OFR 151.pdf - CRC LEME

Plio-Pleistocene. For example, the pile up of equatorial water in the western Pacific resulted
in the largest expanse of warm water on the globe (Western Warm Pool) and probable
intensification of the warm East Australian Current flowing south along the eastern margin of
Australia (Srinivasan and Sinha 1998, Wei 1998).
Otherwise the major palaeogeographic and geomorphic changes to the Australian continent
were those forced by increasing aridity and, around the margins, marine regression and
transgression associated with expansion and contraction of the East Antarctic Ice Sheet. For
example, some silcretes in central and western regions of Australia have been assigned a Late
Miocene age [11-5 Ma]. Retreat of the sea from the Eucla Basin created the broad limestone
Nullarbor Plain at about the same time. During the Early Pliocene [5-2.5 Ma], marine
flooding led to the emplacement of estuarine and beach deposits in the south-west of the
Murray Basin and as far inland as Hamilton in southwestern Victoria. Many ancient river
systems on the Yilgarn Block and in central Australia appear to have become rejuvenated,
allowing sedimentation to recommence in central Australia (Eyre Basin). Tectonic damming
of the Murray Basin in the mid Pliocene [~2.5 Ma] created a mega freshwater lake known as
Lake Bungunnia. Volcanic activity became confined to western Victoria and northern
Queensland. Faulting along the Eastern Highlands created small but deep graben basins such
as at Lake George on the Southeastern Highlands of New South Wales. During the
Pleistocene glacial maxima, large areas of continental shelf were subaerially exposed,
including the North West Shelf, Bass and Torres Straits, and small ice sheets and mountain
glaciers developed in central and southwestern Tasmania. Many of the larger coastal plains
are the result of oscillations in sea level up to 100-120 m in amplitude.
As elsewhere, the Plio-Pleistocene was characterised by alternating cycles of cool-cold, dry
climates (glacial arid conditions) and more temperate (interglacial) climates and fluctuating
sea-levels (Hope 1994). The Barrier Reef and continental dune fields are products of this
climatic forcing. Associated phenomena include a shift from leached/acidic soils to the
formation of alkaline, saline soils, widespread hillslope instability, cycles of erosion and
alluviation in upland areas, and intensified aeolian activity across much of the continent
during Pleistocene ‘glacial arid’ intervals. Deglaciation began about ca. 17 ka and was
essentially complete by the Pleistocene/Holocene boundary at 10 ka B.P. By 8 ka, mean
temperatures may have been 1 ° C higher than today. By 6 ka, sea level had stabilised around
its present day position, completing the isolation of New Guinea and Tasmania.
7.8.2 Palaeobotany
From the minimal evidence preserved off the North West Shelf and in palaeochannels of the
Victoria River in the Northern Territory, it seems likely that the Late Neogene vegetation in
northwestern Australia was not dissimilar to the present day mosaic of tropical evergreen
rainforests, semi-deciduous (monsoonal) rainforests, sclerophyll woodlands, semi-arid
shrublands and arid grasslands. This was not the case in southern or northeastern Australia
where some tree genera that had been prominent in the Palaeogene-Early Neogene rainforests,
survived in local refugia into Plio-Pleistocene time. Examples occur in southwestern
Tasmania, Yallalie in south-west Western Australia, Daylesford in the Central Highlands of
Victoria, the Southeastern Highlands of New South Wales, and the Atherton Tableland in
northeastern Queensland.
Late Neogene palaeoenvironmental change appears to have selected for taxa able to tolerate
high levels of disturbance (Markgraf et al. 1995) and modern sclerophyll taxa, many of which
first appeared in the Early Neogene, became common to dominant during the Late Neogene.
Nevertheless, ecological speciation continued to occur even in cool perhumid environments.
For example, a microflora from western Tasmania demonstrates that by Late Pliocene time,
some species within the Nothofagus (Brassospora) group were well adapted to microtherm
conditions; Early Quaternary macrofossil assemblages from the same region indicate some
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