Geochemistry and geological control of Sonora obsidian: New insights into the provenance study of archaeological obsidians in Mexico

Abstract

Obsidian artifacts found in thirteen archaeological localities of Sonora show a petrological relationship with rhyolitic outcrops scattered in various geological localities (El Pinacate, Sierra Libre, Sierra El Aguaje, Hermosillo, Babidanchi and Sierra Los Mochos). X-Ray Fluorescence geochemical analysis of a group of 133 samples was done, including archaeological artifacts, as well as geological samples and anhydrous cores (raw material-lithic nodules) coming from both geological outcrops and archaeological sites. The geochemical data were compared with reference sample values from known primary obsidian knowing outcrops that also were analyzed by conventional techniques of ICP and XRF previously published. Geochemical results can be integrated into two large groups of obsidian from Sonora, and their spatial distribution holds a direct relation with the geological origin of perlitic outcrops. The first group corresponds to Oligocene rhyolites from the Sierra Madre Occidental. The second group correlates with Middle-Late Miocene rhyolites is associated to the Proto-Gulf of California development. Archaeologically, a distinct temporal sequence was identified as concerning its use according to the cultural areas in which they were found. The geological studies on obsidian sources help us to understand, on the one hand, the origin of perlitic landforms, their spatial situation and, on the other hand, to have a measurable comparative reference, that contributed to know the cultural extension of its indigenous use over time, as well as the reach of the social interaction networks, flaking techniques and use of specific artifact types. Finally, the integration of their geological control and geochemical characteristics allowed us to establish a reliable base to achieve provenance interpretations of obsidian lithic complexes in Sonora. All elements described here represent the obsidian phenomenon in Sonora and have an affinity with obsidian sources of NW Mexico, which provides a unique identity that needs to be located in the context of the interdisciplinary research of lithic in Mexico and SW United States.