Saturday 25 November 2017

Determining the origin of the Yabroud Rockshelter obsidian scraper.

The Middle and Late Palaeolithic stone tool industries of Europe and the Middle East are associated with both Anatomically Modern Humans and Neanderthals, both of which groups appeared to have mastered the heat-treatment of rock for manufacturing tools and the production of sophisticated adhesives for use in toolmaking. However there are thought to have been cogitative differences between the groups, with the claim often made that Modern Humans maintained long-distance social networks, which enabled them to obtain materials over distances of hundreds of kilometres, while Neanderthals lacked this ability, and were obliged to rely on materials sourced from their immediate environment for tool-making. However this is harder to verify than it at first seem, as most such claims are based upon physical examination of chert and quartzite tools, which is useful when determining the origin of objects from a few kilometres away but less so for objects from further away; for example connecting an object with an outcrop 300 km away would require ruling out every other outcrop in an area of 280 000 km², an area larger than that of France.

In a paper published in the Journal of Archaeological Science: Reports in June 2017, Ellery Frahm of the Yale Initiative for the Study of Ancient Pyrotechnology at Yale University and Thomas Hauck of the Institute for Prehistory at the University of Cologne, describe the results of a study of an obsidian scrapper from the Yabroud Rockshelter in southern Syria, made with the aim of determining the object's origin.

Obsidian, or volcanic glass, is extremely rare in Palaeolithic assemblages, and has qualities both for the tool-maker and the archaeologist which other materials lack. Importantly, from an archaeological point of view, the volcanic origin of obsidian means that material from each source tends to have a unique chemical 'fingerprint' which enables obsidian items to be very precisely connected to their points of origin. In the Middle East, obsidian tool-use became common in the Neolithic, with the effect that archaeologists have studied source-outcrops extensively, and built up a database of sources which can be used to pinpoint the origin of most such objects very precisely.

The Yabroud Rockshelter lies in the Skifta Valley of southern Syria, close to the town of Yabroud and about 60 km to the northeast of Damascus. This site was first excavated in the 1930s by German archaeologist Alfred Rust, who found three distinct sequences; Rockshelter I, which produced Early Palaeolithic Material, Rockshelter II, which procuced Middle and Late Palaeolithic material, and Rockshelter III, which produced Epipalaeolithic (End Palaeolithic) objects. 

Location of Yabroud Rockshelter II in the Skifta Valley of Syria. DigitalGlobe/Frahm & Hauck (2017).

The obsidian scraper comes from Layer 4 of the Rockshelter II sequence, which is associated with the transition between the Middle and Late Palaeolithic, and which has also produced over 800 chert artifacts (tools, cores, flakes, shatter), which have been variously attributed to the Ahmarian and Levantine Aurignacian industries, and dated to between 41 000 and 32 000 years ago, around about the time that the last Neanderthals were vanishing in the area.

The obsidian scraper was identified by Rust as being of non-local origin, since there is no plausible origin of such material in the area, though he was unable to give a point of origin for it, since the techniques to analyse the chemical origins of obsidian did not exist in his time. The best suggestion he was able to make was that it might have come from the Eṣ-Ṣafā basalt flows, over 100 km to the southeast, which he had never visited and did not know whether they produced obsidian.

The tool itself is a round scraper roughly 28 x 25 x 10 mm, which shows signs of having been retouched numerous times, and  which had probably reached the end of its useful life when it was discarded.

(a) The obsidian tool from YR2. (b) The corresponding illustration of Rust in its original (incorrect) orientation. Note that features around the perimeter are somewhat exaggerated in this illustration. (c) A new illustration of the tool in its correct orientation. Frahm & Hauck (2017).

Frahm and Hauck used a Thermo Scientific Niton XL3t 950 GOLDD instrument to produce an X-ray fluoresce spectrum of several different parts of the scraper, a technique which enables chemical analysis of an object without removing any material from it. This was compared to a reference collection of samples of Middle Eastern obsidian, using the relative abundances of the elements Rubidium, Strontium, Zirconium, and Iron. This method produced a very good match to obsidian from the Kömürcü outcrops on the eastern slopes of the Göllü Dağ volcanic complex in central Anatolia, roughly 500 km  to the northeast in a straight line, and 700 away avoiding crossing the sea or any other significant obstacles.

The dating of Level 4 at the Yabroud Rockshelter makes the obsidian scraper roughly contemporary with some obsidian flakes from the Shanidar Cave in northern Iraq, which have been connected to the Nemrut Dağ volcano in southeastern Turkey, a distance of 450 km, suggesting that such long-range transportation of artifacts was common in Middle East at this time. The Shanidar Cave is also noted for the presence of several Neanderthal skeletons, which has led to suggestions that Neanderthals may have been using obsidian artifacts from distant sources, though in fact the skeletons come from a different layer to the obsidian chips, so no such connection can be made and the identity of the tool-makers remains unknown.

Southwest Asian obsidian sources (triangles) and Upper Palaeolithic sites with obsidian (squares). The purple line denotes the least-cost path on the modern landscape between Göllü Dağ and the Yabroud Rockshelter. It is 710 km in length, revealing the minimum transport distance on the ground. The dark blue line between Nemrut Dağ and Shanidar Cave denotes the least-cost path, which is 450 km long. United States' National Geophysical Data Center/Frahm & Hauck (2017).

The presence of obsidian objects at locations remote from their sources does not, however, imply direct and international transportation of objects over long distances in the way that modern trade networks operate. More likely these objects were passed from individual to individual and community to community over several generations before reaching their eventual resting places. Nevertheless this long range transport of artifacts would have presented distinct advantages to the communities practising it, providing access to materials outside the immediate area, which could have become essential survival tools in difficult times.

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