A post-Calumet shoreline along southern Lake Michigan |
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| Authors: | Daniel K Capps Todd A Thompson Robert K Booth |
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| Institution: | (1) Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA;(2) Indiana Geological Survey, 611 North Walnut Grove, Bloomington, IN 47405-2208, USA;(3) Earth and Environmental Science Department, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, USA |
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| Abstract: | The southern shore of Lake Michigan is the type area for many of ancestral Lake Michigan’s late Pleistocene lake phases, but
coastal deposits and features of the Algonquin phase of northern Lake Michigan, Lake Huron, and Lake Superior are not recognized
in the area. Isostatic rebound models suggest that Algonquin phase deposits should be 100 m or more below modern lake level.
A relict shoreline, however, exists along the lakeward margin of the Calumet Beach that was erosional west of Deep River and
depositional east of the river. For this post-Calumet shoreline, the elevation of basal foreshore deposits east of Deep River
and the base of the scarp west of Deep River indicate a slightly westward dipping water plane that is centered at ∼184 m above
mean sea level. Basal foreshore elevations also indicate that lake level fell ∼2 m during the development of the shoreline.
The pooled mean of radiocarbon dates from the surface of the peat below post-Calumet shoreline foreshore deposits indicate
that the lake transgressed over the peat at 10,560 ± 70 years B.P. Pollen assemblages from the peat are consistent with this
age. The elevation and age of the post-Calumet shoreline are similar to the Main Algonquin phase of Lake Huron. Recent isostatic
rebound models do not adequately address a high-elevation Algonquin-age shoreline along the southern shore of Lake Michigan,
but the Goldthwait (1908) hinge-line model does. |
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| Keywords: | Lake Michigan Lake level Calumet beach Calumet phase Algonquin phase |
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