Australia: The Land Where Time Began

A biography of the Australian continent 

Great Dividing Range About80 Ma

This range extends along the entire east coast of Australia. It arose in the Late Cretaceous, making possible the charging of the Jurassic sandstone that became the Great Artesian Basin. The Divide and Escarpment range for tens of km to hundreds of kilometres from the coast. It reaches about 700 metres in parts of New South Wales to 1000 m in the north, and to the south it rises to 2230 m at Mt Kosciusko. In the Miocene there was an major episode of faulting that raised a block by up to a kilometre in this section of the range.

The Great Divide rose about 80 million years ago when the Tasman Sea formed, as the New Zealand Subcontinent rifted from the eastern coast of Australia, beginning about 96 million years ago. The watershed was formed by the progressive upwarping of the edge of the continent, tens of hundreds of kilometres inland from the new continental margin

The Gourock Range, though part of the Divide, appears to be much older than most of the Divide. It is here that tributaries of the Murrumbidgee River and Upper Shoalhaven River arise. They flow down opposite sides of the range and characteristics of the beds have led geologists to believe they are ancient rivers. In some parts of the range headward stream migration, erosion of the tops of the range, has produced sharp ridges. In some places plateaus have been isolated from the Divide by erosion. This has occurred with the Bulga Plateua and Comboyne Plateau. West from the Divide mostly flat plains descend to central Australia. To the west of the divide are the tablelands. Here ancient landforms are preserved in places.

Episodes of volcanism have emplaced blocks of basalt at various parts of the ranges, with accompanying uplift. The order of formation of both the Divide and the Escarpment, that has been suggested are: plain erosion, major river pattern initiation, emplacement of basalt in widespread places along the region, uplift and formation of the Divide and retreat of the Great Escarpment

The Great Escarpment About 80 Ma

Ranges running along east of the Great Divide for most of the length of the Divide. To the east is the coastal lowlands and tablelands to the west. It reaches a height of several hundred metres.  The Great Divide and the Great Escarpment both were thrust up by pressure from the spreading plates as New Zealand rifted from the east coast of Queensland. The escarpment has formed by retreat as the edge of the upwarped crust, (scarp retreat) have eroded.

Sources & Further reading

Mary E White, After the Greening, The Browning of Australia, Kangaroo Press, 1994

Author: M. H. Monroe
Last updated 30/09/2011


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