Abstract
The Andes are a unique geological and biogeographic feature of South America. From the perspective of human geography, this mountain range provides ready access to highly diverse altitudinally arranged ecosystems. The combination of a geologically and ecologically diverse landscape provides an exceptional context to explore the potential of strontium isotopes to track the movements of people and the conveyance of material culture. Here we develop an isotopic landscape of bioavailable strontium (87Sr/86Sr) that is applied to reconstruct human paleogeography across time in the southern Andes of Argentina and Chile (31°–34°S). These results come from a macro-regional sampling of rodents (N = 65) and plants (N = 26) from modern and archeological contexts. This “Southern Andean Strontium Transect” extends over 350 km across the Andes, encompassing the main geological provinces between the Pacific coast (Chile) and the eastern lowlands (Argentina). We follow a recently developed approach to isoscape construction based on Random Forest regression and GIS analysis. Our results suggest that bioavailable strontium is tightly linked with bedrock geology and offers a highly resolved proxy to track human paleogeography involving the levels of territories or daily mobility and anomalous events that disrupt home ranges, such as migration. The southern Andes provide an ideal geological setting to develop this approach, since the geological variation in rock age and composition produces distinctive isotopic signatures for each main biogeographical region. Finally, we apply this framework to a set of results from human remains from the Uspallata Valley in Mendoza (Argentina), to assess the incidence of migration in the key period of the consolidation of agropastoral economies between AD 800 and 1400. The application of the isoscape to the values from human remains confirms the persistence of human groups with relatively restricted territories encompassing Uspallata and the adjacent Precordillera between AD 800 and 1500. We also identify a pulse of human migration between AD 1280 and 1420, shortly preceding the Inka conquest. Looking forward, we expect to converge with ongoing efforts in South America to build a continental research framework to track the movement of people, animals, and artifacts across space and time.
Highlights
Strontium isotopes (87Sr/86Sr) in human teeth and bone remains average the biologically available strontium in the landscape(s) inhabited in the past (Price et al, 2002; Bentley, 2006), providing a proxy of the geographic place of origin of an individual and the spatial scale of the territories occupied (Price et al, 2000; Montgomery, 2010; Knudson et al, 2014a; Laffoon et al, 2017)
The bioavailable strontium isoscape reconstructed for the SAST by means of Random Forest can be compared with recent macro-regional results presented for northern Patagonia (Serna et al, 2020), southwards from our study area
The authors suggest that the deposition and reworking of unradiogenic volcanic sediments by aeolian, fluvial, and glacial erosion homogenized the isotopic landscape, decoupling to some extent bioavailable variation from underlying bedrock geology
Summary
Strontium isotopes (87Sr/86Sr) in human teeth and bone remains average the biologically available strontium in the landscape(s) inhabited in the past (Price et al, 2002; Bentley, 2006), providing a proxy of the geographic place of origin of an individual and the spatial scale of the territories occupied (Price et al, 2000; Montgomery, 2010; Knudson et al, 2014a; Laffoon et al, 2017). Resulting from the combination of growing frames of scientific enquiry, robust methodological approaches, and extensive databases, we consider it is fair to describe the present time as a “golden age” of strontium isotopes to geographically source materials across space and time. This advance is highly heterogeneous in the different continents (Bataille et al, 2020). This project allows incorporating Andean regions with different archeological trajectories of socio-economic change, complexity, and possibly diverse incidence of migrations compared to the more systematically studied Central Andes
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