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; LLANO, CARINA; GASCO, ALEJANDRA; MARSH, ERIK J.; NUEVO-DELAUNAY, AMALIA; NOVELLINO, PAULA; FRIGOLÉ, CECILIA; WINOCUR, DIEGO; BENÍTEZ, ANAHÍ; CORNEJO, LUIS; FALABELLA, FERNANDA; SANHUEZA, LORENA; SANTANA SAGREDO, FRANCISCA; TRONCOSO, ANDRÉS; CORTEGOSO, VALERIA; DURÁN, VÍCTOR A.; MÉNDEZ, CÉSAR

Frontiers in Ecology and Evolution

Frontiers Media SA

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 tohighlydiversealtitudinallyarranged ecosystems. The combination of a geologicallyandecologicallydiverse landscape provides an exceptional context to explore the potentialof strontium isotopes to track the movementsof people and the conveyanceof materialculture. Here we develop an isotopic landscape of bioavailablestrontium (87Sr/86Sr)that is applied to reconstruct human paleogeographyacross time in the southernAndesof Argentinaand Chile (310-34°S). These resultscome from a macro-regionalsamplingof rodents (N = 65) and plants (N = 26) from modern and archeological contexts.This "Southern Andean Strontium Transect" extends over 350 km across the Andes,encompassingthe main geological provinces between the Pacific coast (Chile)and theeastern lowlands (Argentina).We follow a recently developed approach to isoscapeconstruction based on Random Forestregressionand GISanalysis.Our resultssuggestthat 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. The southern Andes provide an ideal geological setting to developthis approach, since thegeologicalvariationin rock ageand composition produces distinctiveisotopic signaturesfor each main biogeographicalregion. Finally,we apply this framework to a set of resultsfrom human remains from the Uspallata Valley in Mendoza (Argentina),to assess theincidenceof migration in the key period of the consolidation of agropastoraleconomiesbetween AD 800 and 1400. The application of the isoscape to the values from humanremains confirms the persistence of human groups with relativelyrestricted territoriesencompassing Uspallataand the adjacent PrecordillerabetweenAD 800 and 1500. Wealso identifya 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.