Natural England - Suffolk

Suffolk

The geology of Suffolk is relatively simple. Extensive spreads of till, or boulder clay, deposited over the last million years, cover the gently undulating plateau (underlain by Chalk) that forms much of the county.

Richmond Farm

The late Tertiary to Quaternary Crag deposits are marine sandstones, formed when much of Suffolk was below sea level.

The variable nature of these sediments gives rise to mix of habitat and landscape types, with the fine wind-blown sands of the Brecks supporting heathland and the heavier clays of mid-Suffolk woodlands and pasture. The till plateau is bordered on its eastern edge by marine sands and gravels known collectively as The Crag. These deposits support a mosaic of heathland and conifer plantation and pass eastwards into a largely undeveloped coast comprising a mosaic of estuaries, saltmarsh, eroding cliffs and steep shingle banks. In the far south-east of the county, rocks of Tertiary age occur, but they only outcrop in a relatively few places along the shores of the larger estuaries.

Cretaceous

The most widespread rock in Suffolk is Cretaceous chalk (laid down in an extensive, shallow tropical sea some 90-70 million years ago). However, in Suffolk it is covered by later Tertiary and Quaternary deposits, to leave only small outcrops north of Bury St Edmunds. Earlier Cretaceous and Jurassic rocks also occur but they only exist in the extreme north-west tip of the county, and are poorly exposed.

Tertiary (comprising Neogene and Palaeogene)

The Tertiary rocks present in Suffolk document fluctuations in sea-level and the relative comings and goings of land areas and seas. The earliest Tertiary rocks, the Upnor Beds were deposited in a shallow sea, while the succeeding Reading Beds are estuarine and terrestrial clays and show that sea-level had fallen by the time they were laid down. Around 50 million years ago, renewed marine conditions are represented by the muddy sandstones of the Oldhaven Beds and the more extensive deep water clays of the London Clay. These sediments were deposited in a tropical sea close to land. Bands of harder, cemented sediment (known as cement stones) within the London Clay have yielded a large number of marine fossils including starfish, crabs, lobsters, fish, turtles, bivalves and gastropods.

After the London Clay there was a significant fall in sea level and Suffolk became a land area. The area occupied by the county was re-flooded later in the Tertiary, probably about 10 million years ago, with shallow marine conditions persisting into the earliest Pleistocene, some 1.5 million years ago. During this interval the shelly sands of the Coralline, Red and Norwich Crag were deposited in a shallow temperate sea. The Coralline Crag is exposed in a strip between Aldeburgh and Orford, whereas the Red and Norwich Crags are widespread across the eastern part of the county. Fossil shells are commonly found within the Crag, particularly the Red Crag, and include many species similar to those of today, including whelks, cockles and oysters. Corals are actually relatively rare in the Coralline Crag and its name actually comes from the large number of bryozoan remains that characterise the deposit. In east Suffolk, notably at Minsmere and Westleton, gravels known as the Westleton Beds are prominent in the eroding cliff and on the adjacent heaths and represent the deposits of a former coastal beach of the same age as the Norwich Crag.

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.

Deposits from the Ice Age (or Quaternary) are widespread in Suffolk, comprising a large spread of till (or boulder clay) over most of the county, or as glacial gravels in the east. The gravels were deposited around 600,000 years ago and represent the floodplain deposits of the former Thames-Medway river system that flowed north-eastwards across Suffolk from the London basin. These deposits are known as the Kesgrave Sands and Gravels. Around 450,000 years ago during a severe cold phase known as the Anglian glaciation, an ice sheet occupied almost the whole of the county. As the ice advanced it eroded the ground over which it passed, the eroded material was then deposited at the base of the ice to form a sheet of till. The till of Suffolk contains numerous fragments of chalk and flint, plucked from the underlying rock by the moving ice. Associated with the till are sands and gravels deposited by meltwater streams issuing from the ice front. The Suffolk “clayland” plateau is a relic of the Anglian glaciation, being underlain by this mantle of till.

As the ice melted, blocks buried within the till melted to form small lakes in “kettle holes”. These lakes filled with sediments during the subsequent warm interglacial phase (400,000 years ago) known as the Hoxnian which is named after deposits of this age which were found at Hoxne.

The greatest and warmest interglacial stage during the whole of the Pleistocene was the Ipswichian, which occurred about 120,000 years ago. The Devensian cold stage followed the Ipswichian and ice spread south again to north Norfolk instigating cold tundra-like conditions in Suffolk.

In the last 10,000 years, the sea has risen by 30 m and is currently rising at an estimated 2 mm per year. The relative levels of land and sea during this period have dominated the physical development of the Suffolk coast. Accumulations of shingle, known locally as nesses, have developed at Benacre and Thorpeness, while at Aldeburgh the second largest spit in Europe, Orford Ness, commences. Orford Ness has diverted the mouth of the River Alde for a distance of about 20km south from its original outlet at Aldeburgh. Behind Orford Ness are saltmarshes, which have developed in the calmer conditions provided by the spit.

Along the cliffed parts of the coast, erosion has been very active. Dunwich is one of the best known places in East Anglia to be affected by erosion. Dunwich was an important coastal city in the time of Henry II and has now almost completely disappeared.

Geological Highlights:

  • Exposures of the London Clay at Ferry Cliff on the Deben Estuary have yielded the remains of fossil mammals including the oldest known rodents and hoofed animals from the British Isles. These include fossils of Hyracotherium, a fox-sized ancestor to the modern horse and zebra.

  • A bed of phosphatic nodules with vertebrate teeth and bones occurs at the base of the Coralline Crag. This horizon was exploited as a source of fertiliser in Victorian times.

  • The Coralline Crag has been used as a local building-stone, as evidenced by the presence of small quarries dotted around its area of outcrop. St Peter’s Church, Chillesford is one of only two churches in the whole of England that has a tower built out of coralline crag.

  • Man has worked the fossiliferous sand and gravel deposits of the Red Crag over the years for construction and many small disused pits occur throughout East Suffolk.

  • The Anglian ice sheet moved south across eastern England, eroding chalk and Jurassic clays along its path. The till contains erratics derived from as far away as Scandinavia, indicating the scale of the glaciation. The till is up to 75 m thick on the high ground between Bury St Edmunds and Stowmarket.

  • The County is geologically famous as containing two type (reference) sites for interglacial stages of the Pleistocene, at Hoxne (Hoxnian) and Bobbitshole (Ipswichian) and the type site of the Anglian glaciation at Corton Cliffs near Lowestoft.

  • The city of Dunwich was prosperous in the 12th and 13th centuries, being the biggest port in Suffolk at this time. Subsequently, coastal erosion has gradually removed the cliffs at Dunwich and silted up the original harbour. Since Roman times around 1.5km of land has been lost and erosion rates over the last 400 years have averaged 1m per year. So, the tiny village of today is no more than a remnant of the great lost city.

  • Until the 16th century the entrance to the River Alde was opposite Orford, an important naval and commercial port which had grown up around its Norman castle. The growth of Orford Ness to the south is one of the most spectacular examples of shingle spit formation anywhere in the United Kingdom.

  • The Breckland heath has unique physical features brought about by a combination of freezing and thawing action on its soils during the last ice age (the Devensian, some 60,000 years ago), low rainfall and a semi-continental climate. Its meres (land-locked lakes) and pingos (shallow crater-like hollows formed by the melting of ground ice) are typical of the tundra-like Devensian climate.

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.