Obsidian Sources Research Articles

Is obsidian sourcing about geochemistry or archaeology? A reply to Speakman and Shackley

The response from Speakman and Shackley to my paper highlights a number of important issues currently facing archaeological sourcing research. Many of these issues, however, have little to do with HHpXRF itself and more to do with an artificial crisis triggered by specialists' concerns about a hitherto restricted technique becoming available to a wider community. Despite their mantra of “validity and reliability,” Speakman and Shackley erroneously equate these two concepts with the accuracy of an instrument's measurements. Additionally, they mischaracterise a self-contained test, conducted with specific parameters (i.e., “off-the-shelf” operation), as an endeavour to facilitate or endorse poor-quality data. Paradoxically, their disparagement of experimental internal consistency as “silliness” is incongruous with their own data. Furthermore, a discussion focused on handheld instruments is obfuscated by their inclusion of desktop instruments that are “portable” only in the sense of luggable to an electrical outlet in a laboratory context. Most troubling is that they envision themselves as the arbiters of science vs. “playing scientist.” Contrary to their claims, HHpXRF proliferation will improve reproducibility and archaeological results.

Networks and Neolithisation: sourcing obsidian from Körtik Tepe (SE Anatolia)

This paper details the use of obsidian sourcing to reconstruct networks of interaction (or ‘communities of practice’) amongst populations of south-eastern Anatolia and the Near East in the context of ‘Neolithisation’ during the late 11th–early 10th millennia BC. EDXRF was used to elementally characterise 120 artefacts of Epi-Palaeolithic – Pre-Pottery Neolithic A date from Körtik Tepe in south-eastern Anatolia. Four eastern Anatolian sources are represented, mainly Bingöl A/B and Nemrut Dağ, plus the first evidence for the use of Muş obsidian. When the source data is integrated with the artefacts' techno-typological attributes it is possible to locate the assemblage within an Upper Tigris tradition (with some interesting local differences), which stands in stark contrast to contemporary practices in northern Mesopotamia and the Levant. These local and regional distinctions support recent views of the Neolithic being much more heterogeneous, with a ‘mosaic’ of community-specific/local traditions of subsistence practices, raw material choices and lithic technologies during the Younger Dryas–Early Holocene.

The character and use of the Soros Hill Obsidian source, Antiparos (Greece)

This article details the geological and elemental character of the obsidian from the Soros Hill source on the Cycladic island of Antiparos, Greece. EDXRF was used to analyse 40 geological geo-referenced samples. The products are clearly chemically discriminated from those of the other Aegean sources, and those from the Carpathians and central Anatolia. While the obsidian is of excellent tool-making quality, the small size of its nodules seems to have made it a less attractive raw material, attested at only a handful of prehistoric sites in the central Cyclades.

Empires and resources: Central Anatolian obsidian at Urkesh (Tell Mozan, Syria) during the Akkadian period

Almost all of the obsidian used to craft stone tools in the Near East from the Palaeolithic onward originated from volcanoes in two geographic regions: Central Anatolia and Eastern Anatolia. Five decades of obsidian sourcing has led to the view that Central Anatolian obsidians largely followed the Mediterranean coast and rarely reached farther east than the Middle Euphrates, whereas Eastern Anatolian sources almost exclusively supplied sites east of the Euphrates. This paper discusses the identification of Central Anatolian obsidian artefacts at the Bronze-Age site of Tell Mozan (Urkesh) in northeastern Syria. Most of the obsidians at Tell Mozan (97%) came from the Eastern Anatolian sources, as expected from established distribution models. Artefacts of Central Anatolian obsidian, however, were excavated from one well-constrained context: the deposits on a palace courtyard that date to the height of the Akkadian empire's influence at this third-millennium Hurrian religious and political centre. In particular, the obsidian came from the Kömürcü source of Göllü Dağ. Potential explanations for this exotic obsidian are discussed. This obsidian might have “piggybacked” on the distribution of Central Anatolian metals or arrived at this city as royal gifts or prestige items. Other discussed mechanisms include Akkadian-linked changes in either territoriality involving pastoral nomads responsible for the arrival of Eastern Anatolian obsidians or identity construction of elites based on involvement in Central Anatolian economic and political networks.

AN ASSESSMENT OF THE CURRENT APPLICATIONS AND FUTURE DIRECTIONS OF OBSIDIAN SOURCING STUDIES IN ARCHAEOLOGICAL RESEARCH*

This paper thematically characterizes a large body of recent obsidian sourcing discourse as a means of highlighting the current place of obsidian provenance studies in larger archaeological discourse. It is shown that the field of obsidian sourcing is flourishing, with a clear upward trend in the number of published studies in the past decade. This paper further argues that sourcing is a means to an end, a way to determine where artefacts originate, and thus a means of addressing broader archaeological problems. Through this contextual framework, obsidian sourcing studies—and indeed all provenance studies—are seen as relevant because they transcend the increasingly specialized world of archaeological discourse.

Validity of “off-the-shelf” handheld portable XRF for sourcing Near Eastern obsidian chip debris

Handheld portable XRF (HHpXRF) has received considerable recent attention in archaeology, especially for obsidian sourcing. Published studies largely suggest a high potential for success. HHpXRF, though, has been met with debate and scepticism. Concerns fall into three categories: (1) low accuracy and precision, (2) data correction schemes and calibration, and (3) ignorance of fundamental XRF issues such as specimen size limits and morphology effects. The result is that archaeological interpretations in HHpXRF-based studies are cast into doubt. Should interpretations be believed if authors did not follow the perceived best practices? To address such questions, the validity of HHpXRF for Near Eastern obsidian sourcing was tested under deliberately “sub-optimal” conditions. Irregular obsidian debitage near the minimum size limits was sourced with a success rate of 94% (based on A-rank matches) to 100% (based on A- and B-rank matches) even under conditions chosen to mimic “off-the-shelf” operation.

Obsidian Source Use in Tongan Prehistory: New Results and Implications

ABSTRACT The article presents results of an obsidian sourcing study on artifacts from Tonga and Fiji. New LA-ICPMS data on obsidian source locations on Tafahi in northern Tonga are discussed in relation to inter-island mobility during two important phases in the Central Pacific: the late-Lapita phase in Fiji-West Polynesia at 2700–2600 cal. BP and during the time of the rise of Polynesian chiefdoms at ∼1000–400 cal. BP. The sourcing results indicate that two sources of obsidian were exploited during Tongan prehistory. It is suggested that different modes of interaction were responsible for obsidian movement during the early and late phases of Tongan prehistory.

Preliminary characterization and regional comparison of the Dasht-i-Nawur obsidian source near Ghazni, Afghanistan

Archaeologists have known that an obsidian source exists in the Dasht-i-Nawur basin of central Afghanistan since at least the 1970s; however, regional political turmoil and instability have prevented in-depth study of this source. Data presented here from recent analyses of archival specimens of obsidian collected during a 1976 survey provide a preliminary geochemical profile for this obsidian source. These data suggest that the Dasht-i-Nawur source is easily distinguishable from other obsidian sources in the Near East and southwest Asia. Comparison of these data to an existing database of artifact compositional profiles suggests that initial hypotheses about restricted distribution of the Dasht obsidian may be correct. These data provide for the first time the characterization of a long-known but poorly studied obsidian source. Additionally, this study serves as one example of the benefits gained through working to maintain and preserve data archives of now-closed laboratories.

Advanced signal processing analysis of laser-induced breakdown spectroscopy data for the discrimination of obsidian sources

Obsidian is a natural glass of volcanic origin and a primary resource used by indigenous peoples across North America for making tools. Geochemical studies of obsidian enhance understanding of artifact production and procurement and remain a priority activity within the archaeological community. Laser-induced breakdown spectroscopy (LIBS) is an analytical technique being examined as a means for identifying obsidian from different sources on the basis of its 'geochemical fingerprint'. This study tested whether two major California obsidian centers could be distinguished from other obsidian localities and the extent to which subsources could be recognized within each of these centers. LIBS data sets were collected in two different spectral bands (350±130 nm and 690±115 nm) using a Nd:YAG 1064 nm laser operated at ~23 mJ, a Czerny-Turner spectrograph with 0.2-0.3 nm spectral resolution and a high performance imaging charge couple device (ICCD) detector. Classification of the samples was performed using partial least-squares discriminant analysis (PLSDA), a common chemometric technique for performing statistical regression on high-dimensional data. Discrimination of samples from the Coso Volcanic Field, Bodie Hills, and other major obsidian areas in north-central California was possible with an accuracy of greater than 90% using either spectral band.

NON‐DESTRUCTIVE SOURCING OF BRONZE AGE NEAR EASTERN OBSIDIAN ARTEFACTS: REDEVELOPING AND REASSESSING ELECTRON MICROPROBE ANALYSIS FOR OBSIDIAN SOURCING*

Despite predictions in the 1980s that electron microprobe analysis (EMPA) would become a popular technique for obsidian sourcing, few studies have used it with this goal, and most of them are now outdated and unrepresentative of modern EMPA. For example, Merrick and Brown (1984) recorded their data on punch cards. Furthermore, these studies destructively prepared artefacts for analysis. The research at hand endeavoured: (1) to establish the modern capabilities of EMPA for obsidian sourcing; and (2) to develop and evaluate procedures for non‐destructive artefact analysis. Issues such as diagenetic effects and compatibility with NAA and XRF data were also investigated.

Distinguishing Nemrut Dağ and Bingöl A obsidians: geochemical and landscape differences and the archaeological implications

Distinguishing the geochemically similar Bingöl A and Nemrut Dağ peralkaline obsidians is a major challenge in Near Eastern obsidian sourcing. Despite abundant claims in the literature otherwise, this study reveals that Bingöl A and Nemrut Dağ obsidians are distinguishable with adequate source sampling and highly accurate and repeatable data for geochemically important elements. Earlier research has endeavored to link a simple geochemical trend (peralkalinity) to specific locations at Nemrut Dağ, but existing schemes to distinguish Bingöl A and Nemrut Dağ obsidians cannot validly link compositional clusters to the landscape. This study demonstrates that additional elements are required to attribute artifacts to specific obsidian-bearing lava flows at the volcano. Limitations of this newly analyzed collection of geo-referenced Nemrut Dağ and Bingöl specimens suggests caution is still warranted in sourcing peralkaline obsidians, but a few archaeological implications are clear. New sourcing results from Tell Mozan in northeastern Syria refute a widespread assumption that one can use maximal efficiency to deduce whether peralkaline obsidian artifacts originated from Nemrut Dağ or Bingöl A. The ability to discern among these sources also enables inquiries into issues of cultural and technological preferences regarding these obsidians.

Obsidianas enLa Payunia (sur de Mendoza, Argentina): patrones de distribución e implicancias en la ocupación regional

This paper presents the results of technological analysis of obsidian artifacts from the Volcanic Field of La Payunia (south of Mendoza, Argentina). Previous studies in west central Argentina and central Chile discussed the role of obsidian sources in a regional large scale, interaction networks and human mobility in different scales. In La Payunia two obsidian sources have been identified and located in areas with different environmental characteristics and occupational history. Source El Peceno in the Nevado

Obsidian Subsource Identification in the Sierra de Pachuca and Otumba Volcanic Regions, Central Mexico, by ICP‐MS and DBSCAN Statistical Analysis

Otumba and Sierra de Pachuca obsidian deposits in Central Mexico have been important sources of raw material since pre‐Hispanic times. Numerous archaeological investigations have suggested that the economical and political expansion of major Mesoamerican societies were linked to the control of obsidian sources and distribution of quarried material. Sierra de Pachuca contains several obsidian flows and numerous quarries throughout the region that were preferentially exploited by different cultures. The Otumba Volcanic Complex has four important obsidian domes, but three of them have not been studied in detail. A geochemical characterization of subsources from the Sierra de Pachuca and Otumba Volcanic Complex is an important step toward future sourcing of obsidian artifacts that would help provide insight into spheres of influence and trade by past cultures in Central Mexico. Having this purpose in mind, inductively coupled plasma mass spectrometry (ICP‐MS) was used to analyze obsidian samples collected from five separated locations at Sierra de Pachuca and four at Otumba, followed by statistical analysis (density‐based spatial clustering of applications with noise, DBSCAN). We were able to distinguish three chemically distinctive subsources in Sierra de Pachuca and three in Otumba. This study illustrates the importance of accurate characterization of obsidian raw material when attempting to define subsource usage.

Magnetite grain-size analysis and sourcing of Mediterranean obsidians

The potential of magnetic grain-size variations as an obsidian source characteristic is investigated using geological and archaeological obsidians from five islands of the Mediterranean Sea: Lipari, Sardinia, Palmarola, Pantelleria, Melos. Four parameters are used: magnetic (χ) and anhysteretic (χa) susceptibilities, saturation isothermal remanent magnetizations at room (SIRM293) and liquid nitrogen (SIRM77) temperature. The ratio ST = SIRM77/SIRM293, which depends on the superparamagnetic grains relative abundance, varies little in each individual site, with the exception of Lipari which is characterized by large variations and the highest content of superparamagnetic grains. The χa vs. χ plot (King et al., 1982) shows some within-site dispersion of the samples; but the ratio Qa = χa/χ, which is strongly influenced by the single domain grains content, is characteristic for each site. The combined use of the King and Qa vs. ST plots discriminates the samples from most of the sites and suggests that the grain-size analysis is a promising approach in sourcing obsidian archaeological artefacts. Moreover, the measurements of the four parameters used are simple, quick and feasible with no or little damage to archaeological finds.

Obsidian hydration at high elevation: Archaic quarrying at the Chivay source, southern Peru

We examine obsidian hydration as a means to date archaeological sites at high elevation in the central Andes, and in particular quarry sites that are difficult to date by radiocarbon means. The Chivay obsidian source lies in a volcanic depression above the Colca Valley in Arequipa, Peru (71.5355° S, 15.6423° E) at 4950 masl. We compare obsidian hydration readings from one quarry and two workshop locations. Ninety-one flakes from the quarry pit, and 61 and 33 flakes from the workshops were analyzed for hydration bands. Of these, 68 from the quarry, and 54 and 33, respectively from the workshops produced at least one culturally meaningful hydration band. As expected, obsidian appears to hydrate slowly at this high elevation. Yet, variation in hydration readings is low within stratigraphic contexts, suggesting relatively narrow windows of knapping activities in each excavation level. A small number of radiocarbon dates allow us to develop a preliminary hydration rate for Chivay obsidian in this high elevation location. Hydration data indicate that intensive quarrying began by 3800 cal. BC and stopped ca. 2300 cal. BC. By contrast, the two workshops appear to have been deposited 2900 and 1200 cal. BC, and 2700 and 2400 cal. BC. The data are consistent with an uptick in obsidian use by at least the Terminal Archaic period.

THE PROVENANCE OF OBSIDIAN ARTEFACTS FROM THE WĀDĪ ATH‐THAYYILAH 3 NEOLITHIC SITE (EASTERN YEMEN PLATEAU) BY LA–ICP–MS

The geological sources of obsidian in the Red Sea region provide the raw material used for the production of obsidian artefacts found in prehistoric sites on both sides of the Red Sea, as far afield as Egypt, the Persian Gulf and Mesopotamia. This paper presents the chemical characterization of five obsidian geological samples and 20 prehistoric artefacts from a systematically excavated Neolithic settlement in highland Yemen. The major element concentrations were determined by SEM–EDS analysis and the trace element concentrations were analysed by the LA–ICP–MS method, an almost non‐destructive technique capable of chemically characterizing the volcanic glass. A comparison of archaeological and geological determinations allows the provenance of the obsidian used for the Neolithic artefacts to be traced to definite sources in the volcanic district of the central Yemen Plateau.

MULTIPLE PRIMARY AND SECONDARY SOURCES FOR CHEMICALLY SIMILAR OBSIDIANS FROM THE AREA OF PORTADA COVUNCO, WEST‐CENTRAL NEUQUÉN, ARGENTINA

In west‐central Neuquén Province, Argentina, in the area around Estancia Llamuco, west of Zapala, south of Las Lajas and north‐east of Lago Aluminé, there are multiple primary and secondary sources of obsidian. Primary sources occur within the south‐east extension of the Plio‐Quaternary volcanic chain that runs from Copahue volcano through Pino Hachado. Secondary sources include river‐bed gravels within the valleys of Arroyo Cochicó Grande and Río Kilca as far south as where this river joins with Río Aluminé, and the Quaternary fluvial–glacial sediments cut by the valley of Río Covunco as far east as Portada Covunco. Visually variable obsidians from these two secondary sources include homogeneous black and grey‐translucent types, porphyritic and banded types, and an abundant quantity of oxidized red and black obsidian. However, all these visually distinct obsidians have similar and unique chemistry, with Ba between 220 and 340 ppm, different from any other obsidians previously reported from Neuquén, which all have Ba > 500 ppm, as do obsidians from sources to the north in Mendoza and to the west in Chile. This chemical distinctive obsidian has been exploited and transported over a wide area, beginning prior to 4000 bp, and occurs in local archaeological sites, as well as sites ≥ 300 km to the north‐east in La Pampa Province, ∼430 km to the south in Chubut Province, and >75 km to the west across the Andean drainage divide in Chile.

Non-destructive PXRF analysis of museum-curated obsidian from the Near East

Non-destructive pXRF has the potential to expand sample populations of archaeological provenancing studies by facilitating access to museum collections of artefacts. In this study, we use museum-curated obsidian for the sites of Tell Brak, Mersin-Yümüktepe and Tell Arpachiyah and geological obsidian samples from central Turkey to demonstrate that non-destructive pXRF is comparable to other techniques in differentiating between Near Eastern obsidian sources. Secondly, we use multivariate analysis to evaluate whether non-destructive pXRF is sufficiently accurate and precise to enable comparison with legacy datasets from previous analysis using PIXE and ICP-MS. Multivariate analyses show that instrumental offsets between the results from pXRF and other analytic techniques are less than source-to-source variation typical for most Anatolian obsidian outcrops and pXRF-identified geochemical groups are directly comparable to legacy datasets. Non-destructive pXRF analysis indicates that during the Chalcolithic, East Göllü dağ and Nenezi dağ continued to be the major sources of obsidian to communities in central Anatolia and the Bingöl range and mountains surrounding Lake Van supplied sites east of the Levant. Variations in the analysed assemblages suggest a number of obsidian exchange networks existed during this period.

PXRF: a study of inter-instrument performance

Integrating portable X-ray fluorescence (pXRF) instrumentation into archaeological investigations has generated as much interest as skepticism because several characteristics of the technique limit analytical accuracy and precision. This paper seeks to explore inter-instrument performance in order to assess the potential pXRF instrumentation has in examining the elemental composition of lithic raw materials. Two pXRF instruments, Delta and Omega models both manufactured by Olympus Innov-X Systems, were utilized to obtain the trace element signatures of five fine-grained volcanic sources and four obsidian sources in the Great Basin. We compared the two portable instruments to a wavelength-dispersive instrument extensively calibrated with geologic standards and to a commercial benchtop energy-dispersive system. Our results suggest that the relationships between the data produced by these different instruments are complex, and as we look to the future of pXRF use in archaeological analysis we argue that that the same strict protocols applied in laboratory-based XRF analyses, involving instrument calibration, evaluation of inter-instrument performance, and comparison to accepted geologic standards, need to be applied in pXRF analysis.

Obsidian Evidence of Interaction and Migration from the Mesa Verde Region, Southwest Colorado

A growing body of evidence demonstrates that ancestral Pueblo people living in the central Mesa Verde region of the U.S. Southwest maintained long-distance contacts with other Pueblo peoples. Questions of Pueblo interactions through time and across space have traditionally been addressed using ceramic sourcing data. This research uses obsidian source data to argue that, from A.D. 600 to 920, residents of the central Mesa Verde region obtained obsidian from throughout the U.S. northern Southwest, but that from A.D. 1060 to 1280 they acquired obsidian almost exclusively from the Jemez Mountains area of north-central New Mexico. In addition, importation of obsidian from the Pajarito Plateau increased during the period of population decline in the Mesa Verde region, and population expansion on the Pajarito. Characteristics of the obsidian assemblage from central Mesa Verde region sites also suggest that Jemez obsidian entered the region primarily in the form of finished arrows, arrow points, and arrow-point preforms. We argue that these patterns reflect return migration by early immigrants from the Mesa Verde region to the northern Rio Grande, an early stage in the development of a migration stream between the two regions.