Poster Number 53
Tuesday, 7 October 2008
George R. Brown Convention Center, Exhibit Hall E
The stratigraphy and geomorphology along the eastern front of the Rocky Mountains and the adjacent Great Plains provide evidence of landscapes that coincide with the presence of human populations using Clovis and Folsom artifacts. In the Elkhorn Mountains, deposits at Indian Creek are mostly braided stream sediments and contain the Glacier Peak G tepha (~11,125 RCYBP). At the MacHaffie site, also in the Elkhorn Mountains, a set of muddy sands are overlain by a dark sandy mud. The sands directly below the mud date to ~10,400 RCYBP. At Blacktail Cave, in the Dearborn drainage, a travertine overlies talus deposits dating to ~10,930 RCYBP. The travertine also buries silts and clays with vertebrate fossils dating from ~11,240-10,740 RCYBP. Organic-rich deposits with mammoth remains in the Sun River canyon date to ~11,500 RCYBP. On the Upper Missouri Plains, several stratigraphic sequences provide information on landscape evolution during these times. Along the Marias River, Laurentide till is overlain by a volcanic ash. The tephra is overlain by a silt with a paleosol and another tephra; there appears to have been an interval of aggradation and soil stability after 11,200 RCYBP. Buried soils are also developed within loess sequences in eastern Montana. Near the South Fork of Deer Creek, north of the Yellowstone River, silts containing mammoth remains dated to about 12,300 RCYBP are overlain by a buried soil. The age of Deer Creek soil may be similar in age to a series of buried soils dated to ~11,415-9,330 RCYBP in loess deposits at OTL Ridge, south of the Yellowstone River. The wetter conditions indicated by the organic-rich zones at Sun River, Marias, Deer Creek and OTL Ridge may imply increased precipitation or reduced evapotranspiration. These stratigraphic sequences can be used to infer landscapes that existed during the times associated with Clovis and Folsom.