Holocene vegetation, climate, sea-level oscillation, and human impact inferred from the archaeological site Cabeludo in Maranhão State, NE Brazil

Abstract

This study provides an environmental reconstruction of an archaeological site in the northern part of northeastern Brazil. To understand how the climate, relative sea-level (RSL), and human activities triggered environmental changes in Maranhão State during the Holocene, a multi-proxy analysis has been done in a 450 cm long sediment core. The core has been radiocarbon dated and analyzed by its content of pollen, spores, micromorphological and spot chemical analyzes by Scanning Electron Microscope (SEM), multi-element chemical analyzes, X-ray Powder Diffraction (XRD), charcoal, Loss on Ignition (LOI), and sedimentary characteristics. The site was a tidal channel, part of an estuarine system surrounded by mangrove vegetation between 7920 and 7500 cal yr BP. For this period, the mineralogical and chemical composition showed sediments inputs also coming from marine sources, indicating a transgression of the ocean. The combination of marine transgression and dry environmental conditions allowed mangroves to colonize areas further inland. From 7500 to 1800 cal yr BP, the study site turned into the current freshwater tributary river surrounded by lowlands arboreal and herbaceous vegetation while the Amazon biome expanded. The moister conditions and the RSL regression displaced the mangroves to the current coastal bays about 120 km to the north. The sediment run-off was predominantly continental, as showed by mineralogical and chemical analysis. After 1800 cal yr BP, human influence is noted by increased charcoal and fragmented ceramics in the sediment. Archaeological studies at this region showed that Amerindians built stilt-house villages upon the rivers and lakes, which played stronger role in the environment. These pre-colonial stilt-houses Maranhão lowland are the only ones found South America.