On Sunday 25th November, UKAFH members met for a fossil hunt along the coastline of Overstrand, a village a few miles south-east of the popular holiday destination of Cromer in Norfolk. Despite the time of year, the weather was dry and pleasant and lacking the strong, cold wind of the previous day.
We began with a show and tell presented by UKAFH leaders Sam Caethoven and Nicky Parslow, discussing the local geology and providing examples of what could be found.
Overstrand and the surrounding coastline is somewhat unique in its geology, providing a glimpse into three very distinct periods of time. Firstly, and most prolifically, we find the Boulder clay, a glacial till which consists of sludge, rock and chalk rafts. Campanian and Maastrichtian in age, this chalk is some of the youngest exposed in the UK at around 70 million years old. Chalk formed as a sediment in a relatively deep, warm sea which would have been close to the Mediterranean in latitude at the time. Life was abundant in the sea, not least in the profusion of coccolithophores, a phytoplankton whose calcareous plates formed the striking white sediment – but also in echinoids, belemnites, corals, brachiopods and sponges whose fossils we came to find today.
Whilst boulder clay and chalk is abundant along the Norfolk coastline, it is not local, having been gouged out and transported in huge rafts by advancing glaciers during the ice ages. As a result, the chalk represents an unconformity, overlying younger rocks. Below the chalk, but younger in age, at Overstrand is the Wroxham Crag formation and Cromer forest bed. These deposits are a lot younger than the chalk; in fact they formed 600-500 thousand years ago during an interglacial stage when Norfolk was a vast river basin and flood plain frequented by giant mammals such as the famous Runton elephant (steppe mammoth), woolly rhinoceros, bison and deer as well as small mammals, amphibians, fish and a plethora of freshwater bivalves – remains of which can all be found, washed out from these sandy sediments. The Wroxham and Cromer Forest beds are mostly covered by the slumped boulder clay of the cliffs or are at or below beach level, so are rarely exposed except in scouring conditions, however fossils of this age can be found, many washed ashore from exposures out at sea.
Fossil hunting conditions at Overstrand have not been the best of late; several feet of sand have covered the foreshore for some time and the wave baffles and sea defences significantly reduce coastal erosion. Much of the chalk from which many of our finds are to come from is currently only exposed on the foreshore at low tide as sparsely dispersed pockets. Despite these unfavourable conditions, UKAFH fossil hunters quickly began finding great fossils derived from both the chalk and crag deposits.
Among the shingle built up along the coastal groynes and beyond, UKAFH members found echinoids preserved in flint – mostly of the genus Echinocorys but also including Micraster and Galerites – as well as belemnites and sponges. Numerous Pleistocene mammal bone fragments were also found, several of them quite sizeable, washed out from the Wroxham Crag and Cromer forest bed.
As the tide retreated and we advanced beyond the sea defences we moved from the shingle towards the pockets of chalk exposed further on the foreshore. Here we could see a vast diversity of fauna preserved in situ: echinoids, brachiopods, corals and Ventriculites and other sponges with beautifully preserved detail.
Although the beach was in unfavourable condition, the hunt was unexpectedly productive, particularly as we progressed further along the beach. With fascinating geology and many superb finds, the group proved that even six feet of sand can’t stop our eagle-eyed intrigue.
Thank you to everyone who came and made the day a great success!
Please remember, the cliffs exposed at Overstrand are protected and should not be dug into. Fossils can easily be collected along the foreshore.