Late Glacial and Early Holocene History of the Glacial Lakes Aitkin and Upham Basin, North-Central Minnesota: Implications for the Timing of Post Glacial Eolian Activity

Abstract

Dune formation throughout Minnesota has been attributed to mid-Holocene aridity, however, the environmental setting of dunes in the Glacial Lake Aitkin and Upham basin suggest a Late Glacial and Early Holocene origin that is closely linked with exposure of source sands rather than aridity. Grigal et al. (1976) dated buried soils within a sequence of eolian sand near Lake Winnibigoshish, Minnesota, and identified several phases of eolian activity. These episodes were related to cycles of aridity and lake level fall during the Middle Holocene. Based on the work of Grigal et al. (1976), subsequent studies of eolian activity in Minnesota (Keen and Shane, 1990; Dean et al, 1996; Dean, 1997) concluded that all dunes in Minnesota are a result of Middle Holocene aridity. Glacial Lakes Aitkin and Upham occupied a basin in north-central Minnesota bounded on the north by the Giants Range and to the east, south, and west by hummocky moraines of the Rainy and Superior Lobes, and the St. Louis sublobe. Dune clusters occur sporadically throughout the Glacial Lakes Aitkin and Upham basin and occur in areas with abundant sources of fine sand. Granulometry indicates a 4q> grain size signature characterizes most dunes in the basin. Maximum dune amplitude is ~5 meters and dune morphologies suggest northwesterly winds. A sediment core collected from Hay Lake (93°W,52°N), located within a dunefield at the edge of Glacial Lake Upham, records three prominent peaks in whole-core magnetic susceptibility between 10, 100 and 6,600 yr BP. All dates referred to this paper are in uncalibrated 14C years B.P.. No elastic input is evident after 6,600 yr B.P., suggesting dune stability. Eolian events recorded in the core are interpreted as eolian activity that resulted from episodic lake drainage and exposure of abundant source sediment during the late Glacial and Early Holocene. The timing of dune formation within the basin has important implications for other dune fields throughout Minnesota. Using a Digital Elevation Model (DEM) the elevation of lake basin was adjusted for isostatic rebound based on the highest lake level, then tilted incrementally through several stages to assess relations among beaches, inlets, and outlets over time. The lake eventually drained, which led to the dune formation on littoral areas of exposed source sand.