OSL DATING OF SEDIMENTS IN THE IOWAN EROSION SURFACE LANDFORM REGION MAY SUPPORT MEGAFLOOD HYPOTHESIS OF FORMATION

The Iowan Erosion Surface (IES) landform region, centered in northeast Iowa and extending into southern Minnesota and northern Illinois, is an area of low relief, mantled with loamy sediments and studded with spectacular giant erratic boulders. Since the late 1800s, many have observed and described its features and proposed various interpretations to explain these features. Sediments of the IES were carbon dated in the past, but many of the dates were reported as exceeding the effective range of the technique.

OSL techniques offer the opportunity to develop a more comprehensive chronological framework for the origin and evolution of the IES. New OSL dates, reported here, provide additional information concerning some of the sediments and geomorphic features of the Iowan Erosion Surface such as loess and sand accumulations and streamlined hills containing truncated paleosol surfaces. Additional geomorphic features of the IES include gravel bars, boulder trains, valley fill sediments, deeply incised bedrock gorges, and amphitheater-headed canyons. These resemble similar features that have been described at other paleoflood locations, and our interpretation is that their presence within the IES may be explained by a megaflood event or events.