Postglacial Lakes Minong and Nipissing: Their Effect on the Sedimentary Stratigraphy of Several Lake Basins on Isle Royale National Park, Michigan

Raymond, Randall; Kapp, Ronald; Janke, Robert

During July, 1973, one sediment core was obtained from each of twelve different lake sites on Isle Royale National Park. These sites may be categorized with respect to their relationship with postglacial Lakes Minong and Nipissing: a) those never submerged by the high level of either Minong or Nipissing, b) those covered by Minong waters, but not Nipissing, c) those inland lakes covered by both Lakes Minong and Nipissing. Of the twelve sediment cores collected, nine were stratigraphically complete. These lake sediment cores collected, nine were stratigraphically complete. These lake sediment cores, 1.60m to 7.85m in length, all begin (bottom) in reddish-brown silty clay, which places the origin of all the lake basin deposits during Valders age. The major stratigraphic feature of several of the cores is the homogenous gray clay which overlies the reddish-brown clay in several of the basins. This gray clay is indicative of the incursion of Lake Minong in these basins. Comparisons of the sediment sequences with the maps showing the shoreline of Isle Royale at Minong and Nipissing time aid in separating those basins affected by only Lake Minong from those affected by both Lake Minong and Nipissing. Variation that occurred in the sediments of the lakes sampled did not permit the prediction of sedimentation rates for the Minong and Nipissing gray clays. There is an indication that the low water lake stage, Lake Houghton, may have some effect on at least two of the basins sampled.