Timing of occupation and regional settlement patterns revealed by time-series analyses of an archaeological radiocarbon database for the South-Central Andes (16°–25°S)

Abstract

Developing spatially resolved high-resolution datasets of robust long-term changes in human demography constitutes a major challenge for archaeology. One approach is to use the distribution of summed radiocarbon-age probabilities to infer long-term population dynamics (i.e. palaeodemography). However, these can often be biased by preservation potential, site taphonomy or researcher priorities among other aspects, all of which require large datasets to resolve adequately. For this report, we have created such a dataset for the South-Central Andes (16°–25°S), here termed the South Central Andes Radiocarbon (SCAR) database. SCAR spans the last 15,000 years and incorporates ∼1700 14C-dates from 519 archeological sites reported across an extreme bioclimatic gradient that includes the hyperarid coastal Atacama Desert and adjacent cold, high-elevation Altiplano. Among the possible methodological biases, we first evaluated those related to calibration procedures. Otherwise, changes in summed probability curves show no other relevant biases except for possible research interest/priorities that could be responsible for the gaps in the record from the Bolivian altiplano. Our temporally continuous time-series indicates that prehispanic populations exhibited significant demographic changes during the last 13,100 calBP. Except for coastal populations; most regions show strongly coordinated demographic fluctuations that follow the same major patterns. Thus, we identified two broad scale population events across the South-Central Andes (Atacama inland, Bolivian Altiplano) from 13,100–4000 calBP and then from 4000 calBP to the present. In contrast, the Atacama coastal records suggest a different and more variable occupation pattern over the last 13,460 calBP, which could be driven by the interaction with oceanographic processes (i.e. upwelling). A widespread major decline at 700 calBP clearly predates the Spanish colonization and occurs in all of our regions. This widespread decline does not appear to be due to methodological biases, and suggests that a population crash occurred before European occupation. Overall, the SCAR database constitutes a valuable proxy for establishing the long-term dynamics of prehistoric societies that inhabited the western Andean slope. Time-series analyses that use SCAR will shed new light on the demographic and cultural dynamics at different spatial-scales, and help clarify the processes involved in the migrational trajectories and cultural evolution of the peoples that inhabited the South-Central Andes over the last 15,000 years.