USE OF OSL, GPR AND GIS TO CONSTRAIN BEHAVIOR OF LAKE MINONG'S WATER PLANE AND PATHS OF MELTWATER DISCHARGE ACROSS EASTERN UPPER MICHIGAN, USA

Hundreds of now-stable, parabolic dunes are widely distributed across the low-relief plains of interior eastern Upper Michigan (EUM). We derived 85 optical (OSL) ages on quartz sand from dunes scattered throughout EUM. Results indicate that most of the dunes we sampled were stabilized during the early Holocene, ~10.4 - 8.5 ka. We suggest that dune activity in the Big Two-Hearted, Betsy and Tahquamenon Valleys (draining to Lake Superior) was initiated as the water plane of Lake Minong fluctuated and fell, exposing sandy lake beds to deflation. The fact that dunes of similar age are spread SW beyond the height of land at Danaher to the Manistique River watershed (draining Lake Michigan) is puzzling and requires a mechanism for sand nourishment that is independent of the Lake Minong water plane. To connect our data set with possible explanations, we used GIS to reconstruct rebound-adjusted paleotopography and ground penetrating radar (GPR) to explore subsurface stratigraphy at Danaher. Prior interpretations notwithstanding, GIS demonstrates that, with the Nadoway Barrier intact, the initial outlet of Lake Minong could have stood near Germfask (just SW of Danaher) and drained across the Manitoulin Dolomite SW to Lake Chippewa. This would afford a mechanism for of landscape scouring and a possible sand source for dunes. An OSL age on near-planar bedded sand at Danaher suggests that the site drained (was abandoned as an outlet?) ~10.3 ka. This presumably occurred as retreat of the LIS permitted drainage of the Superior Basin to the northeast and a drop in the level of Lake Minong. GPR reflections at Danaher suggest glaciofluvial sediments that accumulated in Lake Minong prior to abandonment of the Germfask spillway. Those sediments lie beneath several younger sequences we interpret as representing shallow wedges of sandy sediment that were episodically stranded above the standing level of Lake Minong during lake level fluctuation. Rebound of the northerly outlet would have caused a slow transgression of the lake and subsequent changes in meltwater receipt into the Superior Basin may have driven brief spillovers though Danaher and Germfask to Lake Chippewa. Rebound eventually led to the overtopping or sapping-through of the Nadoway Barrier, the destruction of Lake Minong and the establishment of modern drainage ~ 9.0 ka.