Origin, characterisation and lithic management of the Chipana silcrete in the Pampa del Tamarugal basin, northern Chile

Silicified rocks, or silicites, were a highly utilized resource by human groups that traversed the Atacama Desert around 13,000 cal yr BP. The questions of where and how these past groups obtained the raw materials are crucial for understanding the routes they followed and the mechanisms they used for acquiring and transforming the rock. An exemplary case to observe this and to characterize the type of source and rock exploited is “Chipana,” as it is both a source and an archaeological site. It is the largest and oldest known lithic provisioning point in the Pampa del Tamarugal. Using the interdisciplinary perspective of petroarchaeology, the source was characterized, and the lithic technology of the site was analyzed through a techno-economic approach. The main results show that Chipana likely corresponds to a large primary source of rock identified as white silcrete, specifically a heavily silicified limestone with opaline silica. This was identified through scanning electron microscopy analyses, which revealed chemical elements typical of limestone, and through the rock's structure (i.e., fibrous silica) observed via petrographic analysis. Four facies variations of the rock were observed at the source, and its formation is associated with diagenetic activity. It has a conchoidal fracture suitable for lithic knapping, which is why it was sought after by past human groups. The archaeological site corresponds to a lithic workshop focused on bifacial technology for producing large bifaces (13 cm in length). A secondary production is also observed of unifacial technology for knapping a variety of tools. Thus, Chipana provides new data for beginning to map out the lithic landscape of the Pampa and refines our understanding of how humans adapted to and utilized a hyper-arid environment with limited biomass by making use of available local resources such as rock. Additionally, it contributes to our knowledge of the oldest hunter-gatherers who populated the Atacama, as part of the human settlement of South America.