Fred H. Stross

High-Precision Chemical Characterization of Major Obsidian Sources in Guatemala

The important Mesoamerican obsidian source El Chayal has been carefully explored and sampled. Forty new source specimens have been subjected to neutron activation analysis, and the composition patterns are recorded and compared. The westernmost of the known Guatemalan obsidian sources, Tajamulco, has also been studied. Precise analytical data are also reported for the important Ixtepeque and Rio Pixcaya sources. In addition, the complete analytical data for a group of artifacts in Belize excavated by Norman Hammond are reported and compared with the source compositions. The establishment in the literature of a library or collection of precise and intercomparable composition data for the sources of this general region is suggested, and the present paper is offered as a first contribution toward this objective. Elemental analysis of obsidian has been shown to be useful in reconstructing ancient trade routes. A sizable amount of work has been done on Mesoamerican sites and sources (Cobean et al. 1971; Hammond 1972; Heizer et al. 1965; Stross et al. 1976a). In this paper we propose to discuss 2 problems that have naturally arisen in these studies and to suggest at least partial solutions. reliability of the results have tended to differ from author to author. The second problem concerns the cost of reliable analysis and sampling, which is perhaps far higher than necessary. Previous research has shown that in some cases a correlation of an artifact with its source can be made by analysis of only 2 or 3 elements, but in other instances a far greater number of elements must be determined to reach a firm conclusion with regard to the source of the glass. This is true not only for the obvious reason that the chance of overlapping patterns increases with the increasing number of supply sources and archaeological sites, but because a priori statements on the chemical composition pattern of an unanalyzed obsidian source are impossible to make. An obsidian source or supply area may have several outcrops, which may or may not be chemically similar. However, even an individual outcrop may show a systematic variation within its own boundaries (Bowman et al. 1973). A source thus has to be adequately sampled so that its homogeneity may be demonstrated, or if it is found to be heterogeneous, so that the character of the variation in its composition may be defined by analysis. It is thus desirable to develop libraries of composition patterns for all sources of archaeological obsidian in a given region. These composition records should be as complete, accurate, and precise as possible. They should be published in units and in a form that makes it convenient to compare them, in order to be of use to all interested in identifying artifacts according to source. It is also desirable that the data be published in journals that are generally known and accessible to those working on the subject. Comparison of the composition patterns of the obsidian of a given cultural area often reveals that determination of the abundances of a limited number of elements is sufficient to distinguish the sources within the region in question. The determination of these few elements in the artifacts collected within this area should be sufficient to assign provenience to these artifacts, and this would be far less expensive than a complete analysis of the samples. When a generally applicable, detailed catalog of composition patterns is available, it is not too difficult to determine the most economical method for matching artifacts with their respective sources. Existence of

PRECISE CHARACTERIZATION OF GUATEMALAN OBSIDIAN SOURCES, AND SOURCE DETERMINATION OF ARTIFACTS FROM QUIRIGUA

LBL-12252 Revised Preprint eley L boratory ALIFORNIA Submitted to American Antiquity PRECISE CHARACTERIZATION OF GUATEMALAN OBSIDIAN SOURCES, AND SOURCE DETERMINATION OF ARTIFACTS FROM QUIRIGUA ... Fred H. Stross, Payson Sheets, Frank Asaro, and Helen V. Michel November 1981 TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diu is ion, Ext. 6782 Prepared for the U.S. Department of Energy under Contract W-7405-ENG-48

Ecuadorian Obsidian Sources Used for Artifact Production and Methods for Provenience Assignments

A study by neutron activation analysis and X-ray fluorescence measurements of 116 Ecuadorian obsidian artifacts as well as primary and secondary source samples has shown that the material originatedfrom two Andean sources in north-central Ecuador, a flow in the valley of Mullumica, and deposits fou-nd on Yanaurco Chico and the nearby Quiscatola crest. The Yanaurco-Quiscatola deposit complex, homogeneous within our ability to measure, is represented by 18 percent of the artifacts. The Mullumica source has variable, apparently linearly related element abundances that may have resultedfrom the incomplete mixingof two magmas within a magma chamber. Seventy-eight percent of the samples studied are deduced to have originatedfrom that source. Five artifacts from La Chimba cannot be assigned an origin, but four of them have the same provenience. To test the validity of the mixed-magma theory, we present equations to calculate the abundance of any measured element from that of iron. On the average, agreement within about 3 percent is obtained for artifacts.

An Initial Consideration of Obsidian Procurement and Exchange in Prehispanic Ecuador

We have examined the role of long-distance trade in Prehispanic Ecuador using X-rayfluorescence (XRF) and neutron-activation analysis (NAA) of obsidian artifacts from the archaeological sites of El Inga, Chobshi Cave and Site OGSE-46 on the Santa Elena Peninsula. Results indicate that two geological sources east of Quito, Yanaurco-Quiscatola and Mullumica, were the principal source of raw obsidian at these sites. We situate our findings within a broader archaeological context through a review of the literature and a discussion of an earlier provenience study undertaken by us. We express concerns about recent attempts to apply ethnohistoric models to early periods of Ecuadorian prehistory, and argue that despite early exploitation of the principal obsidian sources, long-distance trade in obsidian was initiated at a relatively late date and remained at a surprisingly low level in southern Ecuador during most of prehistory.

Tikal obsidian: sources and typology

The obsidian industry of Classic period Tikal, Guatemala, is discussed with regard to geological source determinations and behavioral typology. The potential of these two approaches for cultural reconstruction is greatly extended when they can supplement each other. Recent source determinations of obsidian artifacts from Tikal indicate (1) a behavioral link between locally-produced prismatic blades of Highland Guatemalan stone and ceremonial incised obsidians and eccentrics, and (2) a Central Mexican origin for a seemingly large portion of Tikals obsidian projectile points and knives. 25 references, 3 figures, 5 tables.

Provenience Analysis of Obsidians from the Central Peten Lakes Region, Guatemala

A set of 296 obsidian artifacts from the lakes area of the Department of Peten, Guatemala, has been provenienced by X-ray fluorescence and neutron activation analysis. The obsidians come from socioeconomic contexts (primarily rural/domestic) and time periods—from the Middle Preclassic period, ca. 800 B.C., up to the time of Spanish contact, A.D. 1525—that have been poorly represented in previous Lowland provenience studies. Thus they provide new data on the acquisition and distribution of this important non-local commodity in the Maya Lowlands.

Obsidian Procurement and Distribution in the Tikal-Yaxha Intersite Area of the Central Maya Lowlands

Obsidian from known outcrops in the Mesoamerican highlands has been recovered from lowland Maya sites, providing significant evidence for long-distance procurement and local redistribution of obsidian by the ancient Maya. Prior chemical-characterization studies of obsidian from the lowland Maya area provide a foundation for the study of Tikal-Yaxha obsidian presented here. The samples used in this analysis came from middens associated with 12 residential units located between Tikal and Yaxha and dating from the Preclassic through Terminal Classic periods. The results of chemical sourcing of the Tikal-Yaxha samples generally lend support to current interpretations of changes in obsidian distribution and procurement in the central Maya lowlands. During the Preclassic period, most obsidian was imported from the San Martin Jilotepeque-Rio Pixcaya source area. Obsidian from the El Chayal source predominated throughout the Classic period, although some Mexican Pachuca obsidian appeared in Early Classic contexts, and Ixtepepque obsidian was apparently restricted to the Terminal Classic period.

Sources of Some Obsidian Flakes from a Paleoindian Site in Guatemala

Neutron activation analysis was used to determine the chemical composition of sources of obsidian artifacts from the Paleoindian site of Los Tapiales in Guatemala with an occupation date of around 10,700 radiocarbon years ago. Three different sources were detected, all between 50 and 75 km from Los Tapiales. The predominant source represented in our ten samples was in the Rio Pixcaya area, and another was in the Tajumulco area. A third source, identified by comparison with other work, appears to be in the area of San Bartolome Milpas Altas.