The earliest archaeological evidence that ochre was used in Australia was found at Lake Mungo (NSW) where the body of a man coated in red ochre was found. His death occurred over 30,000 years ago. Ochres are amongst the earliest pigments used by mankind derived from naturally tinted clay containing mineral oxides. Chemically, ochre is hydrated iron oxide. Mineralogically, it is known as limonite.
Aboriginal people have extracted ochre from these pits for thousands of years. It is still used by the Western Arrernte people, mostly for ceremonial purposes.
The colourful curves and swirls of the soft-stone tell a story rich in tradition and geology. These fragile cliffs represent millions of years of geological history. They date back to a time when the MacDonnell Ranges were submerged beneath a massive but shallow inland sea.
Step 1:
Formation of the Amadeus Basin
As the sea deepened layers of mud and sand were deposited. These sedimentary layers, known as the Amadeus Basin, caused deposits in the pile to be compacted into solid rock.
Step 2: A great upheaval occurred
About 300 million years ago the earth heaved and rolled in a spectacular episode of mountain building pushing the MacDonnell Ranges to heights comparable to the present-day Himalayas. The sediments which had been laid down in horizontal layers were thrust upward to their present, near vertical position.
Step 3:The effects of erosion
Over time wind and rain have carved into the vertical layers to reveal dramatic swirls and curves of colour. The different layers in the 10 metre high cliff face represent mudstone and siltstone. Varying minerals give the ochre its different colours. Tiny fragments of mica and quartz give the ochre its shiny quality.
You may log this Earthcache straight away but then please email your answers to the questions to the CO. We will contact you ONLY if your answers need extra work. Logs with no answers sent will be deleted. The answers can be found by observing the landscape, reading the information boards and a bit of research. Please do not post your answers in your log.Photos of you at the pits are most welcome.
Q1. What is ochre?
Q2. How many years of geological history is represented at this site?
Q3. How thick was the Amadeus Basin at its deepest point?
Q4. Which minerals/rock types cause yellow, red-brown and white ochre?
Q5. Walk to S 23 44.026 E 132 52.143. Turn to face the rock wall. Describe what you can see.
The area is geologically fragile and taking, breaking or digging the ochre carries a $5000 penalty.
Remember to take only photos and leave no trace of your visit. We hope you enjoy your visit to this remarkable Australian geological formation.
FTF - Congratulations to redcentredazza on 27/7/2013.