RECOGNITION OF LATE PLEISTOCENE EOLIAN DEFLATION FEATURES SOUTH OF THE JAMES LOBE, NORTHEASTERN NEBRASKA, USA

Geomorphically-distinctive rolling uplands south of the Missouri River in Cedar County, northeastern Nebraska are cored by Cretaceous bedrock (Niobrara Formation and Carlile Shale), pre-Illinoian till, outwash, glacio-lacustrine sediments, and eolian sand. While some of these deposits are subaerially exposed, they are locally covered with Peoria Loess which exceeds 14 m in thickness. Where present, eolian sand is commonly capped with a thin (<1.5 m) silt deposit, and based on its landscape position it was most likely deflated from either local streams such as Bow Creek or Pre-Illinoisan outwash. We used optical dating methods to test whether the eolian deflation occurred during the Holocene or late Pleistocene. Preliminary optical age estimates from eolian sands (n = 7) fall within typical ages for Peoria loess deposition, ranging between 22 to 14 ka. These ages suggest that local eolian deflation was ongoing during the late Pleistocene and that Peoria Loess was not accumulating on these portions of the landscape at this time. We interpret the thin silt caps that commonly mantle the eolian sands as very late stage Peoria Loess. Our geomorphic relationships and age control indicate that eolian sands were stabilized during the latest Pleistocene, but prior to the termination of Peoria Loess deposition.