Date of Award

1998

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

J.R. Reid

Abstract

An exposure with 15 buried A-horizons near Douglas Creek, Lake Sakakawea, central North Dakota, has provided an excellent opportunity for paleoclimate reconstruction. Analyses included texture, stable carbon, radiocarbon, pollen, and phytoliths. The variations in these properties between individual soil horizons served to reconstruct the former environments of each soil horizon.

The paleosols were developed in a sequence of deposits in a mile-long tributary to the Missouri River. The soils are in a shallow valley fill exposed by wave action along the north shore of Lake Sakakawea. The 1996 exposure was up to 4m high and 51.5m wide. There were up to fifteen buried A- and C-horizons identified along this outcrop; the minimum was seven.

Textural analyses revealed that the A-horizons are silty loams and the C-horizons silty clay loams. Radiocarbon dating of the paleosols indicates they formed between 5240 ± 310 yr BP and 2585 ± 60 yr BP with an average development time of 70 to 110 years for each A-horizon. Although the pollen results proved inconclusive, 8 13C values and phytolith assemblages indicate a relatively cool, moist climate from 5240±310 yr BP until 2585±60 yr BP, with a short warming trend at about 2700 yr BP. These results substantiate other climate studies in this region which indicate cool, moist climate following deglaciation with a subsequent warming period occurring between 3000 and 2000 yr BP.

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