干旱区生态环境知识资源中心

Strong spatial variations in soil weathering processes were identified in the uplands and piedmont zones of the Baturite massif (Ceara, NE Brazil), a medium-elevation tropical mountain characterized by a steep eco-cline between humid climate of the summit zone and semi-arid conditions of the erosional piedmont. With the combined help of field surveys and laboratory analyses, involving micromorphological observations as well as geochemical and mineralogical investigations, this study demonstrates a close spatial correlation between soil weathering processes and present-day water balance (WBI) variations: (i) in the humid massif (WBI > 500 mm.y(-1)), monosiallitization is exclusive in soil and upper saprolite horizons and leads to the neoformation of 1:1 clay minerals (well-crystallized kaolinite) with minor amounts of gibbsite; (ii) in the subhumid peripheral area of the massif (50 < WBI < 500 mm.y(-1)), monosiallitization coexists with bisiallitization in the soil profiles, producing a mixture of 1:1 (kaolinite) and 2:1 (illite) clay minerals along with lower weathering intensity: (iii) in the semiarid piedmont (0