Occurrence and origin of soils with andic properties in Calabria (southern Italy)

Abstract

Andic-like soils, along with Andosols, have previously been reported in non-volcanic ecosystems of the coastal and mountainous areas of the Calabria region (southern Italy), but little is known about their properties, soil formation processes and volcanic source areas. Chemical, mineralogical, microscopic, sub-microscopic and magnetic analyses were carried out on 8 soils which were selected from the major Calabrian geological sectors in order to assess relationships between parent material and bedrock. Soil chemical properties revealed an occurrence of andic or vitric properties in the studied soils as a whole, and the optical microscopy enabled to identify volcanic glass, micro-pumices and soil isotropic matrix, clearly indicating volcanic inputs. Three groups of soils, identified on the basis of the degree of andic properties, showed rather homogeneous also in terms of chemical properties, clay mineralogy and land use, as well as with regard to micromorphology and magnetic susceptibility. Part of the intra-group similarities was a consequence of similar distances between sites and volcanic source area, as suggested by the correlations found between ferrihydrite content, andic (i.e. % of ammonium oxalate extractable Al+0.5 Fe and phosphate retention) and magnetic properties vs. distances from several Sicilian districts. The elemental composition obtained by SEM/EDS analyses of soil glass fragments supported these findings and related the origin of most of the studied soils to the high potassium calc-alkaline magmatism of the southernmost Eolian Islands (mainly Lipari and Vulcano), except for soils from the marine terraces of northern Calabria (PRA) and the Aspromonte Massif (DEL), which were both linked, albeit uncertainly, to Campanian volcanism. Soil magnetic properties were significantly (0.79**) correlated to the andic properties, so confirming the high performance of magnetic susceptibility as low cost proxy for the identification of volcanic constituents.