A new frontier of archaeological dark earth at the northern Amazonia headwaters of Roraima state: Soil attributes and landscape interplays

Abstract

Despite the existence of various studies on Archaeological Dark Earth - ADE, there is still a very large gap concerning the Amazon region, with many areas remaining unexplored scientifically. The aim of this study, therefore, was to characterize and classify areas of Archaeological Dark Earth located on rural properties and in one riverside community in the southern mesoregion of the state of Roraima. At these locations, trenches were dug in a total of 13 areas, and the profiles morphologically characterized and sampled for soil classification and Carbon-14 dating. The areas were georeferenced and measured, and the history of land use was described, together with the predominant vegetation in the region. The following physical analyses were carried out: texture and bulk density. The chemical analysis consisted of pH in water and KCl, exchangeable cations, exchangeable Al, available P, titratable acidity (H + Al), total N and organic matter. To produce the maps, computational processing was used in a Geographic Information System - GIS, employing geoprocessing tools with the aid of the ArcGIS v10.6 software; the attributes prepared from SRTM images were drainage network and terrain. Using the Brazilian System of Soil Classification (SiBCS), the profiles were classified as: Argissolos Amarelos, Cambissolo Háplico, Latossolos Amarelos, Argissolo Vermelho Amarelo, and Nitossolo Vermelho. It is suggested that the anthropogenic subgroup be included in the SiBCS. With the exception of 3 horizons, the anthropogenic horizon of each of the profiles sampled in the region has a eutrophic character, with ages that range from 1120 to 1864 years before present (YBP). Each of the areas of ADE is associated with a drainage network ranging from a small creek, approximately 6m wide, to a fast-flowing river, such as the Branco River, which is over 1,700m wide. The 13 areas are located in places away from the flood area that show little variation in relief, with a predominance of flat to gently undulating terrain.