DETERMINATION OF THE MICROFABRIC OF SHEARED TILL USING HIGH RESOLUTION X-RAY TEXTURE GONIOMETRY

Styles of basal motion control subglacial sediment fluxes and the formation of various subglacial landforms, such as drumlins and flutes. A leading hypothesis credits pervasive shear deformation of unlithified sediment beneath glaciers as a key process of sediment transport and landform development. Basal tills of past ice sheets should contain evidence of the large shear strains in the bed that this hypothesis requires. Pervasive deformation of basal till may lead to the alignment of clay particles, resulting in progressive microfabric development with shear strain. Using a ring-shear device, a series of experiments was run on basal till collected from the Superior lobe of the Laurentide ice sheet. Thin sections of the till were made and then scanned using a high-resolution x-ray texture goniometer (HRXTG) to determine the degree of microfabric development. Preliminary data indicate that progressive microstructural development can be detected using HRXTG up to shear strains as large as 140. HRXTG may be a valuable tool for determining cumulative shear strain in basal tills of the geologic record.