1:100,000 SCALE PRELIMINARY QUATERNARY MAPPING IN NORTHERN BAYFIELD COUNTY, WISCONSIN

The Lake Superior Region in Wisconsin was mapped by Lee Clayton at 1:250,000 scale in the early 1980’s. Quaternary sediments in the area reach a depth of 120 – 150 m and include Marine Isotope Stage 2 (MIS 2) Superior Lobe Copper Falls and younger Miller Creek Formations at the surface. Very little is known about the deepest Quaternary deposits due to a scarcity of subsurface information where thick sediment is located. Glacial deposits of the Copper Falls Formation include sandy tills (~30 – 80% sand) and sand and gravel from meltwater streams. Much of the landscape of the Copper Falls Formation is also covered in extensive ice collapse features such as disintegration ridges, ice walled lakes, and kettles. The Miller Creek Formation occurs in the Superior 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 that formed in the Superior Lowlands (e.g. glacial Lake Duluth). The Members of this Formation were defined west of the Bayfield Peninsula where there are bluff exposures along the shore of Lake Superior. The formation is siltier to the east of the Peninsula, 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, WGNHS geologic logs, laser diffraction grain-size analyses, and Lee Clayton’s field notes (stored at WGNHS). 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. Previously unrecognized glacial features include segments of a moraine near the town of Bayfield and on Mt Ashwabay.