After a filling lunch and much needed thirst quenching we progressed down to the northern side of Culver Cliffs/Bembridge Down, to Whitecliff Bay. On the footpath on the way we could see all too easily how precarious the footpath was becoming due to landslips! Another good winter’s rain and I should think there’ll need to be some re-routing of the Coastal path.
Unfortunately Dan had not been able to reconnoitre this part of the sequence so had to do quite a bit of reading from the GA book. Nevertheless it was a good afternoon. The almost vertical sequences progress up from the Upper chalk at the headland through the Reading, London Clays, Bracklesham, Barton and Becton formations to a band of Bembridge limestone in the Headon Hill formation – late Palaeocene to late Eocene in less than a km. By this stage the strata is much more gently sloping (<15o perhaps). The marked change in angle of strata from nearly vertical (>45o (into the anticline) was noticed by several people just north of the northern set of steps down to the beach.
We started at the Chalk end and Nigel found a sea urchin ( – Echinocorys scutata possibly). There is apparently an unconformity between the chalk and the Reading beds, but I didn’t realise/look for it at the time.
Red staining in the Reading beds is also thought to be indicative of soil formation (similar to the Wessex beds to the south). The clays then start alternating with the (Bagshot?) sands in the London Clays and this continues into the Bracklesham group. These are transgressive-regressive cycles, coarsening up and separated by erosion surfaces. It is the clay beds which have shown the greatest areas of slippage, the multi-coloured sands standing proud in between (the equivalent of Alum Bay on the West coast). There were obvious shell lines of deposition in the clays and apparently sharks’ teeth and turtle plates are found here, but we weren’t so lucky. However a nice pyritised bivalve was found, several bivalve accumulations, pieces of plant material and a brilliant crab specimen – all the legs very evident. In the Bracklesham group, perhaps 30m from the southern steps was a lignite (brown coal) bed. This was thought to be due to a long period of supratidal marshes.
North of the café we find green coloured sandy mud beds – ferrous conditions – part of the Headon Hill formation. There is quite a variety of strata within this in fact and several members of the group stayed to make a closer inspection. Some of us, including me continued on to the Bembridge limestone. Apparently mammal remains can be found in it and the very fine but thin limestone with a bluish tinge above it has given up insect wings. The limestone itself is quite ‘holey’ from remains of snail shells (– Limnium?) and shell debris layers are also evident. In spite of this it has been widely used for building stone in the IoW. Further north the limestone is seen to have a green sticky clay layer above it – with Polymesoda evident, indicative of an increase in salinity. Apparently this is a local feature, not seen at other locations. Above this is apparently the insect layer and Peter and Sally(?) intrepidly climbed up. However they could ‘only’ reach the intermediary Bembridge Oyster bed a pale grey sand with lots of Ostrea easily visible from below when you got your eye in and they brought some samples down for the rest of us.
This was the end of a long and very full day the climb back up to the pub gave a good view over the north-east section of the island and the different strata were easily picked out in the geomorphology. I thoroughly enjoyed it and will definitely go back – to just walk along the beaches and have easy access to the different strata and the very abundant fossils was wonderful. (Lots of comments about the weight of Adrian’s rucksack!) Next time however, I’ll do my reading first and have a better idea what to look out for – or end up spending the whole week just on this stretch!
Many thanks to Dan Pemberton from the Dinasaur Isle Museum at Sandown for showing us the area.
Ailsa Burrows