A STUDY OF SOIL PARTICLE CHARACTERISTICS AND POSTDEPOSITIONAL PROCESSES IN A DEAGON (QUEENSLAND, AUSTRALIA) CLAY PROFILE

An experimental study was undertaken to investigate the distributions of particle sizes acid types in samples taken from a highly overconsol idated coastal clay profile at Deagon, Queensland, Australia. The expe rimentation involved the use of the sedimentation method of particle s izing, and included the development of indices of the levels of microa ggregation in the profile. Systematic depth-related trends in particle sizes and micro-aggregation levels were observed. Superimposed on the se trends were sinusoid-like patterns of variability in micro-aggregat ion levels, which were indicative of stratification. It is postulated that the stratification was associated with seasonal cycles of drying shrinkage and flooding that took place during deposition of the clay p rofile. This hypothesis is based on separate laboratory studies in whi ch levels of micro-aggregation were observed to increase as specimens of Deagon clays underwent drying shrinkage. The study therefore sugges ts the significance of drying shrinkage as a cause of microaggregation during the formation of alluvial clay deposits in semi-arid climates. The study also provides simple techniques for extending existing char acterizations of the size and nature of soil particles. Such data may be indicative of the volumetric stability, erodibility and consolidati on characteristics of soils.