Etched linear dunefields of the Nullarbor Plain; A record of Pliocene-Pleistocene wind patterns across southern Australia

Abstract

The southern Nullarbor Plain is covered by low amplitude (generally 1–2 m) parallel ridges and swales with variable wavelength (300–900 m). The ridges are stony; the swales hold thin deposits of unconsolidated silt and clay. The ridges and swales have previously been attributed to joint control but are not parallel to joints exposed in cave roofs. Instead, they have a striking similarity to central Australian linear sand dunes: they are parallel, regularly spaced and most importantly, fork in a consistent direction. They are here explained as the etched footprints of an extensive linear dune system that once covered much of the southern Nullarbor. Rainwater collecting in the troughs between the sand dunes dissolved the underlying limestone to produce the swales. Recognition of this dune field fills a major gap in the distribution of linear dunes across Australia. The dunes have subsequently disappeared, apart from red aeolian sand in dolines in the southeastern part of the Nullarbor; most of the sand was probably blown offshore.The ridge and swales are oriented predominantly north-south in the west, and northeast-southwest and northwest-southeast in the centre and east, due to deposition by northerly and westerly winds respectively, as shown by directions of forking. The north-south Nullarbor dunes are probably older and may have been deposited in the arid climate of the late Neogene; this would make them the oldest linear dunes in Australia, remnants of an early phase of linear dune activity that has been removed or overprinted elsewhere. The change in wind direction shown by the dune orientation could represent northward migration of sub-tropical high-pressure systems during the late Neogene.