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This research aimed to compare the surface morphology of quartz grains of the E and Bt horizons of an Ultisol of the Aratu stream basin, in the city of Florai, Parana. The Ultisol is derived from sandstones of the Caiua Formation and it is subjected to mesothermal humid subtropical climate. The materials from the E horizon showed abundant porosity compared to the Bt horizon ones, due to the filling of pores by coating of clay and iron oxides. On the surface of the quartz grains of the E horizon, several features were identified such as ";craters";, pyramidal microfeatures, gulfs of dissolution, elongated cavities, and silica reprecipitation, resulting from the chemical change, and fragmented grains resulting from a phenomenon called ";plasma infusion."; In the Bt horizon, nearly all the detrital grains were surrounded by clay and iron oxide. The detrital grains of the Bt horizon were better preserved, showing little corrosion features and rare fragmented grains, compared to the E horizon. These analyzes showed that the water flow accounts for the superficial alteration of detrital quartz grains when they are under the influence of humid subtropical climate. R E S U M O A pesquisa teve como objetivo comparar a morfologia superficial de graos de quartzo dos horizontes E e Bt de um Argissolo da bacia do corrego Aratu, no municipio de Florai, PR. O Argissolo e derivado de arenitos da Formacao Caiua e submetido a clima subtropical umido mesotermico. Os materiais do horizonte E apresentam porosidade abundante quando comparados com os do horizonte Bt, em razao do preenchimento dos poros por revestimentos de argila e oxidos de ferro. Foram identificadas na superficie dos graos de quartzo do horizonte E varias feicoes tipo “crateras”, microfeicoes piramidais, golfos de dissolucao, cavidades alongadas, reprecipitacao de silica, oriundas da alteracao quimica, e graos fragmentados devido ao fenomeno denominado “plasma infusion ”. No horizonte Bt, praticamente todos os graos detritais estao envolvidos por argila e oxidos de ferro. Os graos detritais do horizonte Bt estao mais preservados, exibindo poucas feicoes de corrosao e raros graos fragmentados, se comparados com os do horizonte E. Essas analises demonstraram que o fluxo hidrico e o responsavel pela alteracao superficial dos graos detritais de quartzo quando sob a influencia de clima subtropical umido. Palavras-chave: Argissolo, morfologia de graos de quartzo, alteracao geoquimica, fluxo hidrico

revista brasileira de geografia física

Morphological Analysis of Quartz Grains of Two Horizons in a Ultisol, Paraná – Brazil (Análise morfológica de grãos de quartzo de dois horizontes de Argissolos, Paraná – Brasil)