Date of Award
Master of Science (MS)
The study area includes 220 square miles in southeastern Pierce and southwestern Benson Counties, North Dakota (T. 152 N. through T. 154 N., R. 70 W. through R. 73 W.).
Field mapping and subsequent analyses were attempted to differentiate the drifts of the Leeds and Souris lobes, to determine the sequence and duration of events during and subsequent to glaciation, and to aid in correlating the drifts. Landforms of the area include: ice marginal ridges, ground moraine, proglacial plains, abandoned river channels, and sand dunes.
In the laboratory, very coarse sand lithology percentages, till fabric, texture, and gross lithology were used to differentiate the drifts of the two lobes. The first two methods were the most useful.
The upper Cretaceous Fox Hills Formation is exposed along the banks of abandoned river channels and in ice thrust masses, but everything else is Pleistocene or Holocene.
Four Pleistocene lithostratigraphic units were recognized within the study area: Dahlen Formation, Balta formation (new unit), unit B, and Hansboro Formation. The last two are the most widespread surficial units. The Dahlen Formation occurs only in the subsurface in several test holes. The Balta formation occurs in the western half of the study area and is overlain by unit B.
The Oahe Formation consists of fine sand, silty clay, and organic-rich clay; it is most common in abandoned river channels and in depressions.
Although most previous studies have interpreted the surface till to be the result of supraglacial processes (ablation), the till fabric data suggests that most of the till of unit B and the Hansboro Formation is instead of basal melt-out (lodgement) origin.
During late Woodfordian and early Twocreekan time, unit B and the Hansboro Formation were deposited by the recession, readvance, and final recession of the Leeds and Souris lobes, respectively. The Balta formation sand and clayey silt are interpreted to have been deposited in or near glacial Lake Souris I during the first recession of the Souris Lobe.
Finally, silty clay and organic-rich clay was deposited from 10,000 to 8,500 yrs. b.p., and from 4,500 yrs. b.p. to present, when the climate was much as it is today. Most the fine eolian sand was deposited between 8,500 and 4,500 yrs. b.p., when the climate was warmer and drier than it is today.
As a result of this study a clearer understanding of the geologic and climatic events of the Quaternary of northcentral North Dakota now exists.
Schnacke, Arthur W. Jr., "Glacial geology and stratigraphy of southeastern Pierce and southwestern Benson counties, North Dakota" (1982). Theses and Dissertations. 266.