OFR 151.pdf - CRC LEME

Miocene microfloras are dominated initially by Casuarinaceae (presumed to be
Allocasuarina/Casuarina), Gyrostemonaceae and Restionaceae with minor values of
Mimosaceae (Acacia). Poaceae values increase abruptly towards the end of this interval. The
Pliocene microfloras are dominated by Poaceae, Chenopodiaceae-Amaranthaceae and
Asteraceae (Tubuliflorae), with minor Acacia and Myrtaceae. On present indications, Late
Neogene vegetation in northern Australia seems to have been similar to the mosaic of
rainforest, sclerophyll and grass-dominated formations found in present-day northwestern
Australia. Assuming changes in pollen dominance are not due to erosion or non-deposition,
data from the Argo abyssal plain imply rapid replacement of relatively closed, possibly tall
sclerophyll vegetation types by lower, more open communities in which herbs were
prominent (possibly savannah woodland) during the Late Neogene.
A very sparse microflora, dominated by grass but including pollen of a vine found in semideciduous
(monsoonal) rainforest, is preserved in semi-lithified sediments at the base of a
palaeochannel of the Victoria River, Arnhem Land (M.K. Macphail unpubl. data). The
assemblage is presumed to be of Late Neogene-Early Pleistocene age.
Inferred climate
Macphail (1997b) suggests mean annual rainfall decreased from about 600-1500 mm to below
600 mm and/or became strongly seasonal during the latest Miocene. This drying trend was
maintained during the Pleistocene (Hope 1994).
5.2.2 North-East Australia
1. North-East Queensland
Evidence for Late Neogene climates in northeastern Queensland mostly comes from offshore
sites on the Great Barrier Reef or from the deepwater (>1000 m) Queensland Trough (Hekel
1972, Martin and McMinn 1993). Deposition appears to have been continuous, but the
microfloras will be strongly biased towards wind-pollinated gymnosperms (Neves Effect) and
riparian ferns. The only onshore Pliocene sediment known to preserve microfossils is a subbasaltic
deposit at Butchers Creek at 720m elevation on the Atherton Tableland (Kershaw and
Sluiter 1982). The combined data indicate the coastal vegetation was a mosaic of
Araucariaceae and angiosperm-dominated rainforest and sclerophyll types on the coast.
Possibly small stands of Nothofagus temperate rainforest survive in at higher elevations on
the Atherton Tableland.
2. Queensland Trough
Late Miocene to Late Pliocene microfloras recovered from ODP Site 815 at the southern end
of the Queensland Trough are dominated by Araucariaceae (Agathis) and Casuarinaceae with
lower amounts of Podocarpus-Prumnopitys, Cyperaceae and Cyathea. Frequent taxa include
Pteris, Dacrycarpus, Dacrydium, Gyrostemonaceae, Acacia, Asteraceae, Chenopodiaceae,
Dodonaea and Poaceae. Uncommon to rare taxa include Phyllocladus, Eucalyptus and
Nothofagus (Brassospora, Lophozonia). The site records a progressive decline in the relative
abundance of Podocarpus-Prumnopitys during the Late Miocene and Araucariaceae during
the late Early to Late Pliocene. The relative abundance of Asteraceae, Chenopodiaceae-
Amaranthaceae and Gyrostemonaceae increases over this period.
3. Atherton Tableland
Probable Late Pliocene microfloras from Butchers Creek are dominated by Nothofagus
(Brassospora) with more variable but high representation of Podocarpus-Prumnopitys,
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