Geomorphology of Charles Darwin Reserve

Charles Darwin Reserve is a remnant of one of the most ancient landscapes on Earth. It lies within the Yilgarn Craton of Western Australia which has an exposed area of 657,000 km2, 80 per cent of which is composed of granites, volcanic and sedimentary rocks. The remaining 20 per cent is composed of gneisses, strongly banded granitic rocks that were formed under extreme pressures and temperatures.

Yilgarn Craton

The Yilgarn Craton rocks are of Archean age, ranging from 3,700 to 2,600 million years old. They were formed though the joining of several smaller pieces of crust.

The oldest rocks of the Yilgarn Craton are remnants of early sedimentary crust deposited some 3,300 million years ago. They metamorphosed into the Western Gneiss bedrock. Volcanic lava from 2,700 million years ago formed the greenstone belt now mined for gold, and the intrusion of granites which form the outcrops seen today.

The last glacier dates back to Gondwanaland some 280 million years ago, about 160 million years before Antarctica and India started splitting from Australia.

Huge rivers formed the paleodrainage channels, now the ‘moat’ of salt lakes surrounding our ‘island’ which drain out through the Yarra Yarra Lakes system and into the Moore River, when it rains enough to flow.

This lack of flow allowed the salt from rainfall to accumulate.

The Archaean crystalline basement in the north-east of the Yilgarn Craton eroded to a subdued peneplain earlier than 1,800 million years ago, with a topography similar to today. The whole region was then glaciated during the Carboniferous to Early Permian (about 280 million years ago) when a continental ice sheet about 3-5 km thick covered Gondwanaland 'planed off' the pre-existing land surface. Possibly, valleys would have been created beneath the ice sheet from melt waters.

There has been minimal erosion of the Yilgarn Craton at least since the Jurassic/Cretaceous. Thus the landscape appears to have been moderately stable since the age of the dinosaurs.