NOTE THE AREA NEXT TO THE LAKE HAS BEEN FENCED OFF DUE TO POSSIBLE ASBESTOS FOUND IN THE SOIL. DO NOT ENTER THE FENCED-OFF AREA.
The National Capital Authority, which oversees land in the parliamentary triangle, released a statement "that it had sectioned off a significant portion of Acton Peninsula as a precautionary safety measure to protect the public from possible asbestos contamination. The results came back positive for asbestos within surface soils but negative for asbestos in the atmosphere, meaning it is not airborne and air quality is safe."
PLEASE LET ME KNOW IF ACCESS IS FURTHER RESTRICTED OR THE FENCES REMOVED
This cache is located at a limestone outcrop that is registered on the Commonwealth Heritage List. Please be careful when walking in the area and be sure to follow the 'Leave no Trace' principles so others can enjoy the area too. The bike path to the National Museum runs past this cache or you can choose to drive down and park at the National Museum and take a walk back to GZ.
The Acton Peninsula Limestone Outcrops are a significant group which extend 80-100m along the eastern shore of Acton Peninsula. Very little limestone is now exposed in the area and this limestone contains sparsely distributed fragmentary macro fossils of corals and shells, which makes this outcrop a special place to visit. The outcrop found here and along the Molonglo River is also interesting historically, as the limestone prompted British explorers to name the locality 'the limestone plains'.
Canberra's limestone was laid down 420 million years ago during the Silurian period when the region resembled a tropical, volcanic and shallow sea environment. These limestone formations became exposed when the ocean floor was raised by major volcanic activity in the Devonian period, which formed much of the east coast of Australia. The outcrop provides evidence of the underlying limestone - you are standing on a fossil coral reef on what is known as a karst landscape.
A karst landscape refers to a landscape underlain by limestone, which has been eroded producing caves, underground streams, fissures and sink holes. Caves are formed by the dissolution of limestone. Rainwater picks up carbon dioxide from the air and as it percolates through the soil, it turns into a weak acid, and this slowly dissolves out the limestone along the joints, bedding planes and fractures, some of which become enlarged enough to form caves.
Limestone is a sedimentary rock composed principally of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilized debris. Limestone is commonly white to grey in colour although limestone that is unusually rich in organic matter can be almost black in colour, and traces of iron or manganese can give limestone an off-white/yellow to red colour.
There are interesting records of Canberra's limestone caves and it's underlying karst landscape. Early Canberra settlers' records details of the Lennox House Cave, the only mapped and formerly accessible cave located nearby, below the Acton foreshore of Lake Burley Griffin. This cave is around eight metres deep and was once used as a rubbish tip. The cave was submerged when the lake was created by damming the Molonglo River in 1963.
To earn credit for this earthcache, send answers to the questions below to me via e-mail or messenger. The photograph must be attached to your log. You can log the cache immediately but need to follow up with answers within ten days. Your found log may be deleted if you do not send me answers or attach a photo to your log. I am happy to accept group answers as long as your message clearly sets out individual caching/team names.
Please email me information about the limestone outcrop you can see looking south at GZ:
1. Describe the colours you can see in this outcrop of limestone – what may have caused the limestone to be this colour?
2. How many years ago was the limestone deposited in this area?
Photo Requirement. Take a photograph at the location and include yourself and/or your caching name on a piece of paper/card and include it with your found log. Please make sure your photo does not provide answers for the above questions. Note: as per newly published earthcache guidelines, the photo is required to claim the find.