The oldest rocks in the South West region were formed between 3700 and 2400 million years ago. They are found in the Yilgarn Craton which is a huge piece of the Earth’s crust that underlies much of the South West. Molten magma found its way to the surface to be erupted or crystallised many kilometres below the surface. This was subjected to extreme temperatures and pressures and was transformed into various types of rock such as gneiss.
Between about 2000 and 1800 million years ago the Yilgarn Craton collided with the Pilbara Craton to form the West Australian Craton. This collided with other cratons to eventually form a supercontinent called Rodinia.
About 1100 million years ago another continent probably collided with the West Australian Craton causing a mountain range to be formed along the western edge of the Yilgarn Craton. The Darling Fault, which can be traced from Shark Bay down to the South Coast, marked the edge of this mountain range.
About 750 million years ago Rodinia began to break up into smaller plates.
About 500 Million Years ago these reassembled into a new supercontinent called Gondwana.
About 430 million years ago the Darling Fault became active again and formed an elongate trough called the Perth Basin. Over the next 300 million years this filled up with more than 10km of sedimentary rocks. Part of this time Australia was close to the South Pole and was covered with ice and glaciers and these played a part in eroding the landscape and depositing ground up rocks.
Following the separation of Australia from the supercontinent, the newly formed coastline of the South West was subjected to changes in sea levels. Sometimes it was covered with warm shallow seas rich in sponges and other organisms. Polar icecaps have expanded and contracted many times causing the sea levels to fluctuate. Belts of coastal sand dunes have followed this ever changing coastline and have been preserved as limestone in the cliffs around the South Western coastline. At the end of the last ice age, about 18000 years ago, sea levels began to rise. Islands and reefs offshore from here which were previously connected to the mainland, became separated.
To log this cache as found, please complete the following tasks and email your answers to fairwaydrivers.
Task 1. Look to the west and identify the four main islands offshore. One of them is very small, more of a rock than an island. Estimate how many times longer than Carnac Island is Rottnest Island. You do not need to be very accurate. Just look carefully and say what you think the relative sizes are.
Task 2.. What happened geologically about 18000 years ago?
Task 3. What is your altitude at this viewpoint?
Task 4. Look to the east and identify the Darling Scarp.If Curtin University is 13km away and Kings Park is 10.5km away. Estimate how far away the Darling Scarp is.
Task 5. Although not compulsory, it would be nice if you send a photo of you or your GPS at this view point.
REFERENCES: Iain Copp,2001 Geology & Landforms of the South-West