The lay of land: Strontium isotope variability in the dietary catchment of the Late Iron Age proto-urban settlement of Basel-Gasfabrik, Switzerland

Basel-Gasfabrik (Switzerland) comprises an extensive La Tène (chiefly Lt D, 150-80 BCE) settlement and two associated cemeteries at which strontium (87Sr/86Sr) isotope analysis of human and animal teeth investigated regional and supra-regional contacts. The interpretation of the analytic data, however, requires information on the isotopic baseline values around the site. Using 102 modern vegetation and 9 water samples from 51 localities, this study characterizes the isotopic ratios of the biologically available strontium of geological units and watercourses around Basel and compares these to 28 human infant, 6 pig, and 5 dog teeth from the site. Furthermore, pedological criteria evaluate the suitability of landforms for crop and pasturelands. The 87Sr/86Sr ratios of the environmental samples from geological units in up to 50 km distance varied between 0.70776 and 0.71794. Human infant teeth exhibited much more homogeneous 87Sr/86Sr ratios (0.70847-0.70950), which coincided largely with those of potential arable soils around Basel and indicate targeted exploitation of landscapes for agriculture. The more variable values of the faunal teeth suggest more widely ranging habitats or imports from the site's hinterlands. Two local isotope ranges were defined based on archaeological enamel samples and modern vegetation data from a confined radius around Basel. The study documents the complexity of distinguishing local and non-local individuals in a geologically heterogeneous region as well as the potential of isotope analyses to explore prehistoric land-use patterns.