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Late Pleistocene environments of the Bighorn Basin Wyoming-Montana, USA

Authors: Thomas Minckley*, University of Wyoming, Mark Clementz, University of Wyoming, Marcel Kornfeld, University of Wyoming, Mary Lou Larson, University of Wyoming, Judson B Finley, Utah State University
Topics: Paleoenvironmental Change, Biogeography, Earth Science
Keywords: Pleistocene, Interglacial, paleoclimatology, western North America, pollen, stable isotopes, caves, vegetation dynamics
Session Type: Paper
Presentation File: No File Uploaded

Limited numbers of high-resolution records that predate the Last Glacial Maximum (LGM) make it difficult to quantify how environmental changes impacted terrestrial ecosystems prior to peak glaciation. We examined sediments from Last Canyon Cave in the Pryor Mountains of Montana and Wyoming to construct a >45ka environmental record from pollen and stable isotope analysis. Artemisia pollen was hyper-abundant at the beginning of the record. Carbon isotope values of bulk organic matter from the lowermost cave sediments (>40ka) showed little variation (-25.3±0.4‰) and were consistent with a predominantly arid C3 environment similar to that of today. After 40ka Artemisia pollen decreased as herbaceous taxa increased toward the Last Glacial Maximum. A significant decrease in delta13C values from 40-30ka (~1.0‰) established a new baseline (-26.6±0.2‰), suggesting cooler but seasonally wetter conditions to the LGM. These conditions persisted until variation in delta13C values increased significantly with initial warming after the LGM and is marked by two spikes in values at 14.4ka (-25.2‰) and 13.5ka (-25.4‰) before delta13C values dropped to their lowest values (-26.9+0.2‰) at the onset of the Younger Dryas (12.8ka). These results provide an opportunity to examine late Pleistocene conditions and ecological change in arid intermontane basins of the Rocky Mountains.

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