Isotope dating of rocks
Valley-fill deposits make possible the dating of these palaeodrainages.Late Eocene, 45-34 Ma lignitic deposits formed the valley-fills in the Kalgoorlie region. The same beds under Lake Lefroy and Lake Cowan, these beds are overlain by the 30 m thick Late Eocene Norseman Limestone marine sediments.Narryer and Jack Hill on the Yilgarn Carton in Western Australia that were 4276 million years old.Now, more recently, new detrital zircons were found in the same area with an age of 4404 /- 8 million years ago, which pushed back the age of the oldest known continental crust by about 130 million years. The latest find of zircon crystals also show oxygen isotope ratios that indicate that they formed in the presence of liquid water, and microinclusions of Si O indicate that they formed in molten granite, and hence continental crust.
Then detrital zircon crystals were found in metamorphosed rock at Mt.The granite of these outcrops is very weather-resistant, and hence erosion-resistant, both because the rock is very hard and because many of the outcrops are solid masses with few or no cracks or faults that the forces of erosion can work on.Because of this the erosion that does occur on them is mainly when they are buried and humic acid in the soil can eat at their sides and cause the undercut formations, as with Wave Rock, that only becomes visible when the soil level surrounding the rock has been lowered by erosion.The drainage systems that are present now developed after the glaciers had gone, a watershed runs about north-south, approximately down the centre of the plateau.
This watershed reaches about 600 m in the north and to 300 m in the south.
This event divided the drainage of the area affected into a coastal region, where the rivers still flow to the sea, and the Plateau region.