Quaternary History of the Lower St. Louis River and Estuary, Lake Superior, Northeastern Minnesota
2000-07
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Quaternary History of the Lower St. Louis River and Estuary, Lake Superior, Northeastern Minnesota
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2000-07
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Field research was conducted during the summer of 1999 to determine the extent of possible buried stable landsurfaces along the St. Louis River and estuary. The identification and description of these surfaces was accomplished by three methods: location of paleosols, reconstruction of the paleogeography, and determination of sedimentation and incision rates along the river. Core drilling results show evidence of 5 laterally extensive organic layers within the estuary. The Loss on Ignition method of organic and inorganic carbon analysis was used along with magnetic susceptibility in to identify the surfaces. 14C analysis returned dates ranging from nearly modern for the shallow layer, to almost 1,900 yrs. BP for the deepest. Paleogeographic studies centered around the identification of a subaqueous outwash delta deposited in Glacial Lake Duluth by the Superior Ice Lobe, and the location and relative dating of abandoned meanders along the lower St. Louis River, which has been divided into 3 reaches based on geomorphology. Known dates for abandoned landsurfaces were combined with the elevation of those surfaces above the modern river channel in order to determine the rates of incision along the river. Downcutting has occurred slowly in Reach 1, upriver from the Thomson Reservoir, were the river is controlled by the underlying bedrock. Reach 2 is found mostly in Jay Cooke State Park where the St. Louis River has incised 90 m into the surrounding lake plain. Sedimentation in Reach 3 ranges from 30 to 80 cm per 100 yrs. The sedimentation and incision rates were applied to landsurfaces upon which archaeological sites of unknown age occur. The time of abandonment of the fluvial landsurfaces provides an estimate of the maximum possible age of the archaeological site. In Reach 3, the level of Lake Superior controls the location of sites. A combination of fluctuating lake levels throughout the Holocene and differential tilt in the Superior Basin has buried and submerged shoreline and estuary sites from 9,500 to 6,000 yrs. BP and 3,000 to 0 yrs. BP. These results may aid future archaeologists in the search for deeply buried archaeological sites, as well as provide initial estimates of the maximum age new and previously known archaeological sites.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Kevin Patrick Norton in partial fulfillment of the requirements for the degree of Master of Science, July 2000.
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