Black Head at Gerroa on the South Coast of New South Wales provides a very interesting geological site.
Out on the headland jutting into the Tasman Sea you can find one of the best fossil sites around. The headland is often used for geological excursions and there are other interesting geological features apart from the fossils however these do not form part of this EarthCache.
Fossils
Fossils are the remains of once living animals and plants. We can find out much about our history by examining fossils.
Normally when a plant or animal dies it rots away to nothing. Sometimes though when conditions are right it may be fossilised.
The process of fossil formation can generally be explained in five steps; 1. A plant or animal dies and the skeleton sinks to the sea floor and is buried by sediment 2. Over time the sediment turns into stone 3. The skeleton then dissolves and a mould is formed 4. Minerals crystallise inside the mould and a cast is formed 5. The surrounding stone is worn away and the harder crystallised minerals are left exposed, ready for us to examine the remaining fossil.
The Black Head site
The Sydney Basin
For 80 million years a huge amount of sediment was deposited in the Sydney Basin, starting 270 million years ago. In many places, such as here, the sediment entombed the remains of animals and plants that lived all those millions of years ago, and preserved them as fossils. The sediments of the Sydney Basin belong largely to two geological periods; the Permian, 300-250 million years ago, and the Triassic, 250-205 million years ago. This EarthCache site is situated on part of the basin where the older Permian rocks come to the surface and as such is around 250-300 million years old.
Permian Fossils
The Permian rocks in the Sydney Basin contain two different and generally isolated groups of fossils. Firstly, there are marine invertebrates (shells, corals and echinoderms). Secondly, there are plant fossils associated with rocks that contain coal (coal is actually very concentrated plant fossils).
Animal Fossils of the Permian
The most common marine animals of the Permian are the brachiopods, a group of hinged-shelled invertebrates. The brachiopod, Martiniopsis, is very common. Bivalve molluscs such as clams, mussels and oysters were also common; one example is Myonia. There are also fossils of gastropods (snails) such as Keeneia, echinoderms represented by crinoids (sea lilies), and more rarely starfish.
Bryozoans or moss animals (sea ferns and sea mats) are sometimes very abundant as fossils with the two common types, being fenestellids and Stenopora. Corals are not too common but a solitary rugose coral (cone coral) Euryphyllum is well known.
Very few vertebrates are known from the Permian. The only ones are fish and a couple of salamander-like amphibians.
Finding the fossils
Once at GZ you’ll have to start hunting around down on the ground. The fossils are mainly marine life such as sponges and shells. There are quite a number of different spots so take a little while and explore the area until you find a fossil or two. The more time you take to look should result in the more fossils found. They vary in size- there are some small ones but you shouldn’t need to look too hard as some are up to 15-20cms across.
Of course it goes without saying that the fossils should only be looked at, not broken off or taken. “Take nothing but photographs and leave nothing but footprints” is a good adage for this site.
Take it easy near the sea and keep an eye on the waves although sticking to area around GZ shouldn’t cause you any problems.
Access
There is plenty of parking at S 34 46.750 E 150 49.310 which is at the southern end of Stafford Street. From there follow the rough path down towards the headland to the south-east. Don’t head straight for GZ as there is a cliff in the way.
Claiming the EarthCache
To log your visit:
1. Upload a photo of your caching group at the EarthCache site
2. Upload a photo of a fossil you found on the headland
3. Send an email via the GC profile describing the size and type of fossil you found
Logs without the corresponding email and uploaded photos may be deleted.
References
http://www.oum.ox.ac.uk/thezone/fossils/intro/proof.htm
http://australianmuseum.net.au/Common-Fossils-of-the-Sydney-Basin