Australia: The Land Where Time Began

A biography of the Australian continent 

MacDonnell Ranges

The Macdonnells are close to the exact centre of Australia, and extend for 500 km in an east-west direction. They were formed by folding at least 1000 million years ago, but the sediments that comprise them are 1400-2400 million years old. They were originally about 4500 m high but after millions of years of weathering and erosion they are now only 400-500 m high.  

The first phase of the rise of the MacDonnell Ranges, including the Chewings Range and Harts Range, took place at least 1.0 billion years ago. These original ranges reached a height of about 4500 m. Erosion debris from the ancestral ranges was deposited in the nearby seas. About 500 Ma the next phase of folding raised the south-running ranges, parallel to the ancestral ranges. These include the George Gill Range, Krichauff Range and the Waterhouse Range. 

The final phase of folding occurred about 300 Ma. By this time the older ranges had been greatly reduced. For the last 300 million years there has been only minor uplift of the Macdonnells, but erosion has continued, removing the softer rock, the remaining exposed rock being in the form of folded ridges, separated by long, flat alluvial valleys. The Finke River and its tributaries cut gorges through the ridges during periods that were wetter than the present.

The surrounding plains are now about 600 m above sea level, the MacDonnells being about 400-500 m above that. The predominant rock of the ranges is red iron oxide-stained quartz. There are also strata composed of dolomite, limestone, sandstone, conglomerate, siltstone and shale. Because of the complex nature of their construction, the rocks have weathered into a variety of patterns. Along the walls of the valleys, the rock is in the form of a number of patterns, in places being scalloped layers of different colours, from reds to creams, and in other places the rocks are sharply fractured and of a rusty red colour.

In the Chewings Ranges are a pair of peaks of more resistant rock, Mt Liebig and Mt Zeil, both above 1,500 m, and some others are a bit lower, Mt Heughlin, 1450 m, Mt Edward, 1,480 m, Mt Sonder, 1334 m, and Mt Hay, 1,349 m.

Flora

For at least the last 20,000 years, the only surface water in the region is found in the gorges of this and other ranges, in the form of springs, rockholes and, in some places, larger pools. On the rare occasions when heavy rain in the headwaters puts enough water into the streams to reach as far as the Macdonnells the pools and rockholes are joined as part of a flowing stream, usually for a short time. The white sandy watercourses are lined with river redgums (Eucalyptus camaldulensis). In some of the shaded gorges there are also rare cycads (Macrozamia macdonnellii) that are believed to have grown in the area for about 200 million years.

There are a number of other trees found throughout the Macdonnells, including bloodwood (Eucalyptus terminalis), corkbark (Hakea suberea), ironwood (Acacia estrophiolata) and ghost gums (Eucalyptus papiana). The ghost gums grow on the flat, sandy and grassy areas, as well as on high craggy ledges.

The mulgas, and other acacias, are the predominant low trees in the area. The most popular with the local Aborigines was the witchetty bush (Acacia kempeana), as the witchetty grubs are found in its roots. For most of the year the groundcover is comprised of spinifex (Triodia species), T. clelandii and T. longiceps. There is a transient flourish of wildflowers after rain and in spring.

The scenery is most widely known through the paintings of the local Aboriginal artist Albert Namatjira.

Sources & Further reading

1. Hellen Grasswill & Reg Morrison, Australia, a Timeless Grandeur, Lansdowne, 1981
2. Penny Van Oosterzee, The Centre - The Natural history of Australia's Desert Regions, Reed Australia, 1993
3. Mary E White, Running Down, Water in a Changing Land, Kangaroo Press, 2000
4. Mary E White, After the Greening, The Browning of Australia, Kangaroo Press, 1994

Links

1. Bioregional Description