The effect of Aeolian accessions on soil development on granitic-rocks in south eastern Australia. I. Soil morphology and particle-size distributions

Abstract

Four Alfisols in south-eastern Australia were studied to determine their genesis with special reference to textural profile development and aeolian accession. Sampling sites were located in erosional terrain developed from granitic rocks of similar composition and in hillcrest positions to reduce the chance that colluvial deposition had affected pedogenesis. The sampling transect was placed in such a way that differences in regional aeolian accession could be reflected in soil properties. The chemical and physical characteristics of these soils indicated that strong leaching had been important in their genesis. Detailed particle-size data confirmed that the coarsest fractions in all profiles were derived from weathered granite. The A horizons tended to have a single size mode in the sand range and very little clay-size material. The B horizons tended to be bimodal with the greatest amount of clay in the 0.12-0.06 µm size class and a mode in the sand range close to that of the A horizons. The appearance of a peak in the 62-31 µm size class, which is progressively stronger in the western sites, probably relates to a fine aeolian accession which has penetrated the B and C horizons. The amount of clay contributed by aeolian accession to textural B horizons is unknown. At erosional sites in south-eastern Australia, where the probability of colluvial and fluvial sedimentary layering is minimal, aeolian accession of fine fractions has complicated the interpretation of pedogenesis.