RELATIVE DATING PAIRED WITH COSMOGENIC DATING MAY LEAD TO A BETTER UNDERSTANDING OF BOTH: AN EXAMPLE FROM NEWARK VALLEY, CENTRAL NEVADA

Developing an accurate chronology for Quaternary deposits is challenging. Often times the best results come from a combination of approaches. Using one or more numerical dating techniques in combination with detailed geologic mapping, stratigraphy, and relative dating methods can yield results that are more accurate, or that are contradicting. When contradictions occur, this presents a good opportunity to examine underlying assumptions and interpretations in all approaches and, in the best case scenario, further the capabilities of each technique.

A paleoclimate and soils geomorphic study of pluvial Lake Newark Valley, Central Nevada provides a good example of this contradiction. Initial interpretations, based on soils and geomorphology, were that two ages of shorelines were preserved within the basin, each with common characteristic soil development and preservation. The younger shorelines were dated using ¹⁴C. Regional soil development rates and correlation to the marine oxygen isotope curve were used to estimate the age of the older shorelines. ³⁶Cl analyses of the same beach deposits distinguished four ages of shorelines, three of which were indistinguishable based on soils alone.

This contradiction has led to re-evaluation of both approaches. It might be that soil development reaches a threshold in central Nevada after which Quaternary deposits are not easily distinguished using that approach. When this threshold is reached, however, remains unclear. Stratigraphic changes, unconformities, complex post-depositional histories of erosion and burial, and incorporation of reworked older sediment into younger deposits all could affect modeled cosmogenic ages. In this study area the combination of both techniques will hopefully result in a better understanding of soil development rates, complexities, and limits as well as identify depositional environments and stratigraphic clues that should be evaluated and considered when interpreting cosmogenic ages.