Ancient water management and the evolution of the late Holocene wetlands. First paleoecological evidence from prehispanic raised fields of Urabá, northwestern South America

Abstract

The raised fields discovered recently in the Gulf of Urabá, northwestern Colombia, extends more than 135,000 ha among the floodplains of the rivers León, Suriquí, and Tumaradocito in the Chocó biogeographic region. To understand the mechanisms by which people use the wetlands under climate change of the Late Holocene, the paleoenvironmental and cultural conditions were studied using artifacts, soil micromorphology, geochemical, chronostratigraphic and palynological analysis at El Vergel archaeological site. This study aims to discuss the origin of raised fields development in the León River floodplain and its relationship with progressive drought, groundwater, and wetland management for permanent human occupation. The results suggest that the raised fields were built around the IX century CE, during a period marked by decreased precipitation, probably related to the Medieval Warm Period. The hydrogeology reveals a multilayer aquifer in the region with some shallow springs in the floodplain where earthworks are located. The poor stratigraphic demarcation of the ridges and well-dug channels, with no evidence for agriculture whatsoever, support the idea that some raised fields were strategic for distributing groundwater and rainwater over a large area and thus preserving the productivity of the wetland for fishing and hunting.