THE DIRT HILLS STRUCTURE - AN ICE-THRUST FEATURE IN SOUTHERN SASKATCHEWAN, CANADA

The Dirt Kills structure is expressed al the surface as a broad, arcua te moraine, 7.5 km wide, 120 m high, and 40 km long. The structure is composed mainly of bedrock and drift consisting of three slabs stacked to form a single block 215 In thick. The shear zones that bound the s labs are mainly in clays of the Bearpaw Formation. The Dirt Kills stru cture originated during the last deglaciation when the glacier, under compressive flow, readvanced up the Missouri Coteau escarpment and sla cked the subglacial slabs of bedrock and drift. The subparallel, arcua te ice-thrust ridges are formed presumably by imbricate thrust faults originating from the uppermost shear zone.