OFR 151.pdf - CRC LEME

amplifying, pacing and potentially driving global climatic change over orbital time scales
throughout the Quaternary (Broecker and Denton 1989, Clark et al. 1999).
7.2 Australian backdrop
Tertiary climates in Australia reflect global and regional tectonic and eustatic events, which
were superimposed on strengthening equator-to-pole temperature gradients and decreasing
atmospheric carbon dioxide concentrations. Of particular significance has been the continents
rapid drift into middle-low latitudes. This provided background warming when the earth as a
whole underwent progressive cooling and drying during the Late Palaeogene and Neogene
(Frakes 1999). Although no single factor is likely to be paramount in a given region within
Australia, patterns of Tertiary climatic change are increasingly being linked to changes in
deep-ocean circulation. Long-term warming and cooling trends have been interrupted or
sharpened by a number of short-term excursions in global climate, whose impacts will have
varied across the larger basins and in mountainous terrain.
7.3 Palaeobotanical database
As for the Cretaceous, the bulk of the palaeobotanical evidence for Tertiary climatic change is
palynostratigraphic, and comes from exploration wells and boreholes drilled in southern and
central Australia. The key basins are the Gippsland, Bass, Otway and Murray Basins where
relatively continuous deposition has preserved macro and microfossil records of the
Paleocene-Eocene and/or Oligocene-Middle Miocene vegetation. The coverage, however, is
highly variable, ranging from over 700 wells in eastern Bass Strait, to less than 17 wells in the
Great Australian Bight.
Other regions, which preserve discontinuous Tertiary sequences are offshore basins along the
northwestern margin (Bonaparte and Carnarvon Basins) the southwestern margin (Eucla and
Duntroon Basins), northwestern Tasmania (Sorell Basin), central Australia (Lake Eyre Basin
and small basins near Alice Springs) and northeastern margin (e.g. Yaamba Basin). Apart
from central Australia and the Eastern Highlands and Tasmania (where basalt flows have
buried fluvio-lacustrine deposits) the microfloras mostly represent coastal plain communities.
The richest and most informative macrofossil assemblages are those recovered from thick
brown coal measures in Victoria and South Australia, and analogous but much thinner lignites
in Tasmania.
Palynosequences in the offshore Gippsland, Otway and North West Shelf can be tied to the
International Time Scale using marine microfossils, in particular dinoflagellates, e.g.
Partridge (1976, 1999) and Harris (1985). The Esso-BHP zonation developed for the
Gippsland Basin by A.D. Partridge and Esso/Exxon colleagues is widely used to date and
correlate Tertiary and Late Cretaceous sediments elsewhere in Australia. Potassium-argon
dating of basalts has confirmed that the age ranges assigned to Gippsland zones are applicable
to Tasmania (Macphail et al. 1994).
Numerous unpublished reports that include information on Tertiary microfloras are on openfile
in the Geological Surveys of New South Wales, South Australia, Tasmania and Western
Australia, and Geoscience Australia (formerly Bureau of Mineral Resources and the
Australian Geological Survey Organisation). Studies of Tertiary macrofloras have tended to
focus on specific taxa but the evolutionary histories of the Araucariaceae, Cupressaceae,
Podocarpaceae, Proteaceae and Nothofagus are sufficiently well known to use morphological
trends as evidence of climatic change, e.g. Hill (1983a, 1992a, 1994a, 1995), Hill and Jordan
(1993), Carpenter (1994), Scriven and Hill (1996), Hill and Brodribb (1999). Recent
overviews of Palaeogene flora and vegetation have been published by Truswell (1993),
Macphail et al. (1994), Martin (1994) and Hill et al. (1999). 'Structural’ limitations that
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