Date of Award
Master of Arts (MA)
Field mapping, construction of cross-sections, and laboratory analyses of field samples were used to map, describe, and correlate the Late Wisconsinan glacial sediments of northwestern Cass County, North Dakota and to interpret the glacial history of the area.
The surficial geology of the area was interpreted as: 1) collapsed glacial sediment, 2) glacial sediment draped over pre-existing glaciolacustrine topography, 3) proglacia1 lake sediment, 4) wave-eroded glacial and lake sediments and 5) recent river sediment. Landforms within each of these areas include eskers, abandoned or overfit river channels, transverse ridges, ice thrust masses, kettles and beach deposits.
Seven lithostratigraphic units were identified on the basis of texture, very coarse sand lithology, matrix calcite-dolomite composition, clay mineralogy, density, and stratigraphic position. Three till units, "A", "D" and "G", were distinguished primarily on the basis of density and stratigraphic position. The lowest till, unit "A", was deposited prior to 12,300 years B.P. The upper two till units, "D11 and "G", which are in direct contact throughout most of the study area, were compared to determine if they represented two distinct till units or a single weathered till. Chemical analysis and stratigraphic evidence support the two-till theory. Till Dis interpreted as a lodgement till deposited by a southeast-flowing glacier approximately 11,900 years B.P. The sediment is a dense, homogeneous silty loam with a pre dominantly shale lithology probably equivalent to the Gardar Formation. The upper till, "G", consists of an upper ablation till and a lower lodgement till deposited by a southwest-flowing glacier 11,700 years B.P. The ablation till component is a friable, pebbly sandy loam with lenses of well-sorted sand. The lodgement till is a dense, homogeneous; sandy to silty loam. These till subunits are equivalent to the Dahlen Formation.
Units "B" and "C" are widespread, well-sorted lacustrine silt and sand units deposited from 12,300 to 11,900 years B.P. representing extensive proglacial lake deposits throughout and beyond the study area.
Units "E" and "F" are limited to the central part of the study area and represent collapsed supraglacial lake sediments deposited between 11,900 and 11,700 years B.P.
Differentiation of the units was best demonstrated by their relative stratigraphic positions, density, and lithologic composition. The presence of units nB", "C", "E" and "F" supports the conclusion that prior to the existence of glacial Lake Agassiz several proglacial and supraglacial lakes were present along the margin of the Des Moines Lobe in North Dakota during the late Wisconsinan.
Falcone, Sharon K., "Glacial stratigraphy of northwestern Cass County, North Dakota" (1983). Theses and Dissertations. 87.