Geochemical approach to determine the anthropogenic signal at non-intensively settled archaeological sites - The case of an Iron Age enclosure in Bohemia
Abstrakt
We present a geochemical analysis of a specific Iron Age type of site known as the Viereckschanze - a square enclosure located in Be vlc vice, southern Bohemia. We performed soil coring from the topsoil to ca 100 cm depth, with 200 cores (divided into 456 samples). The samples were measured using portable XRF and the final dataset comprised 16 elements (Al, Si, P, K, Ca, Ti, Mn, Fe, Cu, Zn, As, Rb, Sr, Zr, Pb, and LE - 'light elements'). Because of the compositional character of data expressed in ppm, the data were transformed using isometric log-ratio transformation, which enabled them to carry out a multivariate analysis. This made it possible to determine the anthropogenic and natural content of elements. The site was specific when compared to usual archaeological sites for its 'unconventional' chemical signal:
1) the P signal typical for archaeological settlements was found mainly outside of the enclosure;
2) the conventional anthropogenic signal from the inside of the enclosure was only represented by Mn;
3) other elements related to possible anthropogenic activities were revealed only after applying statistical analysis (specifically As, Pb, Zn, Cu);
4) the unusual manifestation of Si and Ti (usually natural signals) strongly connected to anthropogenic contexts was observed. Increased contents of Cu, Zn and especially Pb were recorded in places indicated by previous magnetic measurements which were possibly related to an onsite metalworking activity. Such results could be characterised as a mixture of typical human-related signals (represented mainly by P and Mn) and typical natural signals (like Si, and Ti). These observations corroborate the hypothesis of a specificity of the Viereckschanzen. They did not have to be used exclusively for residential purposes and could have had a different, more complex socio-economic role in the past. Last but not least, their occupation was probably also rather short-time.