Novel approach for data grouping and provenance analysis of obsidian archaeological artifacts

What is it about?

In provenance analysis, identifying the origin of the archaeological artifacts plays a significant role. Usually, this problem is addressed by discovering natural groups in data measured with spectroscopic techniques. Then, principal component and classical partitioning cluster analysis are employed to reveal the groups that supposedly define the origin of the investigated artifacts. However, this work shows that maximizing the variance and searching for specific cluster structures can be misleading because it fails to discriminate clearly the different archaeological sources. In contrast, the new methodology reveals several acknowledged geological sources present in the materials through the exploitation of emergence and swarm intelligence without prior assumptions about the data structures. A combination of unsupervised and semi-supervised machine learning and chemometric is applied on samples of Mesoamerican geological sources and obsidian artifacts collected from the archaeological site of Xalasco in Mexico. The analysis of the artifacts showed a preference of Xalasco inhabitants to local obsidian deposits. The results show that this approach, in terms of robustness, is suitable for handling unbiased quantitative spectral analysis of archaeological materials revealing the natural groups of archaeological data.

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Why is it important?

Using the raw spectra of obsidian artifacts, a PCA linear planar projection does not accurately discriminate between the existing archaeological sources and does not map the artifacts of unknown provenance to a known source. The topographic map of the generalized u-matrix, using the nonlinear DBS dimensionality reduction (projection method), visualizes the distance- and density-based structures of all the artifacts. Artifacts from the same obsidian source lie within the same valley. Different archaeological sources are divided by mountains, indicating larger distances and smaller densities between them. Besides a small subset (green), all artifacts collected from Xalasco were mapped to known sources.

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