Geochemical variations in Peoria Loess of western Iowa indicate paleowindsof midcontinental North America during last glaciation

Peoria Loess deposited in western Iowa during the last glacial maximum (LGM ) shows distinct geochemical and particle-size variations as a function of both depth and distance east of the Missouri River. Geochemical and particl e-size data indicate that Peoria Loess in western Iowa probably had two sou rces: the Missouri River valley, and a source that lay to the west of the M issouri River. Both sources indicate that LGM paleowinds in western Iowa ha d a strong westerly component, similar to interpretations of previous worke rs, A compilation of loess studies in Iowa and elsewhere indicates that wes terly winds were dominant during loess transport over much of the midcontin ent south of the Laurentide ice sheet, which is not in agreement with paleo winds simulated by atmospheric general circulation models (AGCMs). AGCMs co nsistently generate a glacial anticyclone with easterly or northeasterly wi nds over the Laurentide ice sheet and the area to the south of it. Loess de position in the midcontinent during the LGM may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial ant icyclone. (C) 2000 University of Washington.