By detailed field work and modeling, the late Quaternary sediment record in Illinois will be investigated to determine the origin of subglacial tills that were deposited in the marginal area of the Laurentide Ice Sheet. Massive, homogenous diamictons that classically have been interpreted to be lodgement till may instead have originated primarily through subglacial deformation in a deforming bed. Reconstructions of the Lake Michigan Lobe profile in Illinois and preliminary field study of glacigenic sediment are consistent with evidence of a deforming bed that has been suggested on theoretical grounds. Methods will consist of two summers of detailed sedimentological and structural study of carefully selected sites, focusing on differentiating subglacial till that is relatively undeformed from till that has experienced internal deformation by pervasive subglacial shearing to large strains. Further analysis will consist of: (1) geotechincal analyses in order to evaluate rheological parameters of the till; (2) determining sediment transport fluxes during the maximum of the last glaciation and comparing those data will data derived from different models of glacial transport; and (3) numerical modeling of the Lake Michigan Lobe ice-till system. The results of this research will have significant implications for interpreting the origin of massive, homogenous till units in mid-latitude regions, as well as for understanding and modeling the dynamics of the Laurentide Ice Sheet.
