Stable carbon and oxygen isotope geochemistry as provenance indicator for the picture stones on Gotland (Sweden)

The picture stones from Gotland are one of the most famous and exceptional groups of monuments known from Swedish Prehistory. These carved memorial stones and their extraordinarily rich imagery are a unique source for the study of Late Iron and Viking Age culture and in particular Scandinavian pre-Christian religions. The Gotlandic picture stones are mainly made from the thickly layered limestones surrounding the reefs and bioherms of Gotland’s carbonate platform from the middle part of the Silurian (latest Llandovery to Ludlow, Telychian – Ludfordian). However, the exact origins of the picture stones’ raw materials on Gotland have remained undetermined. In this paper, we investigate the geological origin of the raw material by isotope geochemistry. Whereas the oxygen (δ18O) and strontium isotope ratio (87Sr/86Sr) were strongly altered by diagenesis the carbon isotope ratio (δ13C) is quite stable. Because the different geological units on Gotland show specific isotope signatures, the δ13C values from picture stones can be used to assign them to the respective geological unit, and thus to the source area of the raw material. This also allows for an estimation of transport distance minima between the raw material source area and the find place of each sampled picture stone. Most of the picture stones seem to be produced from local material with short transport distances, less than 10 km and only a few were transported at a far distance exceeding 10 km. In summary, the transport distance was dependent mostly on the local availability of picture-stone-suitable rocks.