Australia: The Land Where Time Began

A biography of the Australian continent 

The arid areas of Australia are not good places for pollen deposits, they need permanent water bodies, lakes or the sea to accumulate. It has been found that the vegetation in the area around Lake Eyre was an open steppe, with chenopods, grasses and daisies, with some casuarinas and Callitris (Luly, 2001a & b) near the end of the last glacial phase. The vegetation prior to the this was not known because of the discontinuous nature of pollen deposition in arid areas. A marine core from a site, GC17, about 60 km from the Pilbara coast (van de Kaars & De Dekker, 2002) fills some gaps.  This core covers the last 100,000 years, but there is a gap in the record from about 64,000 to 46,000 BP.

At about 100,000 BP the vegetation was very similar to the present of open eucalypt woodland. A comparatively high rainfall climate is indicated by the presence of ferns, palms and aquatic species. Between 100,000 BP and 40,000 BP trees became sparser and water-loving plants declined. At about 45,000 BP there was a major change, chenopods became prominent members of the vegetation, until close to the LGM when chenopods decreased and grasses increased. The rate of pollen deposition was highest between about 80,000 BP and 75,000 BP, indicating high density of the vegetation. By about 20,000 BP the deposition rate, and presumably the vegetation density, had declined to a low point, after which the deposition rate, and so density, recovered to the 80,000 BP level by about 5,000 BP. Charcoal concentration declined from a relatively high level at the start of the sequence and declined to low levels towards the end of the sequence.

Excavations of the Carpenter's Gap Rock Shelter demonstrate an increase of spinifex and a decline of other grasses about 33,000 BP (Wallis, 2001, Plate 10), based on the recovery of phytoliths.

Sources & Further reading

• Mary E. White, The Greening of Gondwana, the 400 Million Year story of Australian Plants, Reed, 1994
• Chris Johnson, Australia's Mammal Extinctions, a 50,000 year history, Cambridge University Press, 2006