USING X-RAY FLUORESCENCE SPECTROMETRY TO ASSESS VARIANCE IN OBSIDIAN SOURCE DISTRIBUTION IN SOUTHERN IDAHO by Marielle Loryn Pedro Black A thesis submitted in partial fulfillment of the requirements for the degree of Master of Arts in Anthropology Boise State University May 2014 © 2014 Marielle Loryn Pedro Black ALL RIGHTS RESERVED BOISE STATE UNIVERSITY GRADUATE COLLEGE DEFENSE COMMITTEE AND FINAL READING APPROVALS of the thesis submitted by Marielle Loryn Pedro Black Thesis Title: Using X-Ray Fluorescence Spectrometry to Assess Variance in Obsidian Source Distribution in Southern Idaho Date of Final Oral Examination: 04 April 2014 The following individuals read and discussed the thesis submitted by student Marielle Loryn Pedro Black, and they evaluated her presentation and response to questions during the final oral examination. They found that the student passed the final oral examination. Mark G. Plew, Ph.D. Chair, Supervisory Committee Christopher L. Hill, Ph.D. Member, Supervisory Committee David A. Nolin, Ph.D. Member, Supervisory Committee The final reading approval of the thesis was granted by Mark G. Plew, Ph.D., Chair of the Supervisory Committee. The thesis was approved for the Graduate College by John R. Pelton, Ph.D., Dean of the Graduate College. DEDICATION This thesis is dedicated to my wonderful husband, Brandon Black, without whom this task may have been insurmountable. iv ACKNOWLEDGEMENTS Without the help and guidance of others, this thesis would not have been possible. I would like to thank my advisor, Dr. Mark Plew, whose guidance has been instrumental in creating a manageable project. Dr. Christopher Hill has helped me clarify the missing steps in addressing obsidian sourcing studies. Additionally, Dr. David Nolin has been immeasurably important in tackling the relatively extensive statistical analysis. Obsidian source data for Idaho was graciously shared by Craig Skinner, Program Director, Northwest Research Obsidian Studies Laboratory. Further, access to the archaeological collections at Boise State University and the Idaho Museum of Natural History allowed the study of existing collections. The cooperation and assistance of the Idaho Museum of Natural History, and Idaho State University staff, specifically Buck Benson, Amber Tews, Amy Commendador, and Herbert Maschner, were instrumental in my conducting this thesis research. Funding was provided by the Boise State University Student Research Initiative to run the XRF analysis. v AUTOBIOGRAPHICAL SKETCH OF AUTHOR Marielle Black is a GIS Manager with technical expertise in archaeology. She is currently pursuing an M.A. in Anthropology from Boise State University and holds two graduate certificates in GIS. Marielle has been conducting cultural resource studies in the Northwest since 2007. Her experience includes projects completed for the BLM and Tribal entities in Oregon, Washington, Nevada, and Idaho and conducting GIS analysis, excavation, and data recovery on land and under water. vi ABSTRACT 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. vii TABLE OF CONTENTS DEDICATION ......................................................................................................................... iv ACKNOWLEDGEMENTS ...................................................................................................... v AUTOBIOGRAPHICAL SKETCH OF AUTHOR ................................................................ vi ABSTRACT ............................................................................................................................ vii LIST OF TABLES .................................................................................................................... x LIST OF FIGURES ............................................................................................................... xiii LIST OF ABBREVIATIONS ................................................................................................ xvi CHAPTER ONE: INTRODUCTION ....................................................................................... 1 Regional Setting ............................................................................................................ 3 Idaho Obsidian Source Formation .................................................................... 5 Idaho Obsidian Deposition ............................................................................... 7 CHAPTER TWO: LITERATURE REVIEW ........................................................................... 9 X-Ray Fluorescence Spectrometry of Archaeological Obsidian .................................. 9 A Brief History of X-Ray Fluorescence ........................................................... 9 X-Ray Fluorescence Spectrometry and Obsidian ........................................... 10 Idaho Obsidian Source Studies ....................................................................... 12 CHAPTER THREE: METHODOLOGY ............................................................................... 14 XRF and Obsidian Sourcing Methods ........................................................................ 14 XRF and Obsidian: Methodological Concerns ............................................... 14 viii Idaho Obsidian Source Profiles and Locations ............................................... 17 Comparison of IMNH and NWROSL Obsidian Source Characteristics ........ 21 Mapping of Lithic Sources Relative to Sites .................................................. 21 Data Collection Methods ................................................................................ 22 CHAPTER FOUR: DATA ANALYSIS ................................................................................. 29 XRF Analysis Steps .................................................................................................... 29 Analysis of IMNH Library Standard .............................................................. 29 Analysis of Obsidian Profiles ......................................................................... 32 Summary of Comparisons Between IMNH and NWROSL Source Profiles .. 37 CHAPTER FIVE: ADDITIONAL DATA ANALYSIS ........................................................ 38 Additional XRF Analysis Steps .................................................................................. 38 Analysis of Obsidian Profiles ......................................................................... 40 Site versus IMNH and NWROSL Source Profiles ......................................... 53 Source versus IMNH and NWROSL Source Profiles .................................... 53 CHAPTER SIX: DISCUSSION AND CONCLUSION ......................................................... 55 Discussion of Results .................................................................................................. 55 Statistical Analyses ......................................................................................... 56 Geologic Formation’s Role in Obsidian Sources............................................ 59 Artifact Source Assignment ............................................................................ 60 Theoretical Application .................................................................................. 83 Conclusion .................................................................................................................. 86 REFERENCES ....................................................................................................................... 88 APPENDIX A ....................................................................................................................... 103 ix LIST OF TABLES Table 3.1 Idaho Obsidian Source Profiles by XRF Lab ........................................... 20 Table 3.2 XRF Sourcing of Archaeological Site Samples ........................................ 25 Table 4.1 Bruker Reliability Measured by Element Means ...................................... 30 Table 4.2 Obsidian Artifact Profile Comparison