Creating Port Campbell
During the Tertiary period from approximately 65 million years ago, Australia continued to drift away from Antarctica at rates of up to 6 cm per year. In the middle Eocene age of the Tertiary period approximately 45 million years ago, uplift occurred that formed the Otway Ranges. In this period the rate of sea-floor spreading between Australia and Antarctica increased. By the late Oligocene from 29 million years ago, the Southern Ocean had widened significantly. This created favourable conditions for the biological production of calcium carbonate e.g. shells, bryozoans and calcareous algae. With the sea level fluctuating significantly the sea advanced over former coastal plains, several hundred metres of limestone (Port Campbell Limestone) were laid down in the Port Campbell Embayment. Port Campbell Limestone usually overlies Gellibrand Marl up to 400 m thick. Port Campbell Limestone is middle to late Miocene in age and was deposited in a continental shelf environment. In the late Miocene approximately 5 million years ago, the sea retreated from the Port Campbell Embayment.
Port Campbell Limestone
Limestone is partially soluble especially in acid, and therefore forms many erosional landforms as seen here. These include limestone caves and gorges. Limestone is less resistant to erosion than most igneous rocks, but more resistant than most other sedimentary rocks. It is therefore usually associated with hills and downland, and occurs in regions with other sedimentary rocks, typically clays.
Desription: Calcarenite, minor calcilutite: generally fine-grained; bryozoan, mollusc, echinoid and brachiopod fragments, minor coarse-grained calcarenite, quartz sand and clayey silt; weakly cemented, moderately bedded; continental shelf deposit.
Weathering
Weathering is the breakdown of rock by physical, chemical or biological processes. Limestone areas are predominantly affected by chemical weathering when rainwater, which contains a weak carbonic acid, reacts with limestone. This causes the limestone to dissolve. Carbon dioxide from the respiration of animals (and ourselves) is one cause of increased carbon dioxide in the atmosphere. Burning fossil fuels also contributes to this. Carbon dioxide in the atmosphere forms very dilute carbonic acid when it dissolves in rain.
At the posted coordinates you will be standing on a limestone cliff, look around you and answer the following...
Caution:- there is no need to go near the cliff edge to complete this earthcache.
1. Observing the mushroom type formations how does the top compare to the base in colour and texture?
2. From the information supplied what sort of rock do you think this is and how do you think they were formed?
3. Take a photo of yourself or your team name with the staircase behind you and include it in your log. (Please be careful to not include spoilers in this photo.)
Please email your answers through to our geocaching.com profile.
