MECHANISMS OF GLASS HYDRATION AND A PRELIMINARY INVESTIGATION OF ODDSIMS DATING OF OBSIDIAN ARTIFACTS FROM ÇATALHöYüK, TURKEY

Obsidian hydration dating by Secondary Ion Mass Spectrometry (ODDSIMS, Anovitz et al., 1999), and the related technique of obsidian hydration paleothermometry (Anovitz et al., 2006) are of significant potential applicability in archaeological sites containing significant numbers of obsidian artifacts. Analysis of the mechanism of this process shows that hydration below the glass transition is dominated by molecular water, rather than hydroxyl groups but surface waters are, nonetheless, strongly bound to the glass. Hydration rates are also heavily influence by self-stress and relaxation effects. While experimental calibrations provide temperature-dependent hydration rates, ODDSISMS dating requires calibration relative to external dates because paleotemperatures vary through time. While we have shown that this technique works well for relatively young samples (< 2 ka) from Mound 65 at the Chalco site in central Mexico (Riciputi et al., 2002), we have begun to test its applicability in the much older, and more complexly stratified site of Çatalhöyük, central Anatolia, Turkey. Occupation of this site ranged from approximately 7400 to 5600 BCE (calibrated radiocarbon), and chemical analysis of obsidian from the sites matches two sources in southern Cappadocia, East Göllü Dağ and Nenezi Dağ, the former representing more than one outcrop on the volcano. A few flakes provenanced to West Acigöl in northern Cappadocia were also found (Carter and Shackley, 2007). To begin building calibration curves for these sources, SIMS hydration profiles were obtained from several dated samples. Half-fall depths ranged from approximately 3.68 to 8.05 microns, and fell into three groups with distinctly different hydration rates. The middle group has been tentatively assigned to Nenezi Dağ on the basis of results from a sample of known provenance. A second (faster) sample set is, therefore, likely from the East Göllü Dağ source. A third trend (two samples) appears to have a significantly slower hydration rate, but one of the samples has a very unusual hydration profile, and the location of the other may have been disturbed. While the greater age of all of these samples (relative to Chalco) necessarily implies poorer absolute precision, these preliminary results suggest that useful chronometric results may be obtainable.