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PROVENANCE OF OBSIDIAN EXCAVATED FROM LATE CHALCOLITHIC LEVELS AT THE SITES OF TELL HAMOUKAR AND TELL BRAK, SYRIA (2009)

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X-ray fluorescence and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses conducted on 40 obsidian samples from the Late Chalcolithic 2 levels at Tell Hamoukar and Tell Brak in north-east Syria have shown trends towards
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  PROVENANCE OF OBSIDIAN EXCAVATED FROM LATECHALCOLITHIC LEVELS AT THE SITES OF TELLHAMOUKAR AND TELL BRAK, SYRIA* L. KHALIDI† Centre d’Etudes Préhistoire, Antiquité, Moyen-Age (CEPAM), UMR 6130, CNRS,Université de Nice, Sophia-Antipolis (UNSA), 250 rue Albert Einstein,Sophia-Antipolis, F-06560 Valbonne, France B. GRATUZE  Institut de Recherche sur les ArchéoMATériaux (IRAMAT), UMR 5060, CNRS,Université d’Orléans, Centre Ernest-Babelon, 3D rue de la Férollerie,F-45071 Orléans, Cedex, France and S. BOUCETTA  IRAMAT, UMR 5060, CNRS, Université d’Orléans, Centre Ernest Babelon, 3D, rue de la Ferollerie,F-45071 Orléans, Cedex, France  X-ray fluorescence and laser ablation inductively coupled plasma mass spectrometry (LA–  ICP–MS) analyses conducted on 40 obsidian samples from the Late Chalcolithic 2 levels at Tell Hamoukar and Tell Brak in north-east Syria have shown trends towards the exploitationof obsidian sources in the eastern Taurus. While the Bingöl region appears to provide themajority of obsidian to both sites, there is also evidence of more minor exploitation of asource in the Lake Van area and an altogether unknown source (X). This paper presents thedata acquired from the analyses of the archaeological obsidian and situates these resultswithin their chronological and regional contexts. KEYWORDS:  SYRIA, NORTHERN MESOPOTAMIA, LATE CHALCOLITHIC, TELL BRAK,TELL HAMOUKAR, OBSIDIAN, GEOCHEMICAL ANALYSES, X-RAY FLUORESCENCE,LA–ICP–MSINTRODUCTION Geochemical obsidian provenance studies have become a standard procedure at many archaeo-logical sites. Such analyses have enabled archaeologists to expand on concepts of trade andinteraction in the ancient world by matching obsidian found on archaeological sites with thesource deposits from which they came. Since the seminal work of Renfrew, Dixon and Cann(Cann and Renfrew 1964; Renfrew  et al.  1966, 1968; Renfrew and Dixon 1976) on obsidianexchange in the ancient world, much progress has been made in the field of archaeometry andits application to obsidian source characterization in the Mediterranean and Western Asia(Francaviglia 1984; Cauvin  et al.  1998; Costa 2007). *Received 25 August 2008; accepted 8 December 2008†Corresponding author: email lamya.khalidi@gmail.com  Archaeometry  51 , 6 (2009) 879–893 doi: 10.1111/j.1475-4754.2009.00459.x © University of Oxford, 2009  For instance, a great deal of work has been undertaken in the obsidian source areas withwhich this paper is concerned: Anatolia and Transcaucasia (Francaviglia 1990; Cauvin  et al. 1991; Chataigner 1994; Blackman  et al.  1998; Gratuze 1998; Poidevin 1998; Poupeau  et al. 1998). While a few obsidian sources in the region remain uncharacterized, the available datahas enabled scholars to greatly expand our knowledge of intra-regional obsidian materialprocurement and trade, and its distribution to sites in the greater Mesopotamian region.Chronologically, studies have demonstrated a long-term exploitation of Anatolian andTranscaucasian sources from at least as early as the Neolithic period (Cauvin  et al.  1986, 1998;Bader  et al.  1994; Francaviglia 1994; Gratuze 1994; Balkan-Atli  et al.  1999; Cauvin 2002;Barge and Chataigner 2003; Chataigner and Barge 2005). However, despite the presence of asmall number of lithic studies that have integrated obsidian analyses into wider researchagendas (Fornaseri  et al.  1975–7; Edens 2000: Nishiaki and Matsutani 2003), there has beenlittle focus on obsidian provenance studies in the Late Chalcolithic period.More recent surveys and excavations at Tell Hamoukar and Tell Brak (Fig. 1) are increasinglydemonstrating that this period witnessed the expansion of towns and the establishment of territories and inter-regional contacts (Gibson  et al.  2002; Ur 2002; Oates and Oates 2004;McMahon  et al.  2007; Oates  et al.  2007; Ur  et al.  2007; Ur in press) that were precursors tothe first cities and to large trade networks. Chronological and regional cycles of obsidian versuschert use have been observed in the Syrian Jezira (Khalidi in press) and in north-west Iraq Figure 1  A map of Anatolia and northern Syria, situating Tell Hamoukar among contemporaneous sites and knownobsidian source areas (map prepared by J. Ur). 880  L. Khalidi, B. Gratuze and S. Boucetta © University of Oxford, 2009,  Archaeometry  51 , 6 (2009) 879–893  (Wilkinson and Tucker 1995, 87). Such trends may be useful indicators of changing economic,social and political strategies. The modalities of introduction, movement and choice of certainraw materials over others are significant factors that are likely to have led populations tochange strategies, shift orientations and contacts and expand. It is within the context of mapping out the diachronic and regionally variable cycles of raw material use at these sitesthat we encountered wealth in obsidian availability and use that reached its height in the LC2period and significantly decreased in following periods. While the same cycle of obsidianversus chert use appears roughly contemporaneously at Tell Brak and Tell Hamoukar, theircomparison is interesting precisely because the role of obsidian and its quantity is different ateach of these sites, and very often rare to non-existent at neighbouring sites. Consequently,geochemical analyses of obsidian recovered from sites that fall into this chronological andregional setting are fundamental to our understanding of changes in the accessibility of, andexchange of, raw materials. These economic shifts are likely to have had an impact on thedevelopment of complex societies and the early stages of urbanization in this region.X-ray fluorescence and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses were conducted on 40 archaeological obsidian samples from excavated latefifth millennium (LC2) contexts at the sites of Tell Brak and Tell Hamoukar in north-eastSyria. The results demonstrate that there is a preponderance of obsidian srcinating from theBingöl A and B sources at both sites, but they have also revealed more minute quantities thatwere procured from the Meydan Dag˘ source in the Lake Van region. In addition, two samplesfrom the site of Tell Hamoukar have confirmed the exploitation of an altogether unknownsource (X). METHODS OF ANALYSIS The analyses of the obsidian fragments were conducted at the Centre Ernest-Babelon of theIRAMAT (Orléans). Two virtually non-destructive methods of analysis were used to determinethe srcin of the obsidian (Gratuze 1999; Astruc  et al.  2007): X-ray fluorescence and laserablation inductively coupled plasma mass spectrometry (LA–ICP–MS).X-ray fluorescence was used qualitatively. In other words, geological obsidian samples fromsources in proximity to the study region were analysed alongside the archaeological frag-ments, and a source attribution was realized with the help of graphic aids where net signatures,or otherwise the relation of signatures, were obtained for the different elements detected(calcium, titanium, iron, manganese, rubidium, strontium, yttrium, zirconium and niobium).The X-rays were generated with a tungsten tube operating at 45 kV and 0.8 mA. The analyticalparameters were as follows: acquisition time 1200 s, no beam filter, beam collimator diameter1.5 mm and energy domain for elemental analysis 0–25 keV. The net signal measured for eachelement was normalized by the L a  tungsten X-ray.LA–ICP–MS allows a quantitative analysis of a large number of minor and trace elementscontained in obsidian. Here, the concentration of 23 elements is determined for each selectedsample. Among them we find elements such as zirconium, yttrium, niobium, barium, strontium,cerium, lanthanum and titanium, which appear to be the most dominant in establishingdiscrimination between obsidian outcrops. The attribution to an obsidian source was carriedout by comparing the composition of the archaeological samples to that of the obsidian sourcereference data set. The LA–ICP–MS operates as follows. The object placed in the ablation cell issampled by the laser beam, which is generated by an Nd:YAG pulsed laser. Its frequency isquadrupled, allowing it to operate in the ultraviolet region at 266 nm. The diameter of the Provenance of obsidian from Tell Hamoukar and Tell Brak, Syria  881 © University of Oxford, 2009,  Archaeometry  51 , 6 (2009) 879–893  ablation crater ranges from 60  m m to 100  m m, and its depth is around 250  m m. An argon gasflow carries the ablated aerosol to the injector inlet of the plasma torch, where the matter isdissociated, atomized and ionized. The ions are then injected into the vacuum chamber of aquadrupole system, which filters the ions depending upon their mass-to-charge ratio. The ionsare then collected by a channel electron multiplier. The isotope  29 Si was used as an internalstandard and the Standard Reference Materials 610 from the National Institute for Standardsand Technology were used for external standardization. One of the main advantages of LA–ICP–MS over classical ICP–MS is that it is considered to be a virtually non-destructivemethod. Although a microscopic sample (about 80  m m in diameter) is removed using a laser,it is not visible to the naked eye. The object being analysed thus remains morphologicallyunaltered and intact.Depending on the geographical area under study, these two techniques are used in a concertedway to optimize on the cost and speed of analysis. First, the analysis by X-ray fluorescence isused to make a first grouping and a first allocation of samples to an obsidian outcrop. Becausethis method is only qualitative, the definitive allocation of samples to an obsidian source isthen confirmed using LA–ICP–MS. Objects analysed using the latter technique are chosenaccording to their disparity within each group formed by X-ray fluorescence. PROVENANCE OF THE OBSIDIAN ANALYSED Forty obsidian flakes were studied in total. Eight of these were recovered from excavatedcontexts at the site of Tell Brak and 32 from excavated contexts at the site of Tell Hamoukar.The quantity of samples chosen from each site was partially relative to the quantity of obsidianpresent and studied on each site. Excavations at Tell Hamoukar produced more than 3000obsidian products, while the Tell Brak excavations produced significantly fewer (940 studiedfragments). Due to export restrictions, the selection process was also limited to small fragmentsof obsidian debitage that had little or no technological significance. In addition, the selectionaimed towards a diversity of obsidian varieties, despite the fact that peralkaline obsidianpredominated at both sites. Because the quantities of obsidian were much higher at TellHamoukar, the gamut of small flakes and fragmentary obsidian products (and thus the potentialfor a greater variety of obsidian) to choose from was larger.Of the eight samples from Tell Brak, three were analysed by X-ray fluorescence, while fivewere analysed by both X-ray fluorescence and LA–ICP–MS. Of the 32 samples from TellHamoukar, 21 were analysed by X-ray fluorescence and the rest using both methods. Differentgeological samples were studied in tandem with the archaeological samples. These geologicalsamples originated from the Göllü Dag˘ sources in Cappadocia (Kalatepe and Birtlikelerflows), from the Bingöl sources in the Taurus (Çavuslar – BingölAand Çatak – Bingöl B) as wellas from the region around Lake Van (Meydan Dag˘ flows). A great number of elements wereexamined in the geological and archaeological obsidian samples. Among these, we found theelements that are most used in obsidian provenance studies: rubidium, strontium, zirconium,niobium and barium (Tables 1–3). Obsidian from Tell Brak  The results demonstrate that the eight samples fromTell Brak divide into three different chemicalcomposition groups (Tables 1 and 4; Figs 2–4). Two of these groups, making up seven of theeight samples, correspond to the composition of the geological obsidian from the Bingöl882  L. Khalidi, B. Gratuze and S. Boucetta © University of Oxford, 2009,  Archaeometry  51 , 6 (2009) 879–893  region (Table 4): groups Bingöl A (four fragments) and Bingöl B (three fragments). From ageochemical point of view, the obsidian srcinating from the Bingöl A source is very difficultto distinguish from that of the Nemrut Dag˘ source (Chataigner 1994; Francaviglia and Palmieri1998, 335, 339). Using solely the results of the analyses, it is not possible to favour one or theother of these sources. Given that three archaeological obsidian fragments from the entireassemblage analysed correspond to the Bingöl B source, it is highly probable that the fourother fragments thus correspond to the BingölAsource and not to Nemrut Dag˘. The last sample,which forms the third group, has a composition that corresponds to that of the obsidian fromMeydan Dag˘. Obsidian from Tell Hamoukar  The 32 samples from Tell Hamoukar divide into four different chemical composition groups(Tables 2 and 4; Figs 2–4). Three of these groups, which make up 30 samples, correspond tothe same groups of obsidian found at Tell Brak: Bingöl A group (27 fragments), Bingöl B (twofragments) and Meydan Dag˘ (one fragment). The last two samples form a fourth group. Thesehave a composition that does not correspond to any group of geological obsidian analysed to date.We should keep in mind that for both sites we find some obsidian srcinating from MeydanDag˘. As this volcano is close to the Lake Van and Nemrut Dag˘ areas, it remains possible that Table 1  Chemical composition in minor elements and traces of obsidian samples excavated at thesite of Tell Brak (contents in ppm)Oxide Bingöl A Bingöl B Meydan Dag˘ F2A3 1 F1A 1 F2B 1 F3ATW 1 F4A 1 Li 68 73 67 77 74B 106 75 54 73 39Ca 1 244 5 022 5 927 5 563 3 068Ti 973 1 225 1 227 1 269 488Fe 20 672 12 883 13 149 13 325 10 350Mn 434 296 304 299 524Zn 199 54 57 53 83As 28 5 10 7.8 0Rb 206 228 220 244 177Sr 7.4 35 40 37 18Y 125 28 34 29 53Zr 1 214 305 373 337 267Nb 71 20 20 19 33Cs 8.4 10 10 11 9.4Ba 1.6 317 349 333 67La 90 35 42 37 30Ce 186 68 73 71 62Pr 18 5.5 6.6 5.8 6.1Nd 69 18 26 22 21Hf 24 6 7.5 5.8 7.3Ta 3.4 1.4 1.6 1.7 1.9Th 25 24 30 25 21U 7.8 8.4 8.7 9.3 7.8 Provenance of obsidian from Tell Hamoukar and Tell Brak, Syria  883 © University of Oxford, 2009,  Archaeometry  51 , 6 (2009) 879–893
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