Origin of superparamagnetic particles in Argiudolls developed on loess, Buenos Aires (Argentina)

Abstract

Records from magnetic signals in Buenos Aires loess?paleosol sequences have been published, but their relationship with environmental changes has been difficultto establish. Studies on the superparamagnetic (SP) population in present soils can help to understand these processes. Samples from present soils (Argiudolls) and a paleosol from the Buenos Aires Province (Argentina) were analyzed using low and room temperature magnetic measurements. They show that it is possible to support the hypothesis of a lognormal distribution of superparamagneticparticles, the median diameter near 15 nm. The presence of detritic pseudosingledomain (PSD) titanomagnetite, with low titanium content ranging between TM28 and TM40, has been established. The linear correlationof SP content with ferrimagnetic susceptibility and with magnetization suggests that ferrimagnetic minerals drive the SP generation. Finally, it can be concluded that SP magnetic grains, in the Pampean plain, are generated by aninorganic process in adequate environmental pH and Eh of the soils.