A TALE OF TWO LOBES: THE PLEISTOCENE EVOLUTION OF INDIANA'S LARGEST INTERLOBATE LAKE BASIN
Several lines of evidence indicate that extensive tracts of stagnant Erie Lobe ice were well established in these lake basins before the Saginaw Lobe arrived, and long before deposition of the large eastern fans (Topeka, Leesburg, Rochester) that followed. Individual ice blocks occupied basins as great as 10-12 mi2and were (minimally) hundreds of feet thick; moreover, they persisted for most of the late Wisconsin, greatly altering the behavior of subsequent glaciers and ultimately controlling the distributions and character of younger deposits of both the Saginaw and Erie Lobes.
The deposits from this earliest Erie Lobe event thicken southwestward into eastern Marshall and extreme western Kosciusko Counties, where they form an extensive region of Erie Lobe moraines and fans known as the Bourbon upland. As such, they seem to define a discrete southern edge of the interlobate area—one that lies significantly further north than suggested by historical interpretations. Moreover, these relations reinforce the growing recognition that the history of the interlobate area is not monolithic, but instead consists of a heterogeneous group of smaller regions, each defined by local ice margins competing for space.