Polycyclic soils with Bt and Bw developed on mafic rocks in a forest cerrado transition environment in Roraima, northern Amazon, Brazil

In the extreme north of Brazil, in Roraima, there is an important set mafic, volcanic or plutonic rocks, associated with Juro-Cretaceous magmatism, and one most extensive areas Colônia do Taiano region, first agricultural colony Roraima. addition to basalts, many diabases diorites occur, forming patch soils good suitability, cerrado-forest transition. Two soil profiles developed from diabase were studied, after selecting representative pedons area. P1, Argissolo Vermelho Eutrófico latossólico (Ultisol) P2 típico (Ultisol), described collected. Morphological, physical, chemical, mineralogical analyses, extraction Fe, Al, Ti Si oxides by sulfuric attack carried out; Fe2O3, Al2O3, TiO2, SiO2, plasma emission spectrometry; Fe-DBC (dithionite-citrate-bicarbonate) Fe ammonium oxalate. The presented a typical latosolic morphology at base profile, top B horizon showing waxiness varying moderate abundant, thus revealing polycyclic genesis Bt superimposed on Bw, formed previous cycle. SiO2 contents indicated desilication process, low trace elements TiO2 showed mafic materials poor magnetite, reworking parent material pediment drier climate. Feo/Fed ratio proved be atypical for Amazon consistent lithology.