Glacial and postglacial sediments in Lakes Superior and Michigan
The lacustrine sediment sequence above the glacial till under Lake Superior consists of red clays overlain by gray varved clay and nonvarved gray and brown clay. The Lake Michigan sequence also contains red clay at the base and brown and gray clays above. The red clays in Lake Michigan are found in areas overridden by glaciers of Valderan age as well as in the far southern end of the lake. Deposition of red clay took place in the northern part of the lake as the Valderan glaciers were melting and continued during the Algonquin stadial when the ice front reached a stillstand on the northern peninsula of Michigan. Red and gray clay outwash dumped into Lake Superior may also have escaped from the Superior Basin into the Lake Michigan Basin through the Au Train–Whitefish channel and other channels across the upper peninsula of Michigan. The connection of the two lakes began between about 11,000 C14 yr B.P. and ended about 10,000 C14 yr B.P., when the connection was broken by rebound or by lowering of water levels near the end of the glaciation in the Lake Superior Basin.