Bioavailable strontium, human paleogeography, and migrations in the southern andes: A machine learning and GIS approach

BARBERENA, RAMIRO; CARDILLO, MARCELO; LUCERO, GUSTAVO; LE ROUX, PETRUS J.; TESSONE, AUGUSTO; CARINA LLANO; GASCO, ALEJANDRA; MARSH, ERIK J.; NOVELLINO PAULA; FRIGOLÉ, CECILIA; WINOCUR, DIEGO; ANAHÍ BENITEZ; CORNEJO, LUIS; CORTEGOSO VALERIA; DURAN VICTOR; CESAR MENDEZ

Frontiers in Ecology and Evolution

University of Ottawa

Año: 2021 vol. 9

The Andes are a unique geological and biogeographic feature of South America. Fromthe perspective of human geography, this mountain range provides ready access tohighly diverse altitudinally arranged ecosystems. The combination of a geologically andecologically diverse landscape provides an exceptional context to explore the potentialof strontium isotopes to track the movements of people and the conveyance of materialculture. Here we develop an isotopic landscape of bioavailable strontium (87Sr/86Sr)that is applied to reconstruct human paleogeography across time in the southern Andesof Argentina and Chile (31?34S). These results come from a macro-regional samplingof 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 theeastern lowlands (Argentina). We follow a recently developed approach to isoscapeconstruction based on Random Forest regression and GIS analysis. Our results suggestthat bioavailable strontium is tightly linked with bedrock geology and offers a highlyresolved proxy to track human paleogeography involving the levels of territories ordaily mobility and anomalous events that disrupt home ranges, such as migration. TheFrontiers in Ecology and Evolution | www.frontiersin.org 1 March 2021 | Volume 9 | Article 584325Barberena et al. Bioavailable Strontium and Human Paleogeographysouthern Andes provide an ideal geological setting to develop this approach, since thegeological variation in rock age and composition produces distinctive isotopic signaturesfor each main biogeographical region. Finally, we apply this framework to a set of resultsfrom human remains from the Uspallata Valley in Mendoza (Argentina), to assess theincidence of migration in the key period of the consolidation of agropastoral economiesbetween AD 800 and 1400. The application of the isoscape to the values from humanremains confirms the persistence of human groups with relatively restricted territoriesencompassing Uspallata and the adjacent Precordillera between AD 800 and 1500. Wealso identify a pulse of human migration between AD 1280 and 1420, shortly precedingthe Inka conquest. Looking forward, we expect to converge with ongoing efforts inSouth America to build a continental research framework to track the movement ofpeople, animals, and artifacts across space and time.