OFR 151.pdf - CRC LEME

species (Spinizonocolpites uvatus) in association with unusually abundant Lophosoria
(~12%).
Inferred climate
Oligo-Miocene climates were uniformly wet to very wet (perhumid) but characterised by
marked variations in mean temperatures. For example, the extinction of thermophilous taxa
at the Eocene-Oligocene boundary (Middle/Upper Nothofagidites asperus Zone boundary) is
consistent with an abrupt drop in mean temperatures to microtherm values. Subsequent trends
point to gradual warming during the Early Oligocene-Early Miocene with maximum warmth
(mesotherm range) being achieved in the late Early or Middle Miocene.
Mean annual temperature values appear to have remained within the lower mesotherm range
during the late Early to late Miocene but it is possible that warm SSTs allowed a relative of
the tropical mangrove palm Nypa to migrate into the Gippsland Basin. The record is an
interesting one given the sporadic appearance of warm water benthic foraminifera in southern
Australia during the Middle Miocene (B. McGowran pers. comm.). The relative decline in
Nothofagus (Brassospora) spp. (Fig. 2 in Sluiter and Kershaw 1982) and increasing
representation of taxa typical of low/open community types suggests rainfall may have
become more seasonal at about the same time. Nonetheless moisture levels remained
adequate to support possibly extensive Lagarostrobos swamp forests into the early Late
Miocene.
4.2.7 Tasmania
For reasons that remain unclear many of the Early Tertiary palaeochannels that preserve
macrofossil deposits in Tasmania became infilled (and possibly buried) during Oligo-Miocene
time. The combined macrofossil and microfossil record is unusually comprehensive, both in
terms of geographic coverage relative to the size of the island and in numbers of taxa able to
be identified to genus or species level. Only in exceptional cases are independent age control
available and it remains uncertain if the taxa used to distinguish Proteacidites tuberculatus
and Canthiumidites bellus Zone Equivalent time in the Gippsland were present in the flora of
inland northern and southern Tasmania during the Oligo-Miocene. For example, the earliest
known record of one important accessory species of the Canthiumidites bellus Zone
(Symplocoipollenites austellus) is Late Pliocene. Consequently some floras and sites dated as
Early Oligocene to late Early Miocene may prove to be late Early to early Late Miocene.
1. Bass Basin
Martin (1985) has provisionally identified Proteacidites tuberculatus Zone Equivalent
microfloras in Squid-1 (1400-1855 m) and Tasmanian Devil-1 (600-750 m), Bass Basin.
Range chart data indicate the microfloras are wholly dominated by Nothofagus (Brassospora)
spp. Rare taxa include Araucaria, Dacrydium, Lagarostrobos, Cupanieae, Nothofagus
(Lophozonia), Polygalaceae and (diverse) Proteaceae. Lophosoria was not recorded.
Harris (1965c) has recorded Lophosoria in a probable Proteacidites tuberculatus Zone
Equivalent microflora from Cape Barren Island off the northeastern coast of Tasmania. This
assemblage is unusual in that it includes Dacrycarpus, Dacrydium, Phyllocladus, Beauprea,
Cupanieae and Nothofagus (Brassospora) spp. but not Lagarostrobos or Podocarpus-
Prumnopitys. Araucariaceae are absent.
Inferred climate
The assemblages are depauperate versions of correlative microfloras preserved in the
Gippsland Basin. Without access to quantitative data, it is difficult to determine whether the
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