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Is Obsidian Hydration Dating Affected by Relative Humidity?

Published online by Cambridge University Press:  20 January 2017

Irving Friedman ,
Fred W. Trembour ,
George I. Smith  and
Franklin L. Smith
Irving Friedman
Affiliation:
U.S. Department of the Interior, Branch of Isotope Geology, Box 25046, MS 963, Denver Federal Center, MS 963, Denver, Colorado 80225
Fred W. Trembour
Affiliation:
U.S. Department of the Interior, Branch of Isotope Geology, Box 25046, MS 963, Denver Federal Center, MS 963, Denver, Colorado 80225
George I. Smith
Affiliation:
U.S. Geological Survey, 345 Middlefield Road, MS 902, Menlo Park, California 94025
Franklin L. Smith
Affiliation:
U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225
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Abstract

Experiments carried out under temperatures and relative humidities that approximate ambient conditions show that the rate of hydration of obsidian is a function of the relative humidity, as well as of previously established variables of temperature and obsidian chemical composition. Measurements of the relative humidity of soil at 25 sites and at depths of between 0.01 and 2 m below ground show that in most soil environments, at depths below about 0.25 m, the relative humidity is constant at 100%. We have found that the thickness of the hydrated layer developed on obsidian outcrops exposed to the sun and to relative humidities of 30-90% is similar to that formed on other portions of the outcrop that were shielded from the sun and exposed to a relative humidity of approximately 100%. Surface samples of obsidian exposed to solar heating should hydrate more rapidly than samples buried in the ground. However, the effect of the lower mean relative humidity experiences by surface samples tends to compensate for the elevated temperature, which may explain why obsidian hydration ages of surface samples usually approximate those derived from buried samples.

Type
Articles
Information
Quaternary Research , Volume 41 , Issue 2 , March 1994 , pp. 185 - 190
Copyright
University of Washington

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