OFR 151.pdf - CRC LEME

1.2.3 Central Australia
1. Eromanga and Surat Basins
Cicatricosisporites australiensis-Foraminisporis wonthaggiensis Zone microfloras preserved
in the Eromanga and Surat Basins have been studied by Dettmann (1963) and Burger (1973,
1980, 1988). Commonly occurring taxa are cryptogams (Osmundaceae, Gleicheniaceae,
Cyatheaceae, Lycopodiaceae, Sphagnum) and pteridosperms (Alisporites, Vitreisporites).
Gymnosperm pollen are relatively rare but include Araucariaceae, Cheirolepidaceae and
Podocarpaceae.
Dettmann et al. (1992) have concluded that the Eromanga Basin supported araucarianpodocarp
dominated forests and woodlands (Austral Conifer Forest) in which the understorey
was dominated by tree-ferns, ferns, lycopods and mosses. Sphagnum spores are a persistent
to occasionally common element, indicating the development of peatmoss bogs in the south of
the basin.
Correlative microfloras preserved in the western Surat Basin also point to the presence of
Austral Conifer Forest although araucarians and podocarps are uncommon relative to
pteridosperms, ferns (Cyatheaceae, Osmundaceae) and some fern allies (lycopods).
Sphagnum and dinoflagellates occur only sporadically.
Inferred climate
The data point to humid to wet conditions. Plant growth is likely to have been limited by low
light intensities and temperatures during winter months although increased cryptogam
representation in the western Surat Basin hints that conditions closer to what was the palaeosouthern
margin may have been more equable than those closer to the interior of the
continent. Marine transgressions increased during the period but it is unclear from the
palaeobotanical evidence that climates during the Berriasian were any more equable (less
continental) than during the Valanginian-Barremian. However conditions were seasonally
cold (microtherm range) and wet (humid-perhumid) to support the development of Sphagnum
bogs.
1.2.4 South-West Australia
Early Cretaceous sequences are routinely intersected in petroleum exploration wells but the
only systematic overviews of Berriasian-Barremian (Biretisporites eneabbaensis Zone)
palynofloras comes from the Perth Basin (Backhouse 1988), and Jerboa-1, a well drilled in
the Eyre Basin, western Bight (Powis and Partridge 1980). These sites were located at the
extreme western end of the palaeo-northern margin between palaeolatitudes 50-54 0 S.
1. Perth Basin
Interpretation of the Perth Basin microfloras is complicated by the high degree of variation
between closely spaced sites. Cryptogams are usually abundant and diverse. Araucarians and
podocarps are frequent to common (5-30%) but less abundant than in the Late Jurassic.
Cheirolepidiacean conifers are rare (