Sediment Distribution and Bottom Topography of Southeastern Lake Superior

Sediment distribution in the complex region of troughs and shoals in southeastern Lake Superior was studied by means of echo sounding, coring and surface sediment sampling. The primary factor governing sediment type is water depth with sediment source, water movement, trough morphology and lake history superimposed upon it.Thick accumulations of fine-grained sediment are confined to the trough bottoms whereas coarser sediments occur on the sides and crests. In the southern part of the region subaqueous erosion of red tills leads to the deposition of brown sandy sediments whereas farther offshore dark gray fine-grained sediments show the influence of eroding varved clays. Current action along the south shore and along the trough bottoms produces sediment sorting even in deep water. On slopes greater than one op two degrees, fine-grained postglacial sediment is very thin or absent and lag deposits overlie glacial sediments. Evidence of ice scour indicates that modifications to sediment distribution may have occurred during the low level Houghton stage about 8000 B.P.Stratigraphic evidence suggests that the most probable origin of the complex bottom topography is erosion by moving ice.