ON THE STRATIGRAPHY AND FORMATIONAL PROCESSES OF UNIQUE SUBGLACIAL LANDFORMS IN NE INDIANA, SE MICHIGAN, AND NW OHIO

Numerous unique glacial landforms have been discovered in northeastern Indiana, southeastern Michigan, and northwestern Ohio in the region previously covered by the Huron-Erie Lobe of the Laurentide Ice Sheet. The landforms are known as two-tracks due to their morphology consisting of two parallel, discontinuous, linear troughs. Two-tracks cross multiple recessional moraines and intersect with each other, but are constrained between the Fort Wayne Moraine and the interlobate area with the Saginaw Lobe. Previous work established a connection between the two-tracks and underlying buried bedrock valleys using water well data and passive seismic tomography south of Fort Wayne. Most of the two-tracks are north of Fort Wayne and overlie a different geology, consisting of thick, complex drift (60–120 m) over shale bedrock. Electrical resistivity arrays determined these northern two-tracks also overlie unconsolidated valleys or channels cut into till. Some valleys have been interpreted to be buried tunnel channels, which are directly linked to some two-tracks, marking a transition from a two-track morphology to a buried tunnel channel morphology. Resistivity arrays have also shown distinct breaks in stratigraphy under the outside edges of the two-track channels. The breaks are large (20 m by 30 m) low resistivity masses that separate homogenous high resistivity deposits, with the latter being interpreted as sand and gravel channel fill and the former being interpreted as till. These results have been seen experimentally with a scale model made to form the two-tracks in the lab. In the model, water pressure was applied to a buried valley with a till cap and consistently, the cap would break along the edges of the valley and sediment would be ejected. What is seen in the resistivity surveys is interpreted as a refilling of voids formed as a result of ejection of sediment, where the voids are refilled with till. Therefore, these two-tracks are presumed to be subglacially formed landforms. This has wide reaching implications for understanding changes in subglacial hydrology, sediment transport, and bed morphology of glaciers where conditions exist for two-tracks to form.