This article describes the geology of the Broads, an area of East Anglia in eastern

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

characterised by rivers, marshes and shallow lakes (‘broads’).

The Broads The Broads (known for marketing purposes as The Broads National Park) is a network of mostly navigable rivers and lakes in the English counties of Norfolk and Suffolk. Although the terms "Norfolk Broads" and "Suffolk Broads" are correctly use ...

is designated as a protected landscape with ‘ status equivalent to a national park’. The area is underlain by a suite of generally flat-lying

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

types of which the most recent are those of Neogene age. Almost entirely covered by more recent

superficial deposits Superficial deposits (or surficial deposits) refer to geological deposits typically of Quaternary age (less than 2.6 million years old). These geologically recent unconsolidated sediments may include stream channel and floodplain deposits, beach ...

, they are exposed at the surface to a very limited extent or else are known from boreholes or quarry workings. Overlying these across much the larger part of the 'national park' are

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

s and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

s of Flandrian age, which together with

peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficient ...

deposits form the broad flats of the

Waveney Waveney may refer to: * River Waveney, a river that forms the boundary between Suffolk and Norfolk, England * Waveney District, a local government district in Suffolk, England * Waveney (UK Parliament constituency) * Waveney class lifeboat, a class ...

, Yare, Bure and

Thurne Thurne is a small village and civil parish in the English county A county is a geographic region of a country used for administrative or other purposes Chambers Dictionary, L. Brookes (ed.), 2005, Chambers Harrap Publishers Ltd, Edinburgh ...

valleys. Extraction of the peat in historic times, and subsequent flooding of the workings, has resulted in the pattern of broads for which the area is widely known.

Older subsurface rocks

Borehole, seismic and other geophysical survey evidence suggest that the entire region is underlain at depth by rocks of Silurian age though these do not occur at or near the surface. Much of this region of England is believed to have been emergent i.e. above sea level, during most of the succeeding Devonian period and through the Carboniferous,

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

and

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

periods. Rocks of this age are therefore absent or restricted in occurrence in the region and are unknown beneath the Broads. Rocks of

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

age are known from other parts of East Anglia but again are not known to underlie the Broads.

Cretaceous

In common with most of the rest of East Anglia, the ‘national park’ is underlain by

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

age rocks of the Chalk Group, though these are in turn overlain by younger rocks across the larger part of the area. Only west of

Wroxham Wroxham is a village and civil parish in the English county of Norfolk. The civil parish of Wroxham has an area of 6.21 square kilometres, and in 2001, had a population of 1,532 in 666 households. A reduced population of 1,502 in 653 households ...

and

Hoveton Hoveton is a village and civil parish in the English county of Norfolk. It is located within the Norfolk Broads, and immediately across the River Bure from the village of Wroxham. Whilst Hoveton is north of the river, Wroxham is south; but man ...

in the Bure valley and west of

Brundall Brundall is a village and civil parish in the English county of Norfolk. It is located on the north bank of the River Yare opposite Surlingham Broad and about 7 miles (11 km) east of the city of Norwich. History Brundall's name is of Anglo- ...

in the Yare valley is

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

present immediately beneath superficial deposits. There are some very restricted outcrops of the Upper Chalk in the valley sides between Wroxham and

Coltishall Coltishall is a village on the River Bure, west of Wroxham, in the English county of Norfolk. The village is located within the Norfolk Broads. History Coltishall's name is of Anglo-Saxon origin and derives from the Old English for Cohhede's la ...

, some of which like those around Coltishall Hall have been worked. The Upper Chalk also outcrops northwest of Bramerton and west from Postwick into

Norwich Norwich () is a cathedral city and district of Norfolk, England, of which it is the county town. Norwich is by the River Wensum, about north-east of London, north of Ipswich and east of Peterborough. As the seat of the See of Norwich, with ...

on either side of the Yare valley.British Geological Survey 1991 ‘’Great Yarmouth’’ England and Wales map sheet 162 Quaternary & Pre-quaternary geology 1:50,000 Keyworth, Nottingham BGS

Palaeogene

A small outlier of the

London Clay The London Clay Formation is a marine geological formation of Ypresian (early Eocene Epoch, c. 56–49 million years ago) age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from t ...

is known to exist beneath Langley and Hardley Marshes where a buried valley lies at depth beneath the shallow modern day valley of the Yare. This

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

dates from the

Lower Eocene In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...

epoch of the

Palaeogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...

period.

Neogene

The youngest ‘solid’ rocks of the area are those of the Crag Group which are of Neogene to early Quaternary age. They comprise marine and estuarine sands and other sediments. These and more recent superficial deposits (described below) are all recognised formally as parts of the Great Britain Superficial Deposits Supergroup.

Quaternary

During the early and middle Pleistocene, a major river now referred to as the

Bytham River The Bytham River is said to have been one of the great Pleistocene rivers of central and eastern England until it was destroyed by the advancing ice sheets of the Anglian Glaciation around 450,000 years ago. The river is named after Castle Byth ...

flowed from west to east through the area on the approximate line of the modern Waveney. It left a series of

river terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial te ...

deposits, evident west of Geldeston for example, whose colours betray the origin of their materials in the

English Midlands The Midlands (also referred to as Central England) are a part of England that broadly correspond to the Kingdom of Mercia of the Early Middle Ages, bordered by Wales, Northern England and Southern England. The Midlands were important in the Ind ...

. Some of these sands and gravels have been worked in the past at places such as

Kirby Cane Kirby Cane is a scattered village and civil parish centred west northwest of Beccles and northeast of Bungay. It is in south-east Norfolk. It housed 375 people in 152 households as at 2001 – then 434 in 179 households at the 2011 Census, ...

, just outside the 'national park'.Lee, J.R. et al. (eds) 2015 British Regional Geology: East Anglia 5th Edn. Keyworth, Nottingham BGS pp133-137 Sediments associated with the

Anglian glaciation The Anglian Stage is the name used in the British Isles for a middle Pleistocene glaciation. It precedes the Hoxnian Stage and follows the Cromerian Stage in the British Isles. The Anglian Stage is correlated to Marine Isotope Stage 12 (MIS 12), ...

are collectively termed the

Albion Glacigenic Group The Albion Glacigenic Group is a Quaternary lithostratigraphic group (a sequence of rock strata or other definable geological units) present in those parts of Great Britain which lie north of the southern limit of Anglian glaciation, but south o ...

, having formerly gone under other names. Amongst these the Lowestoft Formation (formerly known by various names: Lowestoft Boulder Clay, Cromer Till (in part), Lowestoft Till Group, Lowestoft Till Formation) comprises deposits of glacial origin along with the

Aldeby Aldeby is a village and civil parish in the English county of Norfolk. It is bounded to the south by the River Waveney, on the other side of which is Suffolk. The village is about five miles (8 km) by road from Beccles. History The name Ald ...

sands and gravels. Likewise the Happisburgh Glacigenic Formation is a modern name for an assemblage of sediments including the former ‘Corton Formation’ and a part of the Cromer Till. The tract of country around Lowestoft, Belton and Blundeston is formed by sands, along with sandy clays and gravels, formerly assigned to the Corton Formation. This is overlain in many places by the Corton Woods sands and gravels which are of glaciofluvial origin. The national park boundaries encompass the margins of this tract and hence of these sediments. The silts and clays of Flandrian age together with peat deposits forming the broad flats of the various river valleys are collectively assigned the name of the Breydon Formation.

References