The relationship between emergence of mound builders in SE Uruguay and climate change inferred from opal phytolith records

The strong correspondence between the spatial arrangement of archaeological sites and wetland environments is one of the main axes of the Merín Lagoon basin archaeology. Without implying a deterministic simplification from the epistemological point of view, the cultural and environmental history of the region hold evidence suggesting a more complex scenario, where cultural responses to climate change were not so mechanical or direct as previously argued. The relationship between paleoclimate and prehistoric mound builders development between 7.0 and 0.6 ka 14C BP was studied in SE Uruguay. Paleoclimatic data were inferred from the phytolith record of three lagoon sediment cores. Four paleoclimatic periods were identified according to temperature/humidity changes. The first period, dated at 7.0-4.5 ka 14C BP, was characterized by a warm/humid climate. Between 4.5 and 3.5 ka 14C BP, the onset of a cool/dry climate was inferred. A hiatus between 3.5 and 2.6 ka 14C BP was identified. In the third period, 2.5-1.2 ka 14C BP, similar climate conditions to those of the present were inferred. Finally, the period 1.2 and 0.6 ka 14C BP, was characterized by warmer and wetter conditions than those of the present. According to these data, it was determined that mounds were first observed during the transition from warm/humid to cool/dry conditions, but the complexity of the mounds increased after the full establishment of cool/dry conditions. With the inception of warm/humid conditions, an increased number of mounds was observed in the plains located close to the Merín Lagoon littoral. The mounds showed lower density and height than those recorded for the cool/dry period. This behavioral modification in mound construction was explained because of the paleoenvironmental change.