STRATIGRAPHY AND CHRONOLOGY OF THE IMLAY CHANNEL IN LAPEER COUNTY, MICHIGAN, USA

Ancestral Lake Erie (ALE) was the proglacial lake that occupied the Huron and Erie lake basins during deglaciation. The Imlay channel in Lapeer County, Michigan was one of two outlets for glacial Lake Maumee, the oldest and highest stage of ALE. The other outlet for glacial Lake Maumee was the older Fort Wayne outlet in northeast Indiana. New radiocarbon and optically stimulated luminescence (OSL) ages from within and adjacent to the Imlay channel constrain the timing of regional deglaciation and sedimentation rates within the channel postdating its abandonment. The deglaciation of the Thumb of Michigan has relied on a single age from the Weaver Drain site located near the Imlay channel. A new radiocarbon age of 16.7–17.0 cal ka BP from 3 km east of the Imlay channel supports this long-standing (~50 year) deglacial age. On average there is a 14 m thick sediment fill within the channel. Radiocarbon and OSL ages reveal that much of the alluvial fill was deposited by 14.9 ka, and alluvial fans building into the channel stabilized in the early Holocene. Peat was deposited on the channel floor during much of the Holocene. Cross-sections along and perpendicular to the Imlay channel, built from geotechnical borings and water-well records, reveal a current-day bedrock sill elevation at 235 masl. The sill’s elevation would have permitted drainage of all stages of glacial Lake Maumee but was above the elevation of the younger Lake Whittlesey water plane.