Climate Change in North Dakota Since the Last Glaciation
By Allan Ashworth
Department of Geosciences, North Dakota State University


Introduction

The Last Glaciation

The Late Glacial

The Holocene

Conclusions

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The Last Glaciation

North Dakota comprises both glaciated and non-glaciated terrains. During the last glacial maximum, the northern and eastern parts of the state were ice covered with flow directed generally southwards following the James and Red River drainages. The western boundary of the ice sheet across North Dakota was east of the Missouri River. Only the southwestern part of the state was ice-free (Figure 1). Fossil polygons, remnants of patterned ground, are widespread indicating cold and possibly arid conditions. The age of the polygons is uncertain and may predate the last glaciation. Are they

indicators of a polar desert? What was the vegetation and fauna of the ice-marginal zone? Sediments from shallow depressions in the unglaciated region are unfossiliferous. There are no pollen records, but based on a profile from a site close to the Rocky Mountains, we can speculate that 15,000 years ago vegetation of the Great Plains was dominated by Artemisia (sage) and other forbs, and grasses. The vegetation was probably what has been referred to as "mammoth steppe." Certainly, the molars of many mammoths have been found in gravel deposits in western North Dakota but for the majority of the specimens, stratigraphic context is either unknown or uncertain. None of the teeth have been dated so it is uncertain whether they are from the last or earlier glaciations. We do know that the woolly mammoth, Mammuthus primigenius, inhabited the western shore of Lake Agassiz about 11,000 years ago and presumably it was from an ancestral population in the southwest. What other large animals roamed the ice margin? Teeth and bones of bison, including partial skulls of Bison latifrons and Bison antiquus (Bison bison antiquus) are also found in alluvium, but as with the mammoth teeth, their age is uncertain.

Perhaps, the best insight about the megafauna is from the Hot Springs site in the southern Black Hills, South Dakota. This site was located about 200 km south of the ice margin in North Dakota, a distance within the migratory range of several of the large animals. At Hot Springs, mammoths and other large animals were trapped in the sediments of a sink hole lake about 26,000 years ago. The most prominent fossils are those of Mammuthus columbi (Columbian mammoth), and M. primigenius (woolly mammoth). The fauna also included the herbivores Camelops hesternus (yesterday's camel), Hemiauchenia macrocephalus (large headed llama), Antilocapra americana (pronghorn), and cf. Euceratherium collinum (shrub ox). The carnivores and scavangers on these animals were Canis lupus (gray wolf), Canis latrans (coyote), and the largest of the late Pleistocene predators, Arctodus simus (giant short-faced bear).


Dr. Allan Ashworth, Chairman
Geology Department
130 Stevens Hall
North Dakota State University
Fargo, ND 58105
Phone: 701-231-7919
E-mail: ashworth@plains.nodak.edu


NDSU Central Grasslands Research Extension Center

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