STRATIGRAPHY OF QUATERNARY VERTEBRATE FOSSIL LOCALITIES IN THE NORTHERN ROCKY MOUNTAINS

Quaternary vertebrates in the Northern Rocky Mountains (NRM) provide important information that is useful for understanding the consequences of long-term environmental change. Sedimentary sequences in the Upper Missouri River basin, primarily in western Montana, can be compared to stratigraphic sequences in the adjacent Great Plains and Snake River Plain/Northern Great Basin regions. For instance, a Late Pleistocene stratigraphic sequence in southwestern Montana in Centennial Valley contains 21 taxa, including 16 genera of mammals. Radiocarbon measurements ranging from >52,000 B.P. to 19,000 B.P. indicate the fauna are younger than the American Falls fossils and may be partially contemporary with Rainbow Beach, Duck Point, Dam and Wilson Butte on the Snake River Plain. Along the Dearborn River, the Blacktail Cave stratigraphic sequence extends from prior to the Last Glacial Maximum (LGM) to the Younger Dryas. The Blacktail strata range in age from 37,000 to 10,200 B.P. and contain both large and small–sized mammal fossils. The pre-LGM strata can be compared to middle-late Wisconsin deposits at Eagle Cave and January Cave in Alberta. Stratigraphic sequences at Sheep Rock Springs, Indian Creek, MacHaffie, and Sun River contain fossils that are younger than the LGM and can be compared to Late Glacial-Holocene sequences in Idaho (Jaguar Cave, Wasden, Kelvin's Cave) and localities on the Northern Great Plains along the Marias River, Deer Creek and at OTL Ridge. A diverse set of environmental and taphonomic contexts are associated with these localities which contain cave, alluvial, eolian and paludal/lacustrine deposits and provide a basis for evaluating site-specific and regional-scale patterns of landscape evolution and biogeography. The stratgraphic sequences in the NRM can be used to examine patterns of ecological change before, during and after the LGM, including conditions associated with the Younger Dryas and the Pleistocene-Holocene transition.