1. Michigan State University
Geology of the
Great Lakes
Lake Michigan focus
David P. Lusch, Ph.D.
Dept. of Geography
Michigan State University

2. Great Lakes Watershed

3. Great Lakes Region Canadian Shield Michigan Sedimentary Basin
Two very different geologic environments
Michigan
Sedimentary
Basin
Canadian Shield

4. Canadian Shield Very resistant to erosion
Very old rocks ( million years)
Very resistant to erosion
Plutonic rocks (e.g., granite, diorite or gabbro)
Metamorphic rocks (e.g., gneiss, schist or slate)
Volcanic rocks (e.g., basalt, obsidian or scoria)

5. Michigan Sedimentary Basin
Younger rocks (542 – 145 million years old)
All sedimentary (mostly marine deposits)

6. Michigan Sedimentary Basin
Mississippian
345 Ma
Equator N
Deposition in shallow seas
North American
Plate
African

7. Michigan Sedimentary Basin
Structural basin – like nested bowls
Oldest rocks at the bottom; youngest at the top
> 16,000 ft

8. Michigan Sedimentary Basin
The Michigan Basin was inundated numerous times by oceans, which eventually filled it with sedimentary deposits.
Four general sedimentary rock types fill the Michigan Basin:
Sandstones
Carbonates (limestone and dolostone)
Shales
Evaporites (halite and gypsum)

9. Facies Concept
Lateral variations in the lithologic characteristics of a volume of sediments of the same geologic age.
Off-shore
non-clastic zone
Near-shore
clastic zone
Wave energy
keeps fine clastic
sediments in suspension; only coarse clastic sediments settle out
No wave energy -
fine clastic
sediments settle out
no clastics so only
non-clastic sediments settle out
Becomes
sandstone
shale
limestone/
dolostone

10. Marine transgression/regression
Sea transgression (sea level rise through time)
Sea regression (sea level fall through time)

11. Origin of the Great Lakes
Relatively recent features in the landscape.
Geologically ancient causes
For Lake Superior - plate tectonics and rifting
For the lower Great Lakes - development of the Michigan Sedimentary Basin
Geologically more recent causes
Glacial sculpting of bedrock, mediated by differences in their resistance to erosion
Isostatic uplift of the region shifting the watershed outlet

12. Geologic origin of Lake Superior
Mid-continent Rift system of North America
A “failed” rift in the center of the North American Craton – rifting began about 1.1 billion years ago.
The rift valley was flooded by oceans and filled with sandy sediments.
Millions of years later, glaciers successfully eroded away the sandstones leaving the lake depression.

13. Origin of the 4 Lower Lake Basins

14. Differential erosion
The various sedimentary rock types are of unequal resistance to physical erosion:
Sandstones and Carbonates are stronger and tend to support highlands.
Shales are weaker and tend to underlie lowlands.

15. Bedrock of the Great Lakes Basin

16. Bedrock of the Great Lakes Basin
Wisconsin
Dome
Thornton, IL

17. Niagaran Escarpment
Major resistant-rock (dolomite) landform in the Michigan Structural Basin

18. Niagaran Escarpment
Scarp
slope
Dip slope

19. Niagaran Escarpment
Rock Island , Wisconsin

20. Fayette State Park, Michigan
Niagaran Escarpment
Fayette State Park, Michigan

21. Niagaran Escarpment
Dip slope
Scarp
slope

22. Niagaran Escarpment
Hwy 401
Niagara Falls
Lewiston, NY

23. Origin of the Great Lakes
Relatively recent features in the landscape.
Geologically ancient causes
For Lake Superior - plate tectonics and rifting
For the lower Great Lakes - development of the Michigan sedimentary basin
Geologically recent causes
Glacial sculpting of bedrock, mediated by differences in resistance to erosion
Isostatic uplift of the region which shifted the watershed outlets

24. At its maximum, the Laurentide Ice Sheet in
At its maximum, the Laurentide Ice Sheet in the Great Lakes region extended south of Michigan into southern Ohio, Indiana, and Illinois.
Lobes of the
ice sheet
followed pre-
glacial valleys
and their flow
regimes were
influenced by
resistant bedrock
formations.

25. Glacial
lobes

26. Lake Michigan bathymetry
Whitefish Channel
Whitefish Fan
Chippewa Basin
Two Rivers Ridge
Mid-lake Plateau
South Chippewa Basin

27. Lake Michigan bathymetry
vs. bedrock type
Point aux Chenes Shale
Antrim Shale
Ellsworth Shale
Coldwater Shale
Shale subcrop
(dashed line
inside the border)

28. Lake Michigan Archipelago