Iron oxides and clay minerals within profiles as indicators of soil age in Northern Italy

Nine profiles representing the Alfisol, Inceptisol and Entisol orders were sampled on three terraces forming a chronosequence. Total iron, dithionite-extractable iron and oxalate-extractable iron were determined for all horizons of all profiles, and the clay mineralogy for horizons of three profiles. The percentage of total Fe (Fe_t) extracted by dithionite (Fe_d) increased with age of terraces, as did the difference between Fe_d and Fe_o (oxalate-extractable). Analysis of variance (ANOVA) of the horizon data showed that the ratios Fe_d/Fe_t and Fe_dFe_o/Fe_t were closely related to the ages of the terraces. Clay minerals were also related to terrace ages, with 2:1 minerals dominant in the profiles on the youngest and mixed-layer minerals and kaolinite more abundant in profiles on the older terraces.