MARQUETTE PHASE (LATEST WISCONSINAN) GLACIOFLUVIAL DISCHARGE TO EARLY LAKE MINONG EMPLACED THE CORE OF WHITEFISH POINT IN EASTERN UPPER MICHIGAN

Approximately 11,500 calendar years ago, glacial Lake Minong stood in the southeastern corner of the Lake Superior Basin in north-central North America, confined on the west by ice of the Marquette Phase of the Laurentide Ice Sheet (LIS). Ice stood at Minong's edge near the present village of Grand Marais in eastern Upper Michigan. A long-standing conceptual model posits that glaciofluvial discharge between the retreating LIS and adjacent uplands followed a set of descending terraces into Lake Minong. To partially test this idea, we used ground penetrating radar (GPR) along four stepped terraces east of Grand Marais to assess their subsurface stratigraphy. Radar reflections along all four terraces suggest sandy substrates and braided patterns of shallow, shifting channels that are oriented east-west. The two lowest terraces lie at elevations between 220 and 225 m, roughly matching a recently identified strong shoreline of Lake Minong (~220 m). Nearly flat topography adjacent to these latter terraces and surrounding the Crisp Point Moraine lie at roughly the same elevation. We suggest the possibility that glaciofluvial sediments sourced from terraces that fronted the Marquette ice sheet were deposited in Lake Minong at or just below 220 m in an easterly prograding platform. After Lake Minong's southeastern rim was breached ~9.3 ka and levels of earliest Lake Superior were established at the Houghton Low, this platform emerged meters above young Lake Superior, comprising proto-Whitefish Point. Beginning with the subsequent Nipissing Transgression and continuing to the present, the core of Whitefish Point has been altered along its periphery by wave-mediated erosion and deposition.