Natural England - Norfolk

Norfolk

The rolling plateau-like landscape of Norfolk may appear to present a face of geological uniformity but this hides a relatively diverse geology covering parts of the last 140 million years of geological time.

The landscape is dotted with dolines, which are formed by subsidence or collapse of the chalk, producing circular lakes such as the Devil's Punchbowl pictured here.

Sands and clays were deposited in a shallow tropical sea during the Cretaceous outcrop with a north-south alignment in series of low ridges between Downham Market and Hunstanton. Elsewhere, expansive spreads of sediments deposited during the Ice Age cover the chalk bedrock, which underlies much of north and central Norfolk.

The plateau surface created by these rocks and the immense physical power of ice sheets descends to meet the wide coastal plain of north Norfolk, or meets the sea as a series of spectacular coastal cliffs in north-east Norfolk. The array of surface sediments has given rise to varying soil conditions, land cover and habitats from the heaths of the sandy Brecks to the woods and copses of the boulder clay plateau of central Norfolk.

Cretaceous

The oldest rocks that occur in the county are found in the north-west, where a ridge of ground marks the transition from the Fens and the margin of the Wash to the higher plateau surface of north and central Norfolk. This ridge, on which the villages of Sandringham, Heacham, Snettisham and Dersingham are located, is formed from rocks that are collectively known as the Lower Greensand. The oldest of these is the Sandringham Sands, which were deposited in the nearshore area of a shallow sea some 130 million years ago. The topmost unit, known as the Leziate Beds, is well exposed in a number of quarries and comprises very pure sands with thin layers of mud.

The overlying Dersingham Beds are sandstones in the south and interbedded sandstones and mudstones in the north, with the sand components having been deposited in shallow nearshore environments and the muds in lagoons. Throughout west Norfolk the top of the Dersingham Beds is a bed of mud known as the Snettisham Clay, which was dug for brickmaking in Victorian times.

There then followed a period of erosion as the sea retreated and more terrestrial conditions were established. One of the more distinctive rocks of the area, the ochre-coloured Carstone, represents a return to marine conditions and overlies the earlier Cretaceous beds. These sandstones have been used extensively for building in the area and form the ridge running between Castle Rising and Heacham. The Carstone grades upward into the Red Chalk, which comprises fossil-rich pink limestone and brick red clay. These rocks were deposited in a shallow, warm sea as evidenced by the common fossil bivalves, ammonites and gastropods that can be found in it.

A major phase of land subsidence and deepening of the Cretaceous sea marked the beginning of the deposition of the chalk. The chalk is a white limestone comprising over 95 per cent calcium carbonate, although it does contain thin beds of marl and nodules of flint, either scattered or in bands. The chalk forms the bedrock over the majority of north and central Norfolk, although throughout much of this area it is obscured by much younger sediments laid down during the Ice Ages (Pleistocene). The cliffs and foreshore at Hunstanton provide a striking example of the colour transition from rusty brown Carstone, upwards into the Red Chalk and then the white chalk.

Quaternary

Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.

At some time during the Tertiary (65-2 million years ago) there was a significant fall in sea level and the area now occupied by Norfolk became land. The incoming of a shallow sea later in the Tertiary and the earliest Quaternary (approximately 2 million years ago) resulted in the deposition of shelly sands, known as the Norwich Crag. The subsequent cold and warm climatic phases of the Quaternary led to deposition of complex sequences of sediments collectively known as the Cromer Forest Bed Series. In Norfolk these include the Weybourne Crag (similar to the Norwich Crag), the famous Cromer Forest Beds themselves and the Kesgrave and Ingham Sands and Gravels.

The Cromer Forest Bed comprises two beds of freshwater origin with estuarine deposits between. The estuarine deposits contain a variety of sediment types, ranging from clay to gravel, and are rich in mammal remains. The Kesgrave Sands and Gravels represent the floodplain deposits of an extensive braided river system (the precursor to the Thames and Medway river systems) which flowed into the North Sea across east Norfolk from the London Basin.

Around 450,000 years ago a severe cold phase known as the Anglian glaciation caused an ice sheet to spread across East Anglia occupying the whole of Norfolk. As the ice advanced it eroded the ground over which it passed, the eroded material then deposited at the base of the ice to form sheets of till (boulder clay). Associated with the tills are suites of gravels formed at the edge of the ice-sheet. These gravels form the impressive Cromer Ridge and a ridge of gravel (known as an esker) south of Blakeney. These vestiges of former glaciation, with the mix of till, sands and gravels, provide the complexity of soils that characterise this area and give rise to the great variation in land cover. Where these glacial sediments outcrop on the coast between Trimingham and Weybourne erosion is a historic and ongoing issue, but the cliff-line remains a dramatic feature, contrasting with the open, flat coastline elsewhere in East Anglia.

After the Anglian a further series of warm and cold phases occurred, but sediments deposited during these phases are poorly exposed in Norfolk. However, during the Ipswichian interglacial a rising sea filled The Wash, the large embayment bordering north-west Norfolk. Originally this embayment extended through into the vast coastal plain that is The Fens. Evidence for this comes from the presence of a complex sequence of brackish water and freshwater sediments marking periods of more marine and freshwater influence.

The relative levels of land and sea have dominated the physical development of the north-Norfolk coast over the past 10,000 years. The sea has risen from 30 m below its present level and is currently rising at an estimated 1 mm per year. The sediments beneath the present landforms record the development of the area over this period. Today, the coastline is a dynamic zone of saltmarshes, tidal flats, barrier islands, gravel ridges, spits and sand dunes which support a diverse range of plants and animals. This zone is up to 4 km wide in places and is a classic area for the study of the relationship between habitats and coastal processes and the development of coastal areas since the end of the last Ice Age.

Geological highlights:

The sand pits at Leziate are the most extensive workings of their kind in the United Kingdom. They were probably begun in the early part of the 19th century as small pits for glass sand. In recent years they have been worked for glass and foundry moulding sands and they now extend over about 2 km2.
The Snettisham Clay brick pits yield a rich bivalve fauna with common gastropods and ammonites. The ammonites are well preserved as uncrushed ironstone casts and they were much sought after when the pits were in work.
Carstone has been used widely in the local area as a building stone. Many of the self-contained estate villages in west Norfolk are characterised by this attractive rock. The brownness of the Carstone buildings led to the town of Downham Market being referred to, at one time, as the 'Gingerbread Town'.
The Cromer Forest Beds are very well known because of the embedded tree stumps and the diverse range of mammals that have been recorded from it. The estuarine deposits have yielded elephants, rhinoceros, deer, hyaena, sabre-toothed tiger, bear, beaver and hippopotamus.
West Runton is famous for the discovery of a West Runton Elephant found in glacial deposits exposed along the coast. The first bones were unearthed in December 1990, though the actual retrieval was not launched until January 1992. First to be found were the ribs, jaw, backbone and part of a leg. In 1995, major excavation work took place to recover the rest of the skeleton. The height of the woolly mammoth when alive was estimated at 4 m weighing in at about 10 tons, which is nearly twice the weight of a modern African elephant. It was aged around forty years at its death. An exhibition of the finding and excavation of the elephant can be seen at Cromer Museum.
Grimes Graves is one of the most fascinating ancient human sites in Britain. Despite its name, it is not a grave or burial place but a flint mine worked between about 2200 and 2500 BC (the Neolithic period). Grimes Graves consists of more than 350 hollows in the ground, marking the location of the former mine shafts. Some of the shafts were sunk as deep as 10 m below the surface; a remarkable accomplishment when you consider that the Neolithic miners used antlers for picks and animal shoulder blades for shovels.
The Norfolk Broads are one of England's unique landscapes. They were formed by medieval peat diggings which became shallow lakes joined by cuts and dykes to the rivers of the area; the Yare, Bure, Wensum, Ant, Thurne, Chet and Waveney.

Local sites

The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.

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