J. Michael Elam

Obsidian-Artifact Source Analysis for the Mixtequilla Region, South-Central Veracruz, Mexico

Neutron activation and statistical analyses establish source ascriptions for 201 obsidian artifacts representing Preclassic, Classic, and Postclassic period contexts in the Gulf Coast region of Mexico. Zaragoza-Oyameles, Puebla, and Pico de Orizaba, Veracruz, are the most common sources, but procurement patterns and technology shifted during the archaeological sequence. Comparative information is discussed for all periods, but especially the distribution of Zaragoza-Oyameles obsidian in the Classic period is examined. The distribution network for this obsidian served several regions. The importance of long-distance obsidian distribution for Teotihuacan is called into question.

Neutron activation analysis of stone from the Chadron Formation and a Clovis Site on the Great Plains

Abstract Cryptocrystalline silicates from the Chadron Formation were widely used by prehistoric human groups in the Great Plains of North America. There are two documented quarry areas: Flattop Butte in Colorado and the White River Badlands of South Dakota. Cryptocrystalline silicates from these sources are visually indistinguishable, making it difficult to determine the sources of artefacts found at archaeological sites. In this investigation, neutron activation analysis is used to distinguish the two sources. This technique also identifies lithic material from the Clovis-age Eckles site in Kansas as being from Flattop Butte.

Exchange Implications of Obsidian Source Analysis from the Lower Rio Verde Valley, Oaxaca, Mexico

excavations at four archaeological sites in the lower Rio Verde valley on the Pacifc coast of Oaxaca, Mexico. Determinations of source locations of these artifacts permit the examination of changes in obsidian exchange patterns spanning the late Middle Formative to the Classic period. The results show that through most of this period the importation of obsidian into the lower Verde region was dominated by sources in the Basin of Mexico and Michoacan. The data allow us to evaluate previous models of interregional relations during the Formative and Classic periods, including interaction with the highland centers of Monte Alban and TeotEhuacan.

Ceramic Production and Exchange in Late/Terminal Formative Period Oaxaca

Patterns of Late/Terminal Formative period (ca. 500 B.C.-A.D. 300) ceramic exchange in Oaxaca are examined through instrumental neutron activation analysis (INAA). Samples of 453 Late/Terminal Formative period sherds were submitted to the Missouri University Research Reactor for INAA to determine elemental composition. The sherds came from 20 exca vated sites and two surveys in the following regions: the Valley of Oaxaca, MixtecaAlta, Mixteca Baja, lower R?o Verde Val ley, and Cuicatl?n Ca?ada. Selected for the study were vessel fragments from three recognized paste categories: grayware (gris), fine brownware (caf? fino), and creamware (crema). We also sampled clays and sherds from known sources in four modern pottery-making towns in the Oaxaca Valley. The research adds to the INAA database for Oaxaca by identifying the chemical signatures of six source groupings that we can link to specific regions and, in two cases, to particular source zones within regions. The evidence from chemical composition and typology indicates continuity in resource use and production practices in bothAtzompa and Coy otepec from pre-Hispanic into modern times. The data show that the exchange of ceram ics in Late/Terminal Formative Oaxaca was multidirectional, with ceramics imported both to and from the Oaxaca Valley.

Obsidian hydration: A new paleothermometer

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14 C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data.

Effects of thermal annealing on the radiation produced electron paramagnetic resonance spectra of bovine and equine tooth enamel: Fossil and modern

The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300–1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of the heat treated fossil sample. We conclude that the hyperfine components are due to sample heating to temperatures/times >100 °C/30 min and that similarities between fossil and MEQ spectra after the 300 °C/30 min MEQ anneal are also due to sample heating. We conclude that the presence of the hyperfine components in spectra of fossil tooth enamel indicate that such thermal events occurred either at the time of death, or during the postmortem history.The concentration of stable radiation-induced paramagnetic states in fossil teeth can be used as a measure of sample age. Temperature excursions >100 °C, however, can cause the paramagnetic state clock to differ from the actual postmortem time. We have heated irradiated enamel from both fossilized bovid and modern equine (MEQ) teeth for 30 min in 50 °C increments from 100 to 300 °C, measuring the electron paramagnetic resonance (EPR) spectrum after each anneal, to investigate such effects. Samples were irradiated again after the last anneal, with doses of 300–1200 Gy from 60Co photons, and measured. Two unirradiated MEQ samples were also annealed for 30 min at 300 °C, one in an evacuated EPR tube and the other in a tube open to the atmosphere, and subsequently irradiated. The data showed that hyperfine components attributed to the alanine radical were not detected in the irradiated MEQ sample until after the anneals. The spectrum of the MEQ sample heated in air and then irradiated was similar to that of t...