Magnetic properties of different soils from La Plata county, province of Buenos Aires

Abstract

This work presents results obtained in the magnetic study of two soils, Argiudol and Ocracualf in La Plata, Buenos Aires Province. Both soils, have been developed in the same parent material, i.e. loess, but at different topographic positions such that they were exposed to different drainage conditions. The magnetic parameters measured were: specific susceptibility (c), frequency-dependent susceptibility (cfd), isothermal remnant magnetization (IRM), anhysteric remnant magnetization (ARM), coercivity of remanence (Bcr), and the Sratio. The behaviour of magnetic parameters (c, ARM, IRM) indicates an increase in ferrimagnetic minerals towards the base of the profiles of both soils, with lower values in the Ocracualf than in the Argiudol. Although the susceptibility frequency-dependent (cfd) is lower than 5 %, the highest values -in both soils- always correspond to the Bt horizons. Coercivity of remanence and Sratios indicate the presence of magnetite as the main ferromagnetic mineral in both soils but the upper horizons of the Ocracualf seem to be enriched with anti-ferromagnetic minerals (probably hematite and goethite). The depletion of c, IRM and ARM values in some levels is interpreted as a consequence of pedogenetic dissolution of detritic iron minerals, a process that seems to increase markedly where bad drainage conditions prevailed.