GSA Connects 2021 in Portland, Oregon

Paper No. 242-4
Presentation Time: 2:15 PM


SODEMAN, Alexander, Geography, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada, FISHER, Timothy, Department of Environmental Sciences, University of Toledo, MS 604, 2801 W Bancroft St, Toledo, OH 43606 and LOOPE, Henry, Indiana University Indiana Geological and Water Survey, 611 N Walnut Grove Ave, Bloomington, IN 47405-2208

Our current understanding surrounding deglaciation of the Huron-Erie Lobe (HEL) of the Laurentide Ice Sheet in Indiana is changing due to the discovery of meltwater-derived landforms thought to be a new variation of tunnel channels. These landforms are called parallel tunnel channels (PTCs) and consist of discontinuous, semi-parallel pairs of depressions separated by a continuous central ridge. The PTCs have been observed cross-cutting multiple recessional moraines and transitioning to standard tunnel channels and proglacial channels in the down-ice direction. Geophysical surveys and water well logs reveal that the depressions are erosional features cut into New Holland till, are filled with lacustrine muds, and are occasionally floored with sand and gravel. Due to the morphology and stratigraphy of the depressions, the PTCs are interpreted to be subglacial, meltwater-derived, erosional landforms. A subglacial origin for the PTCs has significant implications for the deglaciation of the HEL. First, because the PTCs cross-cut recessional moraines, those moraines must be palimpsest and therefore did not form during the final retreat of the HEL. Instead, the recessional moraines were overtopped during a readvance prior to the formation of the PTCs. Second, the down-ice relationship between PTCs, standard tunnel channels, and proglacial channels suggests these may have formed synchronously. If true, this would represent a partially preserved subglacial drainage network with meltwater being transported from subglacial interior, submarginal, and proglacial positions, respectively. To preserve both the recessional moraines after a readvance and this subglacial drainage network, the HEL likely underwent widespread stagnation rather than active retreat during the final stages of deglaciation. This interpretation significantly differs from our current understanding of HEL deglaciation and calls for a reevaluation of HEL dynamics and deglacial chronology.