OFR 151.pdf - CRC LEME

events on other continents and suggest this was due to increasing regional tectonism along the
eastern margin of Australia. Frakes (1999) suggests that much of Australia may have been
subject to dry polar easterly winds blowing from what are now the east and south-east
quadrants.
5.3 Palaeobotanic evidence for Early Cretaceous climates
Early Cretaceous climates in Australia reflect global to regional tectonic and eustatic events
superimposed on relatively flat equator to pole temperature gradients.
Much of the palaeobotanical evidence comes from exploration wells and boreholes drilled in
southern Queensland, central Australia, Western Australia and Victoria. The most closely
sampled regions are the Eromanga and Surat Basins. Other sites preserving continuous
palynosequences occur in offshore basins on the western margin (Perth, Carnarvon and
Canning Basins), the North West Shelf (Bonaparte and Money Shoals Basins), northeastern
Queensland (Carpentaria and Laura Basins), the mid Queensland coast (Maryborough and
Styx Basins), and the Australo-Antarctic Rift System (Bight, Otway and Gippsland Basins).
Infrabasins of Early Cretaceous age underlie the Murray-Darling Basin.
Many of the sedimentary sequences are marine and can be independently dated using
dinoflagellates (Morgan 1980, Helby et al. 1987). The richest macrofloral sequence however
is preserved in freshwater facies in the Gippsland Basin – the Koonwarra Flora (Dettmann
1986a, Drinnan and Chambers 1986, Douglas 1990, 1994).
Numerous unpublished reports providing information on Early Cretaceous palynofloras are on
open-file in the Geological Surveys of Queensland (GSQ), New South Wales (GSNSW),
Victoria (DME), South Australia (PIRSA) and Western Australia (GSWA). Early Cretaceous
palynofloras have not been recorded onshore in Tasmania. Publications dealing with Early
Cretaceous palynosequences include taxonomic monographs. Examples are Dettmann (1963,
1973) and Douglas (1969, 1973a, 1973b) for the Otway Basin, Burger (1968, 1973, 1976,
1980, 1988, 1990, 1993) for the Eromanga and Surat Basins, Kemp (1976a) for the Officer
Basin, Morgan (1980) for the Eromanga Basin, and Backhouse (1988) for the Perth Basin.
Recent overviews of the Early Cretaceous flora and vegetation are Dettmann (1994), Douglas
(1994), McLoughlin (1996 and in press), McLoughlin and Hill (1996), Hill et al. (1999) and
Pole and Douglas (1999).
Plants growing at high to polar latitudes during the Late Mesozoic experienced up to 3-6
months of winter darkness. Nevertheless macrofossil evidence shows that woody species
displayed the growth characteristics of trees that now grow in mid latitude/temperate regions
with relatively long growing seasons. For example, tree-trunks preserved on Alexander
Island, West Antarctica (Jefferson 1992), provide direct evidence of communities dominated
by gymnosperms that were at least 7 m tall and spaced between 3-5 m apart. Thick coal
measures accumulated between palaeolatitudes of 70-80 0 S (Mount Morgan-Stanwell district
and Laura Basin). Accordingly, interpretation of Cretaceous climates in southern Australia
involves explaining how rapid plant growth could be sustained in the face of short growing
seasons (cf. Axelrod 1984, Barron et al. 1995).
5.3.1 Evolution and migration
Most Early Cretaceous genera and species which were found in Australia are extinct, as are
some lower order taxa, e.g. the pteridosperms (a group of plants that combined the
characteristics of modern cycads and conifers) and brachyphyll araucarians. Extant taxa
families such as Araucariaceae, Podocarpaceae and Schizaeaceae had much wider
distributions than now. For example, during the Early Cretaceous, schizaeaceous ferns
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