Rock Doughnut EarthCache

Rock Doughnut

Geology of the North Norfolk Coast
In order to understand the geology of North Norfolk it is necessary to have a basic knowledge of the geological time scale. The Quaternary Period is divided into two Epochs, the Pleistocene (from 2 million to 10,000 years ago) and the Holocene (from 10,000 years ago to the present day). The Quaternary Period has been characterised by a number of glacial and interglacial stages.

The glacial stages or ice ages were cold periods of time when the large areas of the globe such as North America, Scandinavia and Britain were covered by large ice sheets. These glacial stages have alternated with warm interglacial stages when the ice was confined to the Arctic and Antarctic regions. The following points are of importance here:
The Holocene Epoch corresponds to the present day interglacial stage (the Flandrian) in which we live.
The last glacial stage or Ice Age was the Devensian, which lasted from about 115,000 to 10,000 years ago.
The Anglian glaciation was the 3rd from last glacial stage and occurred between 400,000 and 500,000 years ago. This stage was the last time the ice sheets reached East Anglia and it resulted in the deposits known as the Corton Formations (see below)
The Anglian glaciation was preceeded by the Cromerian and Pastonian interglacial, and Beestonian glacial stages. The Kesgrave Formations are believed to have been deposited at this time.

The North Norfolk coastline is primarily composed of Quaternary deposits underlain by chalk bedrock. The Chalk is composed of calcium carbonate, which comes from the remains of microscopic marine organisms that lived in a warm shallow sea that covered this area during the Cretaceous period, between 62 and 132 million years before present. Chalk is a soft rock but is relatively more resistant to erosion than the other deposits found on the North Norfolk Coast. The chalk is visible in the base of the cliffs at Weybourne, while between Sheringham and West Runton it is exposed as a wave cut platform at low water. From there the chalk falls to below low water, just west of Cromer Pier while, to the east of Cromer, the chalk bedrock is not exposed on the East Anglian Coast again.

From Weybourne to Happisburgh pre-glacial deposits are sandwiched between the chalk and the overlying glacial deposits. The bottom (earliest) layer is termed the Weybourne Crag and dates from the early Pleistocene, about 2 million years ago. It consists of grey shelly sands sat above a stone bed of flints, pebbles, and shells. The Crag and stone beds are often cemented together by iron pan (which gives the deposit a reddish colour) and calcrete.
The Crag is overlain by a succession of shallow-water deposits known as the Cromer Forest Bed Series (or Kesgrave formation). The Forest Bed series contains various layers of clays and sands deposited under both freshwater and marine conditions. The deposit represents a complicated series of Pleistocene climatic events that terminate at the beginning of the Anglian Glacial stage. The Forest Bed series is particularly well known for its fossils.
Between 2.5 million and 900 000 years ago the coastline was much further inland than present day, but in many ways the environment and climate was quite similar. Since then Norfolk has experienced cold stages, when the landscape was covered with glacier ice and the climate would probably have resembled that of present-day Iceland. It has also experienced warm stages, when temperatures were much warmer than the present day, and the region resembled the ‘Costa del Cromer’!

Rock Doughnut- Flint

Flint is found in areas with chalk bedrock, this is because flint formed within the sediment that later became chalk. At this point it's worth noting that the chalk was formed in much larger quantities from the remains of microscopic calcareous plankton, particularly Coccolithophoroid algae, whose tiny skeletons are known as coccospheres. Upon death, trillions of these microscopic skeletons rained down on the sea floor, accumulating in layers of white ooze, often falling apart into their component pieces (coccoliths). This white ooze later hardened into chalk.
The majority of silica found in flint nodules is biogenic (produced by living organisms or biological processes). Although today's flint nodules are inorganic, the silica that formed them was originally sourced from the remains of sea sponges and siliceous planktonic micro-organisms (diatoms, radiolarians) during the late cretaceous period (60-95 million years ago). Flints are concretions that grew within the sediment after its deposition by the precipitation of silica; filling burrows/cavities and enveloping the remains of marine creatures, before dehydrating and hardening into the microscopic quartz crystals which constitute flint.
Paramoudras are flint nodules found mainly in parts of north-west Europe including Norfolk. In Norfolk they are known as Pot Stones and can be found on the beach below Beeston Bump just outside of Beeston Regis.
Pot Stones are flint nodules with a hollow center and have the appearance of a doughnut (torus). They can be found in columns resembling a backbone. These flints are trace fossils of the burrows of an organism otherwise unknown except for these relics sometimes referred to as Bathicnus paramoudrae.

To claim this earthcache you will need to visit two convenient waypoint locations (as shown below) to enable you to message the answers to the following questions to the Cache Owner. Any logs not meeting these criteria will be deleted.

1. At waypoint 1 (N 52° 56.672' E 1° 13.642'), describe the potstone and measure it’s outer diameter and inner diameter.

Note- due to the nature of the moving sands this isn't always visible. If you look around you should see another potstone. Note these co-ordinates and put into your log for future explorers.

2. Also at waypoint 1 (or another), what is the rock the potstone is embedded in and from what geological period is this from, stating the approximate age?

3. At waypoint 2, standing at the steps describe the lumps of something you can see just in front of you (towards the cliff) and just behind you suggest what they may be and from which stage, or series. It is not advisable to go to base of the cliff.

4. Optional- take photo of cliff, (not of the one for Q.3 at waypoint 2) to see any changes.

Parking can be found in Sheringham, walk down to beach from ‘Beeston Hills Putting’. Or from West Runton and along the beach. The steps at Beeston Regis are now out of action.

Note- to visit this earthcache you need to consider the state of the tide. It is recommended to only visit at low tide.

Tide Table

Also, make no attempt to climb onto the cliff as very unstable..

Cache placed with the kind permission of North Norfolk District Council