The rocks of the East of England represent some 170 million years of Earth history. The oldest rocks date back to the Jurassic period, although much older rocks are present at depth, and examples of other ancient rocks have been transported to the region during the Ice Age.
The region's geology may be divided into bedrock (sometimes called the 'solid' geology), and superficial (sometimes known as 'drift'), which includes sediments laid down over the last two million years. The structure of the regions bedrock geology is relatively simple: the rocks become younger eastwards, and dip gently towards the North Sea basin. By contrast, the superficial geology is notoriously complex, and continues to excite lively discussion among geologists.
Introducing the geology of the East of England
The sediments and fossils of the East of England provide a physical archive of information about environmental change over deep time. They are particularly important for telling the story of the last 3.5 million years, including changes in wildlife and human occupation.
The oldest rocks in the region are part of the belt of Jurassic limestone which stretches from Dorset to Yorkshire. They include oolitic limestones and clays laid down in warm, shallow tropical seas. The limestones have been used as building stone, as at Barnack near Peterborough.
The Oxford Clay underlies many parts of West Cambridgeshire and Bedfordshire, forming an undulating plain. It has been an important source of clay for brick making in the Bedford and Peterborough areas. It is rich in fossil remains, which include ammonites and large marine reptiles such as plesiosaurs.
The Corallian Beds include a range of marine clays and limestones containing fossil ammonites and bivalves. They outcrop in the St Ives and Ampthill areas, and also in the form of coral-rich rock at Upware.
The Lower Cretaceous Sandringham Sands and Dersingham Beds underlie tracts of heathland in West Norfolk, and are an important source of sand for glass making and foundry moulding.
The Lower Greensand forms a ridge in Bedfordshire. It has been quarried for sand around Leighton Buzzard, Woburn and Sandy. The Carstone rock of West Norfolk is of a similar age, and is quarried for building stone.
Above the red chalk at Hunstanton, the Chalk is a white or grey limestone that totals over 400m in thickness. It forms the prominent scarp of the Bedfordshire and Hertfordshire Chilterns, and continues north as rolling uplands in Essex and Cambridgeshire, with more subdued relief in West Suffolk and West Norfolk. It also forms low hills in the Thurrock area of south Essex. Flints originate in it, and were used by early humans for tool making. It has been extensively quarried over the centuries for agricultural and building lime. Today, the Chalk is the regions most important source of drinking water.
The Reading and Thanet Beds are the earliest rocks of the Tertiary epoch in this region. They outcrop in Essex, Hertfordshire and south-east Suffolk. Tough sarsen stones and puddingstones found in these areas are thought to have originated from a now-vanished layer of the Reading Beds.
The London Clay is a blue-grey rock which underlies much of Essex and parts of Hertfordshire. It was laid down in a tropical sea and may contain fossil plant remains and sharks’ teeth. It has been much used for brick making, and its nodular layers (septaria) have been burned to make cement.
The Crags are a sequence of sandy, marine deposits laid down in the gradually cooling climatic conditions leading up the ‘Ice Age’. They outcrop in the eastern parts of Suffolk and Norfolk. The Coralline Crag is the oldest layer, a limestone which is only found in Suffolk. The Red Crag and Norwich Crag may include the remains of fossil mammals such as mastodon, sabre-tooth and whale.
The Pleistocene ‘Ice Age’ is a complex series of cold glacial and warm interglacial climatic periods. It has left an important legacy of ‘drift’ or superficial deposits across the region. Many classic geological sites for understanding the Pleistocene are found in the region.
During the early Pleistocene the ancestral River Thames flowed diagonally across the south-eastern part of the region, depositing a sequence of river terrace deposits known as Kesgrave Sands and Gravels. The coldest period, the Anglian, saw ice sheets spreading as far south as St Albans, diverting the early Thames southwards and scooping out the broad depression that is now the Fens. It left behind boulder clay and sandy outwash deposits that mantle many parts of the region’s landscape, and which underlie much of the best corn-growing farmland in East Anglia. During cold periods the landscape was also shaped by periglacial freeze-thaw action which mobilized soil layers and shaped the Chalk escarpment and other slopes, while rivers deposited thick sand and gravel sequences in valleys such as the Great Ouse, Lea and Wensum, so providing valuable resources for the aggregate industry. Plants and animals, including humans, were able to colonise the region during warmer interglacial periods. Pakefield in Suffolk has produced evidence of the earliest humans in northern Europe, dating back 680,000 years.
The last 10,000 years are part of the Holocene, which is the name of the present interglacial period. Human life has spread throughout the region, modifying and shaping the landscape in new ways through settlement, farming and other activities. Meanwhile geological deposits continue to form under active geomorphological processes, particularly in coastal areas and river valleys. These deposits include dunes, shingle banks and sandbanks, estuarine salt-marshes and mudflats, and layers of peat and alluvium. Notable tracts of peaty land have formed in the Fens and other low-lying areas like the Norfolk Broads. Thus rocks continue to be laid down for the future.
Rafted chalk - glaciotectonic activity at West Runton, Norfolk
Bedrock geology: Click map for larger version
Superficial geology: Click map for larger version