OFR 151.pdf - CRC LEME

6.5 Time Slice K-4. Turonian-Santonian [91-83 Ma]
Zones: Phyllocladidites mawsonii to Tricolporites apoxyexinus Zone
Palaeohystrichophora infusorioides to lower Nelsoniella aceras Zone
6.5.1 Palaeogeography
Much of the continent remained subject to deep weathering. Australia and Antarctica were
linked via Tasmania and the South Tasman Rise. In the Bass Strait region, depressions,
which may represent part of a failed triple junction, became deep fresh to brackish water lakes
(Marshall 1989, Baillie and Pickering 1991). Eruption of basalts in eastern Victoria and New
South Wales are associated with opening of the Tasman Sea between Australia and the Lord
Howe Rise-Campbell Plateau.
6.5.2 Palaeobotany
Almost all of the palaeobotanical evidence comes from basins on the palaeo-northern and
southeastern margins. Many common microfossil species can be assigned to modern genera
rather than families and taxa that had dominated the Early Cretaceous Austral Conifer Forest.
For example, cheirolepidiacean conifers and brachyphyll araucarians, were mostly replaced
by ‘modern’ gymnosperms such as Dilwynites (Agathis/Wollemia), Dacrydium, and
Lagarostrobos. It is possible that some angiosperms were canopy trees, e.g. Macadamia
(Proteaceae). The apparent rapidity with which the Proteaceae and other angiosperm clades
continued to diversify, is consistent with high levels of tectonic disturbance within the
Australo-Antarctic Rift System (Dettmann and Jarzen 1990, Dettmann et al. 1992). One fern
(Lophosoria), which is first recorded on the palaeo-northern margin during the Albian appears
to have migrated south onto the palaeo-southern margin during the latest Cenomanian or
Early Turonian (see Figure 33 in Helby et al. 1987).
6.5.3 Palaeoclimates
Climatic gradients appear to have strengthened north to south and west to east (southern
margin) on the continent. For example, angiosperms represented by unidentified tricolpate
and tricolporate pollen are relatively common on the palaeo-northern margin whereas
araucarians are prominent only on the palaeo-southern margin: Lagarostrobos swamp forests
are best developed in palaeo-southeastern Australia and northern Tasmania. Austral Conifer
Forest and fern heath remained the dominant vegetation types in coastal regions.
Palaeo-northern Australia
Communities included podocarp-dominated Austral Conifer Forest in the uplands and fern
heath on the coast. Conditions on the coast appear to have been seasonally wet (humidperhumid).
A probable palm (Dicolpopollis) implies seasonally warm (upper mesotherm)
temperatures in the present-day Arnhem Land.
Palaeo-central Australia
Fossil evidence is lacking but it is reasonable to presume the regional vegetation was a form
of Austral Conifer Forest growing under relatively cool (possibly mesotherm range) and
humid conditions.
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