A COMPLEX DEGLACIAL HISTORY SPANNING UP TO 55,000 YEARS GLIMPSED IN EASTERN SARGENT COUNTY, NORTH DAKOTA

The Milnor Beach of the southwestern Red River Valley, if it exists, represents an impoundment of melt water against the western flank of the Red River Valley Lobe of the Laurentide ice sheet prior to the formation of Lake Agassiz. The Milnor beach was first mapped in eastern Sargent County, North Dakota as discontinuous sand ridges and knolls occurring at higher elevations and slightly westward of the well-recognized Herman Beach; the initial perimeter of Lake Agassiz. Our pilot project to evaluate the age, spatial continuity, and sedimentary characteristics of the Milnor beach segments indicates that features that have been mapped as Milnor strandline segments in North Dakota were actually deposited at widely varying times from as recently as ~400 years ago up to as much as ~55,000 years ago. Additionally they have disparate sedimentological characteristic, most of which are not consistent with the later shoreline deposits of Lake Agassiz. One sample location in this study may have provided the first and only age constraint for the Milnor beach, if continuing research can verify that it is a genuine shoreline. The study area in Sargent County has been over-printed by numerous advances of ice through the Red River Valley, as well as channeling of melt water along the flanks of the glacier, and later by features of Lake Agassiz itself. Our preliminary study gives a small but compelling glimpse into the complex deglacial history recorded in a relatively small area of North Dakota.