Abstract A new map, the first based on interpretation of satellite imagery, reveals both the complexity of Australia's dunefields and their relationships with topography, climate and substrate. Of the five main sand seas, the Mallee, Strzelecki and Simpson in eastern Australia cover Quaternary sedimentary basins whereas the Great Victoria and Great Sandy dunefields in the west are formed by reworking of valley and piedmont sediments in a non-basinal landscape of low-relief ridge and valley topography. These dunefields cover large areas of the arid zone and semi-arid zone and small areas of dunes in sub-humid areas around the margins of the continent reflecting past expansion of arid climates during glacial stages of the last several glacial cycles. Several areas of low relief stand out as being largely dune-free: the limestone Nullarbor Plain, clay plains of the Georgina Basin and floodplains of rivers in the Carpentaria, Lake Eyre and Murray–Darling drainage basins where sand is rare or not transported by diminished Late Quaternary rivers. The Yilgarn Block of southwestern Australia is also surprisingly free of dunes, possibly as a result of long, deep weathering. Everywhere the history of climate change is evident in dune morphology and distribution, including large areas where the sand dune orientations are markedly divergent from modern sand moving wind directions.

The Nullarbor Plain of southeastern Australia, ∼200,000 km 2 in area, is flat and mostly treeless. It contains widely scattered collapse dolines and a few hundred caves, some of which are large and extensive. Initial karst development probably occurred during the warm, seasonally wet climatic conditions of the Oligocene, when the withdrawal of the sea exposed the recently deposited Eocene Wilson Bluff Limestone for over ∼10 m.y. Several major conduits probably developed at this time. These were flooded by the return of the sea, which finally retreated in the late Miocene followed by regional uplift. Cave formation in the Pliocene and Quaternary was inhibited by the semiarid climate, which became increasingly arid ca. 1 Ma. The overall dryness caused crystallization of evaporite minerals in cracks and pore spaces within the limestone walls of the caves, and they suffered extensive collapse, producing large passages, dome chambers, and dolines. However, during a wet phase 5–3 Ma, rivers extended across the karst plain, and caves formed where they sank into the limestone. Shallower caves probably also formed at this time, perhaps associated with perched water tables. The Nullarbor Plain did not develop extensive surface and underground karst features, even during the wetter climate of the Oligocene. It appears that the flatness of the plain and the particular characteristics of the limestone (primary porosity and lack of jointing and inception horizons) resulted in relatively uniform downwasting and little cave formation. Climate played a relatively minor role in restricting karst development.