DISTRIBUTION, MORPHOLOGY AND CHRONOLOGY OF THE AEOLIAN CALCARENITES IN SOUTHWESTERN AUSTRALIA

A spectacular landform of pinnacle karst occurs in the southwestern coast of Western Australia. It consists of thousands of pinnacles up to 5 m high, and 2 m wide and only 0.5-5 m apart, particularly well exposed in the Nambung National Park. The pinnacles are formed in the Pleistocene Tamala Limestone, which comprises of cyclic sequences of aeolian calcarenite, calcrete, microbialite and palaeosol. The morphology of the pinnacles varies with the lithology in which they are formed, for examples, typically conical in aeolianite and cylindrical in microbialite. However, the Nambung pinnacles is mainly influenced by joints and fractures. The extensive dissolution associated with pinnacle formation at Nambung resulted in a large amount of insoluble quartz residues, which are redeposited and even bury the pinnacles sometimes. This period of karstification occurred at around 70, 000 years before present, and there was an earlier but weaker stage of pinnacle development during the period 34-38 million years ago.