to the source sediments. This depletion is due to the combined effects of weathering of the feldspar to hydrous mica clays and aeolian sorting. The platy clay mineral grains would be less likely to be incorporated into the aeolian load than the spherical and bladed angular quartz grains, and the partially weathered feldspar grains would be similarly preferentially winnowed. The variations noted indicate that loess deposits formed from a single local source will not have uniform textural characteristics, but will vary in texture, sorting, and mineralogy. Similar variations would be expected in continent-wide loess sheets, although the effects of each local source would be masked by the long-distance transport component of the sediment.

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