THE INTERLOBATE ZONE BETWEEN THE SAGINAW AND LAKE MICHIGAN LOBES OF THE SOUTHERN LAURENTIDE ICE SHEET (MICHIGAN, U.S.A.)

Unlike many interlobate zones, the interlobate between the Saginaw and Lake Michigan lobes in western Lower Michigan is not an easily-identified, hummocky upland. Rather, topographic expression of the interlobate is broad, complex, and generally low-relief, and was likely formed time-transgressively. This circumstance perhaps explains why the exact location of the interlobate is still unclear. The Saginaw lobe advanced out of the Saginaw Lowlands, west, toward the interlobate and reached its maximum extent early during the MIS-2 glaciation. The Lake Michigan lobe advanced east, out of the Lake Michigan basin to as far east as Newago, Kent, Allegan, and Barry Counties, where it probably over-ran and eventually abutted the retreating Saginaw lobe.

We use a variety of geomorphic data, i.e., landforms, as derived from LiDAR-derived 1-m DEMs, as well as a soils/sediment database and sedimentologic data (till texture and clay mineralogy, recovered on the ground), to reconstruct the extent and dynamics of the Lake Michigan and Saginaw lobe across the region where they interacted. Particularly useful in identifying the interlobate are spatial data of drumlin orientations and esker/tunnel valley paths, because each lobe was spreading out as it flowed toward the interlobate. For example, Saginaw lobe drumlins and streamlined till plains indicate that the ice flow was to the northwest in Mecosta and Montcalm Counties, to the west in Kent County, and to the southwest in Ionia and Barry Counties. Also useful for identifying ice marginal locations (both terminal and recessional) were Saginaw lobe eskers that end in outwash fans. The distribution of kettles and ice contact landforms indicate that the interlobate zone is, in places, a broad zone (>50 km wide) that once contained abundant buried ice. This observation points to widespread ice-marginal stagnation and interaction among the two lobes. A network of southward-flowing channels in this general area appears to indicate a likely (early) interlobate suture zone. The focus of our talk will be on spatial data used to identify the interlobate – one that has not been specifically mapped out until now.