Accuracy of post-bomb 137Cs and 14C in dating fluvial deposits

Lisa L. Ely*, Robert H. Webb, Yehouda Enzel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

56 Scopus citations

Abstract

The accuracy and precision of 137Cs and 14C for dating post-1950 alluvial deposits were evaluated for deposits from known floods on two rivers in Arizona. The presence of 137Cs reliably indicates that deposition occurred after intensive above-ground nuclear testing was initiated around 1950. There was a positive correlation between the measured level of 137Cs activity and the clay content of the sediments, although 137Cs was detected even in sandy flood sediments with low clay content. 137Cs is a valuable dating tool in arid environments where organic materials for 14C or tree-ring dating are scarce and observational records are limited. The 14C activity measured in different types of fine organic detritus yielded dates within 1 to 8 yr of a 1980 flood deposit, and the accuracy was species-dependent. However, undifferentiated mixtures of fine organic materials from several post-bomb deposits of various ages repeatedly yielded dates between 1958 and 1962, and detrital charcoal yielded a date range of 1676-1939. In semiarid environments, the residence time of most types of organic debris precludes accurate annual resolution of post-bomb 14C dates.

Original languageAmerican English
Pages (from-to)196-204
Number of pages9
JournalQuaternary Research
Volume38
Issue number2
DOIs
StatePublished - Sep 1992
Externally publishedYes

Bibliographical note

Funding Information:
We thank G. Benito, D. W. Hyndman, and T. S. Melis for assisting with sample collection and J. B. J. Harrison for the particle-size analysis. Reviews by B. F. Atwater, V. R. Baker, P. R. Bierman, T. W. Gardner, R. Hereford, J. Pitlick, and L. Wirt improved early versions of the manuscript. Ely’s and Enzel’s research was supported by the Engineering Directorate, Natural and Manmade Hazards Mitigation Program, National Science Foundation, Grant BCS-8901430. This report is Contribution No. 5 of the Arizona Laboratory for Paleohydrological and Hydro-climatological Analysis (ALPHA), University of Arizona.

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