Soil profile development in some alluvial deposits of eastern New South Wales

Abstract

Soil profile data from river terrace sequences on the New South Wales coast and southern highlands have been summarized. In all sequences the profiles have a progressive increase in soil development from low alluvial benches to flood plains to terraces. The general similarity of soils among these and other alluvial sequences in eastern New South Wales is the basis of a descriptive generalization in terms of five profile stages: stratic stage on low alluvial benches; cumulic stage on flood plains; low-contrast solum stage on low terraces; high-contrast solum stage on high terraces; extended subsolum stage on highest terraces. Sufficient lack of correlation occurs between sequences to suggest that the profile stages are groupings within a continuous spectrum of profile variation, the whole representing the one pedogenetic pathway. Pedogenesis in these alluvial landscapes is considered to progress through the development, first of a biotic profile which reaches a maximum within 1000 years, which is then degraded with the onset of mineral weathering and B horizon development, to a maximum solum form within 30 000 years. The rates of change of biotic and mineral profile components are sufficiently slow that only broad limits of confidence can be applied to soil stratigraphic correlations based on field morphology alone.