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north-west China. It lies north of the Helan Shan range and immediately west of the
Yellow River. It is bounded to the north-west by the Langshan Mountains and merges
north-east into the Hefao Plain. Sporadic outcrops of Holocene lake sediments indicate
that this region was once wetter than it is today. Zhao et al. (
2012
) found evidence of
widespread eolian sands until around 8.3 ka, at which time an extensive freshwater
lake came into being in the northern sector of the desert, attaining its maximum extent
from 7.8 to around 7.1 ka, with a surface elevation of about 1,021-1,026 m. The lake
shrank and became segmented into smaller water bodies after 6.5 ka. The modern salt
lake at Jilantai (now the centre of a major chemical processing plant) is all that remains
today of the once extensive early-middle Holocene desert lake. This work confirms
that the climate in this now hyper-arid region was significantly wetter between 7.8 and
7.1 ka than it is today. The area was a sand desert until around 8.3 ka, after which
conditions became progressively less arid. The climate became more arid again after
about 6.5 ka, and the lake shrank to a small salt lake flanked by episodically active
sand dunes.
11.9 Desert lakes of Australia
We saw in Chapters
8
and
9
that based onmore than 200
14
C, TL and OSL ages, Bowler
(
1998
) and Bowler and Price (
1998
) established that eolian dust began to accumulate
in the lunettes on the eastern side of Pleistocene Lake Mungo and adjacent lakes from
around 35 ka until around 16 ka, with a peak centred around the LGM. Clay dunes
and gypseous lunettes were active on the downwind margins of seasonally fluctuating
lakes in many parts of south-east and south-west Australia immediately before and
between 21 and 19 ka. Major deflation of dry lake floors coincided broadly with the
time of extreme aridity centred on the LGM (e.g., Lake Eyre: Magee and Miller,
1998
). Gingele and De Deckker (
2005
) recorded intervals of enhanced eolian dust
flux in two cores off the coast of South Australia that span the last 170 ka. During
periods of minimum insolation at this latitude, strong northerly winds blew dust from
the continental interior, with peaks at about 70-74 ka, 45 ka and 20 ka. These periods
accord with times of lake desiccation, dune building and sparse vegetation cover in
the centre and south of Australia (Croke et al.,
1996
).
Although these conclusions are broadly true, more recent work by Bowler et al.
(
2011
) suggests that the earlier paleohydrologic models devised for Lake Mungo and
the other Willandra Lakes are in need of some revision. In essence, the Willandra
Lakes form a cascading system of what can be considered reservoir lakes fed from
Willandra Creek, a distributary of the Lachlan, with its upper catchment in the Eastern
Highlands of Australia. Lake Mulurulu was the uppermost lake, which then flowed
into Lake Garnpung, which flowed south into Lake Leaghur. The outflow from Lake
Leaghur fed into the Outer Arumpo Lake but also fed directly into Lake Mungo
(
Figure 11.3
).
Figure 11.6
is a diagrammatic representation of this cascading system.
