n this quarry you are looking at a Silurian coral reef.Limestone is formed from the broken shells and other hard (skeletal) remains of marine organisms. Cemented together mainly by the mineral calcium carbonate.
You can get freshwater limestones and also limestones and muds formed by the deposition of calcium carbonate from water. In the Silurian around 420 million years ago, this part of the world was beneath a shallow sea, something like the seas you find around the Bahama Islands, or the Australian Great Barrier reef of today. BEWARE! Since you are virtually under water in the Voyage, your oxygen supply is going down quicker and you still have a long way to go before returning to land (terrestrial) conditions.
This place in the Silurian
These limestones formed in an environment like that of the Great Barrier Reef off the NE coast of Australia today.
The sea around here and the reef would have been rich in sea creatures.In the Silurian that island in the picture from today’s world, would not have had any vegetation on it.\n\nIf there were any plants, they would look very different from the plants of the Earth today. They would have no flowers, or leaves as we know them.
Close up of the limestone
This lumpy – nodular – appearance is a characteristic of many of the Silurian limestones.See if you could find any fossils amongst the fallen rock (scree). Do not touch the main rock face.
These limestones were forming in warm (20’C or more) clear water, near the edge of the shore, which lay to the east. The sea was deeper to the west, in what is Wales in today’s world.
Many of the rocks you can find in the scree at this site, will show these circular disc like structures. These discs formed the stems of the Crinoids – creatures a bit like present day Sea Lillies.
Crinoids were marine animals. They had an array of branching arms arranged around the top of a globe-shaped, cup-like structure containing the main body of the animal. The cup-like structure was attached to a flexible stem that was anchored to the sea bed.\ We can imagine great areas of the sea bed covered by crinoids, with their arms swaying back and forth in the water currents. They used the arms to capture passing prey.
This trail would have been left by some Silurian creature as it crawled over the sediment while it was still soft. What you are actually seeing is the mold or cast of the trail.
The rocks forming here in the Silurian would sometimes be limestones, then at other times calcite-rich muds. Which was formed depended on how the clear the water was and the water depth. Corals prefer clear water and of a certain depth and temperature. The whole process of what type and purity of limestone forms where, if at all, is strongly influenced by the clarity of the water (lack of sediment), temperature and pH (how acid or alkaline the water is).
Finding Site 11
Be careful not to miss the entrance to site 11 ‘The Canyon’. Near the top of the climb up from the lane, there is point in the hedge where wooden steps lead down into the wood. Follow this short track through the wood to Site 11. After visiting 11 retrace your steps back to this point.
Task Site 10 Questions
What is a fossil?
a) A watch
b) A type of ant
c) An old person
d) Preserved remains of a plant/animal
What is the name of the fossils resembling round discs?
Which modern-day living organisms do Crinoids most closely resemble?
a) A Crab
b) A Sea Lliy
c) An eleephant
d) A tortoise
e) A coral
Another fossil you may find at Lower Farm Quarry is coral. What sort of environments do corals live in?
a) Shallow warm seas
b) Under the ice sheets
c) The desert
What was the likely temperature of the sea in this area during the Silurian period?
a) Just over 20 degrees centigrade
b) Between 0 and 10 degrees centigrade
c) Over 20 degrees centigrade
d) Between 50 and 100 degrees centigrade
Which location has not shown any evidence of past tropical seas?
b) Pudford Hill
c) Rodge Hill
d) Lower Farm Quarry