Year 9 Science Excursion to the Hallett Cove Conservation Park Hallett Cove tells a story that spans over 600 million years. To understand this story we need look for clues in the rocks



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Adelaide High School

Year 9 Science Excursion to the Hallett Cove Conservation Park

Hallett Cove tells a story that spans over 600 million years. To understand this story we need look for clues in the rocks. We will find evidence of huge forces within the Earth, of the gouging and scratching of ancient glaciers as well as more recent invasions by the sea and erosion. By stopping at the various stations around Hallett Cove, we will read the story of Hallett Cove and show how its story has international significance.

Station A: Black Cliff

The ancient sands and silts laid down here have now been changed to sandstones and siltstones and subjected to extreme pressures and temperatures when they were slowly pushed deep underground by the sediments above and by ancient earth movements.

(a) Describe the sandstones and siltstones here. Comment on their colour, the grain size and the width of the layers.

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(b) What evidence is there that there have been earth movements here ? Make a neat sketch of what you see. Name this structure.

(c) You can also see a "wave cut platform". What is a wave cut platform and describe how it is formed. Make a neat sketch of what you see. ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­Station B: The Glaciated Pavement above Black Cliff:

This pavement was formed 270 million years ago during the Permian and almost 300 million years after the end of the Precambrian Era when the rocks of Black Cliff were laid down.

(a) This time gap has produced an "unconformity". What is an unconformity and how was it produced?

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(b) There is evidence of glaciation here. Describe this evidence. We can use this evidence to determine the direction of movement of the ancient glacier. In what direction was it moving and how do you know?

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(c) Other southern continents and India have similar evidence of glaciation during this time. This evidence, along with other evidence, led German meteorologist Alfred Wegener to make, what was considered at the time, an outrageous claim. What was this?

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(d) What further evidence has been found to change everyone's minds about this?

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Station C: Glacial Erratics

Notice the boulders here that are further evidence of the Permian glaciation.

(a) Examine the boulders. Describe the material making up these boulders. Is it the same as the material in the sediments in the area around the boulders? How do you think they arrived here?

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Station D: More Evidence of a Break in Time

Across the creek you will see pale mauve and buff coloured layers over the dark purple folded rocks.

Make a neat sketch of what you see. Show clearly the unconformity on your diagram. Which are the Permian sediments? Label these, as well as the more ancient Precambrian rocks on your diagram.

Station E: Rocks under Stress

Going back to the Precambrian rocks, we can see the effect of stress on the rocks when they were folded during earth movements 500 million years ago.

(a) During what time period did these earth movements take place?

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The rock here is sandstone originally sand in a tidal flat back in the Precambrian. But there is a white mineral running through it in an irregular fashion.

(b) Name the white mineral?

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(c) How did it come to be here?

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(d) How is this evidence of the stress present during the ancient earth movements / mountain building?

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Station F: More evidence of Permian Glaciation

The Precambrian rock that used to be sandstone has been changed by heat and pressure due to deep burial. The sand grains are now welded to one another to form a hard rock called Quartzite. This hard rock contains crescent shaped grooves. Explain how these were formed. Use these to work out the direction the glacier was heading in at this spot. Is this consistent with your earlier findings? ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


Station G: Invasion by the Sea

There is a different rock type here that was laid down during the Tertiary, only 5 million years ago (an epoch during the Tertiary called the Pliocene).

(a) Describe this rock in terms of the colour, the grain size and any other features you notice. What is the evidence that this was laid down at sea? ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

(b) This deposit is way above sea level now. Suggest two ways in which this could have happened.

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Station H: The Youngest Rocks at Hallett Cove

These sediments take us back to two million years ago ( an epoch in the Quaternary called the Pleistocene) when the climate was often warm and wet. The Mount Loft Ranges are being eroded and this is bringing clay minerals in the form of mud and depositing this onto the plains below. The vegetation was lush and so giant wombats and other large marsupials would be grazing here.

(a) Describe the sediments here in terms of colour and grain size ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

(b) Do you think the streams and rivers here were fast, medium or slow flowing ? What is the evidence that confirms your opinion?

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(c) Later, during the Pleistocene , there was an Ice Age and so sea level gradually falling during this time. Looking out to St Vincent’s Gulf, you would need binoculars to see the sea. Why does sea level fall during an Ice Age? Find out what causes Ice Ages. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


(d) But during the last 12,000 years, the sea has re- invaded the Gulf and many are tipping that sea levels will continue to rise for many years to come. Others contend that there will be no change in sea levels in the foreseeable future. From what you have seen today which group do you think is correct? Give reasons. _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________






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