Contourites in Lake Superior

Abstract

Contour currents influence sedimentation in an area 15 km wide and 65 km long at the base of the slope off the Keweenaw Peninsula in Lake Superior, northwestern Michigan. Seismic-reflection profiles (3.5 kHz) from this area show distinct wavy reflectors in a scoured trough at a depth of 200 m at the base of the slope, hyperbolic echoes adjacent to the trough, and overlapping echoes farther lakeward. These acoustic features are identical to those in marine environments where contourites are deposited. Box cores from the lakeward margin of this area contain what appear to be contourites: irregular, thin sand layers with sharp upper and lower contacts, interbedded with sandy clay. The sandy clay layers are trough cross-laminated in some places and plain laminated in others. This is the first report of contourites in a lacustrine environment.