5 Bedded limestone
Approaching Task Site 5
The rocks featured here are located beneath a large tree.
Find out about the name of these rocks and the environment they formed in.
Bedded exposure under tree
We would say the rock here is bedded too – it forms distinct layers (beds). If we drop a spot of dilute hydrochloric acid on it, it fizzes strongly. Find the name used for this rock.
What was the environment like when this rock first formed?
How near the equator was this part of the Earth’s surface when this rock was forming – around 352 million years ago?
Still under the sea
This rock, a limestone, is a product of marine conditions. In the app use ‘then’ to see the kind of environment we think was here around 352 million years ago. As you walk further backward in deep time you will move from from the conditions here of warm shallow seas, to an environment of large rivers crossing semi-arid plains – quite a change!
Are these rock beds dipping eastward?
Limestone is mostly made of calcite which chemically is calcium carbonate. The shells of most sea creatures are made of calcium carbonate. When those creatures die, their shells get broken up by the waves and some of the calcium carbonate dissolves in the sea water. Limestone is formed when the calcium carbonate is redeposited on the sea bed. This may also cement together other shells and broken shell fragments.
Onward to Task Site 6
Task 6 is close to Task Site 5. There is no rock to see, just a usually very muddy section of the path, but that still tells you something about what is going on beneath your feet.
Task Site 5 Questions
When acid makes a rock fizz, it tells us the rock is:
Limestones are usually formed in:
a) A lake
b) A shallow sea
c) Under a glacier
d) A river
Limestone is mostly made of which mineral:
How thick are the beds of limestone here?
a) 5 to 25 cm
b) 1 to 30 cm
c) 20 to 60 cm
d) Over 1 metre