Geology Site Account

Summary

Site of Special Scientific Interest designated for the importance of its geology. Spectacular cliffs of London Clay overlain by Red Crag. Extensive exposure of London Clay on foreshore. Important for Eocene fossils (particularly mammals and birds). Type locality for the Waltonian Red Crag. Also a fine example of rotational landslips.

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Site description

The most spectacular exposure of Red Crag in East Anglia is at the Naze where the red, shelly sand can be seen resting on blue-grey London Clay. The Naze is one of the finest geological sites in Britain; both the Red Crag and London Clay here are of international importance and the cliffs are designated a Site of Special Scientific Interest (SSSI). The Red Crag and the overlying sediments represent a remarkably complete sequence of late Pliocene/early Pleistocene deposits which has yielded information on climatic deterioration at the beginning of the Ice Age. Digging in the cliffs is not permitted but fossil shells are numerous in the slipped masses. The cliffs can be dangerous in wet weather.

The underlying London Clay was laid down in a subtropical sea during the Eocene period, some 50 million years ago. The coastline at the time was some distance away and consisted of rainforest dominated by mangroves, similar to that found in present day Malaysia. Fruits and seeds, twigs, and logs of wood from these rainforest plants were washed into sea and can be found preserved in pyrite (iron sulphide) in great numbers on the beach beneath the cliffs. This fossil wood made up the bulk of the copperas stones, which was the raw material for the local copperas industry. The London Clay at Walton is famous for the best-preserved bird fossils of Eocene age in the world. The fossilised bones of early mammals that lived in the rainforest have also been found on the beach (see entry for Harwich). Also found amongst the beach shingle are fossil sharks teeth and fish bones. The London Clay also contains layers of volcanic ash from eruptions in Scotland during the time the London Clay sea was in existence.

The rust-red colour of the Red Crag sand and its contained fossils is the most distinctive feature of the cliffs and is due to the former presence of pyrite that was washed from the London Clay into the Red Crag and there oxidised. The final product of this chemical reaction is a red iron oxide, which has stained the sand and fossil shells producing attractive colours. Red iron oxide (ferric iron) needs contact with the air to form. Thus the thickness of the iron staining may indicate that the Red Crag was exposed to the air in what is now Essex and East Anglia for a long period before it was submerged again and the next geological stratum (the Norwich Crag) deposited. This is evidence of significant changes of sea level or uplift and subsidence of the land.

The Red Crag is 4-5 metres thick, comprising shelly sands with sedimentary structures indicating that it was deposited in underwater dunes at a water depth of 20-30 metres. The Red Crag Sea was home to an astonishing number of species of shellfish - nearly 300 species have been recorded from the Naze “ which shows the extraordinarily rich fauna of the Red Crag Sea which existed over what is now Essex and East Anglia about two million years ago. Some of these species have a preference for warmer waters and these seem to be less common in the younger outcrops of Red Crag in Suffolk with arctic species beginning to appear. This is taken by some to be an indication of the onset of the Ice Age, which is why the Red Crag was classed as early Pleistocene in age. This argument is not universally accepted and the Red Crag is now placed in the Pliocene.

The Pleistocene deposits overlying the Red Crag, once over 4 metres thick, have been reduced as the cliffs have receded. From the base they consist of sand, a sequence of sands, silts and clays (from which fossil pollen has been obtained), Cooks Green Gravel, further silty deposits and brickearth. The pollen assemblage is dominated by alder and silver fir but there is also a type of pollen that cannot be related to any species known today and is referred to as €œtype X€. This species was thought to be representative of the Hoxnian interglacial stage (see entry for Clacton cliffs) but this cannot be correct, as the overlying Cooks Green Gravel is older than this. The Cooks Green Gravel was actually laid down by the River Thames when it flowed across this area before the arrival of the Anglian ice sheet. The Pleistocene sediments at the top of the cliff are noticeably contorted and deformed which was caused by the freezing and thawing of permafrost during the most recent glacial stage when the climate of the Walton area was similar to the present day arctic.

The Naze cliffs also provide a magnificent example of rotational landslips, a sight that is becoming increasingly rare as much of the coastline is subjected to coast protection works. Another example in Essex is at Hadleigh Castle near Southend. The slippage is mostly caused by water passing through the Pleistocene deposits and Red Crag and resting on the impervious London Clay, creating a spring line. This saturates and weakens the base of the Red Crag, causing the slips.

Above all, the Naze cliffs are a stunning and increasingly rare example of a natural, wild coastline which benefits wildlife and visitors alike. This is in sharp contrast to virtually every other section of high ground on the Essex coast that has been subjected to extensive coast protection work.

The Heritage Centre housed in the old lifeboat house in the town has a few fossils on display.

Aerial photograph of the Naze cliffs. Photo © Essex County Council