The pedogenesis of Planosolic soils, especially of the semi-arid "Agreste" region of Pernambuco State, Brazil, has n ot been properly studied. There are indications and doubts with regard to some aspects such as possible duality or differentiated reworked parent material, total of gains and losses and the relative mobility of the main constituent elements during soil evolution. Three soils with strong texture contrast were studied in a toposequence of the region. Three soils with a strong textural contrast on a topossequence in the Agreste region of the State of Pernambuco, Brazil were studied. The main objectives of the study were to investigate the compatibility of the soils with the underlying geological material and to quantitatively evaluate losses and gains in the soils during pedogenesis. Total chemical analysis, as well as the determination of zirconium and quartz contents were performed for all horizons and parent material to determine a weathering index. It was concluded that the soils were autochthonous with minor indications of surface reworked material. During the weathering process, approximately 50 % of the original soil weight was lost. The mobility of the main elemental constituents decreased as follows: MgO > CaO > Fe2 O3 > Al2O3 > SiO2. The sharp textural contrasts between the A and B horizons were not only due to clay eluviation-illuviation (lessivage), but rather a result of other weathering processes.
B planic; quantitative pedogenesis; weathering indices; zirconium; quartz
