OFR 151.pdf - CRC LEME

Inferred climate
Assuming the microfloras in the Broken Hill district are correctly dated, the pollen data
indicate climates along the upper reaches of the Darling River and tributaries became
temporarily cooler and wetter and/or less seasonal (humid) during the Oligocene to Early
Miocene, allowing temperate rainforest species to survive along rivers as far west as Broken
Hill. Since the gallery flora also included warm temperate-subtropical species, e.g.
Araucariaceae, Austrobuxus-type, Cupanieae and Mallotus-type, as well as cool temperate
rainforest taxa such as Lophosoria and Nothofagus (Lophozonia) spp., a reasonable estimate
is that mean annual temperatures remained within the mesotherm range. Subsequent climates
became either warmer or seasonally drier in the late Early to Late Miocene, resulting in the
expansion of sclerophyll taxa such as Casuarinaceae and Myrtaceae (including Eucalyptus) in
drier sites. The same trend seems to have allowed Asteraceae to migrate into western New
South Wales.
b. North-west slopes
Martin (1999b) has identified Proteacidites tuberculatus and Canthiumidites bellus Zone
Equivalent microfloras in Boreholes GW 096000, and GS-A and GW 069003, respectively, in
the Macquarie River Valley near Narromine. Few details are provided beyond noting the
younger (possible mid-Late Miocene) assemblages include Calochlaena/Culcita,
Haloragaceae (Gonocarpus/Haloragis), Mimosaceae (Acacia) and occasionally significant
amounts of Nothofagus (subgenus not specified). Canthiumidites bellus Zone Equivalent
microfloras from the Namoi, Gwydir and Castlereagh Valley in far northeastern New South
Wales (Martin, 1980, 1981) are dominated by Blechnaceae (2-6%), Cyathea (5-20%),
Dicksonia (1-8%), Dacrydium (up to 4%), Podocarpus-Prumnopitys (1-7%), Casuarinaceae
(2-10%), non-eucalypt Myrtaceae (2-36%), Nothofagus (Brassospora) spp. (7-19%)
Nothofagus (Lophozonia) spp. (4-12%), Proteaceae (up to 6%) and unidentified
tricolpate/tricolporate types (7-38%).
Less common (1-5%) taxa in the Castlereagh microfloras are Araucariaceae (Araucaria),
Podocarpaceae (Dacrycarpus), Cupanieae, Euphorbiaceae (Mallotus-type, Micrantheum),
Escalloniaceae (Quintinia), Mimosaceae (Acacia), Proteaceae, Rubiaceae (Randia),
Symplocos and Winteraceae. Maximum relative abundance values of Dacrydium (4%),
Phyllocladus (2%), Mallotus-type (11%), Nothofagus (Brassospora) spp. (19%) and N.
(Lophozonia) spp. (8%) are significantly higher in the Namoi-Gwydir Valleys than in the
Castlereagh Valley to the south-west. Rare taxa (both areas) include Sphagnum, Pteris,
Calochlaena/Culcita, Ericales, Loranthaceae, non-eucalypt Myrtaceae, Poaceae, Proteaceae,
Restionaceae, Rubiaceae (Randia) and Winteraceae.
Inferred climate
Mean annual rainfall appears to have been sub-optimal (seasonally humid) for Nothofagus
except near the ranges (perhumid). Geographic gradients in the relative abundance of
Nothofagus (Lophozonia) and other cool temperate rainforest taxa imply mean annual
temperatures were within the lower mesotherm range on the lower slopes, decreasing to upper
microtherm values within deeper valley and on the ranges.
4.2.3 Central Australia
Probable Oligocene-Middle Miocene microfloras are preserved in the Namba Formation in
the Callabonna Sub-basin (Martin 1990), the Burt Plain, Santa Teresa, Tempe Downs and Titree
Basins in the Alice Springs District, DH Glenmore-1 drilled 160 km north of Broken Hill
and an unnamed borehole (RN 16861) drilled near Mt. Wedge in western New South Wales
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