Date of Award

1966

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Geology

First Advisor

Dr. John R. Reid

Abstract

Glacial deposits and features in central Walsh County, North Dakota were investigated during the summer of 1965 to determine both their origin and their relationship to the history of glacial Lake Agassiz. The deposits included till and lake sediments exposed in cuts along the Park River, while the features included two end moraines and an esker.

The field study consisted of mapping the deposits, studying their morphology and composition, constructing cross-sections, and collecting selected samples. Laboratory studies of these samples included particle size analyses, feldspar staining, magnetic separation, and mineralogical analyses by X-ray diffraction.

The glacial feature located on the Grand Forks-Walsh County border is a steep-sided, branching, sinuous ridge. It is 4½ miles long, averages 250 feet in width and it varies in height from 15 feet in the northwest to 75 feet in the east. It is concluded to be a combination esker and an interblock or "crevasse" filling on the basis of: (1) the sinuous and reticulate form, (2) the composition, which is chiefly gravel and stratified drift, and (3) the size and shape of the feature. The stream that deposited the esker apparently flowed to the southwest and was diverted to the northwest when its path was probably blocked by sediment or blocks of ice. Evidence for this is: (1) a gradual decrease in height from east to northwest, (2) a gradual decrease in particle size in the same direction, and (3) the truncation of one ridge by another.

The end moraines located immediately north of the esker are only slightly younger than the esker, and represent brief stands of the glacier prior to the formation of the Edinburg moraine, which lies about 4 miles to the northeast. The southernmost moraine is a small branching, northwestwardly trending ridge which is 6½ miles long and averages 15 feet in height, and 250 feet in width. The northernmost moraine, parallel to the one south of it, is a broad, low, ridge, 6½ miles long, averaging 800 feet in width and 25 feet in height. Both moraines have abundant boulders scattered on their surface and are quite variable in composition; they are composed largely of till and fine to medium sands.

Sediments at the Park River site, on the western margin of the Edinburg moraine, indicate that this area was once covered by a proglacial lake. Distorted till and lake sediments indicate subsequent modification by solifluction and frost action. Homme Reservoir sediments one mile east of the Edinburg moraine, reveal evidence of deposition in close association with ice. Furthermore, it is concluded that the processes of glacial, fluviatile, and lacustrine deposition were all occurring at essentially the same time at this site, adding to the complexity of the geologic history.

Additional investigations should support the conclusion that these features were deposited approximately 11,740 years ago, the age of the Upper Herman beach.

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