Pleistocene sand from a Pleistocene shell
Just over three years ago I worked on an archaeological site at Meare in Somerset (sadly unrelated to the famous iron age lake villages). The ‘natural’ was a yellowish brown sand, known as the Burtle sands. These sands were laid down when sea level was much higher than it is today during the last interglacial (Marine Isotope Stage 5e – roughly 130-115 thousand years ago), the warm period before the most recent glaciation. While I was working there I picked up a shell from this sand, a flat winkle (Littorina obtusata).
Looking at the shell recently, I noticed it contained quite a lot of the sand, which I thought it might be interesting to look at
Under the microscope I could see these fragments of an attractive pink and white shell, the pheasant shell (Tricolia pullus)
There was also a very wave-worn foraminiferid, which I think is Ammonia beccarii var. batavus. Forams (foraminifera) are single-celled protozoans that live in the sea. Many of them – like this species – have a calcareous shell called a test which is often well-preserved. Different species of foram have particular preferences for where they live in relation to the sea – some are part of the plankton, some live on the sea bed on the shelf, others are intertidal but live very close to the sea, while others live quite high up in saltmarshes. This species is intertidal, living quite low on the shore, however it has clearly been moved from wherever it died by the waves.
Another shell I wasn’t very sure about. It’s a juvenile, and quite broken. I think it might be Lacuna vincta, another intertidal species.
I think the fact that the winkle shell is quite well-preserved suggests that it has not travelled far by sea, perhaps suggesting that the sand were laid down at a time that the site was intertidal. Really, I would need to look at a much bigger sample to be sure. The sand is probably the same as the Middlezoy Member of the Burtle Formation (see Hunt 2006 for details).
Hunt, C.O., 2006. The Burtle formation, in Hunt, C.O., and Haslett, S.K., eds. Quaternary of Somerset: field guide. London: Quaternary Research Association. pp. 173-86.