Australian Geology

Australian geology is very interesting.
Australia is the world’s oldest, flattest and driest populated continent.
The main reason for its fantastic landscape and impressive rock formations is its geological stability.


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Australian Geological Stability
Away from tectonic plate boundaries, volcanoes don’t erupt and mountain ranges don’t rise. In contrast to the neighbouring geologically active New Zealand, Australian continent hasn’t changed, other than eroded, since the uplift of the Great Dividing Range 80 million years ago.


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This geological stability has given erosion a lot of time to flatten the land and expose some of the world's oldest rocks and most strange rock formations, like Twelve Apostles in Victoria, Remarkable Rocks and Murphy’s Haystacks in South Australia, pinnacles in Nambung National Park and Wave Rock in Western Australia; and Devil’s Marbles, Kata Tjuta and the world’s largest monolith Ayers Rock in Uluru Kata Tjuta National Park in the Northern Territory.


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Australian Red Desert Soil
These fantastic rock formations are often surrounded by the reddest soils you have probably ever seen. It’s so beautiful and it makes the whole landscape so colourful, particularly when the sun sets.


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So why is it? Why is it that in Europe the soils are black and in Australia they are red? It’s because of the climate. Soil is the product of rock erosion, and the erosion is caused by weathering. In cold climate, like in Europe and most of the North America, the main form of weathering is physical, such as jointing, frost wedging, and in places the impact of ancient glaciers. In hot climate like in Australia and in south-eastern USA, the weathering is chemical. Reactions like hydrolysis, hydration and oxidation happen – and the red colour is a result of oxidation, more exactly – iron oxides, just like rust.

History of Australian Geology

Australia in the Geological Time Scale
During most of the Precambrian Eon all the world's continents were joined in the supercontinent Pangaea. At the end of Precambrian, Pangaea broke up and formed two different supercontinents - the northern Laurentia, and the southern Gondwana. Australia was part of Gondwana continent roughly from Cambrian Period until the end of Mesozoic - the era of dinosaurs (it started breaking off in the Jurassic Period and was completely separated only during the Cenozoic Era).


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Australian Geology during Precambrian
Precambrian is the oldest eon in the Earth's history, and Australia's oldest rocks are some large old shields (cratons) in South and Western Australia. Australian precambrian rocks also contain some large orebodies and some evidence of glaciation. Western Australia's famous stromatolites and Banded Iron Formations also originate from this time.


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Australian Geology during Phanerozoic
The next eon, Phanerozoic, started with Cambrian Period evolution when an amazing amount of species evolved during only a few millions of years, something that came to be called the , and the rocks we have from this period suddenly showed a big change in fossils. It was a big step in animalCambrian Explosion. The eastern third of Australia was under the ocean, and shallow seas covered much of central Australia, where many Cambrian fossils can be found in sedimentary rocks in places like MacDonnells Ranges in Northern Territory and Flinders Ranges in South Australia.


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During Ordovician, the eastern third of Australia was still under the ocean, although Cape York and Gulf Savannah had emerged from the water. Across central Australia, a shallow sea called Larapinta Seaway crossed the continent from west to east and divided it to a southern and a northern half. In the south, near Canberra, volcanoes were erupting.


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During Silurian, the uplift of eastern Australia continued and most of Queensland now emerged from the water while New South Wales, Victoria and Tasmania remained under the water. In central and Western Australia, sand dunes formed and sediments were laid, that later turned to sedimentary rocks that carry the first evidence of an animal on the land in Australia.


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During Devonian, eastern Australia emerged from the water, and there was a lot of volcanism in Victoria, New South Wales and eastern and north Queensland. In Western Australia, sediments that later formed the limestones and sandstones of the Kimberley region were deposited.


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Carboniferous period was named after the carbon-bearing coal deposits that formed in the Northern Hemisphere where the climate was much warmer than in the southern Gondwanaland. Fossils from these times represent a cold climate flora and fauna with no coral reef. Australia was freezing cold, covered in ice and geologically active with a lot of volcanism. It was during this period as Australia's youngest mountain range, the Great Dividing Range, was formed.


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In the end of Permian Period the climate got warmer and after Permian Extinction - the world's largest mass extinction where 80% of species were wiped out, it was time for the era of dinosaurs. It was the Mesozoic Era and Australia continued being geologically active throughout it, with active volcanism, and the climate continued being warm and tropical.


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Mesozoic started with the Triassic period and the first - Triassic - dinosaurs. However, it was only the beginning of dinosaur history and there were not so many types of dinosaurs.


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But Jurassic was really the time when the dinosaurs evolved into many different species and there started to be many different types of dinosaurs.


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During the next, Cretaceous period, there were a lot of different species of dinosaurs, but the end of the period saw another mass extinction - the famous extinction of dinosaurs.


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Only after that did the mammals get a chance to start flourishing, and Cenozoic is the era of mammals. Only now did Australian geology become inactive (volcanism also stopped with the exception of Glasshouse Mountains). And it was only now that Australia was completely separated from Gondwana continent.

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