Rock magnetism and pedogenetic processes in Luvisol profiles: Examples from Central Russia and Central Mexico

Despite a vast literature concerning magnetic properties of loess sequences, we still do not fully understand how magnetic components and properties are related to particular soil-forming processes that can vary with each type of genetic horizon. In order to establish the role of lithogenic factors in the link between magnetic properties and soil-forming processes, we carried out a study of two complete profiles of buried interglacial Luvisols, one formed in loess in Russia (Alexandrovsky quarry) and the other in volcaniclastics in Mexico (Barranca Tlalpan). In both profiles, soil genetic horizons have contrasting differences of their magnetic properties. In the Alexandrovsky profile, the magnetic susceptibility (χ) is enhanced in the paleosol compared to parent material. In the Barranca Tlalpan sequence, χ enhancement is absent in the soil profile. Increase of fine-grained magnetic components in the soil is attributed to neoformed minerals. However, this process cannot compensate for the loss of lithogenic magnetic minerals in any of the genetic horizons, and the resulting trend is χ depletion in the whole soil profile. The pedogenic environment of eluvial horizons in both Luvisols is destructive to all magnetic components, both primary and secondary. Higher concentrations of antiferromagnetic components (hematite and goethite) found in E horizons are related to redoximorphic processes.