Geology of the ACT
The ACT began to form many millions of years ago, underwater, during the time known as the Silurian Period. During this time there were mass extinctions of marine life and some of these fossilised creatures are present in other earth caches in the ACT. The most predominant of these, GCHKCK, features many fossilised brachiopods, as well as bryozoans and trilobites like those seen in the picture below.
Most of the younger rocks in Canberra were formed through volcanic eruptions and pyroclastic deposits. The Yarralumla formation is different. It was formed about 425 million years ago and is predominantly made up of sedimentary mudstone or siltstone. This final stage of marine sediments is represented by the Yarralumla Formation of which the Deakin Anticline is a part. The Yarralumla Formation consists of a classic sequence of calcareous and tuffaceous mudstone and siltstone with minor interbeds of limestone and quartz sandstone. The Yarralumla Formation extends throughout the Woden Valley and exposures can be seen at the Yarralumla Brickworks and also here at the Deakin Anticlines. If you look around here at the anticlines you may even see some of the quartz and other calcareous rocks.
How are anticlines formed?
An anticline is a fold that is convex up and has its oldest beds at its core. As seen in the picture to the left, an anticline is formed from compression from the left and right. An anticline is a fold that is arched upward to form a ridge. A syncline is a fold that has arched downward to form a trough Anticlines and Synclines are made up of rock units that have been folded the same way. The tip of this fold is called the nose. An anticline that is joined to another anticline by a limb is always separated by a syncline and vice versa. This forms a sort of wave pattern as seen below.
There are different types of anticlines. These include; Structural domes, doubly plunging and faulted anticlines. Doubly plunging and faulted anticlines are favored for oil and natural gas drilling because they often contain rich reserves.
The Deakin anticline
The Deakin Anticline as it appears today is a product of ancient crustal forces which has been exposed by quarrying activities during the late 1940s and early 1950s. When the Commonwealth Brick Works was established at Yarralumla it required supplies of clay shales suitable for brick manufacturing. The anticline is surrounded by white bark native gum trees and non-irrigated native grasses. There are two anticlines and a syncline in the Deakin anticlines as in the one below.
To log a find
To log a find e-mail me with the answer to these questions:
1. What is the altitude of the listed coordinates?
2. What is the highest point on the anticlines? (metres)
3. What is the lowest point on the syncline? (metres)
Location 2
1. How many horizontal lines on the rock outcrop?
2. Which one is the longest? (include length)
Sources
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