THE DEGLACIAL CHRONOLOGY OF THE STURGIS MORAINE IN SOUTH-CENTRAL MICHIGAN AND NORTHEAST INDIANA

The surficial landscape of south-central Michigan and northeastern Indiana was formed from the retreat of the Saginaw Lobe of the Laurentide Ice Sheet. Studying this landscape aids an understanding of the climate conditions during the retreat of the lobe from its LGM position. The purpose of this study is to generate chronology for the retreat of the Saginaw Lobe by dating the Sturgis Moraine. Previous studies indicate that the Michigan, Huron-Erie and Saginaw Lobes reached their maximum extent at approximately the same time but the Saginaw Lobe retreated first leaving a large re-entrant. Correlations between till stratigraphy and end moraines by others suggest that the Sturgis Moraine formed sometime between 15.5 ¹⁴C and 16.1 ¹⁴C kyrs BP. There is little chronology to support this correlation. To date the Sturgis Moraine, Livingston sediment cores were collected from three scour lakes within tunnel channels associated with the moraine. Scour lakes within meltwater channels are preferred over kettle lakes to minimize the organic accumulation lag from meltout of buried ice. An age of 13.4 ± 60 ¹⁴C kyrs BP is from a log near the bottom of a core from Fennel Lake. This date is similar to the age of 13.6 ± 50 ¹⁴C kyrs BP, when the Huron-Erie Lobe had retreated from the Ft. Wayne Moraine, and 13.8 ± 170 ¹⁴C kyrs BP, the age when the Michigan Lobe had retreated from the Valparaiso Moraine. Forthcoming radiocarbon ages from the same core and the two remaining lake sites will be used to strengthen the chronology of the Sturgis Moraine.