The Distribution of Geologic and Artifact Obsidian from the Silver Lake/Sycan Marsh Geochemical Source Group, South-Central Oregon


Book Description

Geochemical characterization methods are commonly used in the reconstruction of prehistoric raw material use and procurement systems. Trace element studies of lithic source material and artifacts, specifically those made of obsidian, can reveal important information about the environmental and cultural factors which influence the prehistoric distribution of raw material. The current investigation uses geochemical characterization methods and data to document and evaluate the distribution of geologic and artifact obsidian that originates from the Silver Lake/Sycan Marsh (SL/SM) obsidian source. This large and prehistorically significant source is located in western Lake County, Oregon. Few source descriptions or artifact distribution studies exist for SL/SM obsidian. However, over the past decade, a significant increase in the use of geochemical characterization methods has generated a wealth of data for Oregon obsidian sources. This thesis synthesizes the results of the geochemical characterization analysis of 392 geologic obsidian specimens collected from the SL/SM source area and 1,938 SL/SM obsidian artifacts recovered from over 200 archaeological sites in Oregon, Washington and California. The artifact analytical data were derived from previously characterized artifact collections compiled and archived in an extensive database. A subset of artifacts were characterized for the purpose of this study. Based on the results of geochemical analysis of the geologic material, two distinct source boundaries are defined for the SL/SM geochemical source. The trace element data show that the geologic SL/SM obsidian source material originates from two chemically-related obsidian domes which lie in separate drainage basins. Accordingly, this investigation establishes that the natural distribution of geologic obsidian is highly dependent upon the regional topography. Spatial analyses of the artifact obsidian demonstrate a widespread distribution of SL/SM obsidian throughout central and western Oregon and parts of northwest California and southwest Washington. Numerous cultural and environmental variables appear to have affected the artifact distribution at local and regional levels. The findings show a predominance of SL/SM artifact obsidian use along the western slopes of the Cascade Range within the southern half of Oregon. Locally, use of the source appears to be less pronounced due to the abundance of competing central and eastern Oregon obsidian sources. The results suggest that SL/SM artifact obsidian was distributed both intentionally and incidentally as a result of prehistoric procurement and exchange systems.




Obsidian


Book Description

Obsidian was long valued by ancient peoples as a raw material for producing stone tools, and archaeologists have increasingly come to view obsidian studies as a crucial aid in understanding the past. Steven Shackley now shows how the geochemical and contextual analyses of archaeological obsidian can be applied to the interpretation of social and economic organization in the ancient Southwest. This book, the capstone of decades of investigation, integrates a wealth of obsidian research in one volume. It covers advances in analytical chemistry and field petrology that have enhanced our understanding of obsidian source heterogeneity, presents the most recent data on and interpretations of archaeological obsidian sources in the Southwest, and explores the ethnohistorical and contemporary background for obsidian use in indigenous societies. Shackley provides a thorough examination of the geological origin of obsidian in the region and the methods used to collect raw material and determine its chemical composition, and descriptions of obsidian sources throughout the Southwest. He then describes the occurrence of obsidian artifacts and shows how their geochemical fingerprints allow archaeologists to make conclusions regarding the procurement of obsidian. The book presents three groundbreaking applications of obsidian source studies. It first discusses an application to early Preceramic groups, showing how obsidian sources can reflect the range they inhabited over time as well as their social relationships during the Archaic period. It then offers an examination of the Late Classic Salado in Arizona’s Tonto Basin, where obsidian data, along with ceramic and architectural evidence, suggest that Mogollon migrants lived in economic and social harmony with the Hohokam, all the while maintaining relationships with their homeland. Finally, it provides an intensive look at social identity and gender differences in the Preclassic Hohokam of central Arizona, where obsidian source provenance and projectile point styles suggest that male Hohokam sought to create a stylistically defined identity in at least three areas of the Hohokam core area. These male “sodalities” were organized quite differently from female ceramic production groups. Today, obsidian research in the American Southwest enjoys an equal standing with ceramic, faunal, and floral studies as a method of revealing social process and change in prehistory. Shackley’s book discusses the ways in which archaeologists should approach obsidian research, no matter what the region, offering a thorough survey of archaeological obsidian studies that will have methodological and theoretical applications worldwide. The volume includes an extensive glossary created specifically for archaeologists.










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


Book Description

"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."--Boise State University ScholarWorks.