Date of Award

1975

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Geology

Abstract

The bluffs of Lake Sakakawea, west- central North Dakota, provide excellent exposures of the Paleocene Sentinel Butte Formation and Pleistocene glacial deposits of the Coleharbor Group. The dominant sediment type in the Sentinel Butte Formation is thinly-bedded silt. Fine sand, clay, and lignite occur in lesser abundance. Lignite, clay, and peat are most commonly bounded by thinly-bedded silt. No lignite beds greater than five feet are present in the study area. The complete section of the Sentinel Butte Formation was not present in bluff exposures of the study area. The maximum exposed thickness of the Sentinel Butte Formation was 110 feet. Extreme lateral variability of lithology made detailed correlations exceedingly difficult, even across small distances such as from one bluff to the next. Glacial deposits of the Coleharbor Group are more common in bluff exposures in the eastern part of the study area and become less common and extensive towards the western edge of the study area. At least two separate units of pebble loam are present in the eastern part of the study area. Gravel and bedded silt crop out in the eastern part of the study area. Thicknesses of glacial drift in bluff exposures range from 0 to 30 feet. The glacial deposits seem to be restricted to former topographic low areas. Erosion by waves and ground water sapping is substantial, resulting in considerable land loss. This erosion is greater along the south shore of the lake.

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