MICHIGAN BEDROCK TOPOGRAPHY, GLACIAL DRIFT THICKNESS AND BEDROCK OUTCROP MAPS

Few studies exist concerning the thickness of the glacial drift, the underlying bedrock surface or the distribution of outcrops in Michigan. Newly assembled bedrock topography, glacial-drift thickness and bedrock outcrop maps for Michigan show a very irregular bedrock surface which underlies the thickest glacial drift on land in North America.

The bedrock topography map was constructed using data from water, oil and gas, and mineral wells, bedrock shorelines and outcrops, county soil data, waterfalls, and quarries. The glacial drift thickness map was constructed by subtracting the bedrock surface from a National Elevation Dataset digital elevation model.

The bedrock surface consists of high relief resistant bedrock highlands and cuestas as well as lowlands and deep bedrock valleys. Bedrock valleys in places show well defined drainage networks with tributaries while others show long linear parallel valleys. The bedrock surface has been sculpted by numerous paleo-river channels cut into the bedrock during the numerous glacial ice advances over the last 2.5 million years. Others appear to have been cut in preglacial times. Several prominent resistant bedrock cuestas occur, some of which extend into Lake Huron and across southern Ontario Canada. The bedrock surface strongly influenced glacial lobe movement, ice-marginal positions, and interlobate positions.

The Upper Peninsula is characterized by two distinct bedrock surface regions. In the western Upper Peninsula, Precambrian, crystalline bedrock forms large, high relief bedrock uplands. This contrasts with the generally low elevations and relief on the bedrock surface in the eastern Upper Peninsula, which consists of softer Paleozoic sedimentary rocks and subtle cuestas.

Drift averages 270 feet thick and as much as 1,320 feet thick in the Lower Peninsula. Drift in the Upper Peninsula is generally less than 50 feet (with many more outcrops), but is locally thicker overlying bedrock valleys. The land surface topography in the Upper Peninsula generally mimics the underlying bedrock topography.

These maps will assist geologists in understanding lobe dynamics, potential glacial aquifers in bedrock valleys, migration pathways, in seismic data processing for oil and gas exploration, bedrock geology mapping, aggregate, mineral and ground-water exploration.