Fraser Island and the adjoining Cooloola sandmass (covering a total of approximately 200,000 hectares) consist almost entirely of quartz sands that have accumulated during episodic periods of dune building in the Quaternary. At least eight dune systems have been identified at Cooloola and nine systems at Fraser Island marking separate episodes of deposition above sea level. Deposits also overlay older Aeolian deposits below sea level.
Absolute age dating of dune systems is at an early stage but it shows that the youngest systems span 120,000 years while the oldest dunes may have formed 800,000 years ago. These dates show that the age sequence is by far the oldest on record.
Parabolic dunes, open to the onshore winds, dominate the five youngest dune systems. The older dune systems have been reduced to broad whale-back sandhills. The dune systems provide many examples of the various stages in development and degradation of parabolic dunes, from bare mobile dunes showing progressive degradation by water erosion, to the strongly degraded sandhills which have lost their initial Aeolian shape. These form a time series, illustrating the long-term changes in surface morphology from Aeolian deposition to advanced degradation.
Soils on the freely-drained vegetated dunes also show progressive development with age, forming a sequence from rudimentary podzols to giant podzols on the oldest dunes. The depth of podzol development and the dimensions of the soil horizons, far exceed those recorded elsewhere. The dimensions and age span of this podzol chronosequence is of considerable scientific importance, internationally and is invaluable to soil science.
Further, where seasonal water tables rise to the surface in dune corridors and on the coastal plains, a different soil process is involved, forming humus podzols. The black organic B horizon of these soils becomes hard and cemented with time and, where exposed along the beach is known as sandrock.
Marine erosion of the eastern margins of the sandmasses forms sea-cliffs which expose the sands of the various dune systems and multi-coloured sands, particularly at Cooloola. Older sea cliffs and fossil beaches both at Fraser Island and Cooloola provide evidence of past high sea levels and are important in interpreting past geological events.