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, 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. Sydney itself is situated on Triassic rocks and it is only towards the edge of the basin at Wollongong, Newcastle and Lithgow that the older Permian rocks come to the surface.

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.

Plant Fossils of the Permian

Permian plant fossils are nearly always associated with rocks that contain coal (coal measures). Glossopteris is by far the most common and its leaves can be found at many localities around Newcastle and Wollongong and in the west at Lithgow.

Triassic Fossils

Triassic rocks from the Sydney Basin mainly contain fossils deposited in fresh water. These are mostly plants, more rarely fish and a few other vertebrates and invertebrates.

Animal Fossils of the Triassic

Triassic lakes in the Sydney Basin were inhabited by fish and invertebrates. Many fossil fish have been found in brick pits and shale quarries. Many years ago in a brick pit in the Sydney suburb of St Peters, a giant salamander-like labyrinthodont amphibian Paracyclotosaurus davidi was found .

Plant Fossils of the Triassic

Plant fossils can be found along the coastline north of Sydney. Good specimens are often found in recent rock falls. The most common fossils are the horsetail known as Phyllotheca, the seed-fern Dicroidium and the Iycopod (club moss) Cylomeia. These plants lived in and around swamps and lakes in a huge delta complex.

Collecting Fossils

Fossils can be easy to find if you know where to look and what you are looking for. Museum displays are a good place to get to know what to look for but you must remember that the specimens on display are usually some of the best and most spectacular ones that have ever been found. It is more likely that you will find fragments and incomplete specimens. If you do find something that looks very complete or appears that it might be important please mention it to a palaeontologist at the Museum who has the expertise to assess if it is a significant find or not.

Remember:

• Only collect fossils from private property if you have the owner's permission.
• Do not touch fossils on protected sites or reserves.
• Do not destroy sites by collecting too many fossils.
• Always leave some fossils for others.

References

• Herbert C. and Helby R. 1980. A guide to the Sydney Basin. Bulletin 26, Geological Survey of NSW. Department of Mineral Resources, Sydney