The spectacular shapes of Uluṟu (Ayers Rock) and Kata Tjuṯa (The Olgas) dominate the surrounding desert and are the culmination of geological events stretching over hundreds of millions of years. Uluṟu is the exposed tip of a huge vertical body of rock. This rock extends far below the surrounding plain, probably for several kilometers, as an integral part of the earth’s crust.
The traditional Aboriginal owners, Aṉangu, regularly visit Uluṟu and Kata Tjuṯa and both sites remain important in the cultural life of the Pitjantjatjara and Yankunytjatjara people. Many features of Uluṟu and Kata Tjuṯa are an integral part of the ancient Aboriginal culture and some are so sacred that only Aṉangu can visit them. Tjukurpa is the word used by Aṉangu to describe the laws that give meaning and order to all aspects of life. The Tjukurpa provides explanations for the origins of life and all living things as well as features of the landscapes.
The science of geology is similarly based on sets of rules, but the interpretation of the origin of the landscape and its features is very different from those of the Tjukurpa.
It is estimated that Earth formed about 4.54 billion years ago. During the long period between 800 million and 350 million years ago, a shallow sea covered much of southern, central and northern Australia. This vast sea is known as the Centralian Superbasin, and is a depression in Earth’s crust, which received copious amounts of sediment from the adjacent landmass. The preserved part of the Superbasin is referred to as the Amadeus Basin.
At the time the Centralian Superbasin formed, some 200-250 million years before the Uluṟu and Kata Tjuṯa sediments were laid down, Australia did not exist in its present form. It was part of a supercontinent called Rodinia, which assembled from various older continental fragments between about 1100 and 900 million years ago. Subsequently, Rodinia began to break up again, and the continental fragments were widely dispersed. Tens of millions of years later, many of the fragments began to move together again and by 530 million years ago they had coalesced and welded together to form the well-known southern supercontinent, Gondwana. About 550 million years ago, as the sands and gravels that make up the rocks at Uluṟu and Kata Tjuṯa were laid down, Antarctica was attached to the southern margin of Australia, and India and Madagascar lay to the southwest. A northeast-trending line through Adelaide marked the edge of a deep ocean. West of that line, shallow seas covered vast areas of southern, central and northern Australia. These were not inland seas but the marginal parts of seas that were open to the precursor of the Pacific Ocean to the east.
About 570 million years ago, in the late Neoproterozoic just before the beginning of the Cambrian Period, a zone within the Centralian Superbasin that now forms the southwestern margin of the Amadeus Basin was raised above sea level, ending the widespread sedimentation in that area. The rocks were squeezed, crumpled and buckled into folds ranging up to kilometers across, and fractured along huge faults. This geologic episode is called the Petermann Orogeny and it affected all of the region west and south from Uluṟu into Western Australia and South Australia.
During the Petermann Orogeny, 550-530 million years ago, the uplifted land formed a substantial mountain range – sometimes called the Petermann Mountains – which was subjected to very rapid erosion. The sedimentary rocks of Uluṟu and Kata Tjuṯa are the products of this rapid erosion, and they represent a new phase of development of the Centralian Superbasin. Although the rocks at each place look different, in each case they are typical of deposits laid down by very high energy rivers, or by sheet floods on alluvial fans. The difference in character between Uluṟu and Kata Tjuṯa is best explained by deposition on different river systems or alluvial fans.
A new period of folding, faulting and uplift, more widespread than the Petermann Orogeny began aroun 400 million years ago, and it continued, with some pauses, for around 100 million years. In this ‘Alice Springs Orogeny’ the thousands of meters of younger sedimentary rock that had built up were strongly folded and faulted, much like those around Uluṟu and Kata Tjuṯa. Their eroded remains are visible today as the many ridges of the MacDonnell Ranges, Kings Canyon, and numerous other hills and valleys in the region.
Uplift during the Alice Springs Orogeny raised much of central Australia above sea level. Then began a long period of erosion. The area that is now Uluṟu-Kata Tjuṯa National Park has remained above sea level for virtually all of that time – some 300 million years – although the sea may have briefly encroached from the east some 100 million years ago during the Cretaceous Period, a time when sea levels were at their highest and dinosaurs ruled the Earth.
Initially the land surface was much higher than the top of Uluṟu and Kata Tjuṯa. As erosion continued, the ancestral forms of Uluṟu, Kata Tjuṯa and Mount Connor would have appeared as part of a chain of uplands separated by broad valleys. Uluṟu and Kata Tjuṯa probably resisted erosion as a result of compression during the Petermann Orogeny, so that the rocks having relatively fewer fractures were less susceptible to weathering than the surrounding rocks. Once Uluṟu and Kata Tjuṯa emerged from the surrounding countryside, albeit broader and higher than they are today, their domes would have shed water and accelerated the erosion at their margin.
The magnificent sculptured shapes of Uluṟu and Kata Tjuṯa are the product of million of years of weathering and erosion.
It turns out that Tjukurpa says that you can only learn about ancient Aboriginal culture at the actual location where the story took place. So you’ll have to visit Uluṟu-Kata Tjuṯa National Park and go on the ranger led tour (the highlight of the day!) to learn about the place.