Imprint of continental-glacier erosion over space and time: Three examples from Ohio, United States

Glacial erosion, a first order process in glaciated areas varies over time and space. To determine the spatial and temporal variabilities of glacial erosion requires an understanding of the topography prior to and between glacial erosion events. The terminal area of Pleistocene ice sheets provides one such area for examination because glacial erosion disappears at the ice sheet edge. Two interlobate areas near the ice sheet margin in northeastern (NE) and southwestern (SW) Ohio were analyzed using three approaches: (1) bedrock-topography patterns in both the SW and NE study areas; (2) optically stimulated luminescence (OSL) and till stratigraphy data from the NE study area; and (3) glacial geomorphology and stratigraphy of the SW study area. The bedrock-topography studies reveal spatial variations in glacial erosion at the mesoscale (1,000's km2) resulting from ∼2.0 million years of glacial erosion. In both study areas, patterns of preserved bedrock channels parallel and perpendicular to flow reveal adjacent "deep" and "shallow" erosion zones associated with the palaeotopography. The OSL dating and till stratigraphy data of NE Ohio reveal a Late Illinoian kame terrain that survived a later glacial advance, either below cold-based ice or standing as a nunatak during the Last Glacial Maximum. The glacial geomorphic study in SW Ohio shows that a topographic upland was an impediment to glacial advance and was covered by thin, weak/stagnant, possibly cold-based ice. Focused around this upland was thicker, warm-based, ice that was an effective erosive agent. The erosion patterns reported here are the first to demonstrate the long-term, relatively minor, erosive effects of the Laurentide ice sheet margin.