GSA Connects 2021 in Portland, Oregon

Paper No. 193-2
Presentation Time: 2:30 PM-6:30 PM


RAWLING III, J. Elmo, Wisconsin Geological and Natural History Survey, University of Wisconsin-Madison, 3817 Mineral Point Road, Madison, WI 53705, BRECKENRIDGE, Andy, Department of Natural Sciences, University of Wisconsin - Superior, Belknap and Catlin, P.O. Box 2000, Superior, WI 54880 and ULLMAN, David, Department of Geoscience, Northland College, 1411 Ellis Ave., Ashland, WI 53804

The Lake Superior Region in Wisconsin was impacted by the Superior Lobe of the Laurentide Ice Sheet and mapped by Lee Clayton at 1:250,000 scale in the early 1980’s. Quaternary sediments reach depths of up to 150 m and include Marine Isotope Stage 2 (MIS 2) Copper Falls and younger Miller Creek Formations at the surface. Little is known about the deepest Quaternary deposits due to a scarcity of subsurface information where thick sediment is located. The Copper Falls Formation includes sandy tills (~30 – 80% sand) and sand and gravel from meltwater streams. Much of the landscape of the Copper Falls Formation is covered in extensive ice collapse features such as disintegration ridges, ice-walled lakes, and kettles. The Miller Creek Formation occurs in the lake basin lowlands, and includes clay-rich tills of the Hanson Creek and Douglas Members, offshore sediment, and interbedded sand and gravel from meltwater streams. The Miller Creek Formation is typically 9 – 18 m thick, has a sharp contact with the underlying Copper Falls Formation, and was mostly submerged by ice-marginal lakes (e.g. glacial Lake Duluth). The members of this formation were defined west of the Bayfield Peninsula from bluff exposures along Lake Superior. The formation is siltier to the east, although there is considerably less known about the three-dimensional distribution there due to a lack of exposures.

The preliminary mapping presented here is based on field observations, a 1.5-m-resolution LiDAR-derived hillshade model, USDA soil maps (scale 1:15,000), water well construction reports, geologic logs, laser diffraction grain-size analyses, and Lee Clayton’s field notes. The distribution of the Miller Creek and Copper Falls sediment on the resulting map is similar to Clayton’s. However, landforms visible with the LiDAR led to changed and refined interpretations in the Miller Creek landscape. Most of these relate to nearshore landforms of the proglacial lakes including wave-cut benches, spits and dunes. Some of these were interpreted as glacial features (drumlins and moraines) by Clayton using the elevation control available to him. New observations include previously unrecognized glacial features and glacial lake strandlines, 30 borings (10-85 m deep), and radiocarbon ages from wood and plant material (~11.2 cal yr ago).