Semi‐supervised classification to determine the provenance of archaeological obsidian samples

Abstract

AbstractIn archaeometry, the correct assignment of archaeological artefacts with their original geological sources continues to be an indispensable tool for determining exploitation patterns, trade routes, tool production and the movement of goods in ancient times. Statistically, Mahalanobis distance has been an integral part of the artefact provenance methodology. However, this method presents disadvantages when some of the theoretical assumptions are not fulfilled. In this way and with a focus on the veracity of the correct assignment of archaeological samples to their geological sources, we present a technique that employs a semi‐supervised classification based on finite mixture models. This procedure uses labelled and unlabelled data to assign samples to groups with the advantage that it does not depend on the sample size of the groups as required by Mahalanobis distance. This procedure was first applied in a controlled experiment where the exact origin of the samples is known in order to verify the accuracy of the method; afterwards, it was applied to artefacts recovered from the archaeological site of Xalasco, Tlaxcala (Mexico), from both surface and excavation collections and analysed with a portable X‐ray fluorescence spectrometer. The resulting groups defined that the ancient dwellers of Xalasco exploited six supply sources located in Central Mexico.