Bunter (geology)
Encyclopedia
Bunter beds are sandstone
deposits containing rounded pebbles, such as can notably be found in Warwickshire
, Cheshire
, Staffordshire
, Nottinghamshire
, Yorkshire
, Devon
and Dorset
in England
. They are thought to be alluvial deposits and, judging from the rounding of the mainly quartzite
pebbles, to have resulted from prolonged transportation in a large and turbulent river, resulting in powerful abrasion. The deposits in the English Midlands
are thought to have been transported in this way northwards from Brittany
, France
. This supposed river has been called the "Budleighensis", after the Devon village of Budleigh Salterton
, a site where such deposits were discovered. The depositions took place in the lower Triassic
period. Some newer conglomerates, e.g. in Warwickshire, near Ryton
are thought to have arisen during the Ice Age
by reworking and southward transportation of older deposits by ice flows.
The pebble
s, also called cobbles
, which can be used as gravel
, as ballast
or as cobblestone
s, are mainly milky-white quartzite but can vary in colour and composition, including some that are hard, reddish-coloured sandstone. The sandstone in which these pebbles are deposited can be used for building or as an aggregate
for cement
or concrete
.
The name "Bunter" derives from the German
term "Buntsandstein
", "bunt" meaning "variegated" or "colourful", referring to the colour of the sandstone deposit, which varies from reddish to greenish. This sandstone is widespread across central Europe, notably in the Black Forest
and Odenwald
region of Germany
.
The sandstone can be hard enough for building, yet easy enough to "work", resulting in bridge
s, castle
s, cathedral
s and churches constructed of reddish sandstone, throughout the relevant areas of Europe
(e.g. Germany, Luxembourg
, Switzerland
, Alsace
in France
, Denmark
, Poland
).
The land under which these beds lie is generally very well drained, creating heathlike conditions. Because of the drainage, the soil tends to be of low fertility. A notable area in Britain
, which has these characteristics, is Cannock Chase
, a designated Area of Outstanding Natural Beauty
(AONB).
The long shingle
tombolo
of Chesil Beach
in Dorset and the raised beach of Portland
, Dorset are partly composed of Bunter pebbles. As yet, no fully satisfactory and universally accepted geological explanation has been formulated to explain their precise origin and mode of transport, as each proposed theory has its difficulties.
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
deposits containing rounded pebbles, such as can notably be found in Warwickshire
Warwickshire
Warwickshire is a landlocked non-metropolitan county in the West Midlands region of England. The county town is Warwick, although the largest town is Nuneaton. The county is famous for being the birthplace of William Shakespeare...
, Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
, Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...
, Nottinghamshire
Nottinghamshire
Nottinghamshire is a county in the East Midlands of England, bordering South Yorkshire to the north-west, Lincolnshire to the east, Leicestershire to the south, and Derbyshire to the west...
, Yorkshire
Yorkshire
Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...
, Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
and Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. They are thought to be alluvial deposits and, judging from the rounding of the mainly quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
pebbles, to have resulted from prolonged transportation in a large and turbulent river, resulting in powerful abrasion. The deposits in the English Midlands
English Midlands
The Midlands, or the English Midlands, is the traditional name for the area comprising central England that broadly corresponds to the early medieval Kingdom of Mercia. It borders Southern England, Northern England, East Anglia and Wales. Its largest city is Birmingham, and it was an important...
are thought to have been transported in this way northwards from Brittany
Brittany
Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. This supposed river has been called the "Budleighensis", after the Devon village of Budleigh Salterton
Budleigh Salterton
Budleigh Salterton is a small town on the south coast of Devon, England 15 miles south of Exeter. It is situated within an Area of Outstanding Natural Beauty designated East Devon AONB.- Features :...
, a site where such deposits were discovered. The depositions took place in the lower Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period. Some newer conglomerates, e.g. in Warwickshire, near Ryton
Ryton-on-Dunsmore
Ryton-on-Dunsmore is a village and civil parish in the Rugby district of Warwickshire, and is south-east of Coventry, England. The 2001 census recorded a population of 1,672 in the parish. The A45 dual carriageway passes through the village....
are thought to have arisen during the Ice Age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
by reworking and southward transportation of older deposits by ice flows.
The pebble
Pebble
A pebble is a clast of rock with a particle size of 4 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered to be larger than granules and smaller than cobbles . A rock made predominantly of pebbles is termed a conglomerate...
s, also called cobbles
Cobble (geology)
A cobble is a clast of rock with a particle size of to based on the Krumbein phi scale of sedimentology. Cobbles are generally considered to be larger than pebbles and smaller than boulders . A rock made predominantly of cobbles is termed a conglomerate....
, which can be used as gravel
Gravel
Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...
, as ballast
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
or as cobblestone
Cobblestone
Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...
s, are mainly milky-white quartzite but can vary in colour and composition, including some that are hard, reddish-coloured sandstone. The sandstone in which these pebbles are deposited can be used for building or as an aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
for cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
or concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
.
The name "Bunter" derives from the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
term "Buntsandstein
Buntsandstein
The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...
", "bunt" meaning "variegated" or "colourful", referring to the colour of the sandstone deposit, which varies from reddish to greenish. This sandstone is widespread across central Europe, notably in the Black Forest
Black Forest
The Black Forest is a wooded mountain range in Baden-Württemberg, southwestern Germany. It is bordered by the Rhine valley to the west and south. The highest peak is the Feldberg with an elevation of 1,493 metres ....
and Odenwald
Odenwald
The Odenwald is a low mountain range in Hesse, Bavaria and Baden-Württemberg in Germany.- Location :The Odenwald lies between the Upper Rhine Rift Valley with the Bergstraße and the Hessisches Ried in the west, the Main and the Bauland in the east, the Hanau-Seligenstadt Basin – a subbasin of...
region of Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
.
The sandstone can be hard enough for building, yet easy enough to "work", resulting in bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
s, castle
Castle
A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...
s, cathedral
Cathedral
A cathedral is a Christian church that contains the seat of a bishop...
s and churches constructed of reddish sandstone, throughout the relevant areas of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
(e.g. Germany, Luxembourg
Luxembourg
Luxembourg , officially the Grand Duchy of Luxembourg , is a landlocked country in western Europe, bordered by Belgium, France, and Germany. It has two principal regions: the Oesling in the North as part of the Ardennes massif, and the Gutland in the south...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, Alsace
Alsace
Alsace is the fifth-smallest of the 27 regions of France in land area , and the smallest in metropolitan France. It is also the seventh-most densely populated region in France and third most densely populated region in metropolitan France, with ca. 220 inhabitants per km²...
in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
).
The land under which these beds lie is generally very well drained, creating heathlike conditions. Because of the drainage, the soil tends to be of low fertility. A notable area in Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, which has these characteristics, is Cannock Chase
Cannock Chase
Cannock Chase is a mixed area of countryside in the county of Staffordshire, England. The area has been designated as the Cannock Chase Area of Outstanding Natural Beauty. The Chase gives its name to the Cannock Chase local government district....
, a designated Area of Outstanding Natural Beauty
Area of Outstanding Natural Beauty
An Area of Outstanding Natural Beauty is an area of countryside considered to have significant landscape value in England, Wales or Northern Ireland, that has been specially designated by the Countryside Agency on behalf of the United Kingdom government; the Countryside Council for Wales on...
(AONB).
The long shingle
Slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...
tombolo
Tombolo
A tombolo, from the Italian tombolo, derived from the Latin tumulus, meaning 'mound,' and sometimes translated as ayre , is a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar. Once attached, the island is then known as a tied island...
of Chesil Beach
Chesil Beach
Chesil Beach, sometimes called Chesil Bank, in Dorset, southern England is one of three major shingle structures in Britain. Its toponym is derived from the Old English ceosel or cisel, meaning "gravel" or "shingle"....
in Dorset and the raised beach of Portland
Isle of Portland
The Isle of Portland is a limestone tied island, long by wide, in the English Channel. Portland is south of the resort of Weymouth, forming the southernmost point of the county of Dorset, England. A tombolo over which runs the A354 road connects it to Chesil Beach and the mainland. Portland and...
, Dorset are partly composed of Bunter pebbles. As yet, no fully satisfactory and universally accepted geological explanation has been formulated to explain their precise origin and mode of transport, as each proposed theory has its difficulties.