Date of Award
Doctor of Philosophy (PhD)
Northwestern Minnesota is an area at the southwestern edge of the Canadian Shield that is mantled by thick Pleistocene sediment. The Pleistocene material included a variety of glacial, shoreline, offshore, fluvial, and eolian sediment.
The lithology of the glacial sediment reflects the rock and sediment over which the depositing glacier flowed. Glaciers that advanced from the northeast (Canadian Shield) deposited sandy, granitic-rich material. Glaciers that advanced from the north· (Manitoba Lowland) deposited loamy, calcareous-rich material. Glaciers that advanced from the northwest (eastern North Dakota and southwestern Manitobal deposited clayey, shale-ridt material. A variety of fluvial and lacustrine sediments are typically inter bedded with the glacial sediment.
On the basis of the geomorphology and topography, the south ern part of the Grand Forks and Bemidji Quadrang1es (scale 1:250,000) can be divided into the Lake-Plain Province, the Shoreline-Complex Province, the Glacial-Upland Province, and the Outwash Province. The Lake-Plain Province in the western part of the study area is a rather flat, featureless plain that is largely underlain by laminated silt and clay. The surficial sediments of the Shbreline-Complex Province (located just east of the Lake Plain Province} contains largely sand and gravel that was deposited as shoreline sediment of glacial Lake. Agassiz. Differences in topography, relief, and glacial geomorphic features are the basis for a fourfold subdivision of the Glacial Upland Province. Many of the larger lakes are situated either in meltwater channels or on outwash plains of the Outwash Province.
Four units thought to be older th.an late Wisconsinan (.greater than 25 000 B.P.) are present in the study area. The first late Wisconsinan ice advance entered the region from the northeast. Before this northeastern ice had completely melted away a second glacier from the northwest entered the region. The advance of this second glacier appears to have occurred about 22 000 B.P. The ice from the northwestern glacier melted from the area at about 14 000 B.P. Lakes began to form in low areas as water was dammed against the retreating ice front. The largest lake, Lake Agassiz, appears to have been in existence by 13 500 B.P. By about 9 500 B.P. Lake Agassiz drained for the final time as lower outlets to the east and north were opened. Between 13 500 :S.P. and 9 500 B.P. the lake level changed several times due to the lowering of the southern and northern outlets and minor ice advances down the Red River Valley.
Sackreiter, Donald K., "Quaternary geology of the southern part of the Grand Forks and Bemidji quadrangles" (1975). Theses and Dissertations. 256.