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Title: Obsidian Hydration: A New Paleothermometer

Abstract

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data.

Authors:
 [1];  [2];  [2];  [2];  [3]
  1. {Larry} M [ORNL
  2. ORNL
  3. University of Tennessee, Knoxville (UTK)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003714
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; Journal Volume: 34; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; AGE ESTIMATION; ARCHAEOLOGICAL SPECIMENS; HUMIDITY; HYDRATION; MASS SPECTROSCOPY; THICKNESS

Citation Formats

Anovitz, Lawrence, Riciputi, Lee R, Cole, David R, Fayek, Mostafa, and Elam, J. Michael. Obsidian Hydration: A New Paleothermometer. United States: N. p., 2006. Web. doi:10.1130/G22326.1.
Anovitz, Lawrence, Riciputi, Lee R, Cole, David R, Fayek, Mostafa, & Elam, J. Michael. Obsidian Hydration: A New Paleothermometer. United States. doi:10.1130/G22326.1.
Anovitz, Lawrence, Riciputi, Lee R, Cole, David R, Fayek, Mostafa, and Elam, J. Michael. Sun . "Obsidian Hydration: A New Paleothermometer". United States. doi:10.1130/G22326.1.
@article{osti_1003714,
title = {Obsidian Hydration: A New Paleothermometer},
author = {Anovitz, Lawrence and Riciputi, Lee R and Cole, David R and Fayek, Mostafa and Elam, J. Michael},
abstractNote = {The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data.},
doi = {10.1130/G22326.1},
journal = {Geology},
number = 7,
volume = 34,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • In regions where obsidian was abundant, large quantities of the volcanic glass were used by prehistoric peoples to manufacture sharp-edged stone tools. By employing a variety of analytical techniques, these tools are examined by present-day archaeologists to study ancient culture and trade patterns. The geochemical properties of obsidian make it ideal for archaeologists who are interested in the sourcing and dating of obsidian artifacts. Geologic obsidian specimens from more than a dozen sources in northern California, Idaho, and Oregon were characterized by instrumental neutron activation analysis (INAA) at the University of Missouri Research Reactor (MURR). These data are being usedmore » to create an extensive geochemical data-base for obsidian sources located in the Northwest. Although X-ray fluorescence (XRF) data already exist for many of these sources, INAA provides a larger suite of elements that give superior resolution between individual sources and enables discovery of chemically distinct subgroups within complex source systems.« less
  • The effect of relative humidity on the hydration rate of obsidian and other glasses has been debated since the early work of (I. Friedman, R. Smith, Am. Antiquity 25 (1960) 476). While more recent work has been in general agreement that a relative humidity dependence does exist, hydration profiles as a function of relative humidity have not been obtained. In this paper we present the results of a study in which samples of Pachuca obsidian were hydrated for approximately 5 days at 150 C at relative humidities ranging from 21% to 100%, and the resultant profiles were measured by secondarymore » ion mass spectrometry (SIMS). The results suggest that the hydration rate is, indeed, a function of relative humidity, but for the relative humidity levels commonly observed in most soils the effects on hydration dating are expected to be relatively small. In addition, analysis of the surface values as sorption isotherms and comparisons with nitrogen sorption isotherms suggests that water is relatively strongly bound to the obsidian surface. By assuming a situation in which the 'surface' refers to active centers within the glass we have shown that an adsorption model provides a useful approach to modeling the diffusive process.« less
  • The variation of concentrations of hydrogen, sodium, potassium, lithium, calcium, magnesium, silicon, and aluminum as a function of depth in the hydration layer of obsidian artifacts has been determined by sputter-induced optical emission. The surface hydration is accompanied by dealkalization, and there is a buildup of alkaline earths, calcium and magnesium in the outermost layers. These results have clarified the phenomena underlying the obsidian hydration dating technique.