OFR 151.pdf - CRC LEME

pollen dominance almost certainly was influenced by marine flooding. For example, high
values of Callitrichaceae in Apectodinium hyperacanthum Zone assemblages may reflect
coastal freshwater swamps that were periodically inundated by saltwater.
Inferred climate
SSTs within the Otway Basin and Torquay Embayment appear to have been below the (upper
mesotherm) threshold required to support Nypa despite the presence of this mangrove palm in
the Gambier Basin, Gippsland Basin and on the West Coast of Tasmania (see below).
Nevertheless the data are consistent with the expansion of evergreen rainforest communities
whose closest modern equivalent is Araucariaceae (dry) rainforest. If this conclusion is
applicable to the region as a whole, then it is difficult to avoid concluding that mean
temperatures were within the upper mesotherm range as well as being overall wet to very wet
(humid-perhumid) during the Early Eocene, and that summer rainfall remained adequate to
support Nothofagus on, for example, the Otway Ranges.
3. Gippsland Basin
Early Eocene sediments have been recorded from 120 wells in the offshore Gippsland Basin
and reach a maximum thickness of ~350 m (A.D. Partridge, pers. comm.). Much thinner
correlative sections occur at depth onshore but are sampled only by cuttings.
A number of taxa which had been present in the Bass Strait region since Late Cretaceous
times became extinct at or shortly after the Paleocene/Eocene boundary, e.g. Lygistepollenites
balmei, Phyllocladidites reticulosaccatus, Gambierina spp. and Australopollis obscurus. The
base of Malvacipollis diversus Zone is defined by the first appearance of three typically
megatherm taxa – Lygodium (Crassiretitriletes vanraadshoovenii), Nypa and Tiliaceae.
Microfloras are usually dominated (>50%) by angiosperms, chiefly Euphorbiaceae
(Malvacipollis spp.) with variable amounts of Casuarinaceae, Proteaceae and undescribed
tricolpate and tricolporate types. The highest values of the Malvacipollis spp. (>40%) occur
in coals, indicating the Euphorbiaceae (Austrobuxus), like Casuarinaceae (Gymnostoma),
were prominent in coastal swamp or riparian communities. Gleicheniaceae and Acrostichumtype
(Cyathidites splendens) may dominate other swamp assemblages. Agathis/Wollemia is
the most abundant gymnosperm, and Cyatheaceae, Gleicheniaceae and indeterminate trilete
(Cyathidites) and monolete (Laevigatosporites) ferns are the most abundant cryptogams.
Rare to uncommon taxa include a possibly extinct species of the now wholly tropical genus
Bombax (Bombacaceae) and Intratriporopollenites notabilis (Tiliaceae), which in a marginal
marine context may represent the mangrove Brownlowia.
Nypa and a possible extinct species of Freycinetia (Pandanaceae) are most prominent during
the early Early Eocene M. diversus Zone but become rare during Middle and Upper
Malvacipollis diversus Zone time: Proteaceae and Euphorbiaceae increase in diversity and
relative abundance at the same time. Over the same interval, the now extinct Proteacidites
species complex (P. grandis-leightonii) was replaced by another extinct complex (P.
pachypolus-nasus-asperopolus). Since Proteacidites pachypolus first appears in marginal
marine facies, it is reasonable to assume that the succession reflects eustatic forcing (cf.
Macphail et al. 1994). Subsequently Proteacidites pachypolus expanded into a very wide
range of dryland habitats and elevations, including around peat swamps on the Atherton
Tableland in northeastern Queensland during the Pliocene.
Notable first appearances in the Gippsland Basin during the late Early Eocene (Upper
Malvacipollis diversus-Proteacidites asperopolus Zones) are Santalum (Santalumidites
cainozoicus), Sapotaceae (Sapotaceoidaepollenites spp.), the putative early eucalypt
Myrtaceidites tenuis and mistletoes (Gothanipollis). Podocarpaceae (Lagarostrobos) and
Nothofagus (Brassospora) increase in relative abundance (~5-7%) whilst Nypa, Tiliaceae and
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