A few weeks back I went to a place called Putty beach in Bouddi National Park with my family and very close friends. The beautifully coloured sandstone rocks fascinated me and I started doing some research on it. I had a whole bunch of questions.
What are these?
What is the origin?
When were they formed?
What gives it the colour?
These rocks are part of the Sydney Sandstone Basin, commonly referred to as the Hawkesbury Sandstone. Sydney sandstone was deposited in the Triassic Period in a fluvial delta. So, these rock formations date back to 200 – 250 million years, a time before our commonly known dinosaurs like T-Rex even existed. The mere thought of how the world would have been during that time is quite fascinating to think about. A water body which existed over 500 million years ago, created these rocks which subsequently went through so much transformation to result in what we saw there, a beautiful red-brown feast.
These rocks are forms of grains of sand which are quite amazing to look. The stone is porous and is supposed to act as a filter. It is made of very pure silica grains and a tiny amount of iron all held together by clay. The concentric bands of red and brown is a result of oxidation of the iron caused by rainfall. It cuts all the way through the rocks. So, it is not the colour of the deposit or the age which causes the bands, which was what I originally thought. I cannot fail to appreciate the impact of natural forces and time involved to create the beautiful sight.
The Sydney basin comprises of the igneous rocks from the Permian period(250 – 300 million years ago) and the different types of sedimentary rocks from the Triassic period (200 – 250 million years ago).
Here is an article which shares some context of what happened during the Triassic Period in general.
http://www.livescience.com/43295-triassic-period.html
In the course of understanding these, I found a lot of interesting literature available in public domain. I have given the links below for anyone interested.
http://www.blandfordia.org.au/wtdownloads/Topic%2010%20Geology%202011.pdf
Click to access engineeringGeologyOfTheTriassicRocksOfTheSydneyArea.pdf
http://dbforms.ga.gov.au/pls/www/geodx.strat_units.sch_full?wher=stratno=8165
https://australianmuseum.net.au/the-sydney-basin
Demystifying a skeptic's world 