KNO/KS4/Ex/3

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Knowle Quarry, Shropshire

KEY STAGE 4 TEACHING TRAIL: SITE 3
© GeoconservationUK ESO-S Project, 2014


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.

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Key Stage 4 Downloads
Pupil Worksheets (pdf file, 1.1 MB)
Group Leader Notes (pdf file, 986 KB)

Site 3: Knowle Quarry (south)

Take the group on the path away from the ridge top, 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 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.

KNO7f5.jpg
Figure 5: Site 3: Knowle Quarry (South)
KNO7f6.jpg
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 420 million years ago).

Suitable questions at this site Acceptable responses
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 from wave and current action.
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° from north)
Tell the group that the large un-bedded “ballstones” are reefs of fossilised coral and other marine animals, and ask “In what kind of environment the rock must have formed?” Today shelly reefs form in warm shallow seas. (Principle of Uniformitariansim).

[Point out that they grew upwards from the base at the same time as the bedded layers were deposited next to them.]

Ask the group how many “ballstone” reefs they can see in the face. (Point out that the reefs grew up from the bottom.) Two
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.
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 well have overlain and killed off the right hand side of the reef.
Ask the group what these deposits, laid down in a warm shallow tropical sea, are doing in Shropshire? Plate tectonic forces moving the crust northwards, away from the tropics) since they were deposited.
What else has happened to these beds since they were deposited (below the sea)? Uplift and tilting.

Draw the group’s attention to the area in the centre of the face, labelled point “c” on Figure 5.

NOTE: This is a fragile part of the face which should not be damaged. It is a calcite vein infilling a fault plane which runs along the face and just in front of it. The horizontal “scratches” (called slickensides) were caused when one side of the fault slipped (horizontally) past the other and scratched the wall of the calcite vein. (See Figures 7a and 7b)

Suitable questions at this site Acceptable responses
Point out the veneer of a calcite vein, now stained red by iron oxide, at point “c”, (on worksheet 4) and tell the group that it infills a fault plane. Ask the group to describe the marks there on the calcite. Horizontal grooves and ridges.
How might a fault have caused these groves and ridges? By sliding past the calcite vein.
In what direction did it slide?

[It is often suggested that polished fault planes “feel smoother” in the direction of slippage. Suggest members of the group try it].

Clearly it was horizontally, but here it is not clear which side (in this case the “front” or the “back”) of the fault moved left and which moved right.

Using the Principle Of Cross Cutting Relationships, out these 3 events in age order.

Formation of calcite vein

Faulting

Deposition of limestone

The fault moved when it was deep below the surface. What would have been felt at the surface when the fault moved? Earthquake.
If this is a fault plane has largely been quarried away here, where might the fault plane be seen now? Logically, either to the left, or the right of the face. (It is in fact to the left, under the trees. Do not damage or uproot the plants on the bank.)
Use a compass to measure the direction in which the fault plane runs along the front of the face. 290° to 110° north (or roughly NW to SE).


KNO11f7a.jpg
KNO11f7b.jpg
Figure 7a & 7b: The Fault Plane at Knowle Quarry (south)

The plants on the bank here are rare and are protected.

Do not walk on, up root, or otherwise damage the plants at this site.

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