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Soils and Geomorphic Evidence for a High Lake Stand
in a Michigan Drumlin Field
Paul R. Rindfleisch and Randall J. Schaetzl
The objectives of this study were to determine
(1) if and where lithologic discontinuities are present in the Northport
drumlins of NW lower Michigan, and (2) the sedimentary processes responsible
for the discontinuities. Determining the presence of lithologic discontinuities
was achieved through field observations and laboratory analysis. Lithologic
discontinuities with varying strengths of expression were found in all upland
soils. Upland soils typically have a sedimentologic cap dominated by fine
sands at the surface with dense, more gravelly till beneath. The occurrence
of this cap on upland sites, as well as overlying laminated silts and clays
in some inter-drumlin areas, suggests that upland soils in the Northport
drumlin field formed from subaqueously-reworked glacial till. To accomplish
this, the Northport drumlin field must have been inundated by a previously
unidentified proglacial lake, after recession of the ice margin. The lake
may have formed as ice blocks lay in the deep basins to either side of the
drumlin field and high morainic uplands spanned the southern edge of the
field, which at that time would have been severely isostatically depressed.