Pedogeochemistry in NE-Brazil — Compared to Australia and Europe

A soil geochemical dataset (major and minor elements), based on low-density sampling, is provided for NE-Brazil (ca. 1.7millionkm2). It covers an area from about 2°S to 12°S, and from 34°W to 49°W, and refers to top (TOP: 0–20cm) and bottom (BOT: 30–50cm) mineral soils. Results are put in perspective using two recent and comparable studies, the National Geochemical Survey of Australia (NGSA) and the European Geochemical Mapping of Agricultural Soils (GEMAS). All median element concentrations in the Brazilian samples are depleted compared to World Soil Averages (WSA), except for Al2O3 and SiO2, which are respectively similar to WSA and enriched in Brazil. While the depletion is moderate for Fe2O3, MnO, P2O5, and TiO2, it reaches an order of magnitude and more for K2O, MgO, CaO, and Na2O. The difference between TOP and BOT concentrations is lower than the variation of either TOP or BOT concentrations between sample sites. Similar spatial distribution and the high correlation between TOP and BOT concentrations suggest that (1) similar processes and parameters are of general relevance for the geochemical composition of TOP and BOT samples, and (2) topsoil and subsoil are not decoupled. Cluster analysis revealed similar results for TOP and BOT samples, yielding three groups of elements/oxides displaying similar behavior: Gr.1 comprising Al2O3, Fe2O3, TiO2, and P2O5; Gr.2 comprising CaO, K2O, MgO, MnO, and Na2O; and Gr.3 being SiO2. Weathering indicators are significantly positively correlated and show similar spatial distributions in TOP and BOT samples. All elements deliver similar mass removal times (time to export all material from a 10cm soil layer) and clearly discern between the regions: Europe with the fastest “depletion” (12,200±300years), followed by Australia (33,200±3000years) and Brazil (86,700±3000years). Similar results emerge when calculating denudation rates, using independent fluvial denudation data in large basins. ► First large-scale pedogeochemical baseline values for northeastern Brazil ► Site signature variations larger than topsoil–bottom soil variations ► Chemical Index of Alteration higher than for Australian and European soils ► Distinct deviation from PEGS2 data (de Caritat et al., 2012; EPSL 319–320: 269ff.)