From the source to the object : tracing the archaeological materials using LA-ICP-MS. The example of stone ornaments in the ancient societies.

English Abstract:

Ancient societies used various natural resources to make many artefacts (ornaments, tools, weapons), especially lithic resources. Current research is mainly dedicated to the study of chipped stone tools such as flint or obsidian, but the study of other kinds of rocks is less developed. We focus here on the case of “soft” rocks (such as black shale, soapstone, serpentinite) used mainly to make ornaments. The study of these rocks constitutes a real scientific challenge: i) from an archaeological point of view, the geological sources and the distribution away from these sources of the artefacts is unknown, consequently this poses a difficulty in reconstructing ancient economic or cultural exchange networks; ii) from an analytical point of view, these materials are difficult to characterize due to their heterogeneity. The lack of systematic characterization studies has impeded the construction of relevant reference data and therefore to establish precise relationships between the archaeological objects and the geological resources exploited. Consequently, interdisciplinary research is essential because raw material characterization forms the basis of any provenance study. However, the destruction of archaeological objects constitutes a major limiting factor. The use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) which allows to carry out nearly invisible micro samplings was chosen as it presents several advantages. Its application to stone artefacts has provided promising results. Two examples of two kinds of “soft” rocks will be presented in order to show the relevance of this method and the results obtained: i) on ornaments made of black shales by the Celts of Europe (8^th to 1^st century B.C.) and ii) on soapstone beads made by the Iroquoians of the Saint Lawrence Valley in Quebec (15^th & 16^th centuries).