A Fault in the Dungeon EarthCache
Hidden : 5/18/2007
Difficulty:
2 out of 5
Terrain:
2.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Geocaching at times can be dangerous.
Please act responsibly and do not put yourself or others at risk.
Stay on paths (with an optional short detour for a picture) and follow any signs or instructions from the Rangers.
Pick a dry day to visit, as the paths can get muddy and slippery, and always wear appropriate footwear.

Wirral has only one geological Site of Special Scientific Interest (SSSI) - the Dungeon between Thurstaston and Heswall. This is a small wooded ravine, which has a natural stream section flowing through the Tarporley Siltstone formation of the Mercia Mudstone Group, of Triassic age. At the lower southwest end of the section, the faulted contact with the older Wilmslow Sandstone Formation is seen. The Tarporley Siltstone section is similar to that in other parts of the Cheshire basin, being made up of red fine sandstones and siltstones, with parallel and rippled bedding, and salt pseudomorphs.

Siltstones are soft sedimentary rocks of intermediate grain sizes between the coarser and harder sandstones (formed by cementing together of sand grains) and finer mudstones and shales. Siltstones differ significantly from sandstones due to their smaller pores and higher propensity for containing a significant clay fraction. Ocean floors are predominantly fine clay whilst the coarser sand is found closer to shore, thus siltstones are typically formed between these two on the continental shelf.

At the time that these sandstones were laid down, Britain lay in the middle of a vast continent called Pangea, just North of the Equator. Initially conditions were hot and dry punctuated by flash floods that brought vast amounts of sediments from a range of mountains south of Britain that formed the source of much of the Triassic rocks of Britain. As the plates moved and Britain drifted northwards the climate became less arid and there must have been some vegetation as fossil dinosaur footprints have been found on the Wirral. At the end of the Triassic Period the area was submerged under the sea and the sandstones were compressed by marine sediments and then about 50 million years ago the whole area was uplifted and the marine sediments eroded to reveal the sandstones beneath.

As you enter the valley from below, the fault is visible just as the steep part of the valley sides become narrow. It is best seen by walking up the stream for ten or fifteen feet from the onset of the steep sides. The rocks in the stream are often very slippery and extreme care should be taken if walking on them to get to this vantage point. Continue the circular walk up the steps up the left side of the ravine and stay on the path. At the listed co-ordinates you’ll see a lovely little waterfall and from here you can answer the question listed below. Care is needed with children owing to the steep slopes and drops around this area.

Park in the Wirral Country Park Visitors Centre car park on the left near the end of Station Road, and if late in the day, take note when the gates are locked (this circular walk will take over an hour). If the Wirral Country Park Visitors Centre is open (from 10am each day), the rangers have requested you call in and let staff know that you’re going to the Dungeon. Whilst there, it is also well worth having a look at the nature displays & have a visit to their shop. They also have information and leaflets about the country park and surrounding area, and there is a nearby café plus public toilets.

From the Visitors Centre, it’s recommended that you follow a circular walk along the Wirral Way, up through the Dungeon and onto the footpath to Thurstaston village (see map). From the village you can return to the Visitor Centre via Station Road. Take care with children as both cyclists and horse riders also use the Wirral Way, and Station Road is a public road. When the Visitors Centre car park is closed an alternative approach can be made from the South East. Roadside parking is available at the junction of Oldfield Road and Oldfield Drive, from where a footpath leads to the top of the Dungeon. Turn left here and follow the path down the Dungeon via the steps (do not attempt to go directly down the gully, as it is steep, slippery and can be dangerous).

To log a find of Wirral’s only geological SSSI, take a photograph looking up the stream in the Dungeon from, or just above the footbridge, with yourself and GPS in the foreground. Also, answer the following question and e-mail the answers to myself via my profile:

At the listed co-ordinates you will see the small waterfall in the ravine. On the far side, just to the right of the waterfall and the overhanging rocks is an area of siltstone rock face. Estimate both its height and width. If you are also exploring the Dungeon, then see if you can find the small current ripple crests in the stone. If you succeed, in which direction do you think the current ripple crests indicate the sediment was transported? (These crests are like waves on a beach, they travel in the direction of the steeper face, with the gentler slope being in the direction from where they came)

Thanks to James Locke (Senior Ranger, Wirral Country Park) for their permission to list this earth cache.

Additional Hints (No hints available.)



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