Can stable isotopes of carbon and oxygen be used to determine the origin of freshwater shells used in Neolithic ornaments from Central Europe?

Abstract

Neolithic burials rich in grave goods, referred to as “princesses burials”, were excavated in the Kuyavia Lowland, central Poland, Central Europe. The most common elements of grave equipment recorded in these burials were ornaments composed of disc beads made of freshwater bivalve (Unio spp.) shells. Our study was aimed at determining the origin of the shells in question by analysing, for the first time, carbon and oxygen stable isotope compositions (δ13C and δ18O) of the beads and comparing the results with C and O isotope ratios in modern shells sampled in central Poland. In the research, the isotope values of modern shells were grouped into two data sets representing riverine and lacustrine endmembers. Unio spp. shells sampled from rivers were isotopically lighter (i.e. isotope values were more negative) compared with the shells collected from lakes. The range of δ13C and δ18O values in the beads was similar to the one observed in modern Unio spp. shells. However, the isotope values differed within and between the archaeological sites studied. In Krusza Zamkowa and Oslonki, two distinct isotopic groups of beads were recognised—riverine and lacustrine—suggesting changes in the shell source in time. The C and O isotope values of beads sampled from Brześc Kujawski indicated the lacustrine origin of the shells used for their production. Also, it was confirmed that shells used to produce one ornament were derived from a single source, and the choice of sources changed in time. Our research revealed that the selection of specific local sources of shells was important for the prehistoric communities under study, and it may be considered the evidence of the existence of a regional exchange network.