From Earth Science On-Site
Knowle Quarry, Shropshire
KEY STAGE 3 TEACHING TRAIL: SITE 3
© GeoconservationUK ESO-S Project, 2013
It is anticipated that the ideas and materials presented here will be adapted by schools, and others, to be more appropriate for their own purposes and programmes of study.
In such circumstances please acknowledge the source as the Earth Science On-Site project.
Site 3: Knowle Quarry (south)
Take the group on the path away from the ridge, a right fork, along the Lime Kiln Walk. The wide and surfaced path, suitable for wheelchairs, then gives way to a narrow track, off to the left, parallel to the road. After 200 metres the path descends a flight of wooden steps into Knowle Quarry. These steps can become very slippery when wet, so descend with care. At the bottom of the steps turn immediately to the right to find the southern face of the quarry. This is Site 3. It is owned by The National Trust and is a protected site. There is no need to damage the face, as specimens may be found along the foot of the face. Please do not remove them from here, as opportunities for some collecting occur later.
Figure 5: Site 3: Knowle Quarry (South)
Figure 6: Sketch of main features at Site 3
First focus attention of the rock type and the evidence it contains of the conditions at the time of deposition (about 400 million years ago).
|Suitable questions at this site
|Remind the group of their prediction at site 2 and ask them to look closely and describe the features of the rock in the face.
||The rock shows bedding, in places. It contains shelly fossil fragments. It also reacts with dilute HCl. It is a sedimentary rock: a limestone.
|Ask the group to inspect the bedded parts of the face to the right and then to the left of the large un-bedded part in the centre of the face. What differences can they see?
||The beds to the left are coarser grained with shelly fragments. The beds to the right are finer grained and contain more mud.
|Ask the group what might have caused the differences they have found?
||The coarser beds were laid down in a stronger current (wave action) whilst the finer grained ones were laid down in quieter conditions.
|What might have caused these differences in current strength in places so close together?
||The reef may have sheltered the beds to the right.
|Measure bedding plane dip on the left of the face. Use a clipboard as a convenient extension of the bedding to create a surface to measure.
||18° to the SE (160° north).
|Tell the group that the large un-bedded “ballstones” are reefs of fossilised coral and other marine animals, and are 420 million years old.
Ask “In what kind of environment the rock must have formed?”
|Today shelly reefs form in warm shallow seas, so they are likely to have done that 420 million years ago.
[Point out that the reefs grew upwards from the base as the bedded layers were deposited next to them.]
|Ask the group how many “ballstone” reefs they can see in the face
|Ask the group if the two reefs are exactly the same age, or if one is younger?
||The smaller, upper one is younger (Principle Of Superposition), although it co-existed with the upper parts of the larger one.
|Ask the group to describe what happens to the older (larger) reef as it grew upwards?.
||It was laterally more extensive in its younger part. The upper part is narrower, continuing to grow after the lower parts died.
|Ask what might have caused this to happen?
||Something caused the lower parts to die and stop growing. (Reefs are made up of animals that are sensitive to water clarity / muddiness, salinity, depth, and temperature.)
|Which of these factors might have been responsible here?
||Not depth, temperature or salinity changes, which would have killed all of the reef animals. The muddiness of the limestone might have killed off the right hand side of the reef.
|Ask the group what deposits from a warm shallow tropical seas are doing in Shropshire?
||Plate tectonic forces moving the crust northwards since they were deposited.
|What else has happened to these beds since they were deposited (below the sea)?
||Uplift and tilting.