RUI: Direct Determination of Late Pleistocene Periods of Maximum Wetness in the Owens River System: Shoreline Dating in Panamint Valley, California

Hampshire College, Amherst MA

Investigators

Abstract

ABSTRACT We seek to establish the timing of periods of maximum wetness in the western U.S. Great Basin by dating pluvial shoreline features in Panamint Valley, the penultimate basin in the Owens River system. During most of Pleistocene time, the Owens River terminated in Searles basin (upstream from Panamint), forming a complex network of superimposed shorelines and tufa deposits. However, during the relatively rare wettest periods when all the upstream basins (Owens, China, and Searles) overflowed, pluvial lakes up to 310 meters deep formed in Panamint Valley. Tectonic uplift has preserved well-defined shorelines, which are marked by carbonate tufa deposits (which formed in situ in shallow water near shorelines), wave-cut benches, and near-shore lacustrine deposits. We propose to apply two newly refined techniques to date the prominent Gale shoreline in Panamint Valley. The Gale shoreline represents the most recent period of overflow of the Owens Rivers from Panamint into Death Valley, but it has not been reliably dated. Tufa will be dated by measuring cosmogenic chlorine-36 ( 36Cl) buildup, a technique that has proven successful in dating glacial moraines in the Sierra Nevada and elsewhere, but has not been extensively applied to carbonate tufa deposits. Ages of fine-grained shallow water lacustrine deposits associated with the shoreline will be determined by optically- stimulated luminescence dating and a 36Cl depth profile in alluvial fan materials associated with the shoreline will provide additional age control. We believe these combined techniques will confidently identify the ages of the shorelines and therefore periods of maximum wetness in the Owens River system, which so far have only been indirectly inferred from sediment core proxies. Clear recognition of the wettest time intervals will provide a common benchmark to which the existing sediment proxies in Owens, Searles, and Death Valley cores could be standardized, thus providing a more coherent regional paleoclimate reconstruction for the Great Basin region. Well-defined periods of maximum wetness in the Great Basin can be compared with ice core and marine sediment records to assess how temperature and moisture transport in this continental setting responded to global climate changes. This project will involve undergraduate students in every phase, helping to prepare future researchers and science educators. Students from underrepresented groups will be actively recruited from Hampshire and Mount Holyoke Colleges, and the PI will be recruiting high school students from schools in New York City for Hampshire College. The PI is principally involved in undergraduate education and the research results and experiences from this project will be incorporated into his undergraduate courses for science majors and non-science majors, as well as into presentations on climate change for public community audiences. As an active NSF-sponsored researcher, the PI will be better able to convey the nature of global change research, both by virtue of developing important new knowledge through the proposed research activities and also by increasing the visibility and credibility of the PI.