Obsidian Sources in the Regions of Erzurum and Kars (Northeast Turkey)
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bs_bs_banner Archaeometry ••, •• (2013) ••–•• doi: 10.1111/arcm.12002 OBSIDIAN SOURCES IN THE REGIONS OF ERZURUM AND KARS (NORTH-EAST TURKEY): NEW DATA* C. CHATAIGNER Archéorient, UMR 5133, CNRS/Université Lyon 2, 7 rue Raulin, 69007 Lyon, France M. IS¸IKLI Atatürk University in Erzurum, Faculty of Letters, Department of Archaeology, 25240 Erzurum, Turkey B. GRATUZE† IRAMAT CEB, UMR 5060, CNRS/Université d’Orléans, 3 D rue de la Férollerie, 45071 Orléans Cedex 2, France and V. ÇIL Atatürk University, Oltu Faculty of Earth Sciences, 25400 Oltu/Erzurum, Turkey The obsidian sources on the Erzurum–Kars Plateau have not been extensively surveyed, and their geochemical signatures are still poorly understood. Yet a significant number of artefacts from archaeological sites in Georgia and Armenia have produced chemical compositions that are unrelated to any Turkish or Caucasian source analysed so far. Their origins may lie in these poorly known deposits. The objective of the collaborative project undertaken by the University of Erzurum and the French mission ‘Caucasus’ is to study the sources of obsidian in the Erzurum and Kars regions, in order to shed light on the intensity of exploitation of this material, and to highlight the exchange networks that may have existed between north-eastern Turkey and the southern Caucasus. The analyses that we have carried out on the samples taken during this exploratory survey have enabled a definite extension of the territory of circulation of this obsidian to western Transcaucasia. The lack of knowledge concerning the diffusion of obsidian from the regions of Erzurum and Kars thus appears for the moment mainly related to insufficient geochemical characterization of the sources, confirming the importance of future surveys. KEYWORDS: OBSIDIAN GEOCHEMISTRY, NORTH-EAST TURKEY, OBSIDIAN OUTCROPS, LA–ICP–MS ANALYSES INTRODUCTION The Erzurum–Kars Plateau makes up the northern part of the East Anatolian High Plateau, formed by the northward convergence of the Arabian Plate with Eurasia, which began in the Early Miocene. The uplift of this region reached an average elevation of 2 km above sea level during the Middle Miocene (c. 13–11 Ma) and the volcanic activity began immediately after the uplift. This volcanism extended to the entire region, producing lava flows and pyroclastic products that are variable in their composition (from basalts to high silica rhyolites/obsidians). Although *Received 11 July 2012; accepted 5 October 2012 †Corresponding author: email [email protected] © University of Oxford, 2013 2 C. Chataigner et al. fissure eruptions dominated the volcanic activity, there are numerous small volcanic centres, corresponding essentially to central eruption sites (Keskin et al. 1998;Yılmaz et al. 1998; Sengor et al. 2008). These sources of obsidian on the Erzurum–Kars Plateau have not been extensively surveyed, and their geochemical signatures are still poorly understood. Yet a significant number of artefacts from archaeological sites in Georgia and Armenia have produced chemical compositions that are unrelated to any Turkish or Caucasian source analysed so far. Their origins may lie in these poorly known deposits. The collaborative project undertaken by the University of Erzurum and the French mission ‘Caucasus’ has as its objective the study of sources of obsidian in the Erzurum and Kars regions, in order to shed light on the intensity of exploitation of this material and the exchange networks that may have existed between north-eastern Turkey and southern Caucasus. METHODS Surveys To obtain an exhaustive database on the sources of obsidian from north-eastern Turkey, the first step is to conduct systematic geological surveys in order to identify the primary deposits (domes, flows) and secondary deposits (pebbles in the river beds) and to take samples for geochemical and geochronological analyses. The obsidian outcrops known at the present time only represent part of the actual extension of the deposits; the information found in geological publications or transmitted orally indicates the existence of obsidian in zones where it has never been studied. Moreover, the few samples known today for the north-east Turkey sources, and which circulate from laboratory to labo- ratory, come from earlier surveys that recorded the location of the samples in an imprecise or even erroneous manner (‘misidentified’ samples; Frahm 2010). To the criteria (accuracy, pre- cision, reproducibility and validity) necessary for a valid study of provenance (Frahm 2012), it is necessary to add a first condition, without which the other four unfortunately have no value: the exactness of the location of sampling. If this basic piece of data is erroneous, any analysis, even of the highest quality, will give only incorrect results. Thus the phase of survey and inventory is fundamental. These methodical surveys will be carried out following the technique used by Mouralis et al. (2002) in central Anatolia. A thorough study of the geological and geomorphological contexts as well as detailed cartography will establish the exact locations of the obsidian deposits and the succession of eruptive episodes to which they belong. An initial exploratory survey of short duration was carried out in October 2011 in the provinces of Erzurum and Kars (Fig. 1) in order to evaluate the extent of the task that lay ahead in identifying sources of obsidian in these regions. This survey, organised by M. Isıklı, professor at the Atatürk University of Erzurum, was undertaken with the participation of V. Cil, geologist at the Oltu Faculty of Geosciences, Aysegul Akın, student at the University of Erzurum, and C. Chataigner, director of the Caucasus mission of the MAEE (CNRS, Lyon, France). Analyses Laser ablation high resolution inductively coupled plasma mass spectrometry (LA–HR–ICP– MS) is the method that is currently used for obsidian sourcing at the Centre Ernest-Babelon © University of Oxford, 2013, Archaeometry ••, •• (2013) ••–•• Obsidian sources in the regions of Erzurum and Kars (north-east Turkey) 3 Figure 1 The location of the Erzurum and Kars regions in eastern Turkey. (IRAMAT, Orleans, France). All the measurements presented in this paper were carried out using the high-resolution mass spectrometer Element XR (from Thermo Fisher Scientific) coupled with a VG UV Laser probe laser ablation sampling device that operates at 266 nm. The analytical protocol used, which allows the determination of 38 elements in obsidian samples, is the same as the one described in Chataigner and Gratuze (2013a,b). In order to relate the obsidian samples from our recent geological survey to obsidian data published by other research teams, our analytical results are compared with results obtained using different analytical methods, bulk analysis either directly on a solid sample (powder-NAA, XRF: Brennan 1995; Keller et al. 1996; Oddone et al. 1997; Keskin et al. 1998) or on dissolved samples (ICP–OES and ICP–MS: Renfrew et al. 1966; Keskin et al. 1998; Poidevin 1998; Gallet 2001; Delerue 2007) and punctual methods operating either directly on the surface of the object or after polishing (SEM–EDS and WDS, EPMA, PIXE: Delerue 2007; Frahm 2010). Not all of these methods determine the same elements, and it is thus not possible to plot all the published results on the same graphs. © University of Oxford, 2013, Archaeometry ••, •• (2013) ••–•• 4 C. Chataigner et al. THE ERZURUM REGION The Erzurum and Pasinler basins (Fig. 2) were formed during the Miocene as a result of localized extensions associated with the activity of major strike–slip faults when the Arabian and Eurasian Plates collided. Situation Around Erzurum. The basin of Erzurum is drained by the Karasu River, which is one of the two tributaries of the Euphrates. This basin, which was filled with lacustrine deposits during the Quaternary, is bordered on the north by the Dumlu Dag˘ and to the south by the Palandöken Dag˘lari. Several sources of obsidian, both primary (domes, flows) and secondary (deposits in the rivers), were recorded. Bas¸köy. In his study on the volcanism of the region of Erzurum, Pasquaré (1971) men- tions a large pyroclastic volcano north-west of Bas¸köy, which rises to a height of 600 m above the plateau. This volcano presents a mantle of vitreous laminated tuffs, among which some layers consist entirely of pure obsidian up to 15–20 cm thick. This deposit has never been sampled. Güzelyurt (or Tambura). Pasquaré (1971) also mentions obsidian-rich pyroclastic cones in the Kible Tepe system, which presents parallel alignments in a south-west/north-east direction, Figure 2 A map of the Erzurum–Pasinler region, with obsidian deposits and archaeological sites mentioned in the text (after Brennan 2000). © University of Oxford, 2013, Archaeometry ••, •• (2013) ••–•• Obsidian sources in the regions of Erzurum and Kars (north-east Turkey) 5 and rises at the edge of the Erzurum plain upstream from Tambura (the present-day village of Güzelyurt). Some obsidian samples, taken by T. Ercan ‘near Tambura’, were dated by fission tracks to 6.90 1 0.32 Ma (plateau age) (Bigazzi et al. 1998) and then analysed by different laboratories (Oddone et al. 1997; Delerue 2007; Frahm 2010). Certain authors consider this deposit to be the most important obsidian source in the Erzurum region (Frahm 2010). However, during a survey carried out in 2006, K. Kobayashi found only poor-quality, small-grained obsidian there, and stated that this type of obsidian is not suitable for making tools because of its non-vitrified state and small grain size (Kobayashi and Sagona 2008). Adaçay River. A field survey near the Chalcolithic/Bronze Age site of Pulur (located in the village of Ömertepe, 12 km west of Erzurum) led to the discovery of water-worn obsidian cobbles, up to 20 cm in diameter, in the adjacent Adaçay River, which originates in the Palandöken Dag˘ları (Brennan 1995). Other deposits located downstream were mentioned, south of Ilica, not far from the confluence with the Karasu River (Poidevin 1998; Delerue 2007).