http://popups.lib.uliege.be/3041-5527/index.php?id=597 Publications de Auteurs Xavier Savary fr 0 http://popups.lib.uliege.be/3041-5527/index.php?id=708 A brief overview is given of the classification schemes and current terminology of Phanerozoic sedimentary iron deposits, particularly that of ironstones. Representative geological samples of oolitic ironstones (OIS) possibly used as raw materials for prehistoric red ochres have been petrographically investigated. Microfacies differences have been observed between Llanvirn OIS from Normandy (France), Famennian OIS from Belgium and Emsian-Eifelian OIS from the Eifel area (Germany). Petrographical differentiation is based upon contrasting grain size, mineralogy and typology of the ferruginous ooids, as well as differences in mineralogy, diagenetic history and lithologic nature of the host sediments or of the cement. Most conspicuous are the differences in ferruginous ooid typology, including “true” concentric ooids, superficial ooids, algal oncoids and pseudo-ooids (such as ferruginized cortoids and rounded bioclasts). “Flaxseed ore” facies and “fossil ore” facies can be identified, as well as transitional or mixed types. A selection of representative archeological objects (OIS) has been petrographically investigated as well: the first results point to a rather local provenance for the samples of Normandy and Hesbaye (Belgium). Un bref résumé de la classification et de la terminologie moderne des dépôts de fer phanérozoïque est présenté et plus spécialement celle des minerais de fer. Des échantillons géologiques représentatifs des minerais de fer oolithiques (OIS), susceptibles d’avoir été utilisés comme matière première pour la fabrication d’ocre rouge durant la préhistoire, ont fait l’objet d’une étude pétrographique. Des différences de microfaciès ont été mises en évidence entre les OIS d’âge Llanvirnien de Normandie (France), les OIS du Famennien de Belgique et les OIS d’âge Emsien-Eifelien de l’Eifel (Allemagne). La différenciation pétrographique se base sur les contrastes de tailles de grains, l’assemblage minéralogique et la typologie des ooïdes ferrifères ainsi que des différences de minéralogie, d’histoire diagénétique et de nature lithologique du sédiment hôte ou du ciment. Les différences les plus visibles se trouvent dans la typologie des ooïdes ferrugineux tels que les ooïdes « vraies » à structure concentrique, les ooïdes superficielles, les oncoïdes d’origine algaire et les pseudo-ooïdes (cortoïdes et les bioclastes roulés ferruginisés). Deux faciès peuvent être identifiés : “Flaxseed ore” (minerai dont les ooïdes sont en forme de graines de lin) et “fossil ore” (minerai riche en fragments de fossiles), ainsi que des faciès mixtes ou intermédiaires. Une sélection d’artéfacts représentatifs (OIS) a été investiguée pétrographiquement dont les premiers résultats démontrent une provenance locale pour le matériel archéologique de Normandie et de Hesbaye. Fri, 29 Nov 2024 14:24:03 +0100 Fri, 29 Nov 2024 14:24:06 +0100 http://popups.lib.uliege.be/3041-5527/index.php?id=708 http://popups.lib.uliege.be/3041-5527/index.php?id=703 The analysis of ochre archaeological artefacts could be realized without its destruction. The aim of this study is to identify macroscopic characteristics to distinguish on these artefacts oolitic ironstones (OIS) from different origins, in this case norman ordovician and belgian devonian ones. Despite frequent difficulties in observations, it shows that the only relevant criterion in order to determine correctly the origin of OIS lies in the form of the ooids. Other criterions, as the size or the sorting of ooids, or the colour of the cement, alone are not discriminating. The comparison of observations on several objects, both on raw materials or on polished surfaces, should enable to propose a differential diagnosis. Fri, 29 Nov 2024 14:17:18 +0100 Fri, 29 Nov 2024 14:28:46 +0100 http://popups.lib.uliege.be/3041-5527/index.php?id=703 http://popups.lib.uliege.be/3041-5527/index.php?id=650 Oolitic ironstones (OIS) disccovered at archaeological (Early Neolithic & Mesolithic) sites in the Caen region (Basse-Normandie, France) were analyzed and compared with Ordovician OIS sampled in geological sites in Basse-Normandie, in order to establish the source of the raw materials used in prehistory. Samples of OIS were analyzed and characterized by X-ray diffraction (whole rock and clay fraction), LA-ICP-MS, HH-XRF and PIXE. Ironstone objects from Colombelles (early Neolithic) show compositions that are different from those recovered at Biéville-Beuville (final Mesolithic). Those at Colombelles were initially extracted from slightly weathered ironstone layers and it is suggested here that their extraction required extra digging to reach less weathered hematite-rich material. In contrast, OIS from Biéville-Beuville have a mineralogical composition indicative of more intense weathering, which might indicate collection of surface material. The final Mesolithic raw material of Biéville-Beuville seems to have been obtained through a different mode of acquisition than that utilized during the early Neolithic. Our research allows us to conclude that all the archaeological OIS from the Plain of Caen are of local or regional origins and that Devonian (Lower Famennian, Frasnian) OIS from Belgium, Lower/Middle Devonian, OIS from the Eifel (Germany) or Mesozoic OIS from Lorraine (in the three border areas between the Grand Duchy of Luxembourg, Belgium and France) are totally lacking. Early Neolithic sites in Belgium contain no oolitic ironstone imported from Normandy. As a consequence, we can conclude that for this specific raw material, there is a lack of exchange between early Neolithic Belgian populations (Hesbaye and Dendre Springs) and the population of the Plain of Caen. Fri, 29 Nov 2024 13:21:49 +0100 Fri, 29 Nov 2024 13:21:57 +0100 http://popups.lib.uliege.be/3041-5527/index.php?id=650 http://popups.lib.uliege.be/3041-5527/index.php?id=636 The oolithic ironstones (OIS) are one of the main sources of prehistorical red dye. The geological occurrences are well known in Basse-Normandie because they were used into mining industry. The fields are often disappeared today and the samples we took are not always representative. This paper summarizes the main characteristics and the genesis of these oolithic levels. They has been deposited on a subtidal open shelf, exposed to tidal wave activity and located south of the infra-Cambrian continent. The presence of oolithic ironstone artifacts in some archeological sites is an evidence of their use as raw materials for prehistorical red ochres. To compare the geological materials and the archeological artifacts, we set up a protocol of analysis including macroscopic observations, petrography, geochemistry and color analysis. Furthermore, we integrated samples from Belgium and Germany, potentially incriminated in long-distance interchanges in Western Europe. Fri, 29 Nov 2024 13:10:40 +0100 Fri, 29 Nov 2024 14:26:18 +0100 http://popups.lib.uliege.be/3041-5527/index.php?id=636 http://popups.lib.uliege.be/3041-5527/index.php?id=589 Fri, 29 Nov 2024 12:49:01 +0100 Fri, 29 Nov 2024 12:49:06 +0100 http://popups.lib.uliege.be/3041-5527/index.php?id=589