LAKE MINONG AND THE HOLOCENE HISTORY OF THE TAHQUAMENON RIVER, NORTHERN MICHIGAN USA

Optical (Optically Stimulated Luminescence or OSL) dating of dune sand, ground penetrating radar (GPR), examination of stratigraphy and 14C dating of wood fragments collected in lake vibracores, near surface soil stratigraphy, and analysis of digital elevation models (DEMs) and soils maps are used to reconstruct the post-glacial landscape history of the Tahquamenon River valley in eastern Upper Michigan. Optical ages of dune stabilization just below a strand line at ~240 m and fluvial deposits below 210 m document an initial draw-down of Lake Minong of at least 30 m prior to ~10,000 cal yr. BP. This event was perhaps the result of overwash and incision of Minong's outlet after influx of drainage from Lake Agassiz. Under our model, the optical ages of dunes and shorelines subsequently emplaced just below 225 m at ~9,500 cal yr BP require a transgression of Minong prior to another drop to a strand line at ~ 215 m. Since this scenario requires two sequences of early Holocene transgression and outlet incision for Lake Minong, it depends upon some revision of the outlet history for the Superior Basin, one of which has recently been proposed. A subsequent drop of Minong of unknown magnitude after ~8,500 cal yr B.P. is inferred from 14C dating of wood fragments from a vibracore from Muskallonge Lake below a prominent beach scarp. Optical ages of five dunes within the Tahquamenon River basin suggest that a Holocene lake (“Lake Bergquist”) existed behind an elevated bay mouth barrier south of present Tahquamenon Falls. The lake was impounded and persisted for 500-1000 years after the initial withdrawal of a bay of Lake Minong from the area. The outlet of Lake Bergquist was breached after ~9,500 cal yr BP, possibly as a result of a sudden flood surge of water from Lake Agassiz into Lake Minong and thence into Lake Bergquist. Signatures of this event are interpreted from GPR profiles and DEMs. Stratification of soil mapping units (i.e., two-storied soils) in a GIS reveal a 10-15 km long silt plume trending SE away from abandoned Minong shorelines and a well-defined pattern of stratified silt over clay within the Tahquamenon River valley. Distributions of OSL ages obtained during this study suggest that the rapid drainage of large lakes explains most dune building episodes in interior eastern Upper Michigan.