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climatic regime began about 5 ka ago and was characterised by more frequent ENSO
events than the first half of the Holocene.
22.6.2 Dunes and eolian sand plains
Geomorphic evidence of arid zone landforms dated using cosmogenic isotopes shows
that stony desert surfaces, or 'gibber plains', were present in Australia between 4 and
2 Ma, while the earliest recognisable sand dunes appear around 1 Ma ago (Fujioka
et al.,
2005
; Fujioka et al.,
2009
). In contrast to the Sahara, which is only one-fifth
sand, sand dunes and associated sand plains cover two-fifths of the present land area
of Australia (
Chapter 8
;
Figure 8.14
). The younger dunes were episodically active
during the late Pleistocene, including as far south as north-east Tasmania (Bowden,
1983
; Duller and Augustinus,
1997
), most notably at 73-66, 32-25, 22-18 (LGM)
and 14-10 ka (Rhodes et al.,
2004
; Fitzsimmons et al.,
2007a
; Fitzsimmons et al.,
2007b
). Lomax et al. (
2011
) obtained a 380 ka record of dune activity in the western
Murray Basin (
Figure 22.2
) based on ninety-eight OSL ages. Two major phases of
dune accretion were at 72-63 and 38-18 ka, with minor phases at 14.5-13.5, 12-
11 and 8-5 ka. They equated dune deposition with drier conditions and gaps in the
record with wetter conditions. Hollands et al. (
2006
) dated linear dunes in the north-
west Simpson Desert and concluded that there had been an approximately 160 km, or
1.5
, southward displacement of the sand-transporting wind system since the LGM.
Along the eastern margin of present-day Lake Frome, transverse dunes were active
at 111-106, 66-57 and 22-11 ka, and linear dunes were active by at least 66 ka and
again at 43-28 ka, after which soils developed under a wetter climate. Clay pellets
within several horizons of both transverse and linear dunes indicated salt influx and
sporadic deflation of the lake floor, suggesting that local hydrologic conditions, rather
than aridity, controlled dune activity (Fitzsimmons et al.,
2007b
).
The two periods with the greatest number of OSL ages are at around 20 ka, when
sea level was 120 m lower than it is today and the land area of Australia was about
25 per cent greater (
Figure 22.6
), and at 14-10 ka, when temperatures were rising
(Fitzsimmons et al.,
2007a
). The lack of ages between 20 and 14 ka seems to show that
few deposits were preserved from that period, either because of subsequent reworking
or because of minimal activity. We noted in
Chapter 8
that dune sediments survive
best if dune accretion is followed by a humid phase (Swezey,
2001
; Swezey,
2003
).
We discuss source-bordering dunes in
Section 22.6.5
.
°
22.6.3 Eolian dust
The dust record preserved in marine cores collected off the east coast of Australia
shows a threefold increase in dust flux during the LGM relative to the Holocene in
temperate and tropical Australia (Hesse,
1994
). The major present-day sources of dust
