POSTDEPOSITIONAL MODIFICATION OF THE LINEAR SAND RIDGES OF THE WEST KIMBERLEY AREA OF NORTH-WEST AUSTRALIA

Late Quaternary linear dunes of the west Kimberley area of tropical north-western Australia exhibit an extensive degree of post-depositional modification. Evidence for modification includes degraded overall morphology in cross profile, severe reddening, high (typically 20-25 per cent) silt and clay contents, and complete pseudomorphic replacement of some mineral components. All the modification took place subsequent to the emplacement of the dune ridges which, based on luminescence dating, occurred since latest Pleistocene and earliest Holocene times. Accelerator radiocarbon dating of particulate charcoal from discontinuous, sub-horizontal lenses within the dunes was found to produce ages inconsistent both with the chronology erected using luminescence methods and stratigraphic inferences. A combination of petrographic, SEM and XRD investigations suggests that much of the dune reddening is the result of in situ hematite crystallization within kaolinitic grain coatings, which are responsible for the high fines content of the dunes.