Paper No. 122-0
ALBANESE, John P., 3511 Carmel Dr, Casper, WY 82604-4986,

The last major Pleistocene glacial episode in the region occurred between 30,000 22,000 C14 years B.P. The major mountain ranges contained extensive glaciers e.g., a 1,000 m thick, 110 km long ice sheet covered the Yellowstone Plateau. The plains areas were characterized by a periglacial environment and the presence of artic steppe grasslands that supported an extensive mega-fauna, many species of which later became extinct. Warming and deglaciation commenced approximately 18,000 C14 B.P. By 14,000 C14 years B.P., much of the Yellowstone Plateau was ice-free and a tundra steppe prevailed. By 11,500 C14 years B.P., most mountain ranges were essentially free of ice and a coniferous forest prevailed. Between 11,500 10,000 C14 years B.P., the regional climate was generally cooler and more moist than present. Aquoll soils are superimposed on Clovis, Folsom and Hell Gap cultural horizons at a number of sites. A change to a semi-arid to arid climate took place in Late Paleoindian times. Depending on location, this change occurred between 9,300 7,000 C14 years B.P. At the Indian Creek Site, located in the Elkhorn Mountains of Montana, an abrupt change from coniferous forest to sagebrush steppe occurred approximately 8,200 C14 years B.P. Evidence of climatic change is also present in the stratigraphic record. The melting of glaciers with consequential high water run-off resulted in the regional deposition of gravel, which ceased just prior to 11,100 C14 years B.P. The transition to a more xeric environment during late Paleoindian time is also recognizable regionally by abrupt changes in depositional patterns, e.g. initiation of debris flow deposition, cessation of alluvial fan deposition and change in alluvial sedimentation patterns from steady state to erratic.

GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting
Session No. 122
Archaeological Geology and the Pleistocene-Holocene Transition
Hynes Convention Center: 206
8:00 AM-12:00 PM, Wednesday, November 7, 2001

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