SEM-EDS characterization of western Mediterranean obsidians and the Neolithic site of A Fuata (Corsica)

During the Neolithic, obsidians of the Monte Arci (Sardinia) volcanic complex were by far more used in the northern Tyrrhenian area than those of the three other source-islands (Lipari, Palmarola, Pantelleria) in the western Mediterranean. It is shown that merely determinations of content for six major elements with a scanning electron microscope by energy dispersion spectrometry (SEM-EDS) are sufficient to distinguish the four types of Monte Arci obsidians. Because of the compositional similarities between these obsidian types, a multivariate analysis is recommended in provenance studies. Although SEM-EDS, electron microprobe-wavelength dispersion spectrometry (EMP-WDS) and particle induced X-ray emission (PIXE) give essentially concordant results in the determination of these six element contents, subtle technique-related biases prevent the combination of SEM-EDS, EMP-WDS and PIXE data on source samples for provenance purposes. An SEM-EDS test-study reveals the first occurrence of obsidians of Lipari for the A Fuata Middle to Late Neolithic site of NW Corsica (north of Sardinia), in addition to the usual Monte Arci obsidians. Similar to EMP-WDS, the SEM-EDS technique requires only millimeter-sized fragments.     

The magnetic sourcing of obsidian samples from Mediterranean and near Eastern sources

The magnetic properties of obsidians are examined for their potential in sourcing obsidian artifacts. The three simplest to determine magnetic parameters—initial intensity of magnetization, saturation magnetization and low field susceptibility—are found to be effective discriminants of many Mediterranean, Central European and near Eastern sources. Although the between-source precision is not as good as geochemical analyses of minor and rare-earth elements, the technique demonstrated the existence of new sources that were subsequently confirmed by minor element analyses. Unfortunately some key sources do not appear to be readily distinguishable on these three simple magnetic parameters alone, although more sophisticated magnetic analyses may prove diagnostic. Despite this, it would appear that effective discrimination can be made in many cases, occasionally with more precision than minor element analyses. This technique therefore offers, as a minimum, a preliminary sourcing tool for use in many areas of the world, thus reducing the number of expensive geochemical analyses. Furthermore, its very low cost, non-destructive nature and speed open the possibility of quantitative evaluation of trade routes based on obsidian distributions, particularly as versions of the equipment are now suitable for use in the field.     

Early Neolithic obsidians in Sardinia (Western Mediterranean): the Su Carroppu case

All the obsidians from the undisturbed Early Neolithic (Cardial ware phase I) layer of the Su Carroppu rock-shelter (Sardinia island) were studied. Their elemental composition and that of obsidians from the Monte Arci (Sardinia) volcanic complex was determined by ion beam analysis (PIXE). A comparison between the composition of Su Carroppu artefacts, analysed non-destructively, and that of Western Mediterranean analysed in the same conditions shows that the archaeological material belongs to the SA, SB2 and SC Monte Arci-types, to the exclusion of the SB1 type. The typological/technological study of this industry allowed us to reconstruct two chaînes opératoires, for the production of blades (using predominantly SC obsidians) and of flakes (based exclusively on SA and SB2 obsidians), respectively, but on the whole, assemblage blade/bladelet production was performed somewhat preferably with SA and SB2 types. Thus, in the earliest EN culture known on the island, ancient man had, for the making of its obsidian toolkit, a highly adaptive behaviour applied to the reduction of different useful obsidian sources.     

Geochemical composition of source obsidians from Kenya

Here we provide a reference resource to archaeologists interested in the sources of obsidian in Kenya, through electron microprobe analyses of 194 obsidian samples from 90 localities. Averaged analyses of each sample and eleven published analyses are categorized into 84 compositional groups of which only about 21 are known to have been used to produce artifacts, possibly because studies of artifactual material in the region are lacking. We also provide trace element analyses determined by XRF and LA-ICP-MS for these same obsidians. In northern Kenya 27 distinct compositions of obsidian have been found, including some of Miocene age, but the source of the most abundant obsidian found in archaeological sites in this part of Kenya remains obscure. The Baringo region contains at least 13 varieties of low-silica obsidian. The Naivasha–Nakuru region contains an abundance of obsidian with 38 compositional types recognized, and is the only region in Kenya apart from the Suregei (northern Kenya) that contains rhyolitic obsidian. Nine compositionally distinct types of obsidian are known from southern Kenya. Although Kenyan obsidians span the compositional range from phonolite to rhyolite, low-silica, nepheline-normative obsidians occur only south of 1°N latitude. One obsidian type, the Lukenya Hill Group, appears to have been derived from a regionally extensive ash flow tuff with a distribution of over 8000 km². From previous studies it is known that obsidians of lowest (Mundui) and highest iron content were used for tool manufacture, as were some obsidians (e.g., Kisanana) with the highest alkali content, and obsidians with both high (Njorowa) and low (Kisanana) silica content.     

Ancient social landscapes of northwestern Argentina: preliminary results of an integrated approach to obsidian and ceramic provenance

This article presents the results of ongoing instrumental neutron activation analyses (INAA) conducted on archaeological artifacts from the Formative period of northwestern Argentina (NWA). These studies are part of a wider archaeological project that seeks to understand the structure of the social landscape of the period by examining domestic and burial evidence from a wide range of villages across the area known as the southern Calchaquí valleys. Elemental data is discussed in the light of its potential contribution to reassess past social interaction strategies in the region.     

Provenance of prehistoric obsidian artefacts from Kul Tepe,northwestern Iran using X-ray fluorescence (XRF) analysis

Analysis by X-ray fluorescence of 53 obsidian artifacts the main source of obsidian for the workshops in Kul Tepe was Syunik but obsidian sources as far as west as the Lake Van region (Nemrut Da? and Meydan Da?) and as far north as Gutansar were also utilized. These new results indicate a broad network of trade and exchange.     

Linguistic boundaries as barriers to exchange

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) data are used to explore the structure of obsidian acquisition for groups in the King Range National Conservation Area of northern California. The data indicate that, contrary to a distance-decay model, obsidian from more distant sources in the Medicine Lake Highlands, dominates the obsidian found at sites in the area. Furthermore, metric data indicate a positive relationship between size and distance to source with more distant sources represented by larger flakes. It is suggested that this pattern is the result of culturally mediated exchange relations under which Athabaskan speakers concentrated trade relations with one another to the exclusion of trade with linguistic groups to the south, with longer histories in the area, such as the Pomo and Yuki. Additionally, the use of redwood dugouts on rivers in northern California and the importance of northeastern Californian obsidian in ritual practices of California Athabaskan groups may have further encouraged the use of more distant, northeastern Californian, sources.     

From flow to quarry: magnetic properties of obsidian and changing the scale of archaeological sourcing

Previous studies have endeavored to use petrophysical traits of obsidian, particularly its magnetic properties, as an alternative to conventional geochemical sourcing, one of the greatest successes in archaeological science. Magnetic approaches, however, have not seen widespread application due to their mixed successes. In a time when geochemical analyses can be conducted non-destructively, in the field, and in a minute or two, magnetic measurements of obsidian must offer novel archaeological insights to be worthwhile, not merely act as a less successful version of geochemistry. To this end, we report the findings of our large-scale study of obsidian magnetism, which includes 734 geological obsidian specimens and 97 artifacts measured for six simple magnetic parameters. Based on our results, we propose, rather than using magnetic properties to source artifacts to a particular obsidian flow (inter-flow sourcing), these properties are best used to differentiate quarrying sites within an individual flow (intra-flow sourcing). Our results also demonstrate that certain magnetic properties are highly affected by ancient knappers' material selection criteria. Furthermore, depending on the spatial scales of variation, which likely vary from flow to flow, we envision several potential applications of this approach, including integration into minimum analytical nodule analysis (MANA). Magnetic data appear to shift the scale of obsidian sourcing from flows to quarries and, in turn, enable new insights into raw-material procurement strategies, group mobility, lithic technology, and the organization of space and production.     

Multiple origins of Bondi Cave and Ortvale Klde (NW Georgia) obsidians and human mobility in Transcaucasia during the Middle and Upper Palaeolithic

Using PIXE four types of elemental compositions were found among obsidian artefacts from the Bondi Cave and Ortvale Klde, Middle to Upper Palaeolithic sites in NW Georgia. One of those types corresponds to obsidians from the Chikiani source, whose compositions were determined with a very good agreement by PIXE and ICP-AES/MS. The composition of Chikiani obsidians is remarkably constant despite K–Ar and ³⁹Ar/⁴⁰Ar extrusion ages from ca 2.4 and 2.8 Ma. The compositions of two other groups of obsidian artefacts are similar to source materials from eastern Anatolia and Armenia, in particular Ikisdere, Sarikamis, Gutansar, and Hatis. Obsidian is only a minority component in the lithic assemblages at the Bondi Cave and Ortvale Klde. Both Neanderthal and Modern Human populations used obsidian in particular from Chikiani. Considering that the shortest walking distance to this nearest source is at minimum of about 180 km, and to other potential sources of more than 350 km it is suggested that this material reached these two sites mostly, if not exclusively, by a series of ‘down the line’ exchanges.     

Obsidian from the Epipalaeolithic and Neolithic eastern Maghreb. A view from the Hergla context (Tunisia)

In the present paper, it is shown that in the Hergla area (eastern Tunisia), obsidian was present from the early to at least the late sixth millennium cal BC. The presence of cores indicates that obsidian knapping was at least partly carried out in situ. The origin of these obsidians was determined from their elemental composition, by comparison with those originating from western Mediterranean potential sources, including analyses of new samples from the nearby Pantelleria Island. All obsidians were measured following the same protocol, by particle induced X-ray emission or by scanning electron microscopy/energy dispersion spectrometry. All the Hergla obsidians were found to originate from the Balata dei Turchi sources of Pantelleria. A review of the present body of knowledge on eastern Maghreb suggests, in spite of the still very preliminary data available, that Pantelleria was almost its unique provider of obsidians from the Epipalaeolithic to and during the Neolithic. However, the relative importance of the two main Pantellerian sources of Balata dei Turchi and Lago di Venere as providers of obsidian to eastern Maghreb remains to be investigated.     

Geochemical sourcing of rock specimens and stone artifacts from Nihoa and Necker Islands,Hawai'i

We report geochemical analysis of seven rock specimens and six stone artifacts from Nihoa and Necker Islands, Hawai'i. The analyzed rock specimens exhibit chemistry consistent with published data sets and establish a major element distinction between Nihoa and Necker. Their trace element data indicate that the analyzed rocks and artifacts are local in origin and they reliably discriminate from sources on Kaua'i. These preliminary results support Emory's thesis that early (archaic) Hawaiian colonists on Nihoa and Necker relied on their local basaltic stone to manufacture stone tools, containers, and other portable objects.     

Assessing the applicability of portable X-ray fluorescence spectrometry for obsidian provenance research in the Maya lowlands

Recent innovations in portable energy-dispersive X-ray fluorescence (PXRF) spectrometry have increased its utility for the geochemical characterization of obsidian artifacts for archaeological provenance research. However, concerns over the utility of PXRF instrumental analyses have been raised, focused on the validity and reliability of the geochemical data produced. Here we adopt the framework of Richard Hughes (On Reliability, Validity, and Scale in Obsidian Sourcing Research, 1998), whereby reliability addresses instrument stability and issues of measurement while validity pertains to an instrument’s ability to discern geochemical source provenance. This is done in order to test the utility of PXRF instruments for archaeological provenance research. k-Means cluster analysis was used to test the accuracy of PXRF through statistical comparison of data acquired via laboratory and portable energy-dispersive XRF instruments. Multivariate analysis was employed to demonstrate obsidian source representation at two Classic Maya archaeological sites in southern Belize – Uxbenká and Ek Xux – and to test the validity of data obtained from a PXRF instrument in answering archaeological research questions pertaining to regional interactions between lowland Maya polities. Results suggest that portable XRF instruments produce internally consistent results. However, data acquired from a PXRF instrument are not statistically equivalent to other XRF instruments. This is to say that while PXRF is not a reliable technique, it is valid for questions pertaining to geochemical source representation.     

Possible isotopic fractionation of argon in source obsidians and archeological artifacts from Kulkuletti, Ethiopia

Despite uniform geochemistry ⁴⁰Ar/³⁹Ar ages of 0.6, 1.25, and 1.3 Ma on obsidians from a source flow (Worja) and from archeological artifacts at the sites of Kulkuletti (near Gademotta, Ethiopia) have been interpreted to suggest that they derive from different source flows of different ages. A further suggestion is that the magmatic source of the obsidian flows was chemically homogeneous between 1.3 Ma and 0.6 Ma. Chemical analysis of these obsidians indeed suggests that they derive from a single flow. Reexamination of the argon isotopic data reveals that argon isotopes may have been fractionated within the flow, so that the assumption of an atmospheric ⁴⁰Ar/³⁶Ar ratio of 295.5 is inappropriate to use for computing ages. Three groups of data are apparent, and internally all yield ages near 1.3 Ma if the intercept value for ⁴⁰Ar/³⁶Ar from an isotope correlation plot is used for computation instead of using the atmospheric ratio. The Soret thermal diffusion effect provides a possible mechanism of fractionation of argon within the obsidian flow that is of approximately the right magnitude to explain the observations by in-diffusion of already fractionated atmospheric argon.     

Environment and collapse: Eastern Anatolian obsidians at Urkesh (Tell Mozan,Syria) and the third-millennium Mesopotamian urban crisis

The Early to Middle Bronze Age transition in Northern Mesopotamia has received great attention for the apparent concurrence of aridification, deurbanisation, and the end of the Akkadian empire around 2200 BCE. Our understanding of the “crisis” has been almost exclusively shaped by ceramics, demography, and subsistence. Exchange and the associated social networks have been largely neglected. Here we report our sourcing results for 97 obsidian artefacts from Urkesh, a large urban settlement inhabited throughout the crisis. Before the crisis, six obsidian sources located in Eastern Anatolia are represented among the artefacts. Such a diversity of Eastern Anatolian obsidians at one site is hitherto unknown in Mesopotamia. It implies Urkesh was a cosmopolitan city with diverse visitors or visitors with diverse itineraries. During this crisis, however, obsidians came from only two of the closest sources. Two to three centuries passed before varied obsidians reappeared. Even when an obsidian source reappears, the raw material seems to have come from a different collection spot. We discuss the likely exchange mechanisms and related social networks responsible for the arrival of obsidians at Urkesh and how they might have changed in response to climatic perturbations and regional government collapse.     

Measuring prehistoric mobility strategies based on obsidian geochemical and technological signatures in the Owens Valley,California

We compare the organization of obsidian flaked stone technologies in two different time periods at CA-INY-30, a village site in southern Owens Valley, eastern California. Previous archaeological studies suggest a reorganization in settlement patterns between the Newberry (ca. 3500–1500 BP) and Marana (ca. 650-contact) periods, from a highly mobile to a more residentially sedentary one. New geochemical data, based on laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of obsidian artifacts associated with discrete house floors, support this basic settlement model, but reveal new detail in how people moved across the landscape and accessed, extracted, reduced and used obsidian resources. In the earlier Newberry period, there is no relationship between flake size and distance-to-source, and the falloff curve relating frequency of obsidian against distance is more gradual, as expected, but contrary to our expectations, source diversity is not higher. These factors suggest extremely high mobility, but also selective extraction of particular sources. Newberry obsidian may have been acquired by groups of hunters who embedded quarrying within long-distance trips to distant hunting grounds, and subsequently transported bifacial cores to base camps. By contrast, Marana patterns show strong relationships between flake size and distance from source and steeper fall-off curves, suggesting groups acquired their obsidian primarily from closer sources, likely via exchange networks. At the same time, geochemical diversity, especially among smaller resharpening flakes, is higher in the Marana period, highlighting the wide-ranging conveyance systems through which obsidian moved.     

Increasing data (INAA) on Ecuadorian obsidian artifacts: preliminary provenance and a clue for pre-Columbian eastward trade

In this work we carried out INAA major (Na, K, Ca and Fe %) and trace (ppm) elements (plus Mn by FAAS analysis) of 15 obsidian samples (waste flakes) coming from an unknown archaeological site (¹⁴C-AMS age of 1425 AD) located on the south-eastern flank of the back-arc Sumaco volcano (to the east of the Cordillera Real) and from two already known pre-Columbian archaeological localities: La Florida (Quito) and Milan (Cayambe). Literature compositional data of the Ecuadorian obsidian outcrops provide some constraints on the provenance of the analyzed waste flakes, even though different methods of analyses make comparisons a difficult task. Concerning the obsidian artifacts of La Florida and Milan, they come from the well known Sierra de Guamanì obsidian sources (Cordillera Real). By contrast, the obsidian fragments of the Sumaco settlement show some compositional characters compatible with obsidian erratic pebbles recently discovered in some river banks of the Amazonian foothills draining the easternmost flanks of the Antisana volcano in the Cordillera Real as well. In this way, the obsidian artifacts found at the Sumaco site reinforce the opinion that Ecuadorian source inventory is not yet exhaustive. Although the Antisana volcano seems to be the best candidate to find out additional primary outcrops of obsidian sources, it cannot be also excluded that sub-Andean and Amazonian people directly took advantage from obsidian secondary sources (e.g. river banks), rather than procurements from primary outcrops in the Cordillera Real. The new archaeological findings at the Sumaco volcano are really of paramount importance in tracing the ancient routes of a possible obsidian eastward trade toward the Amazonian region.     

Effective hydration temperature of obsidian: a diffusion theory analysis of time-dependent hydration rates

An estimate of effective hydration temperature (EHT) is needed for chronological use of obsidian hydration data. This paper describes a method for calculating EHT by the practicing archaeologist, replacing three techniques that are in general use today: estimates based on mean temperature, numerical integration of models of diurnal and annual temperature variations, and use of temperature cells. The hydration (or diffusion) coefficient of obsidian is a function of temperature and thus is time varying, while the classic quadratic law of hydration is not valid for time-varying diffusion coefficients. This paper presents a mathematical solution to the case of a time-varying hydration coefficient, based on diffusion theory, with a concise definition of EHT. It is shown that the results are not affected by concentration dependence in the diffusion coefficient. A computer program to compute the rigorous solution is described, and data are presented to explore the resulting range of variation. That use of the Lee equation to compute EHT is not appropriate for obsidian hydration studies is evident from the data presented. The effects of paleoclimatic variation are estimated, and an algebraic best fit equation and worksheet are provided as practical aids to the archaeologist.     

Provenance of glass shards in archaeological lime plasters by LA-ICP-MS: implications for the ancient routes from the Gulf of Mexico to Teotihuacan in Central Mexico

We present the chemical characteristics of samples collected from the central courtyard of Teopancazco, a neighbourhood centre in Teotihuacan (Mexico), the most important classic Mesoamerican city. The rhyolitic glass shards used as aggregates have a composition comparable to the glass material sourced from the magmatic system of Altotonga (located along the route to the Gulf Coast). People travelling from the Gulf Coast may have transported the glass shards to Teotihuacan during the Xolalpan phase (350–550 AD). However, the reasons for using glass shards as a construction material remain unknown. These new data confirm the close relationship between inhabitants of Teopancazco and the Gulf Coast already revealed by previous archaeological and archaeometric studies.     

Comparison of XRF and PXRF for analysis of archaeological obsidian from southern Perú

Chemical sourcing is becoming an increasingly important component of archaeological investigation. Instruments used for elemental analysis generally must be operated in a controlled laboratory environment. Further, many methods require destruction of a small portion of the objects under investigation. These facts inhibit the application of chemical sourcing studies in a number of research contexts. Use of portable non-destructive instruments would resolve these issues. Sixty-eight obsidian artifacts from the site of Jiskairumoko, in southern Perú, were examined by X-ray fluorescence spectrometry (XRF) and portable X-ray fluorescence spectrometry (PXRF). Results were compared for consistency in terms of source determination and individual element concentrations. Both instruments determined that the same sixty-six artifacts derived from the Chivay obsidian source and both identified the same two artifacts that could not be assigned to source. Individual element comparisons showed significant differences, but these can be resolved through instrument cross calibration, and differences had no bearing on source identification. PXRF was found suitable for determining obsidian sources in southern Perú and for identifying specimens that require more sensitive analytical methods such as, instrumental neutron activation analysis (INAA). Regular use of Chivay at Jiskairumoko suggests consistent trade relationships developed during the Archaic.