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. 1.7 million km²). It covers an area from about 2°S to 12°S, and from 34°W to 49°W, and refers to top (TOP: 0-20 cm) and bottom (BOT: 30-50 cm) 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 10 cm soil layer) and clearly discern between the regions: Europe with the fastest "depletion" (12,200 ± 300 years), followed by Australia (33,200 ± 3000 years) and Brazil (86,700 ± 3000 years). Similar results emerge when calculating denudation rates, using independent fluvial denudation data in large basins.