Clay mineral facies and lateritization in basalts of the southeastern Parana Basin, Brazil

摘要: Abstract Seventeen samples from two lateritic profiles, each with five facies, were studied. These profiles occur on the old planation surface of plateau basalts southern part ParanaBasin, Brazil. Optical microscopy, X-ray diffraction, electron microprobe, Mossbauer spectroscopy and Fourier Transform Infrared Spectra used to obtain information about nature chemical composition weathering facies. In addition, scanning microscopy analyses clay minerals performed detect microcrystalline environmental changes. Both have major parts: a loose red-clay latosol separated an underlying mottled alterite facies; stone line may or not be present between units. both consists principally kaolinite, hematite goethite. Two shaped by differential weathering, are also in lower profile: halloysite–nontronite clayey matrix well developed fissure system occurs argillaceous network Al–goethite aggregates is typical highly porous cortex boulder that found below it. Gibbsite has crystallized large pores porphyritic but absent small subaphyric alterite. Clay observed fissures include halloysite associated goethite manganese oxides. The basalt hydrothermal green-clays (mixed layers trioctahedral smectites) formed primary plagioclase, pyroxene Ti–magnetite crystals while fresh corestones cryptocrystalline iron-rich material. study these shows one principal evolutionary trend for minerals. This smectite mixed form green clays altered bedrock at base profile intermediate association nontronite kaolinite facies top profile. There another trend; presence material sequence corestones. polycyclic laterites ParanaBasin which closely similar northern ParanaBasin.