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Life on land

“The hot desert sun has turned to autumn and is gentler now. It is here that the water is still deep and cold. The Pied Butcherbird welcomes us with her song”.

Peter Hylands

April 30, 2023

Blue sky, red earth. This is Central Australia, the Red Centre coloured by oxides of iron, covers two million square kilometres, and we are in the West MacDonnell Ranges (Tjoritja) and Ellery Creek, as it is known today, stretches out before us. The Red Centre comprises the Simpson Desert, the central ranges and the rangelands surrounding Alice Springs which stretch to the Tanami, Great Sandy, Gibson and Great Victorian Deserts to the west.

In deep time some 1850 to 1800 million years ago mountain building events occurred throughout Central Australia, these early mountains were formed from granite intrusions as molten lava was forced upwards from deep below the Earth's surface, forming vast domes just below the surface.

The Petermann Orogeny

What we see now is this ancient land eroded by time, by water, by wind and by sand. Once these mountains were 10,000 metres high, the great movements of the Earth’s tectonic plates some 600 million years ago created squeezing pressure from the north and south, the major mountain building event known as the Petermann Orogeny, created mountains to the south side of the Amadeus Basin, the great inland sea.

The Alice Springs Orogeny

A further mountain building event occurred between 400 and 300 million years ago, the Alice Springs Orogeny, folded the deep sedimentary layers to heights above sea level. This material is what has formed the very beautiful Uluru and Kata Tjuta which are the tips of folded strata that extends deep underground.

The geological history of this place is revealed in detail.

An ancient land

This is indeed an ancient land, what was once a desert became a shallow sea. Around 1700 million years ago streams originating in mountains to the north carried vast amounts of sediments here, depositing them in the shallow seas of the time. These deposits are now sedimentary rocks known as Chewing Gum Quartzite.

We are standing in a place in the southern part of what is now the Northern Territory of Australia which was once a vast inland sea. Over a period of 500 million years or so a complex set of sediments, some quartz rich, were deposited before the waters retreated around 410 million years ago.

It is the combination of the layers of sediment, cracked and turned on edge by the dynamic movement of the earth, as the mountains were formed, and the subsequent erosion by wind and water that have created the spectacular formations and landscapes that surround us.

The Heavitree Quartzite around us, mostly quartz sand cemented by silica, was formed more than 800 million years ago as the sand was compacted to form a rugged sandstone of interlocking quartz grains, more resistant to erosion. As the inland sea became shallower and turned to a series of inland lagoons, Stromatolites flourished. The lime rich muds of the drying lagoons formed dolomite and the silts formed siltstone. The low spinifex covered hills to the south of where we are standing show off their ancient dolomite along the higher outcrops of the range. 

Erosion occurred during the ice ages of around 750 and 625 million years ago as glaciers split and churned the rocks to form vast deposits of pebbles, rock powder and larger boulders. As the ice melted, at 600 million years ago the inland sea became deeper and with it came far more complex life forms which included jellyfish.

The Amadeus Sea existed in its various states of shallow and deep, saline and hyper saline for 500 million years covering a vast area of Central Australia. The inland sea deposits contain many fossils and their tracks. The ancient movements of living things recorded on the sea floor as these animals went about their lives so long ago.

So these are the stories written in the land and preserved in the rocks that we see around us. Today there is a new beauty formed by nature and time.

There are of course ancient and wise cultures here, who understand this land in its many layers and in its power and ancient resilience.

We stand silently contemplating the world around us.