Deposits containing this large fossil oyster, Deltoideum delta or Liostrea delta, were clearly visible on the shore at Ringstead Bay in Dorset after winter storms had rearranged and largely removed the normal thick layer of pebbles. They are recorded as being characteristic of several late Jurassic Period strata. I observed them in situ in the Ringstead Clay Member waxy clays at the top of the shore in the western half of the beach. I also noticed them in rocky outcrops on the water line of the lower shore where the different composition of the matrix makes me think the exposed strata were probably from the Sandsfoot Formation which lies beneath the Ringstead Formation and pre-dates it.
In the eastern half of Ringstead Bay, the part which was inaccessible on that particular visit of 1st March 2014, I had previously seen this species of fossil oyster shell in deposits of Kimmeridge Clay from the Kimmeridge Formation which were laid down after the Ringstead Formation layers. So this particular species of oyster was around for a long time, geologically speaking. Its appearance and disappearance in the various strata is due to the changing and cyclical nature of the environment in this location – meaning that very specific conditions were required for the species to thrive but changes in water depth, salinity, and temperature made the environment more or less suitable for their existence at different successive times.
There are more posts about Deltoideum delta in both Jessica’s Nature Blog and Oysters etc.
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Jessica's Nature Blog 
Those Oyster shells look like a couple I found on Blackpool Beach recently. One measures 5 inches across and the other is 4.5 inches. One of them looks like it has a piece of an Icelandic cyprine attached to it as well. I found them not long after the storms we had. Unfortunately mine now look as if they have rust on them.
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Sounds interesting. Do you think the oyster shells you found are fossil or recent? Some of the fossil oysters I have found have rusty deposits on them – but fairly modern ones can also have a rusty colouration if they have been shallow buried in sand or mud for some time.
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Hi, it’s hard to say. I initially thought they might be fossils but then found that some people get carried away with thinking they have found really, really old shells. I have read that shells like these can often be thrown up from the sea bed when there is a really rough storm. Are visitors to your site allowed to post photos? I could put them up for perusal.
However, I thought I’d start a blog of my own on word press so will soon be posting my photographs there.
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Hi, Tracy. If you are going to start a WordPress Blog of your own, that’s great. You could post the photos there to see what other people think. Or, if you would like to, you could send me some pictures by e-mail and I will give you my opinion before you post them on your own blog. I have been studying oyster shells for about forty years and have another blog called Oysters etc. with details of all my publications on the subject.
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