OSL DATING INDICATES WIND EROSION IN LOESS LANDSCAPES OF NORTHEASTERN NEBRASKA OCCURRED DURING THE LATE PLEISTOCENE

The surficial geology throughout much of south-central and eastern Nebraska is dominated by Peoria loess that generally thins with distance from the Nebraska Sand Hills. However, the Peoria on uplands along the Missouri River valley in northeastern Nebraska varies considerably in thickness, with deposits that locally range from less than 2 meters to over 18 meters. In several locations distinct troughs with either no loess or minimal loess are bounded by uplands of thick Peoria. The thin loess within these troughs commonly contains varying thicknesses of eolian sand that is approximately 1 to 3 m thick. We interpret both the presence of troughs and other areas of thin loess cover on these landscapes to result from eolian deflation, an interpretation which had been made in other studies, however, the timing of the wind erosion had not previously been established. We attribute the eolian deflation of these uplands to the presence of saltating sand that was sourced from either adjacent stream valleys or sandy pre-Illinoisan outwash deposits that are common in the region. The orientations of the troughs indicate that northerly and northwesterly winds would have carried the sand to the uplands along low relief slopes and gently sloping valley walls. Dating results from 14 OSL samples indicate that eolian sand was actively moving and that loess deflation was occurring between 19-11 ka during the termination of Peoria deposition. The presence of thin (less than 1.5 m thick) blankets of Peoria on some of the eolian sand deposits suggests loess deposition continued for a short period after the sand had stopped moving.