Ice scouring as a geologic agent: Pleistocene examples from Scarborough Bluffs and a numerical model

摘要

In southern Ontario, extensive outcrops of glaciolacustrine muds and shoreface sands of Late Pleistocene age are exposed near Toronto, and were deformed by floating ice masses in an ancestral ice-dammed Lake Ontario. Outcrop mapping and a GPR survey identify ice scour structures up to 4 m, 10 m wide and at least several hundred metres; long and underlain by sub-scour sediment deformations up to 5 m below the scour. The scours also have ridged margins, as observed in modern scours.;Paleoenvironmental information can be derived from ancient ice-scoured strata using an FEM numerical model of sub-ice scour deformation. For the largest ice scour exposed at Scarborough, ice mass is 0.04 Mt, keel draft is 10 to 30 m and scouring force is 5 x 103 kN, consistent with a small ice berg or pressure-ridged lake ice. Estimates of ice mass dimensions are consistent with independent sedimentological reconstructions of paleobathymetry.