Ringstead Bay Fossil Bivalve – Ctenostreon proboscideum

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Most of the examples of this fossil bivalve, Ctenostreon proboscideum, were partial specimens embedded in the rocks at Ringstead Bay in Dorset, England. However, the large strongly-ribbed shell is unmistakable and easily recognised in the many boulders on the beach at the west end of the bay – at least they were easily seen when the pebbles had all been washed away after the storms. The photographs in the gallery above show Ctenostreon shells as they were found on the beach last week. The boulders had fallen from the Ringstead Coral Bed which is a narrow layer,  packed with fossils, of no more than 30 centimetres depth, and which can be seen in short lengths in the vertical section through the strata at the top of the beach.

The almost complete fossil specimen shown with the blue background (photographed at home) was found many years ago after similar severe weather. You can see that the two valves are still together and the space between them filled with marly limestone material, indicating that the original animal was already dead, with the two shells gaping open, when it was buried under new sediments.

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7 Replies to “Ringstead Bay Fossil Bivalve – Ctenostreon proboscideum”

  1. I’m sure I would have walked by these without recongnising them as fossils. Hopefully studying your posts will help me to “get my eye In” and I’ll be able to spot these details.

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  2. Yes, I am sure that if there are any fossils to see, you will begin to notice them now. Any books you might buy about the geology of the areas in which you walk will probably give you clues as to what fossils you might find.

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  3. Just come across your lovely and informative blog while searching for (rather scant) information of Ringstead clay ecology & environment. Return visit after 40 years was rewarded with sections of the Ringstead coral bed undermined by last winters storms and sizeable slabs broken on the beach. Good recoverable fossils both of coral & Ctenostreon proboscideum you illustrate. What I was searching for was understanding the source of considerable amounts fossilised charcoal that seems to occur through much of the Ringstead clay … semi arid forest subject to regular fires?

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  4. Hello Kevin.
    I am not certain that I can help you with the fossilised charcoal you found in Ringstead Clay without seeing it myself in context. I’ve had a quick look in the literature and although I cannot find a reference to charcoal in the Ringstead Clay, I have found one that might be relevant in the Abbotsbury Ironstone Formation (co-eval with the Ringstead Clay Member and overlying Osmington Mills Ironstone Member) which is said to contain bioclastic material, wood debris and well-rounded “lydite” (i.e. black chert) granules. So wood debris (not however specified as burnt) has been recorded from neighbouring strata. You can find the details in the British Geological Survey publication “Geology of south Dorset and south-east Devon and its World Heritage Coast” by Barton, Woods, Bristow, Newell, Westhead, Evans, Kirby and Warrington, 2011, ISBN 978-085272654-9, page 61.
    Another thought is that the charred remains you have observed could be related to an historical deposit that has become incorporated in the slumping strata. I am thinking of The Burning Cliff, composed of Kimmeridge Clay, a site of spontaneous combustion that started in 1826 and continued to burn for four years. I believe that it has also burned to a lesser extent in recent decades. In the Geologists’ Association Guide No 22 “Geology of the Dorset Coast” by John C. W. Cope,2012, ISBN978-0900717-61-1, page 117, it says that there is no trace of the big 19th century burn today but that the famous geologist Arkell in 1947 recorded occasional clinker-like material on the beach.
    The on-line site compiled by Ian West concerning the geology of the Wessex Coast, including the Osmington and Ringstead areas, is an absolute mine of information. I had a quick look but I couldn’t immediately find any reference to fossilised wood for the clays at Ringstead in it .. but maybe you would like to investigate for yourself.
    Hope this helps.
    Jessica

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