SEDIMENTOLOGY AND CHRONOLOGY OF FILL IN LAKE MAUMEE’S IMLAY CHANNEL

Proglacial Lake Maumee formed in the ancestral Lake Erie (ALE) basin as the Laurentide Ice Sheet deglaciated the Great Lakes region. Located on the thumb of Michigan, the Imlay channel is one of the outlets that drained Lake Maumee from the Huron-Erie basin, i.e. ALE, westward to the Lake Michigan basin. Little work has been done on the Imlay channel and a detailed understanding of its chronology has not been established. One radiocarbon age of 13,770 ± 210 ¹⁴C yr. BP (16.1–17.3 kcal yr. BP; I-4899) from the Weaver Drain, ~6 km NE of the channel divide, has been associated with activity in the channel. Burgis (1970) used topographic maps to determine the elevation of the channel divide, but the work never considered that the floor of the channel might be buried by post-glacial alluvium. New radiocarbon dates from channel fill consisting of laminated sand and mud as well as bedded gravelly sand from vibracores suggest a minimum fill-thickness of 12 m was deposited before 10,250 ± 35 ¹⁴C yr. BP (11.8–12.1 kcal yr. BP; OS-135589). Water well data from the Michigan department of environmental quality and an interpolated bedrock surface indicate that a bedrock high is located about 15 m below the area surrounding the channel divide. Geotechnical borings were used to construct a cross-section of the Imlay channel along Clear Lake Road, about 760 m SE of the channel divide. Unconsolidated sediment from geotechnical borings collected include diamicton, organics, marl, sand and gravel, sand, silt and sand, and silty/sandy clay. Laminated silt and clay is found in the center of the channel 12 m below the surface near the center of the channel. A strandline associated with Lake Maumee approximately 6.5 km south of the divide indicates the channel-bottom elevation extends more than 25 m below the Maumee water planes, which has implications for the duration and occupation history of the channel.