102 The Wishbone Core: Identifying Sediment Components to Determine the Paleoclimate of Lake Bonneville

Faculty Mentor: Andrea Brunelle (Geography, University of Utah)

Abstract

Climate reconstructions of the Great Basin region has led to unique discoveries during the Pleistocene-Holocene Transition, ~ 11,000 years ago (Palacios-Fest et al., 2021). The timeline of Lake Bonneville, a prehistoric pluvial lake, has largely been established, yet there are many unknowns about the specific timing of events and climatic conditions throughout each stage. For this study, we present lake sediment core data that expands the existing literature on the climate variability of the Bonneville Basin within the last 30,000 years. The Wishbone Core (WB19B), extracted from the Utah Test and Training Range in the West Desert of Utah, was sampled and analyzed using charcoal counts (CHAR), loss on ignition (LOI), and magnetic susceptibility (MAG SUS). These data were used to evaluate the variability of climate throughout the Late Pleistocene and Early Holocene. Our findings show an increase in charcoal abundance during the Stansbury Oscillation (SO) (~ 24,000 cal yr. B.P). Our working hypothesis for the high charcoal during the SO focuses on two components. First, an increase in fire activity may be attributed to dryer conditions during the oscillation, allowing existing fuel to burn. Additionally, lower lake levels expanded the exposed area which may have permitted more vegetation to grow, therefore, increasing fuel during the dry period.

Another distinct interval, known as the black mat, is found at the 80-84 cm mark of the core. The abundance of organic material in the black mat, dated to be ~ 12,000 cal yr., B.P, indicates a moist and wetland-like environment. The increase in organic material concurs with the Younger Dryas Event, a global return to near-glacial conditions. As suggested by Haynes (2008), it is possible the colder climate during the Younger Dryas reduced evaporation which allowed incoming precipitation to raise water tables in the hydrographically closed Bonneville Basin. The findings from our analysis of the black mat are consistent with other geoarchaeological sites in the Western United States, which have similarly identified this dark organic layer (Haynes, 2008). The information collected for this study through the paleoclimate reconstruction of Lake Bonneville may be relevant to archaeologists, climate scientists, and policymakers in the Great Basin region.

References

Palacios-Fest, M. R., Duke, D., Young, D. C., Kirk, J. D., & Oviatt, C. G. (2021). A paleo-lake and wetland paleoecology associated with human use of the distal old river bed delta at the pleistocene-holocene transition in the Bonneville Basin, Utah, USA. Quaternary Research, 106, 75–93. https://doi.org/10.1017/qua.2021.49

Haynes CV Jr (2008). Younger Dryas “black mats” and the Rancholabrean termination in North America. Proceedings of the National Academy of Sciences of the United States of America 105(18): 6520–6525.