Geology of Great Britain

Geology of Great Britain 1

Geology of Great Britain

Geological Map of Great Britain KEY:

The geology of Great Britain is renowned for its diversity.As a result of its eventful geological history, Great Britainshows a rich variety of landscapes across the constituentcountries of England, Wales and Scotland. Rocks of almost allgeological ages are represented at outcrop, from the Archaeanonwards.

Overview

Seismographical research shows that the crust of the Earthbelow Great Britain is from 27 to 35km (17 to 22 miles)thick. The oldest rocks are found at the surface in north westScotland and are more than half as old as the planet. Theserocks are thought to underlie much of Great Britain andIreland (although boreholes have only penetrated the first fewkilometres), but next appear extensively at the surface inBrittany and the Channel Islands. The youngest rocks arefound in south east England.

Bedrock

The bedrock geology consists of a complex mix of generallyolder metamorphic rocks overlain by varying sequences ofsedimentary rocks, into both of which igneous rocks havebeen intruded at different times. The complexity of Britain'sgeology is due ultimately to its being subject to a variety of plate tectonic processes over a very extended period oftime. Changing latitude and sea levels have been important factors in the nature of sedimentary sequences, whilstsuccessive continental collisions have affected its geological structure with major faulting and folding being a legacyof each orogeny (mountain-building period), often associated with volcanic activity and the metamorphism ofexisting rock sequences.

Superficial depositsOverlain on this bedrock geology ("solid geology" in the terminology of maps) is a varied distribution ofunconsolidated material of more recent origin. It includes material deposited by glaciers (boulder clay, and otherforms of glacial drift such as sand and gravel). "Drift" geology is often more important than "solid" geology whenconsidering building works, drainage, siting water boreholes, sand and gravel resources and soil fertility. Although"drift" strictly refers to glacial and fluvio-glacial deposits, the term on geological maps has traditionally includedother material including alluvium, river terraces, etc. Recent maps use the terms "bedrock" and "superficial" in placeof "solid" and "drift".


Geological historyThis description of the geological history of Britain is based on that of P.Toghill.

Precambrian

Archaean eon

The Lewisian gneiss, the oldest rocks in Great Britain or Ireland, date from at least 2,700 Ma (Ma = million yearsago) in the Archaean eon, the Earth itself being about 4,600 Ma old. They are found in the far north west of Scotlandand in the Hebrides, with a few small outcrops elsewhere. Formed from rock originally deposited at the surface ofthe planet, the rocks were later buried deep in the Earth's crust and metamorphosed into crystalline gneiss.

Proterozoic eon

South of the gneisses are a complex mixture of rocks forming the North West Highlands and Grampian Highlands inScotland. These are essentially the remains of folded sedimentary rocks that were originally 25km thick, depositedover the gneiss on what was then the floor of the Iapetus Ocean. The process started in about 1,000 Ma, with anotable 7km thick layer of Torridon Sandstone being deposited about 800 Ma, as well as the debris deposited by anice sheet 670 Ma.Palaeomagnetic evidence indicates that 520 Ma, what is now Great Britain was split between two continents,separated by 7,000km (4,300mi) of ocean. The north of Scotland was located at about 20 south of the equator onthe continent of Laurentia near the Tropic of Capricorn, while the rest of the country was at about 60 south on thecontinent of Gondwana near the Antarctic Circle.In Gondwana, England and Wales were near a subduction zone. Both countries were largely submerged under ashallow sea studded with volcanic islands. The remains of these islands underlie much of central England with smalloutcrops visible in many places. Around 600 Ma, the Cadomian Orogeny (mountain building period) caused theEnglish and Welsh landscape to be transformed into a mountainous region, along with much of north west Europe.

Palaeozoic era

Cambrian period

In the early Cambrian period the volcanoes and mountains of England and Wales were eroded as the land becameflooded by a rise in sea level, and new layers of sediment were laid down. Much of central England formed a stableblock of crust which has remained largely undeformed ever since. Sandstones were deposited in the north ofScotland. The first animals with hard shells evolved at this time, consequently, fossils become much more commonin rocks formed during this and later periods.

Ordovician period

500 million years ago, in the Ordovician period, southern Britain, the east coast of North America and south-eastNewfoundland broke away from Gondwana to form the continent of Avalonia, which by 440 Ma had drifted (by themechanisms of plate tectonics) to about 30 south.During this period north Wales was subject to volcanic activity. The remains of these volcanoes are still visible, oneexample of which is Rhobell Fawr dating from 510 Ma. Large quantities of volcanic lava and ash known as theBorrowdale Volcanics covered the Lake District and this can still be seen in the form of mountains such as Helvellynand Scafell Pike.The Ordovician also saw the formation of the Skiddaw slate deposits around 500 Ma.


Silurian period

Deposition continued into the early part of the Silurian period, with mudstones and sandstones being laid down,notably in Wales.Avalonia had now joined with the continent of Baltica, and the combined landmass collided with Laurentia at about20 south between 425 and 400 Ma, joining the southern and northern halves of Great Britain together. The resultingCaledonian Orogeny produced an Alpine-style mountain range in much of north and west Britain. The continentalcollision was probably at an oblique angle rather than a head-on collision, and this probably led to movement alongstrike-slip faults trending north-east to south-west across Scotland, the Great Glen Fault being the best example(some of these fault zones may have been old lines of weakness from earlier earth movements).Volcanic ashes and lavas deposited during the Silurian are still found in the Mendip Hills and in Pembrokeshire.

Devonian period

The Old Red Sandstone Continent in the Devonian

The collision between continents continuedduring the Devonian period, with continuinguplift, and more volcanic deposits such asthose now forming Ben Nevis. Sea levelsvaried considerably, with the coastlineadvancing and retreating from north to southacross England. The uplifted region wasgradually eroded down, resulting in thedeposition of numerous sedimentary rocklayers in lowlands and seas. The rocks ofmarine origin in the county of Devon gavethe period its name, though deposits of thisage are found in many other places, such asthe Brecon Beacons, the Midland Valley ofScotland, and the Orkney Islands. Most ofthese are of terrestrial origin and areinformally known as the Old Red Sandstone.

The Caledonian mountains had largely been eroded away by the end of the period during which the country wouldhave experienced an arid desert climate as it was located close to the equator at between 10 and 15 south.

Carboniferous period

Around 360 Ma at the start of the Carboniferous period Great Britain was lying at the equator, covered by the warmshallow waters of the Rheic Ocean, during which time the Carboniferous Limestone was deposited, as found in theMendip Hills, north and south Wales, in the Peak District of Derbyshire, north Lancashire, the northern Pennines andsoutheast Scotland. Caves developed more recently in the limestone of some of these areas by the action of carbonicacid and other organic acids in rainwater and groundwater.These were followed by dark marine shales, siltstones, and coarse sandstones of the Millstone Grit. Later, riverdeltas formed and the sediments deposited were colonised by swamps and rain forest. It was in this environment thatthe cyclic Coal Measures were formed, the source of the majority of Britain's extensive coal reserves that poweredthe Industrial Revolution. Coal can be found in many areas of Britain, as far north as the Midland Valley of Scotland,as far south as Kent, although coal mining has largely been concentrated in the English Midlands, northern Englandand Wales.


Throughout the period, southwest England in particular was affected by the collision of continental plates. Themountain building period known as the Variscan orogeny, which occurred around 280 Ma, caused majordeformation in south west England. Towards the end of this period granite was formed beneath the overlying rocksof Devon and Cornwall, now exposed at Dartmoor and Bodmin Moor, giving rise to mineralised deposits of copperand tin. The general region of Variscan folding was south of an eastwest line roughly from south Pembrokeshire toKent. The main tectonic pressure was from the south or south-east, and may have resulted in dextral strike-slipfaulting. The Devon-Cornwall massif may originally have been some distance further east, then to be movedwestwards. Lesser Variscan folding took place as far north as Derbyshire and Berwick-upon-Tweed.By the end of the Carboniferous period the various continents of the Earth had fused to form the super-continent ofPangaea. Britain was located in the interior of Pangea where it was again subject to a hot arid desert climate withfrequent flash floods leaving deposits that formed beds of red sedimentary rock, somewhat similar to the later,Triassic New Red Sandstone.

Permian period

The Permian was characterised for 30 million years by arid desert conditions and the erosion of the land that haduplifted in the Variscan Orogeny, southwest England and adjacent areas of the present-day English Channel. Later,much of Great Britain was submerged in shallow waters as the polar ice sheets melted and the Tethys Ocean andZechstein Sea formed, depositing shale, limestone, gravel, and marl, before finally receding to leave a flat desertwith salt pans.

Mesozoic era

Triassic period

As Pangaea drifted during the Triassic, Great Britain moved away from the equator until it was between 20 and 30north. Red beds, including sandstones and red mudstones form the main sediments of the New Red Sandstone. Theremnants of the Variscan uplands in France to the south were eroded down, resulting in layers of the New RedSandstone being deposited across central England, and in faulted basins in Cheshire and the Irish Sea. A basindeveloped in the Hampshire region around this time. Rifting occurred within and around Britain and Ireland, prior tothe breakup of the super-continent in the Jurassic period.Rock fragments found near Bristol appear to indicate that in 214 Ma Great Britain was showered with a fine layer ofdebris from an asteroid impact at the Manicouagan Impact Crater in Canada, although this is still being debated.

Jurassic period

As the Jurassic period began, Pangaea began to break up, sea levels rose and Britain and Ireland drifted on theEurasian Plate to between 30 and 40 north. With much of the British Isles under water again, sedimentary rockswere deposited and can now be found underlying much of England from the Cleveland Hills of Yorkshire to theJurassic Coast in Dorset. These include sandstones, greensands, oolitic limestone of the Cotswold Hills, corallianlimestone of the Vale of White Horse and the Isle of Portland.The burial of algae and bacteria below the mud of the sea floor during this time resulted in the formation of NorthSea oil and natural gas, much of it trapped in overlying sandstone by salt deposits formed as the sea levels fell toform the swamps and salty lakes and lagoons that were home to dinosaurs. [citation needed]


Cretaceous period

The modern continents having formed, the Cretaceous saw the formation of the Atlantic Ocean, gradually separatingnorthern Scotland from North America. The land underwent a series of uplifts to form a fertile plain.After 20 million years or so, the seas started to flood the land again until much of Britain and Ireland were againbelow the sea, though sea levels frequently changed. Chalk and flints were deposited over much of Great Britain,now notably exposed at the White Cliffs of Dover and the Seven Sisters, and also forming Salisbury Plain. The highsea levels left only small areas of land exposed, which accounts for the general lack of land-origin sand, mud or claysediments found from around this time. Some of the late Cretaceous strata are, in fact, almost pure chalk.

Cenozoic era

Palaeogene period

In the early Palaeogene period between 63 and 52 Ma, the last volcanic rocks in Great Britain were formed. Themajor eruptions at this time produced the Antrim Plateau, the basaltic columns of the Giant's Causeway and the lavasand igneous intrusions of the Inner Hebrides of Scotland.The Alpine Orogeny that took place about 50 Ma was responsible for the shaping of the London Basin syncline, theWeald-Artois Anticline to the south, the North Downs, South Downs and Chiltern Hills.During the period the North Sea formed, Britain was uplifted. Some of this uplift was along old lines of weaknessleft from the Caledonian and Variscan Orogenies long before. The uplifted areas were then eroded, and furthersediments, such as the London Clay, were deposited over southern England, while the English Channel wascharacterised by mud flats and river-deposited sands. Much of the midlands and north of England may have beencovered by Jurassic and Cretaceous deposits at the start of the Palaeogene, but these were lost through erosion. By 35Ma the landscape was colonised by trees such as beech, oak, redwood and palm, along with grasses.

Neogene period

Miocene and Pliocene epochs

In the Miocene and Pliocene epochs of the Neogene, further uplift and erosion occurred, particularly in Wales, thePennines, and the Scottish Highlands. Plant and animal types developed into their modern forms, and by about 2million years ago the landscape would have been broadly recognisable today.

Quaternary period

Pleistocene epoch

The Merton Stone, one of the largestglacial erratics in England

The major changes during the Pleistocene were brought about by severalrecent ice ages. The most severe was the Anglian Glaciation, with ice up to1,000m (3300ft) thick that reached as far south as London and Bristol. Thistook place between about 478,000 to 424,000 years ago, and was responsiblefor the diversion of the River Thames onto its present course.

There is extensive evidence in the form of stone tools that southern Englandwas colonised by human populations during the warm Hoxnian Stage thatfollowed the Anglian Glaciation. It is possible that the English Channelrepeatedly opened and closed during this period, causing Britain to become anisland from time to time. The oldest human fossils found to date in the British Isles, which include the skull ofSwanscombe Man from 250,000 years ago, and the earlier Clactonian Man, also date from this period.

The Wolstonian Glaciation, between about 352,000 to 130,000 years ago, which is thought to have peaked around 150,000 years ago, was named after the village of Wolston southeast of Coventry which is thought to mark the


southern limit of the ice.The Wolstonian Stage was followed by the Ipswichian Stage, during which hippopotamus are known to have livedas far north as Leeds.During the most recent Devensian glaciation, which is thought to have started around 115,000 years ago, peakedaround 20,000 years ago and ended a mere 10,000 years ago, the Usk valley and Wye valley were eroded by glaciers,with the icesheet itself reaching south to Wolverhampton and Cardiff. The oldest human remains in Britain orIreland, the Red Lady of Paviland (29,000 years old) date from this time. It is thought that the country waseventually abandoned as the ice sheet reached its peak, being recolonised as it retreated. By 5,000 years ago it isthought that Great Britain was warmer than it is at present.Among the features left behind by the ice are the fjords of the west coast of Scotland, the U-shaped valleys of theLake District and erratics (blocks of rock) that have been transported from the Oslo region of Norway and depositedon the coast of Yorkshire.

Holocene epoch

The last twelve thousand years are known as the Holocene Epoch. Amongst the most significant geological featurescreated during this period are the peat deposits of Ireland and Scotland, and of coastal and upland areas of Englandand Wales. Many of the lowland deposits, such as the Somerset Levels, The Fens and Romney Marsh have recentlybeen artificially drained.Since humans began clearing the forest during the New Stone Age, most of the land has now been deforested,speeding the natural processes of erosion. Large quantities of stone, gravel and clay are extracted each year, and by2000 11% of England was covered by roads or buildings.At the present time Scotland is continuing to rise as a result of the weight of Devensian ice being lifted. Southern andeastern England is sinking, generally estimated at 1mm (1/25inch) per year, with the London area sinking at doublethe speed partly due to the continuing compaction of the recent clay deposits.In addition, rises in sea level thought to be due to global warming appear likely to make low lying areas of landincreasingly susceptible to flooding, while in some areas the coastline continues to erode at a geologically rapid rate.Great Britain continues to be subject to several very minor earthquakes each month, and more occasional light tomoderate ones. During the 20th century 25 earthquakes with a moment magnitude of 4.5 to 6.1 were felt,[1] many ofthem originating within the Isles themselves.

Geological features Cheddar Gorge - the largest gorge in Great Britain Jurassic Coast - a UNESCO World Heritage Site Great Glen Fault Highland Boundary Fault Southern Uplands Fault Midland Valley of Scotland Fingal's Cave - columnar Tertiary basaltic formation (similar to the Giant's Causeway in Northern Ireland) Salisbury Plain Tees-Exe line Whin Sill Siccar Point in Berwickshire provided early proof of the immense age of the Earth. The Moine Thrust was the first thrust belt to be discovered by geologists. London Basin Hampshire Basin


North Downs Weald South Downs London-Brabant Massif Cornubian batholith - early Permian intrusion in the South West of England, forming moors where exposed at the

surface, such as Dartmoor Lizard Complex - a piece of obducted oceanic crust, (i.e. an Ophiolite). Iapetus Suture - line of closure of the Iapetus suture.

Geological resourcesBritain's complex geology has provided it with a wide range of geological resources including abundant supplies ofcoal, the initial extraction of which powered the Industrial Revolution. During the 20th century the exploitation ofNorth Sea oil and gas provided further energy supplies for the nation. Geothermal energy and onshore oil have alsobeen exploited to a lesser extent.A wide variety of stone has been worked for building and general construction needs (e.g. sand and gravel) whilstother minerals have been mined or quarried for the chemical industry (e.g. salt), the production of metals (e.g. copperand tin) or other uses (e.g. china clay).

Events Storegga Slides, caused a tsunami c. 6100 BC Bristol Channel floods, 1607 was caused by a tsunami 1755 Lisbon earthquake caused a tsunami that hit Cornwall. Colchester earthquake, 1884 2002 Dudley earthquake 2008 Lincolnshire earthquake

Institutions

Government agencies British Geological Survey

Learned societies Geological Society of London Edinburgh Geological Society Royal Geological Society of Cornwall

Pioneers of British Geology Mary Anning 17991847 Thomas George Bonney 18331923 William Buckland 17841856 William Conybeare 17871857 James Hutton 17261797 the "Father of modern geology" Charles Lapworth 18421920 Sir Charles Lyell 17971875 Gideon Mantell 17901852


Sir Roderick Murchison 17921871 John Phillips 18001874 Adam Sedgwick 17851873 William Smith 17691839 the "Father of English geology"

Awards Wollaston Medal

Geology of the UK: Section from Snowdon to Harwich showing underlying strata. Thiscross section shows what would be seen in a deep cutting nearly E. and W. across

England and Wales. It shows also how, in consequence of the folding of the strata and thecutting off of the uplifted parts, old rocks which should be tens of thousands of feet down

are found in borings in East Anglia only 1000 feet or so below the surface.

References[1] http:/ / www. quakes. bgs. ac. uk/ hazard/

eqlst. htm

Further reading

Bennison, G.M.; A.E. Wright(1969). The Geological History ofthe British Isles. London: EdwardArnold. pp.406 + x.ISBN0-7131-2226-9.

Owen, T.R. (1976). The GeologicalEvolution of the British Isles. Oxford: Pergamon Press. pp.161 + viii. ISBN0-08-020461-9.

Rayner, D.H. (1967). The Stratigraphy of the British Isles. London: Cambridge University Press. pp.459 + x.ISBN0-521-06047-8.

Woodcock, N.H.; Strachan, R.A. (Eds.) (2002). Geological History of Britain and Ireland (http:/ / www.blackwellpublishing. com). Oxford: Blackwell Science. pp.viii+423. ISBN0-632-03656-7.

External links British Geological Survey Publications Catalogue (http:/ / www. bgs. ac. uk/ catalogue/ home. html) The BGS Lexicon of Named Rock Units (http:/ / www. bgs. ac. uk/ lexicon/ ) BGS Geology of Britain Viewer (http:/ / mapapps. bgs. ac. uk/ geologyofbritain/ home. html) UK Earthquakes (http:/ / www. quakes. bgs. ac. uk/ ) UK Peak District Geology (http:/ / www. thepeakdistrict. info/ fast/ html/ peak_district_geology. html) Northern Ireland Geology (http:/ / www. geographyinaction. co. uk/ Geology files/ Geol_index. html) UK Geology/Fossil locations (http:/ / www. discoveringfossils. co. uk) Geology map of Europe (http:/ / www. soton. ac. uk/ ~imw/ jpg/ eurogy. jpg)

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Article Sources and ContributorsGeology of Great Britain Source: http://en.wikipedia.org/w/index.php?oldid=591005018 Contributors: 16@r, A Karley, AWhiteC, Adamsan, AnFu, Arpingstone, BD2412, Ballista,BanyanTree, Ben MacDui, Blathnaid, Bobblewik, Bryan Derksen, CanisRufus, Canterbury Tail, Carandol, Chilepine, Chill doubt, ChrisGualtieri, Ciaurlec, Corpx, D6, Dave souza, Decltype,Derek Ross, Dlloyd, Dyvroeth, ERcheck, EdH, Epbr123, Finnrind, Francs2000, Gasta220, Gene Nygaard, GeoGreg, GeoWriter, Geopersona, Geosciencewriter, Graeme Bartlett, Grunners,Gsmgm, Gvotno, Halsteadk, Harkey Lodger, Heron, Hmains, Hugo999, Jamiesuthzerland, Jeepday, Jpbowen, Kate, Kbthompson, Kwekubo, Lancevortex, Lapsed Pacifist, Light current,LilHelpa, Lumos3, Lysy, Materialscientist, Mattcymru, Mejor Los Indios, Mikenorton, MisfitToys, Mkrab, Mr Stephen, Nojer, NotoBritishirredentism, OrenBochman, Pahazzard,PaleCloudedWhite, Paul H., Pcpcpc, Pedro, Petrb, Pterre, R'n'B, RJPe, Ray Gabbro, Red King, RedWolf, Rich Farmbrough, Richerman, Robinspw, Rubberstamp, Rushton2010, Selyabd,Silverchemist, Simple Bob, Sjorford, Skirrid, Smb1001, SteinbDJ, Steinsky, Steven J. Anderson, Stone, Str1977, SuzanneKn, Sylvain Mielot, Tagishsimon, Thelb4, Timwi, Tithon, Vsmith,Wmahan, Woohookitty, Worldtraveller, Wotapalaver, Wurzeller, Zeimusu, .., 115 anonymous edits

Image Sources, Licenses and ContributorsFile:Geology Map UK.svg Source: http://en.wikipedia.org/w/index.php?title=File:Geology_Map_UK.svg License: Creative Commons Attribution-Sharealike 3.0 Contributors: AlexDFile:Euramerica en.svg Source: http://en.wikipedia.org/w/index.php?title=File:Euramerica_en.svg License: Creative Commons Attribution-ShareAlike 3.0 Unported Contributors: ThomasROBERTFile:The Merton Stone - geograph.org.uk - 1954360.jpg Source: http://en.wikipedia.org/w/index.php?title=File:The_Merton_Stone_-_geograph.org.uk_-_1954360.jpg License: CreativeCommons Attribution-Share Alike 2.0 Generic Contributors: Ashley DaceFile:Geology of UK - Section from Snowdon to Harwich.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Geology_of_UK_-_Section_from_Snowdon_to_Harwich.jpg License:Public Domain Contributors: S. Baring-Gould

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Geology of Great BritainOverview Bedrock Superficial deposits

Geological historyPrecambrianArchaean eonProterozoic eon

Palaeozoic eraCambrian periodOrdovician periodSilurian periodDevonian periodCarboniferous periodPermian period

Mesozoic eraTriassic periodJurassic periodCretaceous period

Cenozoic eraPalaeogene periodNeogene periodQuaternary period

Geological featuresGeological resourcesEventsInstitutionsGovernment agenciesLearned societies

Pioneers of British GeologyAwardsReferencesFurther readingExternal links

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Geology of Great Britain