Powdered obsidian for determining hydration rates and site thermometry

Part of : Mediterranean archaeology & archaeometry : international journal ; Vol.4, No.2, 2004, pages 17-31

Section Title:
Obsidian hydration dating shares the disadvantage of all the chemical reaction dating systemsin its reliance on experimentally determined short-term rate constants for long-term ageextrapolation. In archaeological applications the extrapolation may need to encompass localedaphic variation and longer range environmental changes. Before the contribution of thesevarying field related rate determinants are considered the initial trajectory of the extrapolationneeds to be determined. In many studies the extrapolation is circumvented by adoptingradiometric systems that provide reference-age frameworks that are then used to calibratehydration depth readings. The relative hydration ages that are attached to the reference age stillrequire -that the hydration rate constants be experimentally determined. This is to ensure thatany discrepancies between the observed artefact hydration readings and the experimentally foundhydration rate can be identified and, if possible, explained. Given that deposit perturbation andartefact weathering are factors in many archaeological sites it is therefore still necessary to knowthe inherent hydration rate of the obsidian being dated. This paper seeks to develop obsidianpowder systems to derive short-term rate constants that can apply to ambient conditions atarchaeological sites. Three cases employing obsidian powders for hydration dating research are presented here in pursuit of this aim.The first case employs rate constantsestimated from the powder data andoptically measured hydration; thesecond combines obsidian powderdata and SIMS measurement on solidflakes; the third case attempts toapply simple powder diffusion datato determine effective hydration ratesat two sites near Talasea in PapuaNew Guinea (Figure 1). The resultsof the powder experiments supportthe view that 'water' rather than Halone is responsible for the hydration process.
Subject (LC):
Obsidian, Hydration, Thermometry, SIMS