Archaeological Research at MURR

Since its inception, the Archaeometry Lab has collaborated on hundreds of research projects from around the world. Among the foremost of these has been the characterization and compilation of obsidian sources in Mesoamerica. After more than two decades of research, the resultant obsidian database contains chemical "fingerprints" for 25–27 elements each for all of the major and most minor obsidian sources in Guatemala, Honduras, and central Mexico using INAA and XRF. The database represents the most comprehensive collection of information on Mesoamerican obsidian sources known (Glascock et al. 1998). As MURR assembles its database of chemical fingerprints, a portion of each obsidian source is being stored for future reference, experiments in hydration dating, and exchange with other analysts and archaeologists. Sourcing of obsidian artifacts is now so routine that of more than 20,000 artifacts from archaeological sites around the world characterized to date, greater than 99% have been successfully assigned to one of the sources in our database. Collaborations with a number of archaeologists in Mesoamerica and elsewhere in the Western Hemisphere continue to help expand MURR's obsidian database such that almost 500 sources from northern Alaska to the southern tip of Chile have been studied. In addition to these New World source characterizations, we continue to expand our database of Old World obsidian sources to regions such as the Russian Far East, Japan, the South Pacific, and the Mediterranean. In certain regions (Glascock et al., 1994), abbreviated-NAA and XRF methods that measure a limited suite of elements have been developed to source obsidian artifacts more economically.

Although the Archaeometry Lab initially focused its attention on obsidian characterization, interest in pottery analysis has since grown rapidly such that more than 60% of the samples we analyze each year are pottery, clays, and other raw materials used in the production of ceramics. Whereas obsidian occurs in compositionally and spatially discrete sources, sources of ceramic raw materials are widespread primary or sedimentary soils, between which there are only fuzzy spatial and compositional boundaries. Potters further confound the analysis of pottery by intentional addition or subtraction during paste preparation. Routine analysis of pottery at MURR generates a fingerprint for up to 33 elements in most instances. Approaches being applied on MURR-associated projects include intensive raw material sampling, studies of firing temperature and shell-tempering effects, thin-section petrography, and SEM imaging of the ceramic microstructure. Regions with large numbers of pottery samples analyzed at MURR include the Pacific coast of Guatemala, the Valley of Mexico, the American Southwest, the Mississippi Valley, and the eastern Mediterranean. Currently, our ceramics and clays database and ceramics archival collections contain nearly 50,000 samples.

Cryptocrystalline silicates include lithic materials such as chert or flint and were widely used by prehistoric peoples to manufacture stone tools. In contrast to obsidian and pottery, cryptocrystalline silicates (chert hereafter) have proven far more difficult to source by most analytical techniques, including NAA. In cases where chert is obtained from a single geological formation that outcrops at widespread locations, the within-source variation for many elements, if not most, is as great as the between-source variation. This problem suggests that analytical methods that determine the largest possible number of trace elements offer the greatest potential for success in identifying source-specific compositional profiles. The success achieved at MURR in the source analysis of chert is due in part to the large number of elements determined (approximately 30) and the excellent precision obtained for most elements. Thus far, more than 4,000 chert samples have been analyzed from sources throughout the Great Plains, Midwest, Alaska, Belize, and France.

Other archaeological materials such as basalt, copper, glass beads, steatite, limestone, marble, tephra, turquoise, shell, bones, and teeth are analyzed by the Archaeometry Lab on an infrequent basis.