Australia: The Land Where Time Began

A biography of the Australian continent 

Zanthus 6 Coal Project Bore

This site is a Late Eocene lignite sequence near Balladonia on the eastern edge of the Eucla Basin. Pollen and spore flora of the formation displays a diverse range of plants. It has ferns, conifers and angiosperms. There are 10 species of Nothofagus that comprise 35-58 % of the sample dominating the assemblage. These Nothofagus species are mostly of the bassii pollen type, the fusca type being rare and the menziesii are absent. Among the Gymnosperms were celery-topped pines (Phyllocaldus). Among the Angiosperms CASUARINAACEAE makes up 30 %, 4-16 % are PROTEACEAE, being very diverse. There is also pollen from grasses and Acacia, and SPARGANIACEAE (burr rushes). A swamp type environment is suggested by the presence of CYPERACEAE and horsetails (Equisetum). The assemblage here resembles one from the Wilkinson 1 Bore in the Pidinga Formation in western South Australia.

Acacia appears later at some other sites, the Late Oligocene in the Murray Basin and in the Miocene in the Gippsland Basin. Sedges don't appear in the eastern Australian floras until the Miocene, but they were widespread in the southeast Eucla Basin, the St Vincent Basin and the Lake Eyre sub-basin of South Australia, and in the Eocene at Napberby in Central Australia.

Other bores in the Eucla Basin and Bremer Basin show the same Nothofagus abundance and very diverse PROTEACEAE. Of the PROTEACEAE, the sclerophylls included genera such as Stirlingia and Adenanthos (blueboy and woollybush). These and others generally evolved in the rift zone that formed as Australia separated from Antarctica. 33 of the 39 species of Stirlingia are still restricted to the southwest of western Australia, in association with dry sclerophyll or heath vegetation types.

The forest type represented by these floras have no analogous forest types in present-day Australia. They are mixed like no present forests, being composed of species associated with cool temperate, sub-tropical, many conifers and ferns, and both sclerophyll and broadleaf angiosperms.

The degree of mixing found at this time, with the abundance of southern beech and much different composition of other plant types, is in accord with other evidence of climate change during the later Eocene. The Middle Eocene was subtropical, but during the Late Eocene the ocean temperatures around Australia dropped by about 5o C. Later in the Eocene the cooling trend was reversed.

Eastern Australia also had an increase of Nothofagus during the Middle Eocene, indicating the temperatures were dropping. The vegetation suggests that rainforest with no seasonal dry period, and rainfall of 1500-2000 mm per year, were present at the time. During the Late Eocene, the southern parts of South Australia had a cover of rainforest with many tree-ferns, ferns, mosses, and peat moss -Sphagnum.

Around the more inland Lake Eyre, the climate is believed to have been drier and probably seasonal.   Nothofagus and podocarps were much less common. There were many CASUARINAACEAE and there was a lot of pollen from CUPRESSACEAE - the native cypress pine (Callitris) in the Middle to Late Eocene in Central Australia. This pollen doesn't appear in southeastern Australia until the Miocene to Pliocene.

Sources & Further reading

  • Mary E. White, The Greening of Gondwana, the 400 Million Year story of Australian Plants, Reed, 1994
  • Mary E White, After the Greening, The Browning of Australia, Kangaroo Press, 1994
  • Penny Van Oosterzee, The Centre - The Natural history of Australia's Desert Regions, Reed Australia, 1993
 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading