Hunter-gatherer mobility decisions and synchronous climate change in the Southern Andes: The early and middle Holocene occupations of ARQ-18, San Juan, Argentina (29.5°S)

Abstract

In the southern Andes, Holocene climate records show drastic changes in moisture during the early and middle Holocene. To generate a more refined chronology of climate changes in this region, we present a Bayesian model that combines published cosmogenic dates from the Encierro Valley (29.1°S) and radiocarbon dates on peat and soils from the western slope of the Andes (27–33°S). We compare this to a similar model from the high-altitude archaeological site ARQ-18 in the Las Taguas Valley (29.5°S), San Juan, Argentina. These chronologies indicate synchronous changes in climate and occupational intensity, which shed light on hunter-gatherer mobility decisions. This site was first occupied in the early Holocene, when nearby valleys were deglaciated by around 10,700 cal BP. ARQ-18 was occupied a few centuries later around 10,100 cal BP. The site was first colonized during a regional wet phase, probably by hunters from the highlands to north who moved quickly among humid high-altitude valleys. As regional moisture began dropping around 8700–7800 cal BP, occupational intensity at ARQ-18 reached a maximum as diverse groups gathered in the valley. At this point, an important environmental threshold was crossed as groups reversed their mobility patterns and decisions and did not occupy the site for 1700 years. This “archaeological silence” correlates closely with the middle Holocene's hyperaridity during 7800–5700 cal BP. As soon as humidity returned, groups began visiting the site again. From this point on, strategies increasingly incorporated herding in response to less stable environmental conditions.