Northeastern (46th Annual) and North-Central (45th Annual) Joint Meeting (2022 March 2011)
Paper No. 5-2
Presentation Time: 8:20 AM-8:35 AM

SAGINAW LOBE TUNNEL VALLEYS, SOUTH-CENTRAL MICHIGAN: DEPTHS OF SUBGLACIAL INCISION AND SEDIMENT FILL

KEHEW, Alan E.1, ESCH, John M.2, EWALD, Stephanie K.1, and KOZLOWSKI, Andrew L.3, (1) Geosciences, Western Michigan University, Kalamazoo, MI 49008, alan.kehew@wmich.edu, (2) Michigan Dept. of Environmental Quality, Office of Geological Survey, P.O. 30256, Lansing, MI 48909, (3) Geologic Survey, New York State Museum, 3140 Cultural Education Center, Albany, NY 12230

Saginaw Lobe terrain in south-central Michigan includes of a set of open to partially buried NE-SW trending tunnel valleys that terminate within a broad tract of high relief hummocky topography interpreted as a stagnant marginal zone. The valleys have undulatory long profiles, contain eskers, and trend parallel to the inferred hydraulic gradient of subglacial meltwater.

Over the past several years, 6 deep, continuously cored, rotasonic borings have been drilled within and near these valleys in conjunction with mapping projects funded by the Great Lakes Geologic Mapping Coalition. Subsurface data of this type are necessary to constrain hypotheses used to determine the origin of the valleys, as well as to investigate their aquifer potential.

Based upon the drilling conducted to date, the depth of incision of the valleys and the thickness of sediment fill appear to increase in the down-ice direction. Tunnel valleys north of the E-W trending Thornapple River valley are shallow, open, and contain only several meters of coarse sediment. By contrast, valleys south of the Thornapple are incised to a depth of 60 m or more, and are filled to a greater degree with extremely coarse gravels. A comprehensive genetic model for the valleys remains elusive, but their origin could include erosive, subglacial bursts of meltwater followed by deepening and filling in the stagnant marginal area by meltwater derived from surface melting. The presence of eskers within the valleys requires ice creep into the subglacial conduits, decreasing their size, so that final sediment deposition to form the eskers occurred within smaller conduits during ice stagnation.

Northeastern (46th Annual) and North-Central (45th Annual) Joint Meeting (2022 March 2011)
General Information for this Meeting
Session No. 5
Quaternary History of the Great Lakes
Omni William Penn Hotel: Conference B
8:00 AM-12:00 PM, Sunday, 20 March 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 1, p. 57

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