Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

A.M. Cvancara


The Seibold Site on the Missouri Coteau in northwest Stutsman County, North Dakota, contains a late Quaternary lacustrine deposit with a spectaculary preserved and diverse biota; more than 150 species occur, of which the mollusks and fish are figured and discussed in detail in this study. The stratigraphic sequence, in ascending order, is a follows: 1) pebbly silt; 2) clayey silt; 3) organic mud; 4) calcareous mud; 5) sandy silt and clay; 6) silty sand; and 7) sandy silt and clay.

The stratigraphic sequence and biota suggest a 5-phase history for the area during the last 11,000 years. During phase 1 (units 1 and 2, late Wisconsinan) an oligotrophic lake developed in a depression on superglacial drift. During phase 2 (units 3 and 4, latest Wisconsinan and earliest Holocene) an eutrophic lake was surrounded first by an open spruce and popular forest and then by tall grass prairie with scattered stands of trees. During this time the lake shallowed in response to the warmer climate that caused the change in vegetation. Phase 3 (unit 5, early Holocene) represents a shallow slough surrounded by tall grass prairie. Phase 4 (unit 6, middle Holocene) represents an arid period during which the slough was probably dry much of the time. Short grass prairie was probably the dominant vegetation. During phase 5 (unit 7, late Holocene) the slough was similar to those on the Missouri Cateau today.

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