Using X-Ray Fluorescence Spectrometry to Assess Variance in Obsidian Source Distribution in Southern Idaho

This study explores the use of portable X-ray fluorescence (pXRF) and X-ray fluorescence (XRF) spectrometry to assist in associating artifacts with geological sources of obsidian from Southern Idaho. XRF spectrometry measures trace element abundance within obsidian artifacts, which is then compared, using a variety of statistical techniques, with known obsidian source geochemical profiles. Results from previous obsidian provenance studies have been used in archaeology as a proxy in measuring prehistoric hunter-gatherer mobility. Artifacts from 11 site assemblages were measured using pXRF to augment data for previously analyzed sites and to collect artifact geochemical data from previously unanalyzed sites. Using pXRF geochemical reference profiles from only one lab, artifact-to-source assignment resulted in 75% of analyzed artifacts attributed to an obsidian source. The addition of XRF geochemical reference profiles from a second lab and standardized values of all geochemical reference profiles and artifacts allows for a more complete assignment of artifacts to sources. With the original and additional geochemical reference profiles, artifact-to-source assignment increased to 87%. This study demonstrates the need for regional databases of standardized geochemical reference profiles as well as a thorough understanding of the underlying XRF technology to inform conclusions regarding prehistoric mobility. An additional, and possibly even more important, conclusion of this study is to question the validity and assumptions of previous XRF analysis studies based on past methodologies