Northwestern Patagonia is located in a tectonically active part of the southern Andes (Argentina), which has facilitated the formation of obsidian, including pyroclastic deposits that have been affected by geomorphic processes, resulting in a complex obsidian landscape. To date, the geomorphic relocation of obsidian in the landscape has not been a focus of systematic research, and this hampers our understanding of prehistoric human mobility. We present an updated assessment of the regional availability of different obsidian types based on results from our research program, which combines geoarchaeological survey and geochemical characterization to understand the properties and distribution of obsidian. This robust “source‐scape” provides the foundation for reconstructing patterns of lithic provisioning and discard. Our results suggest that interpretations of obsidian availability across the landscape should be more nuanced than is typically acknowledged. Based on our improved “source‐scape,” we discuss the patterns observed in an archaeological X‐ray fluorescence database. When compared with the geoarchaeological reconstruction of obsidian availability, the archaeological record conforms to a distance‐decay pattern. Contrary to previous interpretations, we suggest that the distribution of obsidian types is not isomorphic with human home ranges. This geoarchaeological research program provides a basis for integrating the archaeological record of different Andean regions.

Red mineral pigment use is recognized as a fundamental component of a series of traits associated with human evolutionary development, social interaction, and behavioral complexity. Iron-enriched mineral deposits have been collected and prepared as pigment for use in rock art, personal adornment, and mortuary practices for millennia, yet little is known about early developments in mineral processing techniques in North America. Microanalysis of rock art pigments from the North American Pacific Northwest reveals a sophisticated use of iron oxide produced by the biomineralizing bacterium Leptothrix ochracea; a keystone species of chemolithotroph recognized in recent advances in the development of thermostable, colorfast biomaterial pigments. Here we show evidence for human engagement with this bacterium, including nanostructural and magnetic properties evident of thermal enhancement, indicating that controlled use of pyrotechnology was a key feature of how biogenic iron oxides were prepared into paint. Our results demonstrate that hunter-gatherers in this area of study prepared pigments by harvesting aquatic microbial iron mats dominated by iron-oxidizing bacteria, which were subsequently heated in large open hearths at a controlled range of 750 °C to 850 °C. This technical gesture was performed to enhance color properties, and increase colorfastness and resistance to degradation. This skilled production of highly thermostable and long-lasting rock art paint represents a specialized technological innovation. Our results contribute to a growing body of knowledge on historical-ecological resource use practices in the Pacific Northwest during the Late Holocene.Figshare link to figures: https://figshare.com/s/9392a0081632c20e9484.

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<p>En el norte neuquino existen depósitos piroclásticos que contienen nódulos de obsidianas. Las investigaciones en la región dieron a conocer las principales fuentes utilizadas por las poblaciones que allí habitaron. Para profundizar el conocimiento de cada fuente de obsidiana se adoptó un programa de estudio geoarqueológico y geoquímico. Así, se han descubierto nuevas ocurrencias de obsidianas, la más destacable de las cuales es la obsidiana Varvarco que aquí se presenta. Se dan a conocer los muestreos realizados en el valle del río Varvarco, su contexto geológico y geomorfológico, la presencia de obsidiana, el tipo de yacimiento, forma de presentación, distribución y abundancia. Luego, se describen las principales características observadas bajo microscopio petrográfico. Por último, se presentan los resultados de análisis geoquímicos de fluorescencia de rayos X y activación neutrónica. A partir de los primeros la obsidiana Varvarco se diferencia de la de Cerro Huenul, pero no de la obsidiana Maule 1 y 2. Los segundos análisis discriminan bien esta nueva obsidiana de las ya conocidas para Neuquén. Los resultados obtenidos permiten reinterpretar la disponibilidad de recursos líticos de buena calidad para la talla y revisar las interpretaciones de movilidad e interacción de poblaciones en esta región.</p>