Doctoral Dissertation Improvement Grant: Oxygen Isotope Signatures and the Identification of Chert in the Southern Plains

Southern Methodist University, Dallas TX

Investigators

Abstract

Under the supervision of Dr. David J. Meltzer, Joanna Roberson will investigate the application of oxygen isotope analysis as a method for identifying the source of the chert - a cryptocrystalline sedimentary rock - used by late Ice Age peoples on the Southern Plains of western North America. Chert has properties that make it an excellent material for producing stone tools, but because outcrops of this stone are geologically uncommon and scattered in the Southern Plains, these hunters and gatherers often had to track great distances across the landscape to obtain the stone. Thus, knowing where stone was quarried becomes a means of revealing just how far groups had to move to obtain this resource vital to their tool-making, and therefore opens an important window into understanding human adaptations to what was a very different landscape than is present today. However, identifying the source of the stone in use is complicated, not least because of problems that stem from the nature of chert itself. Complex formation processes can create great diversity among cherts, including visible, microscopic, and chemical variations. In addition, some cherts have extensive geographic distributions, while others have look-alikes that occur elsewhere, and still others may not be documented or even visible today. This research will test the feasibility of identifying chert through isotopic analyses of elemental oxygen, a technique common in geology, but not regularly used on chert in archaeology. While other methods are hindered by the variations in chert, oxygen isotope analysis may, in fact, benefit. Oxygen isotopic ratios (18O/16O) vary according to the environmental origin of the material in which the oxygen occurs, such that the isotopic make-up of chert reflects the original sources of the sediments, the local conditions of chert deposition, and any post-depositional influences. Thus, isotopic ratios are expected to exhibit measurable variation between chert sources. If successful, this method can improve stone sourcing by eliminating ambiguity in identification methods, by discriminating between visually similar materials, and by recognizing variability between spatially separated outcrops of a single material type. Although this study will focus on chert sources and artifacts from the Southern Plains, if the method proves viable it will be of great use to archaeologists working in any geographic region and chronological period, and is thus poised to make important contributions beyond this area. Moreover, by bringing together archaeologists and geologists, it will have a broader impact by fostering inter-disciplinary relationships and encouraging others to seek solutions to research problems from diverse and unconventional sources. Such collaborations will make great contributions to numerous disciplines, as techniques and information are shared between research fields.