Origin of deep saline groundwaters in the Vienne granitic rocks (France): constraints inferred from boron and strontium isotopes

As part of a preliminary geological characterization programme to assess the feasibility of an underground laboratory in granitic rock, a series of 17 deep boreholes (maximum depth, 900 m) was drilled by ANDRA in the Vienne district, France. A salinity gradient was demonstrated in the granitic waters with concentrations varying from approximately 1 g L^?1 at 150 m depth at the top of the basement (beneath the sedimentary cover) to 10 g L^?1 in the deeper part (from 400 to 600 m depth). Sr and B isotope ratios were measured in order to better understand the origin of the salinity and to evaluate the degree of water–rock interaction in the system. The results obtained were compared to those of mineral spring waters emerging from the granitic basement in the Massif Central. Evidence in support of a significant marine contribution include: (i) the Cl–Br investigations agree with a marine origin for the saline groundwaters without evolution from seawater; (ii) the ⁸⁷Sr/⁸⁶Sr ratio of the Vienne deep groundwaters (0.7078–0.7084) is in agreement with a palaeo‐seawater isotopic signature; (iii) measured δ¹¹B values for the deepest brine samples are enriched in ¹¹B (up to 36.1‰) relative to the granitic springs. The combined use of δ¹¹B, Cl, B, Br, Sr contents and ⁸⁷Sr/⁸⁶Sr ratios makes it possible to define and quantify a mixing model between marine and crustal end‐members in order to explain the origin of the deep saline groundwaters in the Vienne granitic rocks.     

STATISTICAL ASPECTS OF POTTERY QUANTIFICATION FOR THE DATING OF SOME ARCHAEOLOGICAL CONTEXTS*

This paper describes some statistical analyses of a particular archaeological material (pottery) originating at some sites in the city of Tours. An important part of the archaeological study of pottery is the comparison of ceramic assemblages to establish the absolute dates of contexts. In this paper, a statistical model is built to assess this comparison. The statistical procedure uses classical tools (correspondence analysis, linear regression and resampling methods) in an iterative scheme. Archaeologists may find in the paper a useful set of known statistical methods, while statisticians can learn a method of ‘arranging’ well‐known techniques. No method is new, but their combination is characteristic of this application.     

RADIOCARBON DATING OF MESOLITHIC OPEN‐AIR SITES IN THE COVERSAND AREA OF THE NORTH‐WEST EUROPEAN PLAIN: PROBLEMS AND PROSPECTS

This paper discusses the problems with sampling materials and sampled contexts in the framework of radiocarbon dating of Mesolithic sites situated in generally dry, acid and bioturbated coversand deposits within north‐western Europe. The case studies presented all relate to the coversand regions of northern Belgium and the Netherlands, two areas for which very large sets of radiocarbon dates performed on different organic components are currently available. The study points out that charred hazelnut shells from surface hearths and charcoal from hearth pits guarantee the most secure dating results, while the dating of calcined bones and food crusts from Final Mesolithic pottery so far remains problematic.     

LITHIC RESOURCES IN THE EARLY PREHISTORY OF THE ALPS*

Rocks, which are ubiquitous in archaeological sites as chipped or polished tools, were important factors in the prehistoric Alpine economic system. Archaeometric characterization and identification of source areas open the path to a more detailed understanding of the production and diffusion mechanisms behind Alpine lithic industries. An overview of the situation from the eastern to the western Alps in the Mesolithic, the Neolithic and the Copper Age illustrates current debates and issues.     

ISOTOPES ON THE BEACH,PART 1: STRONTIUM ISOTOPE RATIOS AS A PROVENANCE INDICATOR FOR LIME RAW MATERIALS USED IN ROMAN GLASS‐MAKING

The provenancing of Roman natron glass is one of the most challenging problems in the field of archaeometry. Although the use of Sr and Nd isotope ratios and trace element signatures as an indication of provenance has proven promising, there are still many unknowns. In this study, the influence of the different raw materials on the final Sr isotopic composition of Roman natron glass is examined. It is shown that the ⁸⁷Sr/⁸⁶Sr ratio in natron glass is significantly influenced by the silicate fraction of the sand used and does not always provide a clear indication of the lime source used.     

NATURE AND MICROSTRUCTURE OF GALLIC IMITATIONS OF SIGILLATA SLIPS FROM THE LA GRAUFESENQUE WORKSHOP*

The red glaze (slip) that characterizes the Terra Sigillata potteries greatly contributed to their success during the Roman period. The colour of the slip can in fact be partially explained by the microstructure (crystalline phases, grain sizes) and the physico‐chemistry (composition) of the ceramics. However, the precise process and the diffusion of this technique are still not fully known. In particular, we do not know yet how the production of sigillata took place in the south of Gaul, and the role that was played by the production under Italian influence (pre‐sigillata) preceding the first local sigillata. In this work, a combination of transmission electron microscopy (TEM) and X‐ray synchrotron diffraction techniques was used to study the microstructure of pre‐sigillata slips from the main southern Gaul workshop (La Graufesenque), in order to compare their characteristics with those of high‐quality sigillata. These first results seem to indicate that the antique potters chose clays adapted to their firing conditions and to the type of coating that they wanted to make. These productions cannot be described as an initial phase for the later sigillata production and, rather, seem to correspond to the intention of developing a specific type of pottery only inspired by the famous Italian sigillata forms.     

Inferring intermediate‐scale fluid flow in a heterogeneous metasedimentary multilayer sequence during progressive deformation: evidence from the Monts d’Arrée slate belt (Brittany,France)

Quartz veins in the early Variscan Monts d’Arrée slate belt (Central Armorican Terrane, Western France), have been used to determine fluid‐flow characteristics. A combination of a detailed structural analysis, fluid inclusion microthermometry and stable isotope analyses provides insights in the scale of fluid flow and the water–rock interactions. This research suggests that fluids were expelled during progressive deformation and underwent an evolution in fluid chemistry because of changing redox conditions. Seven quartz‐vein generations were identified in the metasedimentary multilayer sequence of the Upper Silurian to Lower Devonian Plougastel Formation, and placed within the time frame of the deformation history. Fluid inclusion data of primary inclusions in syn‐ to post‐tectonic vein generations indicate a gradual increase in methane content of the aqueous–gaseous H₂O–CO₂–NaCl–CH₄–N₂ fluid during similar P–T conditions (350–400°C and 2–3.5 kbar). The heterogeneous centimetre‐ to metre‐scale multilayer sequence of quartzites and phyllites has a range of oxygen‐isotope values (8.0–14.1‰ Vienna Standard Mean Ocean Water), which is comparable with the range in the crosscutting quartz veins (10.5–14.7‰ V‐SMOW). Significant differences between oxygen‐isotope values of veins and adjacent host rock (Δ = ?2.8‰ to +4.9‰ V‐SMOW) suggest an absence of host‐rock buffering on a centimetre scale, but based on the similar range of isotope values in the Plougastel Formation, an intraformational buffering and an intermediate‐scale fluid‐flow system could be inferred. The abundance of veins, their well‐distributed and isolated occurrence, and their direct relationship with the progressive deformation suggests that the intermediate‐scale fluid‐flow system primarily occurred in a dynamically generated network of temporarily open fractures.     

TRACING THE RESOURCES OF IRON WORKING AT ANCIENT SAGALASSOS (SOUTH‐WEST TURKEY): A COMBINED LEAD AND STRONTIUM ISOTOPE STUDY ON IRON ARTEFACTS AND ORES*

Lead and strontium isotope analyses were performed by thermal ionization mass spectrometry (TIMS) on Roman to Byzantine iron artefacts and iron ores from the territory of ancient Sagalassos (south‐west Turkey), to evaluate Pb and Sr isotopes for provenance determination of ores for local iron production. It can be demonstrated that for early Roman artefacts and hematite iron ore processed in early Roman times from Sagalassos proper, as well as for magnetite placer sands and early Byzantine raw iron from the territory of the city, Sr isotopes are much less ambiguous than Pb isotopes in providing clearly coherent signatures for ore and related iron objects. Late Roman iron objects were produced from iron ores that as yet remain unidentified. Early Byzantine iron artefacts display more scatter in both their Pb and Sr isotope signatures, indicating that many different ore sources may have been used. Our study demonstrates that iron objects can be precisely analysed for their Sr isotopic composition, which, compared to Pb isotopes, appears to be a much more powerful tool for distinguishing between chronological groups and determining the provenance of raw materials.