Welcome to Camel rock, one of our favourite NSW destinations. This striking rock formation was identified and named by Bass and Flinders during the first mapping of the coastline of the colony of New South Wales.
Camel Rock is a popular scenic attraction with car parking, a picnic area under the shade of several large trees and toilet facilities. Camel Rock Surf Beach is well known for its great surf, swimming, with rock pools to explore, snorkelling and fishing. The beach is patrolled during the summer months and is well sheltered if there is a north easterly wind. It is best to attempt this cache when the tide is low, you can check the tides Click here
For to todays earth science lesson we need you to understand geological periods.
A geologic period is one of several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.
These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history.
Today we are looking at the Ordovician Period.
The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago. During this period, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater.
The Ordovician is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, tetrahedral spores that are similar to those of primitive land plants have been found, suggesting that plants invaded the land at this time.
From the Lower to Middle Ordovician, the Earth experienced a milder climate — the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Upper Ordovician, massive glaciers formed, causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterise the end of the Ordovician in which 60% of all marine invertebrate genera and 25% of all families went extinct.
Now you know a little about the Ordovician period we need to talk about how it relates to this region ‘Bega Terrane’.
The 450-500 million year old Ordovician rocks in the region are made up of layers of mudstone and sandstone. These sediments were shed down the continental slope in watery avalanches called turbidity currents.
Over time the flat layers on the seabed built up a thick mass. The sequence includes some chert beds – chert is a chemical sediment composed of fine grained silica. As well as accumulating a great thickness, the sediments were laid down over a huge area of this ancient ocean. The base of the sediment pile was under great pressure from the overlying mass and began to heat up, which baked the wet sediment into rock, and formed some new minerals in the process, and squashed the soft mudstone into layered shale.
Carried along on a tectonic plate for over 1000 km from its origin off Antarctica, the mass of sediment eventually met the ancient eastern continental margin of Australia. Around 440 million years ago, this margin lay where western NSW and Victoria are now. The sediment accreted to the continental edge, undergoing further hardening and consolidation to become part of the continent and extending it several hundred kilometers eastwards.
The region’s Ordovician rocks form the geological ‘basement’ into which the Bega Granite and Dromedary Igneous Province were intruded and upon which sandstones were deposited. Other younger deposits, including the Late Devonian sediments and volcanics and the Tertiary-age sandstones, also covered up this basement. The Ordovician rocks have been variously baked, squeezed, buried, exhumed and eroded to form the landscapes we see today. The chert beds form V-shaped folds, but each bed is so brittle that it finally breaks up into tiny blocks.
These rocks are often highly deformed, often partially melted, reflecting their history of deep burial and deformation. The practiced eye can often detect a number of different deformation events.
The Ordovician rocks are relatively easily eroded, forming steep slopes which retain only thin, infertile soils compared with granite-based soils. Thin soils and steep slopes are not suited to agriculture and so you will find them comprising a large part of the bedrock in the region’s national parks and state forests. The hard sandstones of the Ordovician rocks are relatively erosion-resistant and buttress coastal headlands around Twofold Bay. Softer mudstone beds between the sandstones allow rain penetration into the bedrock, causing erosional collapses around the bay. This kind of erosion of alternating soft and harder layered rocks also accounts for the gullied landscapes in the mountainous areas formed on Ordovician rocks.
Now you are familiar with the way in which the Ordovician Bega Terrane plastered itself against the growing continent. There was another later Ordovician interloper in the area, the Narooma Terrane, which rafted some even older Ordovician and Cambrian rocks some 2500 km across the ocean to pile up against the Bega Terrane.
The Narooma Terrane extends from areas near Batemans Bay and down to around Mallacoota in Victoria. The terrane is interpreted as being ocean floor. It includes cherts derived from deep ocean ooze, submarine (oceanic) basalt and a range of younger Ordovician sediments that accumulated as the terrane slowly approached the continent before collision.
A distinctive feature of this terrane is Camel Rock. Camel Rock is made up of turbidite. Adjacent to it is oceanic basalt, possibly of Cambrian age around 500 Million years, making them the oldest rocks in NSW outside of Broken Hill.
Lets look a little closer at Turbidites.
Turbidites are sediments which are transported and deposited by density flow, not by tractional or frictional flow.
The distinction is that, in a normal river or stream bed, particles of rock are carried along by frictional drag of water on the particle (known as tractional flow). The water must be travelling at a certain velocity in order to suspend the particle in the water and push it along. The greater the size or density of the particle relative to the fluid in which it is travelling, the higher the water velocity required to suspend it and transport it.
Density based flow, however, occurs when liquefaction of sediment during transport causes a change to the density of the fluid. This is usually achieved by highly turbulent liquids which have a suspended load of fine grained particles forming a slurry. In this case, larger fragments of rock can be transported at water velocities too low to otherwise do so because of the lower density contrast (that is, the water plus sediment has a higher density than the water and is therefore closer to the density of the rock).
This condition occurs in many environments aside from simply the deep ocean, where turbidites are particularly well represented. Lahars on the side of volcanoes, mudslides and pyroclastic flows all create density-based flow situations and, especially in the latter, can create sequences which are strikingly similar to turbidites.
Classic, low-density turbidites are characterised by graded bedding, current ripple marks, climbing ripple laminations, alternating sequences with pelagic sediments, distinct fauna changes between the turbidite and native pelagic sediments, sole markings, thick sediment sequences, regular bedding, and an absence of shallow-water features. A different vertical progression of sedimentary structures characterise high-density turbidites.
Lithified accumulations of turbidite deposits may, in time, become hydrocarbon reservoirs and the petroleum industry makes strenuous efforts to predict the location, overall shape, and internal characteristics of these sediment bodies in order to efficiently develop fields as well as explore for new reserves. Turbidite deposits typically occur in foreland basins.
To successfully log this cache please use your own judgment and the information in the texts and charts provided above to answer the following questions and send us your answers to the best of your ability;
1. The first and possibly the hardest task (reflected in the D rating of this cache) is to find Deformed turbidite at Camel Rock, There are several examples, have a stroll (be careful on the rocks also reflected in the T rating of this cache) around and find it, how many examples can you find and what size are the sections?
2.Whilst looking around pick up small pieces and feel them, what gives them the texture they have, are they Turbidite or another type of rock?
3. Is the Camel Dromendary or Bactrian?
4. A photo of your team, GPS near GZ with your log and answers. (optional)
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: Wikipedia & Local Geologists (who I thank very much) who are happy to remain anon.
