Australia: The Land Where Time Began

A biography of the Australian continent 

The Last Interglacial – Desert Dunes and Dust

A counterpoint to the records of palaeohydrology from rivers and lakes is provided by the history of desert dunes. A chronology of dune activity has been reconstructed in increasing detail, and at scales that range from vertical accretion and longitudinal growth of individual dunes through to the history of the entire dunefields, as a result of the widespread availability of luminescence techniques. As has been shown in the case of Southern African deserts, in Australian deserts this has complicated the conventional view of dune systems having straightforward correlations with arid periods (Lancaster, 2008).

Interactions between sediment supply and availability and wind speed have been suggested by recent work to govern the response of dunes to climate change, as well as defining a series of states of systems of dunes (Kocurek, 1998). It is shown by Kocurek’s model of aeolian response shows that an aeolian system will be caused to flip from dune construction to dune reworking by sand starvation. An implication of this is that some apparent gaps in chronologies of dunes may be processional, not simply climatic. Winds play a major role in determining the periods of dune activity where sediment is freely available (a transport-limited system). Variations in rainfall and vegetation cover play a dominant role in the development of dunes where sediment is not freely available (an availability-limited system). Dune activity in the arid zone of Australia is mostly limited by vegetation cover. It has been argued that wind speed determines the mobility of dunes in the arid core, the sparse vegetation in that region being not sufficient to stop sand movement at the present (Ash & Wasson, 1983). Unlike linear desert dunes source-bordering dunes are dependent on stream flow for the transport of sediment and at times of seasonally dry conditions to allow it to be blown into transverse dunes.

A widespread phase of linear desert dune construction across the arid zone of Australia has been shown by dune chronologies to have taken place, beginning at 76-60 ka, at the close of MIS 5. It has been shown by OSL ages around Lake Frome that were phases of dune activity at 66-57 ka and 22-11 ka (Fitzsimmons, Bowler, Rhodes et al., 2007). The onset of major dune activity has been dated to 70 ka in the Strzelecki and Tirari dunefields (Lomax et al., 2003; Fitzsimmons, Rhodes, Magee et al., 2007) and there were a number of dune reactivation periods at 73-45 ka, 35-28 ka, 22-18 ka, and 14-10 ka, these phases being punctuated by periods of stability. Phases of linear dune activity dating to 75-65 ka and 28 ka, occurred on the western margins of the Simpson desert dunefields (Hollands et al., 2006). On the northern margin of the desert Lake Gregory linear desert dunes built up over the old lake floor at 70 ka (Bowler et al., 2001). Among these records there is a broad consistency indicating widespread dune activity after 70 ka, which peaked during the last glacial maximum 30-18 ka.

Dust records recovered from the Tasman Sea indicates dust concentrations increased from 74 ka, with distinct peaks at 61 ka and 52 ka (Hesse, 1994)  Disturbance to the vegetation and ground cover across the interior as climatic changes brought increasing aridity and conditions that were more seasonal, and the weakening of the northern monsoon.

Sources & Further reading

Smith, Mike, 2013, The Archaeology of Australia’s Deserts, Cambridge University Press