Virginia L. Butler | Search USGS

USGS2021

Reconstructing paleohydrology in the northwest Great Basin since the last deglaciation using Paisley Caves fish remains (Oregon, U.S.A.)

The arid northwest Great Basin underwent substantial hydroclimate changes in the past 15,000 years, greatly affecting its desert ecosystems and prehistoric people. There are conflicting interpretations of the timing of hydrologic changes in this region, requiring more records to resolve the dominant climatic drivers. The Paisley Caves archaeological site, located near former pluvial Lake Chewaucan, contains well-dated, stratified sediments best known for evidence of early human occupation in North America. We present a novel paleohydrologic record for the Chewaucan basin based on the frequency of fish remains (Salmonidae and Cypriniformes, likely tui chub) and their carbon, oxygen, and strontium isotope compositions, from the Paisley Caves. Cypriniformes abundance peaks first at the start of the Bølling/Allerød warm interval (∼14.7 ka) and again during the early Younger Dryas (∼12.8 ka). Isotope compositions indicate tui chub were derived from an expansive Lake Chewaucan throughout the Bølling/Allerød, but mainly from spring- or stream-influenced sources by the late Younger Dryas to the present. Fish abundance dropped sharply through the Younger Dryas and early Holocene, when isotope compositions indicate a mix of habitats. Isotope compositions indicate the driest conditions during the middle Holocene, followed by slightly wetter conditions up to the present. This record agrees with recent pluvial lake reconstructions, supporting the hypothesis that a northward shift in the winter storm track supported deep lakes throughout the Bølling/Allerød in the northwest Great Basin. Lake level decline during the Younger Dryas suggests drying climate, differing from more southerly records. During the Holocene, however, shifts in Chewaucan basin hydrology are consistent with the rest of the western U.S. This highlights the need for region-specific records to inform predictions of the hydrologic impact of climate change on arid regions.

Oregon↗

USGS2017

Chronology and ecology of late Pleistocene megafauna in the northern Willamette Valley, Oregon

Since the mid-19th century, western Oregon's Willamette Valley has been a source of remains from a wide variety of extinct megafauna. Few of these have been previously described or dated, but new chronologic and isotopic analyses in conjunction with updated evaluations of stratigraphic context provide substantial new information on the species present, timing of losses, and paleoenvironmental conditions. Using subfossil material from the northern valley, we use AMS radiocarbon dating, stable isotope (δ 13 C and δ 15 N) analyses, and taxonomic dietary specialization and habitat preferences to reconstruct environments and to develop a local chronology of events that we then compare with continental and regional archaeological and paleoenvironmental data. Analysis of twelve bone specimens demonstrates the presence of bison, mammoth, horse, sloth, and mastodon from ~ 15,000–13,000 cal yr BP. The latest ages coincide with changing regional climate corresponding to the onset of the Younger Dryas. It is suggested that cooling conditions led to increased forest cover, and, along with river aggradation, reduced the area of preferred habitat for the larger bodied herbivores, which contributed to the demise of local megafauna. Archaeological evidence for megafauna–human interactions in the Pacific Northwest is scarce, limiting our ability to address the human role in causing extinction.

Oregon↗