Chemical discrimination of obsidian sources in the Kirigamine area and provenance analysis of obsidian artifacts from the Hiroppara prehistoric sites I and II, central Japan

Chemical discrimination of obsidian sources and chemical classification of obsidian artifacts is an essential tool for studying the provenance of obsidian artifacts. The Hiroppara prehistoric sites (I and II) are associated with a cluster of obsidian sources within the Kirigamine area (Nagano Prefecture), central Japan. More than 1000 obsidian artifacts were recovered during excavations in 2011-2013. Here, we conduct a provenance analysis for these obsidian artifacts using Wavelength and Energy Dispersive X-ray Fluorescence (WDXRF and EDXRF, respectively). Quantitative, destructive WDXRF analysis on geological obsidian samples reveals that the Kirigamine obsidian sources can be classified into 12 geochemical groups. Qualitative EDXRF analysis of these geological obsidians samples can also discriminate these 12 chemical groups. To test the reliability of the EDXRF approach, which is non-destructive and rapid, for provenancing obsidian artifacts, we selected 40 obsidian artifacts and compared EDXRF and WDXRF measurements. The results obtained by WDXRF method achieved a success rate of 93% (37 samples) compared to 65% (26 samples) by the EDXRF method. The EDXRF results from four samples are inconsistent with the results from the WDXRF data. While the non-destructive EDXRF method is straightforward and convenient it is evidently less reliable than the destructive WDXRF method. With these results in mind, we performed provenance analysis for all obsidian artifacts (689 samples) from Hiroppara site I using the EDXRF method, and successfully classified 60% of the analyzed artifacts (411 samples). The majority of these samples (352 samples) identify with the Higashimochiya and Takayama sources. Additional information about morphological features, including texture, shape, color, and transparency of samples, can improve the discrimination that is possible by chemical analysis alone.