Geoscience Reference
In-Depth Information
deserts were derived primarily from local bedrock with very little subsequent eolian
transport. In those instances where the sand source was several hundred kilometres
distant from the present-day dune field, transport had been dominantly fluvial and
not eolian. They concluded that there had been some recent localised sediment input
from modern fluvial systems in the Simpson, Strzelecki and Tirari deserts, while in
Great Victoria Desert, Quaternary eolian transport or reworking of sand had been
minimal.
The relationship between dune orientation and present-day wind direction is still
unclear (Brookfield,
1970
; Sprigg,
1979
; Nanson et al.,
1995
), with most observers
noting the broad general accordance between linear dune alignment and the general
direction of wind flow associated with the anticyclonic air flow patterns over central
Australia. Hollands et al. (
2006
) studied and 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.
Sprigg (
1979
) had earlier argued that the dunes were active during glacial maxima
and thus reflected the wind systems of those times. He believed that there had been an
equatorward shift of more than five degrees of latitude in the southerly stream of dune-
forming winds during the last glacial relative to the present interglacial in response
to an intensification and northward displacement of the westerlies along the southern
margin of Australia. This inference has received some support from the wind-blown
dust record in marine cores off the east coast of Australia, with the marine record
showing a threefold increase in dust flux during the LGM relative to the Holocene in
temperate and tropical Australia (Hesse,
1994
). We discuss the Australian desert dust
record in
Chapter 9
.
During and immediately after the LGM, dunes were active across the continent,
including as far south as north-east Tasmania (Bowden,
1983
; Duller and Augustinus,
1997
; Duller and Augustinus,
2006
). OSL ages for linear dunes in the Strzelecki and
Tirari deserts are concentrated at 73-66, 35-32, 22-18 (LGM) and 14-10 ka (Rhodes
et al.,
2004
; Fitzsimmons et al.,
2007a
). The two intervals with the most samples are
at 20 ka, when sea level was 120 m lower than today and the Australian land-mass was
about 25 per cent greater in area, and 14-10 ka, when temperatures were becoming
warmer (Fitzsimmons et al.,
2007a
). The apparent gap between 20 ka and 14 ka
suggests that few deposits have been preserved from that period. There was either
little dune building at that time or subsequent reworking has removed the evidence. It
will be interesting to see whether future closer sampling intervals for OSL dating of
the desert sand dunes in Australia confirm or refute the various age clusters claimed
by different workers.
Fitzsimmons et al. (
2007b
) obtained OSL ages for both transverse and linear dunes
located on the eastern (downwind) margin of ephemeral Lake Frome immediately
west of the arid Flinders Ranges. The ages for both types of dunes clustered at 66-57
and 22-11 ka. Transverse dune building began around 111-106 ka, while linear dunes
°
