Melville's Stripey Shirt
!WARNING! - This site is on the 'Register of the National Estate' as a site of geological importance. Please DO NOT damage the feature in anyway. Take only photos and leave only footprints!
This earthcache takes you to Melville Point, on the beautiful south coast of NSW! Please be aware that this cache is located at a sea cliff and is subject to changes in tide which may limit access. Furthermore, there is a bit of a rock scramble around the headland to get to GZ so enclosed footware is advised! The Terrain rating reflects these topographical challenges. However, don't be put off as the effort is well-worth the reward 
Chert
The medium you will be working with here is chert, a fine-grained sedimentary rock which forms the fabric of Melvlle's shirt! Chert is a pretty broad term in geologist-speak, covering any form of microcrystalline or cryptocrystalline quartz. Basically, these are crystals of silica (SiO2) that are very very small. Because the crystals are so small, chert is a VERY hard mineral weighing in at a whopping 7 on the Mohs hardness scale (and trust me, if you happen to do this one barefoot, YOU WILL KNOW 
).
The hardness of chert has made it to a useful tool for millennia. If you happen to stumble across an iron-bearing surface, a few strikes with a piece of chert and you will have yourself a fire 🔥! Similarly, its lack of cleavage means that it conchoidally fractures and can be lithically reduced to form blades. Examples of these tools have been found all around the globe! This is because chert also happens to be exceptionally abundant. Chert is a siliceous ooze that occurs on the deep ocean floor, created by the compaction of petrified remains of fossils like diatoms, silicoflagellates and radiolarians. It is generally associated with other carbonate minerals, such as limestone, chalk, greensand and dolomite. Its these associations that determines its name (for example, when chert occurs with chalk or marl, it is known as flint).
Now Melville was a pretty fashionable fellow, and he likes his striped shirts in a wide variety of colours. But how can a simple matrix of silica vary in colour so wildly? Impurities of course! These impurities come in the form of trace elements; iron, manganese, copper, nickel, zinc, the REEs, the LILEs, HFSEs and of course the transition metals. But what you are most likely seeing here are impurities caused by lithophilic elements transported over the ocean as dust. In addition to creating the colours you see, the inclusion of the impurities can also increase or decrease the rate of weathering of the mineral. That is why there are some narrow fins of rock visible at the water's edge. Now if you worry about how your kids fold shirts, avert your eyes because Melville has made quite a mess of his chert. That's because this is part of the...
Lachlan Fold Belt
The Lachlan Fold Belt or Lachlan Orogen or even the Lachlan Geosyncline (depends if you remember the time before plate tectonics became an accepted theory) stretches from Queensland all the way to Tasmania and covers 200,000 km2. This geological subdivision hails from the middle Paleozoic, formed approximately 450 to 340 million years ago. What you are looking at is the Adaminaby Group, part of the Narooma Accretionary Complex. In addition to the chert present at Melville Point, there are also turbidites, breccia and volcanics. It is believed that this formation could either be an accretionary prism or the toe of a subducting plate.
However, for this simple chert, it was not the simple life of horizontality promised by Nicolas Steno. During the early Silurian era, the entire Narooma Accretionary Complex was deformed by the Benambran Orogeny. A major characteristic of the rocks in this area are the tight chevron folds that display a dextral shear. You can see examples of this in the cliff at GZ. Now Melville here doesn't know how to fold his shirt very well. The folds you see all over the shirt can actually be classified by their shape. When the fold resembles a ∩ shape, it is refered to as an anticline. Conversely, when the shape of the fold resembles a ∪ shape it is called a syncline. A common fold you will see at this site is the chevron fold, as mentioned above, which will have a pointed apex rather than a rounded one. There are also many parasitic folds present, which appear as smaller deformations within larger folds.
This brings us to the fun part...
Questions
- Follow the bands to the water's edge, which colours appear to be most resistant to weathering?
- Look east from GZ, do you see an anticline or syncline at the point of the headland?
- Take a photo with yourself (or GPS) and your favourite fold in the rock face. Please do not use the one mentioned above, it is quite obvious but there are plenty of other folds at this site! Include this photo with your log.
Please send the answers to these questions to me via email or messenger. However, you need not wait for a reply. I will contact you if there are any problems.
Enjoy!