Incredibly, on the Jurassic Coast, which is famous for its fossils, you can also see evidence of the way marine creatures lived – like the burrows and tunnels that they dug in the soft sediments long in the past. An example of this phenomena is the layer of Arenicolites worm burrows buried in rocks from over 135 million years ago.
Fossils can also be formed when the original dead animal decomposes whilst at the same time leaving a perfect mould of its shape in the burial sediments. This mould can either remain hollow or eventually it may fill up with other percolating minerals or sediments; these harden to form a fossil that looks just like the original structure but is actually a cast of it – without any interior details and made of entirely different materials.
The Arenicolites beds at Ringstead are not the fossilised remains of the worms themselves by either of the two processes described above. They represent a third kind of preservation called trace fossilisation – that is, the preservation of evidence of the activities of the living animals such as the remains of burrows, tunnels, and tracks. Trace fossils are also known as ichnofossils. The photographs in this post show preserved burrows and tunnels made by marine invertebrates like crabs and worms that can be seen in a section of rock jutting out from the base of the cliff nearest to Bran Point. [Bran Point marks the junction between the most western edge of Ringstead Bay and neighbouring Osmington Bay].
Nearby to the worm burrow fossils are small fossil scallop shells (similar in appearance and size to the ones I have photographed at Studland Bay – see the posts of Sea shell from Studland & Scallop shells from Studland Beach) are embedded in the strata of the adjacent Bran Point ledge. These scallop shells give their name to this rock layer, the Chlamys qualicosta Bed.
Revision of a post first published 30 April 2009
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