Tendances actuelles dans la caractérisation des obsidiennes pour les études de provenance

Les recherches de provenance des obsidiennes de sites paléolithiques et néolithiques connaissent actuellement une grande expansion, notamment par leur intégration dans les études de chaînes opératoires, qui nécessitent de déterminer l’origine de la matière première de séries importantes de pièces archéologiques. Il existe par ailleurs une forte demande de mesures peu à non destructives et éventuellement à effectuer in situ. D’où un certain nombre de développements méthodologiques récents. Le but de cette contribution est d’en présenter le statut actuel.Sourcing studies involving obsidians from Palaeolithic and Neolithic sites are presently undergoing a period of change, notably in terms of the average number of samples analyzed per project, due largely to their integration into the chaînes opératoires approach of lithic technologies. This can entail working with a large number of artifacts from an archaeological context. There is also an ever-increasing demand to employ quasi non-destructive characterization methods and completely non-destructive methods that eventually could be performed in situ. As such, recent methodological advances have taken several directions. The purpose of this short note is to give an overview of these approaches

The geochemical characterization of two long distance chert tracers by ED-XRF and LA-ICP-MS. Implications for Magdalenian human mobility in the Pyrenees (SW Europe)

We geochemically characterize two chert formations outcropping in the Pyrenees and presenting similar characteristics at the visual and microscopic scale: The Montgaillard flysch cherts and the Montsaunès cherts. Cherts presenting identical textural and micropalaeontological features as both types have been found in several Magdalenian Pyrenean sites. We are face to a long distance chert type whose geochemical characterization is essential for knowing where the tracer comes from. Analyses have been done using Energy-dispersive X-ray fluorescence (ED-XRF) and laser ablation inductivelycoupled plasma mass spectrometry (LA-ICP-MS). Results show that despite obtaining similar data concerning major and minor elements, differences have been observed regarding trace elements. The establishment of differences between both formations at the geochemical level has allowed specifying the origin of this chert type recovered at the Magdalenian levels of Parco Cave (Alòs de Balaguer, Spain). Results demonstrate long lithic raw material circulation and thus, human mobility in the Pyrenees during the Upper Palaeolithic

Micro-PIXE studies on prehistoric chert tools: elemental mapping to determine Palaeolithic lithic procurement

This paper contributes to an understanding of the distances and choices involved in raw material procurement strategies by Upper Palaeolithic communities through a Pyrenean geoarchaeological case study. Methodologically it involved using Particle Induced X-ray Emission (PIXE) with a focused proton beam to determine the concentration and distribution of elements in geological samples from three natural primary outcrops belonging to two geological formations outcropping in the French side of the Pyrenees. While it was not possible to distinguish the formation through reference to major and minor elements, some variations were revealed at the trace elemental level. With the aim to determine if these elements were associated with the Si matrix or to a specific inclusion, elemental maps were acquired and the elemental composition of the identified inclusions were also determined. These chemical signatures were then compared to those generated from archaeological artefacts from sites in northern Spain as a means of reconstructing the catchment areas used by prehistoric groups for their chert procurement. The results indicate the existence of trans-Pyrenean long distance procurement strategies during the Magdalenian (13700 to the 18800 cal BP)

Earliest known human burial in Africa

The origin and evolution of hominin mortuary practices are topics of intense interest and debate1,2,3. Human burials dated to the Middle Stone Age (MSA) are exceedingly rare in Africa and unknown in East Africa1,2,3,4,5,6. Here we describe the partial skeleton of a roughly 2.5- to 3.0-year-old child dating to 78.3 ± 4.1 thousand years ago, which was recovered in the MSA layers of Panga ya Saidi (PYS), a cave site in the tropical upland coast of Kenya7,8. Recent excavations have revealed a pit feature containing a child in a flexed position. Geochemical, granulometric and micromorphological analyses of the burial pit content and encasing archaeological layers indicate that the pit was deliberately excavated. Taphonomical evidence, such as the strict articulation or good anatomical association of the skeletal elements and histological evidence of putrefaction, support the in-place decomposition of the fresh body. The presence of little or no displacement of the unstable joints during decomposition points to an interment in a filled space (grave earth), making the PYS finding the oldest known human burial in Africa. The morphological assessment of the partial skeleton is consistent with its assignment to Homo sapiens, although the preservation of some primitive features in the dentition supports increasing evidence for non-gradual assembly of modern traits during the emergence of our species. The PYS burial sheds light on how MSA populations interacted with the dead.Additional co-authors: Pilar Fernández-Colón, Nikos Kourampas, Jorge González García, David Larreina, François-Xavier Le Bourdonnec, Laura Martín-Francés, Diyendo Massilani, Julio Mercader, Jennifer M. Miller, Emmanuel Ndiema, Belén Notario, Africa Pitarch Martí, Mary E. Prendergast, Alain Queffelec, Solange Rigaud, Patrick Roberts, Mohammad Javad Shoaee, Ceri Shipton, Ian Simpson, Nicole Boivin & Michael D. Petragl

Les obsidiennes du site de Rio Saboccu : provenances, réduction et relations avec le Néolithique ancien de la zone tyrrhénienne

Très peu d’analyses technologiques ont été effectuées sur des assemblages d’obsidiennes du Néolithique ancien sarde et, plus généralement, de Méditerranée occidentale. Une telle approche est présentée ici, en association avec une étude visuelle/instrumentale de provenance, pour le site Néolithique ancien de Rio Saboccu (Sardaigne), où plus de 1000 artefacts ont été collectés. Il est montré que cette industrie, pour l’ensemble peu investie, a été réalisée à partir d’une exploitation non opportuniste des quatre types d’obsidiennes du massif volcanique voisin du Monte Arci. Le choix de la matière première a principalement été guidé par la dimension des produits finaux espérés et les aptitudes à la taille, d’où la détermination de lieux d’exploitation spécifiques (sources primaires et/ou secondaires). Les industries en obsidienne des sites du Néolithique ancien de la zone Nord-Tyrrhénienne présentent des affinités certaines avec celles de Rio Saboccu et d’autres sites voisins. Il semblerait donc que les communautés proches du Monte Arci aient pu, à cette époque, exercer une certaine influence régionale.Technologic analyses of Neolithic obsidian assemblages are quite rare in Sardinia, like in the wider Western Mediterranean. Such an approach is presented here in conjunction with a visual/instrumental provenance study for the Rio Saboccu Early Neolithic (EN) site, which yielded more than 1000 obsidian artefacts. It is shown that this mostly expedient industry was realized from a non-opportunistic exploitation of the four obsidian types of the nearby Monte Arci (Sardinia) volcanic massif. The choice of the raw materials was chiefly guided by their intrinsic knapping qualities and in function of the maximum size of the expected final products; hence some selection in the (primary and/or secondary) sources exploited. The obsidian industries of EN sites from the northern Tyrrhenian area present clearly some affinities with that of Rio Saboccu and of other EN Sardinian sites, mainly those located in its vicinity. This suggests a regional influence of the EN communities settled in the proximity of the Monte Arci.</p

Les bracelets celtiques en verre du site de Lacoste (Mouliets-et-Villemartin). Approche technologique

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FTIR-Based Crystallinity Assessment of Aragonite–Calcite Mixtures in Archaeological Lime Binders Altered by Diagenesis

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FTIR-Based Crystallinity Assessment of Aragonite–Calcite Mixtures in Archaeological Lime Binders Altered by Diagenesis

Lime plaster and mortar are pyrotechnological materials that have been employed in constructions since prehistoric times. They may nucleate as calcite and/or aragonite under different environmental settings. In nature, aragonite and calcite form through biogenic and geogenic processes that lead to different degrees of atomic order. The latter is a result of defects in the crystal lattice, which affect the properties of crystals, including their interaction with infrared light. Using Fourier transform infrared spectrometry (FTIR) with the KBr pellet method, it is possible to exploit these differences and assess the degree of atomic order of aragonite and calcite crystals and thus their mechanisms of formation. Here we use FTIR to characterize the degree of short-range atomic order of a pyrogenic form of aragonite recently observed in experimental and archaeological lime binders. We show that pyrogenic aragonite has a unique signature that allows its identification in archaeological sediments and lime binders of unknown origin. Based on these results, we developed a new FTIR-based method to assess the integrity and degree of preservation of aragonite and calcite when they occur together in the same material. This method allowed a better assessment of the diagenetic history of an archaeological plaster and finds application in the characterization of present-day conservation materials, such as lime plaster and mortar, where different polymorphs may nucleate and undergo recrystallization processes that can alter the mechanical properties of binders

Raman micro-spectroscopy of western Mediterranean obsidian glass: one step towards provenance studies?

International audienceThis paper presents the first results of the Raman characterization of obsidians from the western Mediterranean. About 40 geological samples, from the islands of Lipari, Palmarola, Pantelleria and Sardinia, representative of the seven archaeologically significant obsidian sources, were analysed. Apart from the general shape of the spectra, which characterize three islands, a detailed treatment of the stretching massif part was performed to obtain quantitative discriminating parameters. The combination of these factors seems to provide a complete discrimination of all archaeologically significant western Mediterranean sources. These sources have provided raw material of Meso- and Neolithic artefacts distributed around the Tyrrhenian basin and nowadays provide key evidence of ancient exchange networks. Because some alternatives to classical geochemical fingerprinting are currently being sought, Raman spectroscopy could be a complementary or even alternative technique in provenance studies of archaeological obsidians

Monte Arci (Sardinia) obsidians: new geochemical data from electron microprobe and ion beam analysis

International audienceWe bring new geochemical data on Monte Arci (Sardinia) obsidians from elemental analyses by electron microprobe (EMP) and proton-induced X-ray emission (PIXE). Obsidians from the geochemical groups SA, SB1, SB2 and SC can be sorted out from their major element contents by EMP and from their trace element contents by PIXE. While EMP analysis requires for analysis a few milligrams polished fragment, PIXE is strictly non-destructive. Forty samples were part of a program aimed at the geochemical characterization of Monte Arci secondary sources.Si presentano in questo lavoro nuovi dati geochimici sulle ossidiane del Monte Arci (Sardegna) sulla base di analisi della composizione elementare effettuate alla microsonda (EMP) e per emissione di raggi X indotta da protoni (PIXE). Le ossidiane appartenenti ai gruppi geochimici SA, SB1, SB2 ed SC possono essere discriminate in base al loro contenuto in elementi maggiori mediante EMP ed in base al loro contenuto in tracce mediante PIXE. Mentre le analisi EMP richiedono un frammento lucidato di pochi milligrammi, PIXE è un metodo del tutto non distruttivo. Sono stati analizzati quaranta campioni prelevati nell'ambito di un programma finalizzato alla caratterizzazione dei depositi secondari del Monte Arci