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Programme collectif de recherche "Réseau de lithothèques en Centre-Val-de-Loire". Rapport d’activité 2019


Abstract and Figures

Depuis 2016, le PCR « Réseau de lithothèques en région Centre - Val de Loire » (PCR CVDL) s’inscrit dans une perspective de recherche sur les modes d’exploitation des ressources lithiques et sur la territorialité des groupes humains préhistoriques. Outre l’étude ou la révision de séries archéologiques de l’espace régional, la caractérisation précise des silicites (silex, chert, silcrète, jaspéroïde) dans leur contexte géologique revêt une importance toute particulière en ce qu’elle permet de dessiner des espaces parcourus (parfois sur de très grandes étendues) et, couplée à la technologie lithique, d’identifier des modes de transport des artefacts. Ces réalités renseignent sur les formes sociales et les régimes de mobilité des groupes humains, permettant de matérialiser des processus d’interaction qui mettent parfois en jeu des entités culturelles perçues comme distinctes.
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Petro-archaeological analysis of the lithic industry of the Lower Paleolithic of La Belle-Roche cave (Sprimont, Belgium), according to the grids developed in recent years by various research programs in France, allows a new reading of this industry. Although the anthropic character of certain objects seems well-estabilished, their accumulation in the deposit remains problematic. In this respect, the taphonomic and weathering analysis of the industry raises questions about the origin of the deposit, the age of the industry and the notion of “site”: is the “La Belle-Roche site” as a prehistorian or prehistoric construction?
Describes a new type of spherulitic millstone which has been found among siliceous nodules from the Berry lacustrine limestone (Eocene) of the Saint-Amand region, Cher, France. It contains veins of opal (rather than fibrous silica).
Article Editor embargo until May 2022. For several years, multidisciplinary archaeological operations organized by the Ministry of Culture and named ‘Collective Research Projects’ (PCR) have enabled the design and use of a descriptive database for a part of southern and central France. This data base describes and stores the main geological aspects of sedimentary silicified rocks of chemical, biochemical or diagenetic origin (abbreviated SSR in the rest of the text) and their primary and secondary outcrops. Data were collected through a survey form describing the flint formations and using different observation grids which make up complete identity cards for each type of flint. Using their spatial attributes, these different data are linked to a shape file for flint formations, themselves digitized with ArcGIS and QGis on the basis of harmonized protocols with several layers of the WebMapService (WMS) Infoterre of the BRGM. Today, data sharing is made possible through the use of the ArcGisOnLine platform (AGOL) meeting the needs of the various users. Applied to an archaeological series, the database considers the concept of an evolutionary chain of SSR and extends an enquiry into the prehistoric relationship between SSR and their environments. According to the same criteria as those defined for the characterization of geological samples (petrology and alterology forms), it allows one to reconstruct the route traveled by any flint before its collection by prehistoric humans and then, by the use of a taphonomic form, decrypts the post-depositional SSR evolution in order to decipher the intensity and chronology of the mechanisms likely to have taken part in the sedimento-genesis of the archaeological site. In terms of understanding paleogeography, the ultimate aim of this approach, the accuracy of petro-ar- chaeological studies is firmly established rather than being anecdotal. By demonstrating that only quantity, genetic and gitological diversity and the way in which materials from coherent geological spaces (i.e. geotopes) are introduced into the archaeological sites, allows one to discuss the method of acquisition of the materials concerned and thus to approach an understanding of the organization of prehistoric societies through their management of landscape and their relationship to territoriality. After the application of this method using the database the results are presented for particular materials coming from the Middle Gravettian series of la Picardie (Preuilly-sur-Claise, Indre-et-Loire, France).
Gloss patina is a natural post-depositional surface alteration frequently present on flint artifacts. Features of this patina include reduced surface topography, smoothness, and a pronounced luster. Gloss patina is distinct from stain patina, desilication (white) patina, and the dark glossy patina known as desert varnish. Glossy river patina has similar features but is produced by abrasion accelerated dissolution whereas gloss patina is primarily a result of soil solution related chemical processes. Artifact adsorption of amorphous silica from its depositional environment can produce gloss patina but advanced examples of gloss patina have surface topography reduction, smoothness, luster and thickness strongly indicating dissolution and concomitant re-precipitation of artifact surface silica.
The geochemical characterization of several lacustrine chert formations outcropping in the Central-Eastern Pre-Pyrenean area is presented. Four geological formations were considered: one Upper Cretaceous (Tremp formation), two Oligocene (Castelltallat and Tartareu-Alberola formations) and one Miocene (Aragonian limestones formation). Furthermore, lacustrine cherts appearing in the Magdalenian levels of Forcas I and Cova Alonsé (Huesca, Spain) were also considered. Analyses were done using energy-dispersive X-ray fluorescence (ED-XRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Results show different geochemical features between formations, in some cases also between outcrops, concerning major, minor and trace elements. Archaeological samples from Cova Alonsé and Forcas I fit in some of the established groups, being the dispersion area slightly different between sites. Consequently, results determine the presence of diversified lithic procurement strategies.