Withington (Fields of Echinoids), Cheltenham

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Free

8th October 2022 – 10:15m

Join us at a very special event, situated on privately owned ploughed farm fields near Withington which we had obtained permission from the landlord to visit. The proximity of the topsoil to the Inferior Oolite below in this locality means that ploughing brings rock to the surface which contains a large variety of fossils. A field hunt (with landlord permission) really is an excellent way to find fossils with little effort other than to look patiently and “get your eye in”. It is comparatively easy to find rocks on the surface of the topsoil and inspect them for fossils, many of which are already loose from the rock. No tools or equipment are required other than a container for your finds and, at this location, a bucket was ideal as fossils were plentiful and they are easy to carry and drop the robust fossils into as you go along.

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Description

* Suitable for children 4+ (All children must be accompanied by an adult).
* NO PPE! Just make sure your either wearing bright clothing, or a High Visbility Vest and sensible footwear for walking on fields.
* Members MUST Arrive on time, as we will be driving on from the meeting place in convoy to the hunt site.

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Please note, many of our locations will not have toilet facilities, water, or other amenities.

Join us at a very special event, situated on privately owned ploughed farm fields near Withington which we had obtained permission from the landlord to visit. The proximity of the topsoil to the Inferior Oolite below in this locality means that ploughing brings rock to the surface which contains a large variety of fossils. A field hunt (with landlord permission) really is an excellent way to find fossils with little effort other than to look patiently and “get your eye in”. It is comparatively easy to find rocks on the surface of the topsoil and inspect them for fossils, many of which are already loose from the rock. No tools or equipment are required other than a container for your finds and, at this location, a bucket was ideal as fossils were plentiful and they are easy to carry and drop the robust fossils into as you go along.

Expect to finds echinoids, bivalves and other molluscs, with ammonites also commonly being found. In particular the large flat famous echinoid, Clypeus ploti is popular from here.

The Cotswold Escarpment rocks are almost exclusively marine and were deposited mainly in warm tropical seas. Plate tectonics has transported this part of the Earth’s crust northward over the last 150-200 million years to its current location. The Middle Jurassic rocks here are the characteristic ‘Cotswold Limestone’; soft, yellow, sandy limestone at the base of the Inferior Oolite (literally egg stone), a sedimentary rock formed from ooids, spherical grains composed of concentric layers. Towards the top of the Inferior Oolite the limestone becomes more fossiliferous and is referred to as ‘grits’ due to its coarser texture. Such an Inferior Oolite exposure is exposed at the farm and the fossils that this limestone contains date from between 167 to 175 million years ago at a time when this farm was at the bottom of a warm tropical sea. The rocks exposed near the farm comprise the Salperton and Aston Limestone and, from a fossil perspective, the most interesting layers are the Grits (Clypeus, Upper Trigonia Grit and Lower Trigonia Grit), named from the index fossils found in those rocks.

The commonest fossil found at this location is the sea urchin (echinoid) Clypeus ploti. These are more commonly known as Chedworth Buns (after the nearby village where they were often found) or Pound Stones, because their weight was usually a good approximation to 1lb. Clypeus lived in burrows on the seafloor, and burrowed their way through the sediment to get nutrients. They had fine hair-like spines and are an example of what is known as an “irregular” echinoid because they are shaped, not rounded. Because these irregular echinoids lived in the sediment, they didn’t need the spiky and sometimes poisonous spines that the spiny sea urchins (known as regular echinoids) that we can see on the seafloor today have for protection. As well as the Clypeus Ploti we find other echinoid species which are “regular” and would have had sharp spines. Unfortunately the spines rarely fossilize still attached, but they can frequently be found individually in the same sediment.

Trigonia bivalves gave their name to the second grit since they are very common at this horizon. Trigonia are a family of saltwater clams, noticeable because the exterior of the shell is highly ornamented. Other fossils to be found comprise of brachiopods, bivalves and gastropods. Brachiopods are a marine animal that had hard valves (shells) on the upper and lower surfaces. They are distinguished from bivalves which also have two valves/shells but in a left/right arrangement rather than upper and lower.

Brachiopods are bottom dwelling marine animals and, although rare today, in Jurassic times they dominated the sea floor and were frequently found in large colonies. One characteristic unique to brachiopods is the pedicle, which is a long, thin fleshy appendage which is used to burrow into the sea floor as an anchor while the brachiopod could feed clear of the silt. Although the fleshy pedicle itself does not preserve in the fossils, the opening at the top of the animal from whence the pedicle connected (known as the foramen) is clearly visible. Brachiopods are filter feeders, gathering microscopic organisms and bits of organic matter from the water that flows by them using a specialized organ called a lophophore. This is a tube like structure with cilia (hair like projections). The cilia move food particles down the lophophore to the mouth.

FAQ

Can I bring a younger child?

We are sorry, but to comply with insurance cover and to ensure the safety of the event, we do not allow any exceptions.

Can I book over the phone?

Unfortunately, as terms and conditions and waivers need to be signed, we can only accept bookings online.

Do I have to bring my printed ticket to the event?

This will greatly help us and speed things up, but leaders will have a list of those attending on the day.

Are toilets nearby?

Most events will not have access to toilets. The best places to find fossils are mostly areas away from built up areas, and tend to be quite remote. There are a few exceptions where toilets are close by, but it is best to presume they wont be available.

What happens if the event is cancelled?

We try very hard to avoid having to cancel, but if an event needs to be cancelled due to adverse weather conditions or unforeseen circumstances, we will notify you immediately.

Can I bring my dog/pet?

UKAFH does not permit members to bring dogs or pets, unless under exceptional circumstances such as guide dogs. Some members may suffer from Cynophobia, or allergies. In addition, we need to ensure the safety of all members. Many beaches also do not permit dogs.