Trends in thermoluminescence date distributions for the Angostura micro region in Central Chile

This article presents a series of thermoluminescence dates obtained from archaeological sites in the Angostura micro region, at the southern edge of the Santiago basin, an area occupied by Bato and Llolleo groups during the Early Ceramic period (200 BC-AD 1300). This series of dates, which cover a time span of around 1500 years, shows moments when dates are abundant and others when they are remarkably scant. We propose that a comparison of the relative frequency of dates can be used as an indirect measure of variations in the intensity of occupation of each of these groups in the zone. We used a summed probability analysis by decade to evaluate sets of dates according to cultural context and sectors of the study area. The results show that while the Bato and Llolleo were irrefutably contemporaneous, the Bato emerged slightly earlier, and that both -but especially the Llolleo-coexisted in later times with Aconcagua groups. At a micro regional scale significant differences as well as changes in Bato and Llolleo population dynamics were made clear. While the Bato display a natural growth curve and then declines, Llolleo increased their population significantly after AD 700, probably because of their reliance on maize crops. Not only did the chronological curves differ; the sectors where they placed their settlements varied over time depending on their specific horticultural practices, local climatic fluctuations, and each others proximity.