EVIDENCE FOR EARLY HOLOCENE EOLIAN ACTIVITY, NORTH-CENTRAL MINNESOTA

Postglacial eolian sediments and landforms are ubiquitous throughout Minnesota. Observations of dune distribution and morphology on the beds of Glacial Lakes Aitkin and Upham combined with a 10,000-year record from a lake sediment core in north-central Minnesota records early Holocene eolian activity. Evidence suggests that dune-building events are likely the result of an unvegetated postglacial landscape rather than mid-Holocene aridity. Eolian activity in Minnesota has commonly been attributed to cycles of mid-Holocene aridity. However, given our present knowledge of the mid-Holocene vegetation of Minnesota, it is difficult to conceive of a landscape that could provide the necessary source of sand to form large dense fields of sand dunes. Determining the timing of this eolian activity is critical for accurate paleoclimatic reconstructions of mid-continent North America.

Dunes are most common near the western shoreline of the basin. They occur as dense clusters adjacent to source areas, but are scattered when more distal. Maximum dune amplitude are ~2.5 meters. Granulometry indicates a 4phi grain size signature characterizes dunes throughout the Glacial Lake basin.

An 8.57 meter sediment core was collected from Hay Lake, located within a dunefield on the bottom of Glacial Lake Upham. Three prominent peaks in the whole-core magnetic susceptibility record are evident between 10.1k and 6.6k 14C years B.P. Granulometry and microscopy confirm these peaks are due to influx of 4phi clastic sediment. No clastic input is evident after 6.6ka, suggesting dune stability.

The dune fields of north-central Minnesota are intimately related to sand source areas and supply, which were at their peak immediately after the drainage of the Glacial Lakes. Thus, a significant component of dune formation in north-central Minnesota likely took place during the early Holocene.