Le Morvan à l'âge du Bronze, dynamique d'occupation d'après les données archéologiques

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Un site d'acquisition du schiste pour la fabrication d'anneaux au Néolithique ancien à Saint-Germain-du-Corbéis "l'Ermitage" (Orne)

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Volumetric Obscurance as a New Tool to Better Visualize Relief from Digital Elevation Models

International audienceThe use of digital elevation models (DEMs) has become much more widespread in recent years, thanks to technological developments that facilitate their creation and availability. To exploit these data, a set of processing techniques has been developed to reveal the characteristic structures of the relief. This paper presents a new method based on the volumetric approach, and two derivatives. These methods are evaluated on three DEMs at different resolutions and scales: a freely accessible DEM from JAXA DEM covering part of NorthEast Tanzania, a DEM corresponding to rock art in Siberia, and a DEM of an archaeological Bronze Age funeral structure. Our results show that with the volumetric approach, concave and convex areas are clearly visible, with contrast marking slope breaks, while the overall relief is attenuated. Furthermore, the use of volume reduces the impact of noise, which can occur when processing is based on sky visibility (e.g., sky-view factor or positive openness) or second derivatives. Finally, the volumetric approach allows the implementation of a vertical exaggeration factor, the result of which will enhance the particular characteristics of the landscape. The present study comes with a standalone executable program for Windows, a QGIS plugin, and the scripts written in Python, including GPU compute capability (via CUDA) for faster processing

ERA: A new, fast, machine learning-based software to document rock paintings

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Impact of trace metals from past mining on the aquatic ecosystem: a multi-proxy approach in the Morvan (France).

10 pagesInternational audienceThis study seeks to determine to what extent trace metals resulting from past mining activities are transferred to the aquatic ecosystem, and whether such trace metals still exert deleterious effects on biota. Concentrations of Cd, Cu, Pb and Zn were measured in streambed sediments, transplanted bryophytes and wild brown trout. This study was conducted at two scales: (i) the entire Morvan Regional Nature Park and (ii) three small watersheds selected for their degree of contamination, based on the presence or absence of past mining sites. The overall quality of streambed sediments was assessed using Sediment Quality Indices (SQIs). According to these standard guidelines, more than 96% of the sediments sampled should not represent a threat to biota. Nonetheless, in watersheds where past mining occurred, SQIs are significantly lower. Transplanted bryophytes at these sites consistently present higher trace metal concentrations. For wild brown trout, the scaled mass and liver indices appear to be negatively correlated with liver Pb concentrations, but there are no obvious relationships between past mining and liver metal concentrations or the developmental instability of specimens. Although the impact of past mining and metallurgical works is apparently not as strong as that usually observed in modern mining sites, it is still traceable. For this reason, past mining sites should be monitored, particularly in protected areas erroneously thought to be free of anthropogenic contamination

Morphometry of Middle Bronze Age palstaves. Part II - spatial distribution of shapes in two typological groups, implications for production and exportation.

10 pagesInternational audienceFor archaeologists, metallic artifacts are key materials to assess Middle Bronze Age production areas and cultural exchanges. Here, a set of 629 bronze palstaves excavated in northern France, belonging to Breton and Norman typological groups, was treated by (open) outline-based morphometrics with orthogonal polynomial regression. Using robust statistics developed for outlier detection, these Norman and Breton palstave outlines can be divided into two groups: those for which the shape fluctuates close to the standard shape, called "congruent" axes, and those which are far enough from this standard to be considered as "non-congruent", although they possess most of the features of the typological group. The highest density of discovery (whether congruent and non-congruent in shape) is in the extreme east of Brittany for the Breton axes, while the Norman axes are concentrated in northern Normandy, hence the choice of names. However, the distribution of congruent and non-congruent artifacts appears to be spatially dependent for the Norman group, and to a lesser extent for the Breton group, as there are proportionally more congruent specimens inside the supposed production areas than outside. This contradicts the generally accepted archaeological scheme which hypothesizes that all axes in a group originate from the same production center, and that some items were exported from there to supply neighboring regions. Other minor production centers probably existed, copying the original model with greater shape variation

Tracking archaeological and historical mines using mineral prospectivity mapping.

13 pagesInternational audienceThe present study proposes a technological transfer from modern mining prospection to the field of archaeology, providing a methodology to facilitate the discovery of ancient mining sites. This method takes advantage of the thousands of geochemical analyses of streambed sediments, performed by national geological surveys to inventory mineral substances. In order to delineate geochemical anomalies, the datasets are treated following two different approaches: Exploratory Data Analysis and a fractal-based method often recognised as more powerful. Mineral prospectivity maps are then obtained by combining the results with a geographical information system. The surroundings of the Celtic oppidum of Bibracte, French Massif Central, known to have been mined at least since the Late Bronze Age until Modern Times, have been chosen to exemplify the method's potential in archaeology. First, an exhaustive record of the mining sites was undertaken over a pilot area by pedestrian prospection. If mineral prospectivity maps had been used as guidelines, ∼70% of these mines would have been discovered by prospecting only ∼15-20% of the whole area whatever the method used to treat the dataset. At least for our specific case, the multifractal approach is as powerful as EDA. Besides saving a significant amount of time and effort, the methods described here may supply clues for determining the nature of mineral substances exploited in the past, when such information cannot be straightforwardly obtained from the field or from textual archives. It should however be noticed that this approach is proposed as a first step before peer archaeological investigation following more conventional methods. Technically, there is no real obstacle to the application of the methodology proposed here, because (i) software and associated packages are freely available from the web, as well as original geochemical datasets (at least in France), and (ii) minimal mathematical skills are required

Serial production circa 1500 BC: manufacturing rules in the Middle Bronze Age, from the English Channel to the Alps, in the light of geometric morphometrics

13 pagesNational audienceSome European Bronze Age objects were produced by what has been described as serial metalworking. One particularexample is the Middle Bronze Age palstave, massively produced and used in Western Europe during the mid-second millennium BC.These artefacts were often voluntarily buried together in hoards, meaning they were removed from the production network, thus avoidingany recycling. They are found intact, either as rough castings or ready for use. These homogeneous objects are grouped in sets of severalitems, or in tens, or even in hundreds. Such discoveries have immediately led to numerous questions as to the possible interpretation ofthis behaviour. It is clear that prehistoric craftsmen must have been seeking to reproduce the models they had designed, as faithfully aspossible. Macroscopic observations reveal a quest for the same general shape and ornamentation, suggesting great homogeneity in productionduring this period. Many examples have been found of palstaves that were produced from exactly the same mould.Considering the entire production as a whole, and regarding all palstaves as belonging to the same type, some disparities are neverthelessvisible, even to the naked eye, particularly with regard to shape. The question is therefore to discover what degree of consistencyexists among types usually identified only with the naked eye. It becomes necessary to measure the degree of determination required toduplicate so many objects over such a vast territory (up to several thousands of km²). The overarching question is to understand how theproduction of metallic objects was organised during the mid-second millennium BC, from the English Channel to the Alps.Macroscopic observations are no longer adequate to answer such questions. It has become necessary to concentrate on methodologicaltechniques commonly used in the life sciences. Mathematical analysis systems are indeed capable of discriminating between populationsaccording to shape. So far, two methods have been selected: 1) the Discrete Cosine Transform (DCT) and 2) orthogonal polynomials.These analysis techniques were used to translate naked eye observations into mathematical expressions. The two typological groupsconsidered in these studies are the Breton type and the Norman type, named after their areas of highest discovery density. Mathematicalanalysis confirmed the statistical validity of these two typological groups, but with an overlap in the morphometric space. This resultproves that each group was seeking to reproduce a specific model, and also confirms that these prehistoric populations were aware oftheir territorial affiliation: 1) the Breton peninsula, for the Breton type and 2) the Seine Valley, for the Norman type. These statisticalmethods also make it possible to quantify the variability present in each type. Shape thus acquires a geographic identity, giving rise to acultural identification, even if the objects differ somewhat from the original model.As the distance from the two high discovery density zones increases, some palstaves presenting a visual similarity to standard modelsare in fact mathematically identified as outliers, distant from the centre of the morphospace. This result raises the question of possiblelocal copies, or even imitations, in areas outside the two high discovery density zones, taken to be the two major manufacturing centres.To conclude, this example of prehistoric metal production illustrates that the rule in manufacturing seems to be the desire to get evercloser to a reference model, but that all copies do not have to be perfect.The degree of congruence does not seem to be the most important aspect, as long as the objects appear similar to the naked eye.Parmi les productions métalliques connues de l'âge du Bronze en Europe, certaines sont considérées comme des productionsen série et sont nommées comme telles. Il s'agit en particulier des lames de haches à talon du Bronze moyen au milieu du deuxième millénaireavant notre ère, produites et utilisées massivement en Europe occidentale. Ces objets sont le plus souvent retrouvés en contextede dépôt, c'est-à-dire qu'ils ont été retirés du circuit de production, qu’ils ont échappé à un éventuel recyclage, puis ont été volontairementrassemblés et enfouis sous terre. On les retrouve entiers, bruts ou prêts à l'emploi. Ils forment des ensembles homogènes de quelquesobjets ou de plusieurs dizaines, voire de centaines de pièces. De tels ensembles ont d'emblée suscité de nombreuses questions d'interprétationmais de toute évidence, les artisans bronziers protohistoriques ont cherché à reproduire à l'identique les modèles qu'ils avaientconçus. Une simple observation macroscopique montre une recherche des mêmes formes et des mêmes décors, ce qui donne souventl'impression d'une grande homogénéité de la production de cette période. Il existe même de nombreux exemples de lames de haches donton peut affirmer qu'elles ont été produites dans le même moule.Pourtant, si l'on examine la production d'un type dans son ensemble, c'est-à-dire tous les exemplaires considérés comme appartenant àce même type, il existe, même à l'oeil nu, des disparités – notamment de forme – assez importantes. La question est alors de savoir dansquelle mesure les types identifiés à l'oeil nu sont réellement cohérents, autrement dit de mesurer le degré de précision dans la reproductionà l'identique des objets si nombreux et ce, au sein d'un territoire très vaste (plusieurs milliers de km2). Au-delà de cette question, il s'agitde comprendre les processus de fabrication des objets métalliques au milieu du deuxième millénaire avant notre ère, entre la Manche etles Alpes.Pour répondre à cette problématique, l'observation macroscopique ne suffisant plus, nous nous sommes attachés à mettre en oeuvre desméthodes issues des sciences du vivant, qui utilisent depuis longtemps des outils et des analyses mathématiques permettant de comparerdes populations entre elles à partir des formes des individus qui les composent. Jusqu'à présent, nous avons sélectionné deux méthodesprincipales : la transformée en cosinus discrète (TCD) et les polynômes orthogonaux. L'emploi de ces techniques d'analyse nous permetde quantifier ce que l'on observe à l'oeil nu. Ces études ont tout d'abord montré que pour une même famille d'objets, ici les lames de hachesdites « à talon », les deux types différents – distingués par leur répartition géographique (type normand et type breton) – avaient une réellevalidité statistique en termes de forme, avec toutefois un chevauchement dans l'espace morphométrique. Ce fait prouve que les populationsprotohistoriques avaient conscience de leur appartenance territoriale, ici la péninsule armoricaine (type dit « breton ») et la valléede la Seine (type dit « normand ») et qu'elles cherchaient à reproduire un modèle établi. Ces méthodes statistiques permettent égalementde quantifier la variabilité de forme présente dans chacun des types ; on voit donc bien que l'important est de se rapprocher d'une formequi porte une signification spatiale et donc culturelle, même s'il ne s'agit pas d'exactes reproductions. Dès lors que l'on s'éloigne des zonesde plus grande concentration géographique, on trouve des exemplaires qui ont l'aspect des modèles standards, mais qui se retrouvent enpériphérie des espaces morphométriques formés par ces derniers. C'est alors que se pose la question de l'existence de productions localesd'imitations (et de transfert de technologie) dans les secteurs qui ne sont pas censés être des pôles majeurs de fabrication. Ainsi, à traversl'exemple des productions métalliques de haches, la règle de fabrication semble résider dans la volonté de se rapprocher au maximumd'un modèle de référence, sans pour autant que l'imitation soit forcément parfaite. Le degré de conformité ne semble pas être la notion laplus importante, tant que, à l'oeil nu, les objets se ressemblent

Le programme « Identification et impact des sites miniers abandonnés sur les écosystèmes aquatiques et terrestres actuels ». Bilan au sein du Parc naturel régional du Morvan

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