HURON-ERIE LOBE MELTWATER INFLUENCE ON SAGINAW LOBE TERRAIN IN SOUTH-CENTRAL MICHIGAN

Meltwater originating from the Saginaw Lobe (SL) and Huron-Erie Lobe (HEL) of the Laurentide Ice Sheet controlled the development of drainage networks within South-Central Michigan after the Last Glacial Maximum (LGM) of the Wisconsin episode. The area north of the SL Kalamazoo Moraine (KM) within Eaton County, Michigan, displays two prevalent valley orientations, one northeast-southwest (VO1), and the other northwest-southeast (VO2). South of the KM, previous studies indicate that meltwater originating from the HEL flowed westerly across the SL terrain, approximately 15.3 ka. Ages obtained from outwash near the Michigan-Indiana border suggest that this area was likely deglaciated shortly after the LGM (24.2 ka). Newly obtained Optically Stimulated Luminescence (OSL) ages from atop the Sturgis Moraine indicate that it may have been ice free prior to the LGM, approximately 25 ka.

Results from this investigation show that VO1 valleys are primarily filled with outwash and generally contain eskers. These valleys typically have undulating hummocky bottoms and trend parallel to SL ice flow and are interpreted as subglacial tunnel valleys. The VO2 valleys also contain outwash but do not contain eskers, are generally wider than, and appear to crosscut the VO1 system, and are perpendicular to SL ice flow.

Longitudinal profiles of VO1 are undulatory and typically rise in elevation down-ice to an apex, after which they continue to slope to the south. Longitudinal profiles of VO2 generally decrease in elevation from the east toward the west. Terrace profiles along VO2 slope from the SL-HEL interlobate area and decrease in elevation through the study area in a northwesterly direction. Four sand samples were collected via hand auger for OSL analysis from VO1 and VO2 and are currently being analyzed. Based on the results of this investigation, we propose the following three stages of drainage development: Stage 1 - VO1 is created by incision and deposition in tunnel valleys associated with the SL while it is at or near its KM position, Stage 2 - VO2 is created as SL ice retreats allowing meltwater from the SL-HEL interlobate area to establish ice marginal drainage in a westerly direction across the study area, and Stage 3 - Drainage adjustments continue as remaining stagnant ice melts and meltwater from the SL and HEL are diminished.