the prevailing geological feature … is the great abundance of … sandstone … The sterility of the country … has been frequently noticed in these volumes. …
A deposit, upwards of 1200 feet thick, forms the Blue Mountains … although declining towards the sea at … at an angle of about 10 with the horizon ; yet it is traversed by ravines, which increase in depth, in proportion as the sandstone attains a greater elevation, and present perpendicular crags and cliffs of a very remarkable character.
These ravines were carved out from the end of the Triassic, 201 million years ago, when the Blue Mountains started to rise and the Cumberland Plain to descend, at the Lapstone Fault. The sandstones around what is now Sydney Harbour were pushed upwards as well. During the Jurassic which ended 145 million years ago, these ravines cut back into the mountains. Erosion also gouged out the gorge that became Sydney Harbour after it was drowned by rising seas.
Fossils show that Araucarias (hoop and bunya pines) Agathis (kauri pines) and Wollemia (Wollemi Pine) diverged from a common ancestor after the ravines had dissected the sandstones. At this time, the Blue Mountains were in southern Gondwana - with a cool moist climate. The most recent ancestor of Agathis and Wollemia in the fossils is 110 million years old. Genetics suggest that they diverged during the Cenozoic which began about 60 million years ago. A molecular study indicates that they diverged only 18 million years ago, when volcanic basalt flows were covering some sandstones in the mountains. One remnant flow is the basalt cap now known as Gospers Mountain.
Wollemi Pine, dubbed the Dinosaur Tree, appeared after the Cretaceous – Tertiary mass extinction 66 million years ago. Nevertheless, it survived millions of years of natural climate change as Sahul (New Guinea, Australia and Tasmania) broke away from Gondwana and 'drifted' north, becoming hotter and drier. The deep easterly ravines, now containing a hundred odd surviving Wollemi Pines, were a perfect refuge, providing shade and shelter from the sun and from drying winds and lightning fires.
People arrived in Australia at least 65,000 years ago, and by 40,000 years ago they had taken control of fire and changed vegetation across Australia. For example, on the Atherton Tablelands, Aboriginal burning converted Araucarian dry rainforests into grassy, eucalypt woodlands. Charcoal deposition (from biomass burning) declined with increasing aridity, as the last ice age advanced.
The oldest known Aboriginal site in the Blue Mountains is 22,000 years old. It has art galleries under overhangs and rock slabs used to grind stone axes. About 12,000 years ago, extreme climate change brought a massive rise in sea levels when the ice age ended. Tasmania was separated from the mainland, and then, New Guinea. Gorges in sandstone country east of the mountains were flooded and became Broken Bay and Sydney Harbour. Coastal areas where Aborigines lived are now part of the continental shelf under the Tasman Sea.
Rainforest reinvaded the Atherton Tablelands as climate became warmer and wetter. Charcoal deposition increased as Aborigines tried to maintain country. When it became too wet to burn, charcoal declined to low levels. A genetically distinct race of pygmies developed in the extensive tropical rainforests of north Queensland. The new soft-leaved rainforests were protected from wildfires by mild fires lit by Aborigines in open grassy woodlands.
There seems to be only one sediment core from the Blue Mountains that extends as far back as the earliest known Aboriginal site. This record of vegetation and fire around Mountain Lagoon was analysed by a university student in a B Sc thesis that was never published. I suspect that it challenges prevailing academic wisdom. Otherwise, it would surely have been the basis for a Ph D and copious scientific publications. Anyway, it seems that Aboriginal people maintained the Blue Mountains in an open, healthy, safe and productive condition for at least 20,000 years before explorers were disappointed by their sterility.
Whitefellas progressively occupied and developed grassy sites with more productive soils on shales, or particularly on basalts. For example, 80 acres around the fairly remote Uraterer Mountain were allocated to Robert Gosper as a Conditional Sale in 1877. An adjoining 100 acre block was a Conditional Purchase by Clive Pickup in 1907 and another 300 acres adjoining both blocks were alienated from the Crown later on. Uraterer Mountain became Gospers Mountain in 1970.
Wilderness guru Myles Dunphy assembled an elite group of city-dwelling bushwalkers – the Mountain Trails Club – in 1914. They formed the National Parks and Primitive Areas Council in 1932 to lobby government to establish national parks as exclusive playgrounds for a privileged few. Blue Mountains National Park was secured in 1959. After the National Parks and Wildlife Service was established in 1967, Colong Foundation took on the mission for wilderness.
NPWS acknowledged that wildfires were more frequent and less intense in the sandstone country prior to 1970, when 'strategic' burning with general fire suppression was introduced. Reduced frequency and increased intensity of fire resulted in scrub development, impaired access, reduced floristic diversity, disease and a self-perpetuating regime of high intensity fires. Wollemi National Park was gazetted in 1979.
Discuss in our Forums
See what other readers are saying about this article!
Click here to read & post comments.
7 posts so far.