DEGLACIAL CHRONOLOGY OF THE STURGIS MORAINE IN SOUTH-CENTRAL MICHIGAN AND NORTHEAST INDIANA
Previous correlations between till stratigraphy and end moraines suggest that the Sturgis Moraine formed between 15.5 14C and 16.1 14C kyr BP, but with little direct supporting chronologic data. To date the Sturgis Moraine, Livingstone sediment cores were collected from three scour lakes within tunnel channels at the distal side of the moraine. Scour lakes were preferred over kettle lakes to minimize any organic accumulation lag from meltout of buried ice. Basal ages from gravelly sand in these cores are 13.7±0.06, 13.75±0.08, and 13.3±0.06 14C kyrs BP. These ages are similar to basal ages from Clear Lake (13.3±0.03 14C kyrs BP), a kettle lake on the distal side of the Valparaiso Moraine of the Lake Michigan Lobe, and the Hyre (13.69±0.05 14C kyrs BP) and Kenan (13.88±0.07 14C kyrs BP) sites from kettle lakes on the distal side of the Fort Wayne Moraine of the Huron Erie Lobe. The minimum-limiting ages for the Sturgis Moraine presented in this study suggest a younger ice margin and smaller Saginaw re-entrant than currently envisioned.
OSL dated sand dunes from within an outwash valley distal of the Saginaw Moraine (14.3±0.6 and 14.1±0.5 ka) and from dunes that migrated out of the valley (12.6±0.4, 12.3±0.4, 12.4±0.5 and 12.0±0.4 ka) appear to record two separate aeolian activation periods. These ages agree with other sand dune chronologies from northwest Indiana and northwest Ohio suggesting regional variation in climate at these times. The radiocarbon and OSL ages from this study provide a minimum age of 13.8 kyr BP for deglaciation at the Sturgis Moraine.