Fossils and Fossil Hunting

The Jurassic Coast is a great place to find fossils and the best place to find them is around Charmouth and Lyme Regis. The Jurassic clays here formed in a deep tropical sea, the soft muddy bottom of which was often stagnant, creating a sulphurous and anoxic environment, the best conditions for preserving the shells, bones and even soft tissue of dead prehistoric creatures.

It is these stagnant seabed conditions which have given the cliffs around Charmouth their dark colour (and smell!), and it explains why the sediments found here, the 195 million year old Green Ammonite beds and 197 million year old Belamnite Marls, are some of the richest fossil bearing deposits to be found anywhere along the Jurassic Coast.

How Fossils are Formed Learn about Time Periods
© offonone 2003	The animation to the left shows how fossils were formed in the Jurassic Sea. The example shows an icthyosaur alive and then dying on the sea floor. The flesh rots away, leaving the skeleton which becomes covered in deep marine sediments raining down from above. These sediments create an anoxic environment, one which is ideal for the preservation of bones as there is no oxygen present to support the bacteria or creatures which may feed on the skeletal remains. Over time the sediments built up, compressing into rock. These rocks were later uplifted during the mid Cretaceous Period and became exposed to erosion, shown in this example by the sea. Eventually the bones become exposed on a modern day sea shore where they can be found by fossil hunters.

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Safety

Many fossils can be found loose on the beach, and this is the best place to find them, where they have been washed clean by the sea. It isn’t safe to look for fossils in the cliffs as they are unstable and any digging may cause the cliff to collapse. The famous Lyme Regis fossil hunter, Mary Anning, lost her dog when she left it guarding a fossil spot. The cliff crashed down on him and in her own words “twas but a moment between me and the same fate”.

Always hunt for fossils on the beach on a falling tide tide, and be aware that if you stay too long, you can be cut off when the sea comes back in.

Keep away from cliff falls, landslides and mudflows, particularly during or after wet weather when they may still be active.

Take care when walking on wet rocks, algae and seaweed make them slippery.

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Fossil Hunting Code

Do not collect or dig into the cliffs. Many fossils can be found washed loose on the beach in patches of sand and gravel between the boulders.

A hammer should only be used to split a loose rock in which a fossil is located. Wear eye protection when using a hammer.

Only collect small loose fossils. Fossils in ledges, large specimens such as Giant Ammonites and geological features like Sunstones should be left for everyone to enjoy.

If you make an important find, register it with the World Heritage Team on 01305 225101.

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Types of Fossil

The quantity and types of fossil found on the Jurassic Coast are dictated by the environment in which the sediments were deposited.

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Triassic Fossils

The Triassic sediments in East Devon were formed in a vast sandy desert which had rivers, flood plains and salt pans, an environment far from ideal for the formation of fossils.
The fresh water of the river would have attracted a lot of life and been home to fish and amphibians. Most of the larger life here was terrestrial, living along the edges of the river where the vegetation grew.

The richest fossil bearing sediment from this time is that of the Otter Sandstone Formation which was deposited on the bottom of a shallow, oxygen rich river flowing through a desert. These are far from ideal conditions for creating fossils and carcasses only had a chance of becoming preserved if they were buried very quickly, such as when the river deposited vast amounts of sediment when it was in flood. The reason many of the fossils found are only fragmentary is because carcasses were preyed upon by scavengers and became dispersed as they floated down stream.

Despite this the Otter Sandstone Formation is regarded by many as the richest reptile locality from the Mid-Triassic Period to be found any where in the world. Finds include fish, invertebrates and 10 reptile and amphibian species.

It must be remembered the fossils here are fragmentary and a more fruitful fossil hunting expedition can be carried out in other parts of the Jurassic Coastline.

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Jurassic Fossils

The Jurassic sediments were laid down on the bottom of a warm ocean floor. The water was often deep allowing soft, deep clays to form which excluded oxygen. These are the best conditions for forming fossils. The sulphurous environment created by the anaerobic bacteria that thrived here combined with the soft, deep clays meant that even very delicate creatures or soft tissue had a chance of being preserved.

Once a carcass had sunk to the seafloor it would be quickly covered by the clay. Over time more and more fresh seafloor deposits would build up increasing the weight and pressure on the sediments deep below. Over millions of years the old seabed and whatever lay trapped within the clay would be turned to rock, becoming fossilised.

Fossils from the Jurassic Period mainly consist of sea creatures, though the remains of insects, flying reptiles and dinosaur carcasses have also been found.
Towards the end of the Jurassic Period sea levels dropped forming pockets of land where swampy forests grew.

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Cretaceous Fossils

The Cretaceous sediments were mainly deposited on the bottom of a shallow sea and are dominated by the skeletal remains of plankton blooms which lived in the warm, clear water. These solidified with the application of pressure over millions of years to form the white chalk cliffs found within the World Heritage Site today.

Most of the fossils from Cretaceous Period originate from the marine environment, though the seabed conditions were less favourable for creating fossils than during the Jurassic. Significant fossils from the Early Cretaceous when the environment was more terrestrial, a time when dinosaurs roamed through the swamplands, are very rare.

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