Abstract

Red Deer Hill is 5 km long, 3 km wide, and 70 m high. The hill is a glaciotectonic structure formed by a single 106 m thick thrust block, presumably derived from the 80 m deep, upglacier Holmes depression. The thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first (Mennon) glaciation. The hill–depression structure was formed by the Battleford glacier, which drumlinized Red Deer Hill before depositing a veneer of till over the structure. The Holmes depression was filled with glacial Lake Saskatchewan lacustrine and deltaic sediments. Horizontal displacement along a décollement in the direction of the activating force resulted in a stress environment changing from extension to compression. In the zone of extension (Holmes depression), an active Rankine state developed and beds stretched and thinned. In the zone of compression (Red Deer Hill), conversely, a passive Rankine state developed and the beds resisted compression and thickened. Drumlinization of the thrust block occurred as lateral pressures in the block mass changed from passive (stoss slope) to active (lee slope) downglacier.

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