OFR 151.pdf - CRC LEME

surrounding basins. Thick sands eroded from these uplands began to accumulate along the
palaeo-western and southern margins. A Chilean-type volcanic cordillera located in
northeastern Queensland shed detritus westwards into the interior of the continent. A major
rise in relative sea level during the Hauterivian to Barremian resulted in the formation of a
seaway, which extended from the Gulf of Carpentaria southward into the Eromanga Basin.
Sediments deposited at this time covered (and helped preserve) much of the pre-existing
landsurface (Twidale and Campbell 1991). Gosses Bluff records one of a number of multiple
meteorite impacts in central Australia during Early Cretaceous time (Plummer 1998).
5.4.2 Palaeobotany
Like the Late Jurassic, the Early Berriasian-Barremian floras were dominated by
Araucariaceae, Podocarpaceae, Bennettitales and diverse cryptogams. Several archaic taxa
had become extinct by the end of the Barremian whilst some angiospermids had migrated into
the Australian region from West Gondwana by the Aptian (Douglas 1994).
5.4.3 Palaeoclimates
Floristic differences between regions are likely to reflect differences in palaeolatitude and
proximity to the ocean and other large water bodies as well as climatic change per se.
Palaeo-northern Australia (~45-60 0 S)
Climates in present-day southwestern and northwestern Western Australia probably were
humid, and it is unlikely that plant growth was limited by low light intensities during winter
because of the relatively low palaeolatitude. Some fossil woods possess prominent growth
rings, implying strong seasonal variation in temperature and/or rainfall. Mean annual
temperatures are presumed to have been 'warm' rather than 'cool' (lower mesotherm). The
hypothesis that temperatures warmed from west (present-day south-west Western Australia)
to east (present-day North West Shelf) along the palaeo-northern margin (Dettmann et al.
1992) cannot be tested by the current evidence.
Palaeo-central Australia (~60-70 0 S)
Climates were wet (humid-perhumid) and average temperatures were adequate to support
tree-growth during summer months despite the relatively high palaeolatitude.
Palaeogeographic constraints imply mean temperatures are likely to have been seasonally
cold (microtherm range) and probably frost-prone. Glendonites in the Eromanga, Surat and
Carpentaria Basins provide the only direct evidence that winter temperatures fell below
freezing point: plant growth will have been limited by low light intensities as well as low
temperatures during winter.
Palaeo-southern Australia (~70-85 0 S)
Climates in present-day southeastern to northeastern Australia almost certainly were wetter
(humid-perhumid) than in palaeo-northern Australia and it is reasonable to assume that mean
temperatures varied from cold (lower microtherm) during winter months to cool (upper
microtherm to lower mesotherm) in summer months. Plant growth in northeastern New South
Wales and southern Queensland will have been strongly seasonal due to short summers, and
freezing temperatures and prolonged darkness during winter. Evidence from palaeo-central
Australia implies temperatures in palaeo-southern Australia also fell below freezing in winter.
There is weak evidence that conditions within the (then) north-south orientated Australo-
Antarctic Rift System were more temperate and supported denser vegetation than in the
interior of the continent, possibly due to a marine influence.
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