Late Holocene environmental dynamics and their influence on human occupation in the Santiago basin (33°S), Central Chile

Fluvial-alluvial deposits provide high-resolution records for reconstructing paleoenvironments and deciphering archaeological site-formation processes. Despite their prevalence in the Mediterranean-climate region of central Chile, a significant research gap persists in linking prehistoric human trajectories with hydroclimatic dynamics. This study addresses this gap through an interdisciplinary geoarchaeological approach that integrates sedimentology, pedostratigraphy, geomorphology, archaeology, and historiography to reconstruct the Late Holocene evolution of the Colina basin, using the Cacique Sur-1 site as a case study. Stratigraphic evidence, characterized by alternating fine-grained alluvium, coarse fluvial beds, and paleosols, reveals two major hydroclimatic regimes between 1850-1650 and 1650-500 cal yr BP. This sequence is punctuated by at least five major high-discharge fluvial events driven by extreme precipitation, likely linked to El Niño-Southern Oscillation coupled with the Southern Westerly Wind variability: two around 1850 cal yr BP, one between 1773 ± 29 and 937 ± 32 yr BP, another between 937 ± 32 and 606 ± 20 yr BP, and a final event at 558 ± 21 yr BP. These hydroclimatic fluctuations align with regional paleoclimate trends and directly influenced local settlement patterns. Archaeological data indicate initial occupation during the Early Ceramic Period (200–1000 CE), followed by partial site abandonment after a catastrophic flood. Although the site was intensely reoccupied during the Late Intermediate (1000–1450 CE) and Late periods (1450–1536 CE), habitation definitively ceased following a subsequent major flood. These findings underscore the alternating resilience and vulnerability of prehistoric societies to climate-driven geomorphic changes and demonstrate the value of integrated geoarchaeological, historical, and stratigraphic records for assessing modern and future environmental risks in Mediterranean-type environments.