Coffin Bay consists of numerous natural inlets, bays and sandy beaches. Discovered by Matthew Flinders in 1802 and named in honour of his friend Sir Isaac Coffin, Coffin Bay is a beautiful holiday destination surrounded by National and Conservation Parks with an abundance of wildlife, bird life and magnificent wildflowers to be seen.
The exposed jagged cliffs, sand dunes, long white beaches and wild seas of the Coffin Bay Peninsula contrast starkly with the sheltered tranquil waters of the bays.
Massive dune fields, both modern and ancient, dominate the Coffin Bay Peninsula. Sand which accumulated during the Pleistocene Period has cemented to form the Bridgewater Limestone facies. Erosion by wind and wave action has formed this limestone into spectacular coastal cliffs and other features, for which the area is well known. More recent sediments form extensive mobile dune systems in the Avoid Bay, Misery Bay and Gunyah Beach areas. The northern
coastline of the Peninsula is characterised by sheltered bays and beaches, lining the protected waters of Coffin Bay.
Coffin Bay National Park occurs within the geological province known as the Gawler Craton formed between 2400 and 1490 million years ago. The ancient Archaean to Mesoproterozoic crystalline basement rocks of the Gawler Craton are now covered with a relatively thin layer of more recent sediments of Tertiary to Quaternary age.
Outcrops of basement rocks within the National Park is generally restricted to coastal exposures although minor inland outcrops do occur, often forming spectacular peaks inland and prominent points and bluffs on the coast. The majority of the park is covered with Quaternary and Tertiary sediments. The most extensive of these being the Bridgewater Formation, a white to fawn coloured calcarenite, often showing karstic weathering and forming the spectacular high and steep cliffs on the coast. Recent and Quaternary sand dunes also cover extensive areas.
The Coffin Bay National Park contains older rocks of Archaean age which were emplaced approximately 2380 to 2316 million years ago. The Wangary Gneiss, a massive to compositionally layered quartz-feldspar-biotite-muscovite gneiss and Kiana Granite, a course grained, tabular feldspar granite with minor biotite and muscovite, are the main rocks types within the area. Outcrops are limited to coastal exposures with inland areas entirely covered by Bridgewater Formation and sand dunes.
Standing at the indicated co-ordinates you need orientate yourself with your back to the sea and looking towards the seating area. In front of you will be a series of layers that are clearly visible. You need to look carefully at the composition of the rock and then answer the questions below in order to be able to claim this EarthCache. Submit your answers, by e-mail, to cincolcc(at)gmail.com
1. How many different “layers” can you count in the mini cliff face before you?
2. Place your hand against the rocks. How do they feel and why do you think they feel they way they do?
3. Estimate the average depth of the sedimentation you can see.
4. Do you think the nearby beach sand is of similar composition? Explain your answer.
References consulted.
http://www.environment.sa.gov.au/parks/pdfs/PARKS_PDFS_COFFIN_BAY_MP.PDF
FTF goes to = Orange Angels - Well Done!
