Obsidian Sources of Prehispanic Artefacts from Cultures near Ceboruco Volcano, Nayarit, Mexico

Ceboruco, located in the western part of the Trans-Mexican Volcanic Belt is an active stratovolcano in Nayarit, Mexico, with the last historic eruption in 1870-1875. The fertile valleys around this volcano have been occupied for several thousands of years. The recognised pre-Hispanic human settlements include the Shaft tomb and Aztatlan cultures, which were present in the vicinity of the volcano before and after the well-studied Plinian Jala eruption in 890 AD, respectively. Both cultures left abundant archaeological materials in housing units and cemeteries, including obsidian tools. In this study, we compare archaeological samples (poorly preserved tools or parts of them) with obsidian samples from local outcrops, as well as other known regional obsidian mine sites. We use hand sample and chemical analyses of main and trace elements. The results are statistically evaluated by using the Mahalanobis distance-method in order to assign probable sources. We show that obsidian has been locally extracted from long-known obsidian mines near Ixtlan del Rio, but also from obsidian layers at the nearby Sierra Madre Occidental Mountain Range and the Pochotero obsidian dome. Nevertheless, clear evidence for obsidian trade since the earliest occupations has also been found, as we identified sources from the neighbouring states such as Jalisco.