Interaction of time sequences and geomorphology in the soils of the Lower Macquarie River plain in south eastern Australia

The riverine plain of the Lower Macquarie River has a series of alluvial sedimentary formations that have been dated from the Late Pliocene to the late Holocene. The soils formed on these alluvial sediments provide an opportunity to make some observations about the pedological processes that formed these soils. The main soils on the coarser alluvial sediments on the meander plains include Black Dermosols and Phaeozems and Stratic Rudosols on the youngest Holocene alluvial sediments, with texture contrast developing in the profiles to form Red Chromosols and Red Dermosols or Luvisols and Sodosols on the oldest alluvial sediments. On the finer sediments of the backplains, Vertosols or Vertisols are the dominant soils both on the backplains of the youngest Holocene alluvial sediments and on the oldest alluvial sediments. On the meander plains pedological processes generally have resulted in the reduction in the clay content of the A horizon within 10 000 to 15 000 years and the reddening of the subsoils, as well as an increase in the exchangeable Ca:exchangeable Mg ratio in the surface soil. The oldest soils (>400 000 years) have a deep red subsoil. On the backplains, pedological processes have produced minimal changes in the soil properties except perhaps for some darkening and reduction of colour intensity of the subsoil. The pedology of the salinity and sodium levels in the soils is complex and appears to be affected by climate change and dust depositional events during the period of soil formation.