OFR 151.pdf - CRC LEME

Zone microfloras imply temporary warming occurred during the Late Eocene, possibly into
the upper mesotherm range. The latter is presumed to correlate with transient warming
recorded elsewhere along the southern margin (McGowran et al. 2000) although it is unclear
whether higher temperatures were sufficient to influence plant successions at higher latitudes
or higher elevations in southeastern Australia. For example, one probable thermophilous
Proteaceae species, Triorites magnificus is not recorded in southern Tasmania and it seems
probable that mean temperatures here and in the Eastern Highlands remained within the upper
microtherm to lower mesotherm range throughout the Middle and Late Eocene. Ginkgo and
deciduous species of Nothofagus provide circumstantial evidence that mean minimum
temperatures fell below freezing during winter in the southeastern Tasmania during the
Middle-Late Eocene.
2. Rainfall
The abundance of Nothofagus (Brassospora) spp relative to gymnosperms appears to
increase, and the diversity of uncommon angiosperms with subtropical NLRs decrease, quasisystematically
from west to east along the southern margin. Assuming this trend reflects
differences in the seasonal distribution and reliability of rainfall, then summer rainfall was
lowest (or least reliable) in the Eucla Basin and adjacent inland regions, and highest (or most
reliable) in Tasmania, the Gippsland Basin and, possibly, the Eastern Highlands. Any
increase in orographic cloudiness almost certainly will have reduced evapo-transpiration
losses and increased effective annual precipitation in mountainous regions.
7.7 Time Slice T-4. Oligocene-Middle Miocene [33.7-11.2 Ma]
Zones: Upper Nothofagidites asperus to Canthiumidites bellus Zones
Phthanoperidinium comatum and informal Oligospheridium Zones
Figure 10: Earliest Oligocene (35 Ma) palaeogeography (from Veevers et al. 1991)
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