Utilização do Microscópio Eletrônico de Varredura (MEV) para o reconhecimento de revestimentos argilosos

Abstract

Many authors have been pointing out the difficulties of identification of clay coatings infield and laboratory observations. This work aims at estimating the importance of the Scannin g Electron Microscopy (SEM) at the characterization and identification of these pedologicals features found in Affisols in Bauru (SP) region. The studied region is located in the western part of Sāo Paulo State, where the regional geology is dominated by sedimentary rocks from Marilia Formation of Bauru Group (Cretaceous period), associated with soils of Alfisol and Oxisol type (figure 1). The studies were developed at the INRA/Rennes Soil Science laboratory. A Phillips XL20 scanning electron microscopy connected to an EDS spectrometer make the observation and punctual chemistry characterization of the samples possible. Soil thin blades of small dimensions (4,5 × 7,0 cm) and small soil lumps (1,0 cm3) with preserved structure were used. The SEM showed to be an effective tool in soils genesis studies. The results showed that the clay coatings found in the chambers porosity from the superior portion of argillic horizon in Alfisols present a clear boundary with the immediately underlying soil materials, strong birrefringence, micro lamination, besides the orientation of the clays parallel to the pores wall, indicating a mechanic illuviation process of the clay (figures 2 to 6). The microanalyses done in clay coatings found in the argillic horizon, gave additional information to those acquired from the micromorphological studies, especially for showing the existence of a strong variation of the oxides elements through the micro laminations (figure 9 and table 1).