Contrasting environmental memories in relict soils on different parent rocks in the south-western Italian Alps

Soils on the Alps are usually weakly developed, both because of the extensive Pleistocene glaciations, and because of slope steepness and climate enhancing erosion. However, on some stable, relict surfaces, particularly in the outermost sections of the Alpine range, some highly developed soils are apparently in contrast with Holocene soil forming conditions. In this work we assess the extent of pedogenesis in some of these soils, located under montane-level vegetation in the Ligurian Alps (SW Piemonte, Italy), and relate it to the effects of climate and parent material. The considered well developed profiles showed signs of extremely different pedogenetic processes on the different lithotypes. In particular, Podzols with extremely thick E horizons (up to more than 2 m thick) and very hard, thick ortstein or placic horizons were formed on quartzite. Reddish “terra rossa” Luvisols were formed on limestone. Red, extremely acidic Alisols were formed on shales. The chemical properties, the micromorphology and the clay mineralogy demonstrated high intensity pedogenic trends, and were characteristic of processes usually occurring under different climates. They may therefore represent excellent pedo-signatures of different specific past climatic/environmental conditions, as a response of different lithologies to specific soil-forming environments, which range from warm and humid climates typical of red Alisols and Luvisols, to cool and humid/wet climates leading to the formation of Podzols with ortstein/placic horizons.