OFR 151.pdf - CRC LEME

Inferred climate
The southern limit of latitude of Bruguiera is in northern New South Wales, ~4 0 latitude north
of Little Bay. If the northward drift of Australia is taken into account, this implies a shift in
mean temperatures equivalent to about 11 0 latitude in present day terms. Accordingly the
macroflora indicates very warm (upper mesotherm) and wet (humid) conditions. Since the
sediments were deposited under a relative sea level some 30 m higher than present, it is
reasonable to conclude the Little Bay sequence represented conditions at sea level during the
mid Miocene thermal optimum although conditions before and after this optimum may have
been cooler (lower mesotherm).
4. Gippsland Basin
Oligocene-Middle Miocene macrofloras from the Berwick Quarry site near Melbourne and
the Latrobe Valley, onshore Gippsland Basin have been described in great detail by Pole et al.
(1993), and Kershaw et al. (1991) and Blackburn and Sluiter (1994), respectively. Additional
palaeobotanical records are provided by Rozefelds (1995), Rozefelds and Christophel (1996)
and Jordan and Hill (1996).
The Berwick Quarry Flora is dated as Late Oligocene to possibly earliest Early Miocene,
based on a K/Ar date of 22 Ma for the overlying basalts. The assemblage preserves some of
the earliest known Eucalyptus leaf remains as well as the remains of Araucariaceae (Agathis),
Podocarpus (Dacrycarpus), Casuarinaceae (Gymnostoma), Lauraceae, Nothofagus and
Proteaceae. The flora appears to represent a mosaic of rainforest and open forest
communities growing under relatively cool (lower mesotherm) and wet (perhumid) conditions
with a pronounced dry season.
Reconstruction of floras and vegetation occupying the Latrobe Valley are centred around
brown coal measures forming the Early Oligocene-late Early Miocene (Proteacidites
tuberculatus Zone) Morwell Formation and much thicker late Early-early Late Miocene
(Canthiumidites bellus Zone) Yallourn Formation. Both sequences are believed to be
ombrogenous (rain-fed) peat bogs whose development was periodically interrupted by marine
flooding of the basin (Holdgate and Sluiter 1991) and dominance is strongly correlated with
depositional environment due to local sourcing of the plant remains. Close sampling and
good exposures mean that it is possible to trace lateral as well as vertical changes in plant
community composition.
Floras at the base of the Morwell Formation are dominated by Proteaceae (Banksieaephyllum,
Orites/Darlingia) and Myrtaceae (Acmena, Baeckea, Melaleuca, Neomyrtus, Tristania):
Elaeocarpaceae are uncommon. Higher in the section, the dominants are Podocarpaceae
(Dacrycarpus, Dacrydium) and Proteaceae (Banksieaephyllum), associated with frequent to
common Araucariaceae (Agathis, Araucaria), Cunoniaceae? (Phyllites), Escalloniaceae
(Quintinia), Myrtaceae (Acmena, Eugenia, Tristania), Oleaceae, Blechnaceae and
Gleicheniaceae. The low fusinite content indicates wildfires were rare.
Sediments at the base of the overlying Miocene Yallourn Formation have a very high (up to
56%) fusinite content, indicative of frequent wildfires. The wetland macrofloras are
dominated by Hepaticae, Blechnaceae, Gleicheniaceae, Podocarpaceae (Phyllocladus),
Casuarinaceae (Allocasuarina, Gymnostoma), Cyperaceae, Elaeocarpaceae (Elaeocarpus),
Epacridaceae (Styphelieae), Myrtaceae (Baeckea, Leptospermum, Melaleuca), Proteaceae
(Banksieaephyllum, Xylomelum), Restionaceae, Sparganiaceae and/or Typhaceae. More
recently, Wilkinsonia (cf. Athertonia) and an extinct Elaeocarpus sp. with close links to an
undescribed living tree in montane northeastern Queensland have been found at the same
stratigraphic level. Higher in the same section, the floras are dominated by Podocarpaceae
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