OFR 151.pdf - CRC LEME

4.2.1 North-West Australia
1. North-West Shelf
Middle Miocene turbidites accumulating at water depths of >4000 m on the Argo Abyssal
Plain, north of Port Hedland, preserve trace numbers of Casuarinaceae, Chenopodiaceae and
Restionaceae pollen (Martin and McMinn 1994).
Inferred climate
It is unclear whether these pollen represent coastal wetland and (Chenopodiaceae) salt-marsh
communities or whether the regional dryland vegetation was dominated by Casuarinaceae and
Chenopodiaceae-Amaranthaceae. If the latter, then the regional climate is likely to have been
seasonally dry (subhumid to semiarid). The absence of Poaceae is against climates being very
dry (arid).
2. Pilbara region
Possible Early-Middle Miocene (maximum age Late Oligocene) microfloras are preserved at
depth below the western Fortescue Plains (Truswell 1987b). These are dominated by
Gleicheniaceae (14-37%), Casuarinaceae (11-24%), Eucalyptus (22-31%) and Nothofagus.
Species belonging to the subgenus Fuscospora are more common (5-13%) than Brassospora
spp. (5-9%). Gymnosperm pollen are sporadically frequent, e.g. Dacrydium (up to 3%) and
Podocarpus-Prumnopitys (1-2%). Apart from Nothofagus, the only other frequent (1-6%)
angiosperm types are Restionaceae (Milfordia hypolaenoides) and unidentified Proteaceae
and tricolporates. Rare taxa include Acacia, Isopogon and Xylomelum occidentale-type. The
mix of sclerophyll, rainforest and wetland taxa may represent gallery forest or scrub
communities growing along the banks of streams draining the Hamersley Ranges.
Inferred climate
Local humidity on the Fortescue Plain may have been augmented due to stream flow or
groundwater discharge. Conditions on the Fortescue Plain are likely to have been sub-humid,
and/or characterised by a pronounced dry season, although Nothofagus values imply wetter or
more uniform condition, within gorges and higher valleys on the Hamersley Ranges. Mean
annual temperatures are suggested to have been in the mesotherm rather than megatherm
range.
4.2.2 North-East Australia
1. Central Queensland
Beeston (1994) has documented in great detail microfloras recovered from the Suttor
Formation at Mt. Coolon and equivalent rock units at Riverside in central Queensland inland
of Mackay. These lack age diagnostic species but are likely to be Early to Late Miocene
based on occurrences of Rugulatisporites cowrensis (cited as R. mallatus and R. sp. cf. R.
micraulaxus), Acaciapollenites miocenicus (cited as A. myriosporites) and a species
(Haloragacidites suttorensis) that may be related to H. haloragoides. The maximum ages are
Late Eocene (Middle Nothofagidites asperus Zone Equivalent), based on Perfotricolpites
digitatus, or early Early Oligocene (Upper Nothofagidites asperus Zone Equivalent), based on
Striasyncolpites laxus (cited as Cupanieidites sp. A) and Malvacearumpollis mannanensis.
The minimum age may be early Miocene, based on the last occurrence of Tricolpites
retequetrus in the Gippsland Basin.
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