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Evidence Suggesting That Methods of Rock-Varnish Cation-Ratio Dating Are neither Comparable nor Consistently Reliable

Published online by Cambridge University Press:  20 January 2017

Paul R. Bierman
Affiliation:
Department of Geological Sciences, University of Washington, Seattle, Washington 98195
Alan R. Gillespie
Affiliation:
Department of Geological Sciences, University of Washington, Seattle, Washington 98195

Abstract

Using samples from a prehistoric quarry site in the Mojave Desert, we tested and compared the two principal methods of rock-varnish cation-ratio dating, analysis of rock-varnish scrapings (R. I. Dorn, 1983, Quaternary Research 20, 49-73 and 1989, Physical Geography 13, 559-596) and analysis of rock varnish in situ (C. D. Harrington and J. W. Whitney, 1987, Geology 15, 967-970). Because we found no consistent relationship between the varnish cation ratio (K + Ca)/Ti, and the relative age of the varnish, neither method could be used to "cation-ratio date" the underlying chert artifacts. Moreover, in situ analyses yielded systematically higher cation ratios and lower Ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section. Our results, when considered along with other recently published evidence, indicate that these two methods of varnish chemical analysis and cation-ratio dating may not be comparable, nor consistently reliable, chronometers.

Type
Articles
Copyright
University of Washington

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