A GIS-BASED STUDY OF SEDIMENT TRANSPORT RATES IN THE LAKE MICHIGAN LOBE OF THE LAURENTIDE ICE SHEET

The rate at which sediment is transported by a glacier is indicative of the types of processes acting at the glacier bed. An accurate estimate of sediment transport is therefore important in attempting to study subglacial processes. Estimates of sediment transport rates require an accurate estimate of the sediment volume deposited over a period of time. By combining volume estimates generated using ArcView GIS with bounding radiocarbon age estimates from Hansel and Johnson (1996), we have calculated the average sediment flux in the Lake Michigan Lobe of the southern Laurentide Ice Sheet. The study area is a five-mile-wide band along a flow line of the Peoria Sublobe of the Lake Michigan Lobe. Within this area, over 600 well logs were collected and interpreted according the accepted lithostratigraphic classification. Well stratigraphy data were then used to create triangular irregular networks that represent the top and bottom of each major lithostratigraphic unit deposited by the Lake Michigan Lobe. The sedimentation rates estimated by this method are based on the sediments currently present. They do not include sediments that might have been eroded or were transported out of the study area in melt water. The sedimentation rates therefore represent a minimum estimate of the glacial sediment flux. Our calculations for each lithostratigraphic unit show that the sediment transport rate ranges from 107 to 1420 m³ per radiocarbon year per meter width in the study area. These estimates encompass the 400 m³ per year per meter width rate calculated by Hansel, Johnson, and Stiff (1991), and reveal remarkable differences in transport rate between each readvance of the Lake Michigan Lobe. By expanding our study to include the Green Bay Lobe, we will next be able to compare and contrast the sediment fluxes and subglacial processes between adjacent lobes of the Laurentide Ice Sheet.