GLACIAL GEOMORPHOLOGY OF CENTRAL UPPER PENINSULA OF MICHIGAN, USA

A detailed geomorphological study of surficial glacial deposits has been completed in Central Upper Peninsula of Michigan, USA to track the pattern of recession of the Laurentide Ice Sheet. Two competing hypotheses suggest down-wasting or rapid recession and readvance over the time interval of approximately 13.7-11.6 yr BP. The purpose of this mapping exercise is twofold; (i) to extend and correlate glacial surficial mapping from Wisconsin into Michigan, and (ii) to test two hypotheses by reconstructing ice history via features such as moraines, drumlins, eskers among others.

At least ten moraines/ice contact slopes on the west side of the Green Bay sublobe of the Laurentide Ice Sheet were identified. Drumlins oriented radially from the center of the lobe trace to these positions indicating these formed when the ice sheet was active. Well mapped moraines in Wisconsin were correlated to moraines distinguished in Michigan extending the known position of the Two Creeks interstade. Recessional moraines on the lateral side of the Green Bay lobe are spatially compressed in comparison to moraines positioned on the center line of the lobe indicating differential retreat rates.

To contextually place these landforms in time, 25 new radiocarbon minimum ages were used with existing data to refine recession chronology. New chronological data refined the age of recession between the time interval of approximately 13.1-11.2 yr BP. The concentric geometry of at least eight moraines and new chronology suggests that the Laurentide Ice Sheet retreated in steps through this region supporting ice sheet down-wasting.