Update 16/08/2024
I have emailed the company who work inside this building to explain about geocaching and EarthCaches in particular. I have explained that we are just admiring the fossils and are not the sort of people to damage the walls. They have apologised and will be letting the security staff know about us admiring the fossils. If anyone does have issues in the future, please state that the security manager, Richard McLean is fully aware of what we are doing.
By visiting the listed coordinates, you should be able to locate some fairly obvious fossils in a 4foot high lightly coloured wall. Your tasks are to identify these fossils, answer a few questions and send me the answers before logging a find.
Questions
Q1) Have a look for any fossils that you can see within a 5m area at the posted coordinates. How many types can you see and explain how they vary in size and shape.
Q2) Find one of the largest belemnites. Describe its size, colour(s) and shape. Please refer to the photograph below if you get stuck - the belemnites have been blocked out to help you locate them.
Q3) Based upon your answers to Q2, explain which part is the pro-ostracum, phragmacone and guard.
Q4) Please add a photo of yourself, a piece of paper with your caching name or something personal to you, to your log. This is an optional task
Sedimentary Rocks
Some common sedimentary rocks include limestone, chalk, clay, sandstone and shale, which covers approximately 75% of the earth's surface. These rocks are predominantly made when sediment, including dead plants and animals build up at the bottom of rivers, lakes and oceans. When buried, they lose water and become cemented to become rock. Limestone is prone to holding fossils, such as ammotites and belemnite fossils. The three variants are:
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Roach – the youngest limetone (the top layer) with the most colour variation and texture, often including impressions of shells and other marine life. As there is less pressure from other forms of deceased sea life pressing down on this layer, it is more likely that there will be evidence of marine life in the form of fossils. |
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Whitbed – slightly more textured and with a touch more variation in the colour. |
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Basebed – the most pure of colour and grain (from the bottom layers of limestone when quarried i.e. the oldest). As this is further below ground, it is highly unlikely to contain fossils or remnants of oceanic life, due to the immense pressure from above squashing the limestone until nothing but the basebed exists |
Fossils found in sedimentary rocks
Belemnites (Belemnitida) were squid-like animals belonging to the cephalopod class of the mollusc phylum, and therefore related to ammonites of old, as well as to modern squids, octopuses and nautiluses. Now extinct, their fossils are found in rocks of Jurassic age (201.3 million to 145 million years ago) and Cretaceous age (65 million years ago), with a few species hanging on into the early part of the Tertiary period (66 million years ago). The fossils will be found in sedimentary rock.
The animal’s soft parts very rarely fossilise, (although there are very few around), leaving us with only the hard parts: the guard and the phragmacone, which is most common. Belemnites first appeared about 360 million years ago. Along with ammonites and dinosaurs, they died out at the end of the Cretaceous period 65 million years ago. In the UK, belomnite fossils have most commonly found in the chalks in Norfolk.
As they have fossilised in sedimentary rocks over millions of years, and these fossils are in abundance, scientists have been able to research the belemnites to better understand the earth's history and also predict its future. Unlike nautiloids and ammonites, belemnites had a very solid internal skeleton called a rostrum. Many people will be familiar with belemnite rostra, they are straight, and look rather like bullets. Apart from their shells, palaeontologists have also found some belemnite fossils that show their internal structure and soft parts. These fossils tell us a great deal about the way these animals lived. Belemnites had large eyes, and swam quickly using a form of jet propulsion. Like the octopus they could probably squirt clouds of black ink at their enemies to avoid attack.
In any one layer of chalk, there is rarely more than a single species of belemnite present. This is very useful for correlating rocks of the same age. Belemnites lived in relatively shallow waters and close to the shore. Some rare fossils have shown that they possessed ink sacs, like modern squid and octopuses. Belemnite ecology closely resembled that of modern squid, that they were both predators, grew extremely rapidly. They also bred once, laid their eggsand then died. Belemnites were very common during the period when the Norfolk Chalk was being deposited approximately 73 to 78 million years ago.
Originally, the guard of the belemnite was made of alternating thin layers of calcite and organic material. Fossilisation re-crystallised the guard so that it is denser and heavier than it was in life. Fossil belemnites consist of crystals of calcite radiating from the centre of the guard. If you look at a complete guard, you can see that there is a circular hole at one end. This is the entrance to a conical hole called the alveolus. There is also a narrow slit connecting the outside of the guard to the alveolus. This is the ventral fissure, and indicates where the underside of the animal would have been. The phragmacone is the chambered, conical-shaped part of the shell. The external part of the phragmacone is quite fragile and is usually not found in fossils.
