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The types and spatial distribution of subsurface sedimentary deposits in the Calumet and Toleston Beaches of ancestral Lake Michigan were studied to better understand the evolution of the southeastern shore of Lake Michigan. Deposits of eight depositional environments were recognized: (1) dune, (2) foreshore, (3) upper shoreface, (4) lower shoreface, (5) offshore, (6) back-barrier lacustrine, (7) paludal, and (8) glacigenic.

The Calumet Beach formed at the end of a rise in lake level following the Two Creeks phase, a time period of low lake level in the Lake Michigan basin, to the Calumet level. This trasgressive event was primarily erosional and produced a ravinement throughout the study area. Locally, however, relief on the underlying till of the Lake Border Moraine was instrumental in the preservation of nearshore sediments. Progradation of the Calumet shoreline produced a vertical stacking of shallow-water coastal sediments over deeper water deposits. Lakeward translation of the shoreline occurred for an unknown period of time, until the altitude of the lake dropped to the level of the Chippewa phase of ancestral Lake Michigan.

Unlike the transgression from the Two Creeks level to the Calumet level, the post-Chippewa transgression to the Nipissing I level was dominantly depositional. This transgressive event is recorded in an ascending sequence of back-barrier lacustrine, dune, and foreshore deposits in the western part of the study area and by the onlap of the toe of the Calumet dune and beach complex by back-barrier lacustrine, palustrine, and dune sediments.

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