Dating the Cooloola coastal dunes of South-Eastern Queensland, Australia

The Cooloola sand dunes are part of a series of aeolian parabolic dunes that stretch along the east coast of Australia. They form a chronosequence showing increasing weathering, soil formation and water erosion across six geomorphically recognized soil landscapes. These landscapes were recognized from air photographs and further refined on the basis of some 150 auger holes across the dunes. Data about the structure and fioristics of the vegetation were collected at the same time. There is a significant body of literature about the Cooloola dunes but there are two areas that have not been satisfactorily considered. First the previous dating which gave inconsistent results has been superseded by single grain OSL dates and second Cooloola has not been considered in a regional context. Here we report the results of single grain optically stimulated luminescence (OSL) analyses for 31 samples for 21 sites across the geomorphic landscapes. The sites were selected near the apex of each dune as this represents the last depositional date and the least disturbed by sand movement. We recognized 10 units across the dunes on the basis of the dates available. The dune ages ranged from recent to 725 ka. The largest dunes at some 320 m high were dated at around 140 ka and these dunes carry the maximum vegetation biomass of this dunefield. Beyond this vegetation maximum the dunes had lost their parabolic shape due to prolonged weathering and erosion and the vegetation is greatly reduced in height and biomass. The depth to the soil B horizon gradually deepens with age to form giant podzols in the older dunes. The depth to the B horizon was remarkably consistent within the geomorphic landscapes across the length and breadth of the dunes. These studies place the Cooloola dunes in a unique position as the chronosequence is intact. The possible processes that lead to the formation of the dunes and the regional implications are discussed. Secondly, it shows the buildup and decline of the dune ecosystems and acts as a model for all ecosystems. Forest succession models which place less emphasis on soil development miss this important process.