Soil genesis, morphodynamic processes and chronological implications in two soil transects of SE Sardinia, Italy: traditional pedological study coupled with laser ablation ICP-MS and radionuclide analyses

Soils are characterized by an intrinsic variability through time and space at different scales of observation andare often affected by morphodynamic processes strictly interacting with pedogenesis, under changing (paleo)environmental/climatic conditions. We focus on exploring this interplay in modern soils and paleosols ofsoutheast Sardinia (Italy), integrating two innovative techniques to a traditional pedological study: (i) laserablation ICP-MS spot analyses applied to detect microscale distribution of trace elements in discrete soilfeatures of organic-mineral (A) and argillic (Bt) horizons in thin sections, and (ii) radioactive disequilibria astracers and chronometers of pedogenetic alteration and geomorphic dynamics. The Pleistocene paleosolsdeveloped mainly during interglacial periods, with important clay illuviation and rubification. The other soilsare essentially characterized by organic matter incorporation into the profiles. Field discontinuities describedwithin soil profiles, related to phases of sediment aggradation and/or surface erosion, are often supported bylaboratory results, mainly micromorphological and geochemical data. LA-ICP-MS data show an overall trendof increase of most trace elements (REEs included) from skeletal rock fragments to both clayey and organicrichsoil matrix to clay coatings. This pathway is clearly controlled by the degree of weathering of primaryminerals and by pedogenetic processes, where element adsorption onto reactive sites of organic matter andclay particles and clay illuviation play prominent roles. Recent trends of the studied soils/paleosols in terms ofgeomorphic stability (equilibrium) or morphodynamic processes (erosion/accumulation rates) are estimatedusing radionuclide disequilibria in the order of 1 cm/a or lower.