OFR 151.pdf - CRC LEME

palaeolatitudes into the late Early Eocene, are sufficiently well grounded to challenge
the value of GCM estimates (predictions) at the local or regional level.
• Plant fossils and/or coldwater minerals preserved in the Perth, Eromanga and Surat
Basins provide a detailed record of Early Cretaceous climates. The Gippsland and
Murray Basins provide a more or less continuous palaeobotanical record of
Palaeogene and Neogene climatic change in southeastern Australia although these
records are of limited use in inferring climatic trends in northern Australia. Lack of
suitable deposits in northern Australia is compounded by the absence of regional
palynostratigraphies to date and correlate the few known fossil floras.
• Two sites have the potential to provide exceptionally detailed (world class)
information on climatic change during short periods of Late Tertiary time. These are
the ~34 m thick, possibly earliest, Oligocene rhythmite sequence at Lemonthyme
Creek in northwestern Tasmania, and the 110 m thick mid Pliocene lacustrine
sequence at Yallalie in south-west Western Australia.
8.1.2 Palaeoclimatic gradients and seasonality
• At no time during the Cretaceous or Tertiary have homogeneous climates existed
across the length or breadth of the Australian continent, although climatic gradients
have strengthened during the Late Cretaceous and Tertiary (markedly so during the
Late Tertiary). It is important to note that, due to rotation of the Australian Plate
about the geographic South Pole, the orientation of latitudinal gradients in
temperature and rainfall will appear to have altered during the Cretaceous.
• For the same reasons, conditions on the coast are an unreliable guide to environments
occurring inland or at higher elevations. The lapse rate (mean decrease in mean
temperature with increasing elevation) in southeastern Australia appears to have
steepened during the Late Palaeogene and Neogene.
• Seasonality during the Cretaceous was most strongly expressed via temperature and
(southern and central Australia) photoperiod, not precipitation. Comparisons of the
Early Cretaceous data imply that seasonal variations in temperature increased away
from the coast.
• Seasonality during the Tertiary was most strongly expressed via rainfall.
Comparisons of the palaeobotanical data demonstrate that seasonal variation in the
distribution and reliability of rainfall has increased markedly during the Late
Palaeogene and Neogene.
8.1.3 Photoperiod
• Photoperiod was a major forcing factor on plant community composition and
structure during the Cretaceous and (southern Australia) Early Tertiary and therefore
may have had an indirect influence on weathering.
8.1.4 Temperature
• Oxygen isotope data, glendonites and dropstones demonstrate that temperatures were
below freezing during winter months; and conceptualising Early Cretaceous climates
as warm is misleading despite the undoubted presence of timber-sized trees at high to
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