AN OUTBURST HYPOTHESIS FOR THE ORIGIN OF THE KALAMAZOO RIVER VALLEY,KALAMAZOO AND ALLEGAN COUNTY, MICHIGAN

The channel morphology of the Kalamazoo River Valley between Battle Creek and Plainwell, Michigan suggests that the channel may be the result of an outburst event. Recent field work as part of an EDMAP project has revealed new stratigraphic information on the glacial processes responsible for the valley. The study area is located in a complex interlobate region impacted by the Lake Michigan and Saginaw lobes of the Laurentide Ice Sheet. Exploration boreholes including three rotosonic borings and geophysical surveys reveal surficial deposits consistent with the outburst hypothesis. The channel occurs as an incised trench over a mile wide and 250-300 feet deep. As the channel approaches the Kalamazoo Moraine it turns almost 90 degrees and cuts through the Moraine and terminates into a glacial lake basin. Stratigraphic data obtained from exploration boreholes indicatethat the uppermost unit within the valley consist of gravel, cobbles and boulders to an approximate depth of 40 feet within the valley. Underlying this coarse alluvial deposit is a diamicton interpreted to be a glacial till. This unit is between 15 and 20 feet thick and pieces of wood were recovered in the easternmost borehole. The wood dated at >52670 years BP and may suggest that Wisconsinan sediments were eroded away during formation of the valley. Immediately underneath this diamicton was an oxidized, mottled assemblage that may represent a paleosol. The easternmost borehole also contained two additional diamicton units, a silty clay lacustrine unit and terminated at the Coldwater Shale at 144 ft. The stratigraphic sequence of the upper valley fill is moderately consistent throughout the course of the valley. The near surface coarse deposits most likely represent outburst flood lag deposits. A large debris fan is located at the point where the valley enters the lake basin, suggesting that the outburst originated from the east, perhaps from the Saginaw Lobe. Field work is ongoing into the stratigraphic relationship between the valley fill and the flanks of the valley within the moraine.