Joselisa Maria Chaves

Metal accumulation in soils derived from volcano-sedimentary rocks, Rio Itapicuru Greenstone Belt, northeastern Brazil

Many countries and some Brazilian regions have defined the guideline values for metals in soils. However, the local geological features may be so heterogeneous that global or even regional guideline values cannot be applied. The Greenstone Belts are worldwide geological formations of vast extension, containing mineralization of various metals (e.g., Au, Cr, Ni, and Ag). Natural concentrations of soils must be known to correctly assess the impact of mining. We studied the soils of the Rio Itapicuru Greenstone Belt (RIGB), of Paleoproterozoic age, sampling at 24 sites (0-0.20m) in the areas not or minimally human impacted, equally distributed in the three units of the RIGB: Volcanic Mafic Unit (VMU), Volcanic Felsic Unit (VFU), and Volcano-clastic Sedimentary Unit (SU). The natural pseudo-total concentrations of Cr, Ni, Cu, Zn, Pb, Fe, and Mn were obtained by acid digestion (EPA3050b) both in the soil and the particle-size fractions (sand and clay+silt). The concentrations of metals in RIGB soils, especially Cr and Ni, are generally higher than those reported for other regions of Brazil or other countries. Even the sedimentary soils have relatively high metal values, naturally contaminated by the VMU of the RIGB; a potential impact on Mesozoic and Cenozoic sedimentary rocks located near the study region is highly expected. Metals are concentrated (80%) in the fine particle-size fraction, implying an easy availability through surface transport (wind and runoff). We introduced a new index, called the Fe-independent accumulation factor - AF-Fe, which reveals that 90-98% of the dynamics of the trace metals is associated with the iron geochemical cycle. We primarily conclude that determining the guideline values for different soil classes in variable geological/geochemical environment and under semiarid climate is meaningless: the concentration of metals in soils is clearly more related to the source material than to the pedogenesis processes.

MAPEAMENTO E CARACTERIZAÇÃO GEOMORFOLÓGICA: Ecorregião Raso da Catarina e Entorno NE da Bahia

This paper aimed to develop a systematic geomorphological mapping and characterization of part of the ecoregion Raso da Catarina, Bahia and environs using geomorphological mapping methodologies enshrined in national (ROSS, 1990 and 1992), supported by technical and methodological in geomatics (remote sensing and geographical information system). As the main material used to map the data were obtained by remote sensing as the Digital Elevation Model DEM Program SRTM / NASA resolution 90 m. The resolution of the DEM were reÞ ned to 30 m using kriging, since that was generated by maps of slope, hipsometric and Shaded Relief (auxiliary products for characterization and mapping). This was followed by the methodological assumptions of Ross (1992), reaching up to 4rd characterize taxon proposing mapping on the scale 1:100,000. The 3rd and 4th taxon was foreclosed by tracing on screen and identiÞ ed by determining the rate of dissection of relief through the preparation of topographic proÞ les automatically and interactive GIS software, was the perceived effectiveness and practicality of this procedure. This disclosed the possibility of applicability of Geomatic allied methodologies devoted to geomorphological mapping.