Geology of Great Britain 520744 220827617 2008-06-21T20:04:50Z Finnrind 3865283 rm link deleted image {{Nofootnotes|date=February 2008}} The '''Geology of Great Britain''' is hugely varied and complex, and gives rise to the wide variety of landscapes found across the islands. This varied [[geology]] has also meant that the island has been an important source for the formation of many geological concepts. == Seismographical results == [[Seismology|Seismographical]] research shows that the [[Crust (geology)|crust]] of the [[Earth]] below [[Great Britain]] is between 27 and 35 km (17 to 22 miles) thick. The oldest rocks are found at the surface in north west [[Scotland]] and are more than half as old as the [[planet]]. They are thought to underlie much of [[Great Britain]] and [[Ireland]] (although boreholes have only penetrated the first few kilometres), but next appear extensively at the surface in [[Brittany]] and the [[Channel Islands]]. The youngest rocks are found in south east [[England]]. === Bedrock === The [[bedrock]] consists of many layers formed over vast periods of time. These were laid down in various [[climate]]s as the global climate changed, the landmasses moved due to [[Plate Tectonics]], and the land and sea levels rose or fell. From time to time horizontal forces caused the rock to undergo considerable [[deformation]], folding the layers of rock to form mountains which have since been [[erosion|eroded]] and overlain with other layers. To further complicate the geology, the land has also been subject to periods of [[earthquake]]s and [[vulcanism|volcanic]] activity. === Deposits by glaciers === Overprinted on this [[bedrock]] geology ("solid geology" in the terminology of the maps) is a somewhat variable distribution of soils and fragmental material deposited by glaciers ([[boulder clay]], and other forms of [[Glacial_landforms#Depositional_landforms | glacial drift]] in the recent past. Maps showing the distribution of this "drift" geology are frequently produced as either separate maps, or as literal overprints on the solid geology maps. When ordering maps, this distinction should be kept in mind. Catalogues often distinguish them as "S", "D" or "S+D" maps. "Drift" geology is often more important than "solid" geology when considering building works, drainage, siting water boreholes, sand & gravel resources, soil fertility, and many other issues. Although "drift" strictly refers to glacial and fluvio-glacial deposits, the term on geological maps has traditionally included other material including alluvium, river terraces, etc. Recent maps use the terms "Bedrock" and "Superficial" in place of "Solid and Drift". ==Geological history== <ref name=Toghill>{{cite book |title=The Geology of Britain: An Introduction |last=Toghill |first=Peter |authorlink= |coauthors= |year=2000 |publisher=Swan Hill Press |location= Shrewsbury|isbn=1 85310 890 1 }}</ref> ===Proterozoic Era=== The [[Gneiss]]es, the oldest rocks in [[Great Britain]] or [[Ireland]], date from at least 2,700 Ma (Ma = millions of years ago) in the [[Archaean]] period of this era, the [[Earth]] itself being only about 4,600 Ma old. They are found in the far north west of [[Scotland]] and in the [[Hebrides]], with a few small outcrops elsewhere. Formed from rock originally deposited at the surface of the planet, the rocks were later buried deep in the Earth's crust and [[metamorphic rock|metamorphosed]] into crystalline gneiss. South of the Gneisses are a complex mixture of rocks forming the North West [[Scottish Highlands|Highlands]] and [[Grampian]] Highlands in Scotland, as well as the [[Connemara]], [[Donegal]] and [[County Mayo|Mayo]] mountains of Ireland. These are essentially the remains of folded [[sedimentary rock]]s that were originally 25 km thick, deposited over the gneiss on what was then the floor of the [[Iapetus Ocean]]. The process started in about 1,000 Ma, with a notable 7 km thick layer of [[Torridon Sandstone]] being deposited about 800 Ma, as well as the [[Moraine|debris]] deposited by an [[ice sheet]] 670 Ma. [[Palaeomagnetism|Palaeomagnetic]] evidence indicates that 520 Ma, what is now the UK was split between two [[continent]]s, separated by 7000 km (4500 miles) of ocean. The north of Scotland was located at about 20° south of the [[equator]] on the continent of [[Laurentia]] near the [[Tropic of Capricorn]], while the rest of the country was at about 60° south on the continent of [[Gondwana]] near the [[Antarctic Circle]]. In Gondwana, England and [[Wales]] were near a [[subduction]] zone. Both countries were largely submerged under a shallow sea studded with [[volcano|volcanic]] islands. The remains of these islands underlie much of central England with small outcrops visible in many places. Around 600 Ma, the [[Cadomian Orogeny]] (mountain building period) caused the English 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 became flooded by a rise in sea level, and new layers of [[sediment]] were laid down. Much of central England formed a stable block of crust which has remained largely undeformed ever since. [[Sandstone]]s were deposited in the north of Scotland. As this is when the first hard shells evolved, [[fossil]]s become much more common from this period onwards. ====Ordovician period==== 500 million years ago, in the [[Ordovician]] period, southern Britain, the east coast of [[North America]] and south-east [[Newfoundland (island)|Newfoundland]] broke away from Gondwana to form the continent of [[Avalonia]], which by 440 Ma had drifted (by the mechanisms of [[plate tectonics]]) to about 30° south. During this period north Wales and south Mayo experienced [[volcanism|volcanic]] activity. The remains of these volcanoes are still visible, for example [[Rhobell Fawr]], dating from 510 Ma. Large quantities of volcanic [[lava]] and ash known as the [[Borrowdale Volcanics]] covered both Wales and the [[Lake District]], still seen in the form of mountains such as [[Helvellyn]] and [[Scafell Pike]]. The Ordovician also saw the formation of the Welsh [[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 about 20° south between 425 and 400 Ma, joining the southern and northern halves of [[Great Britain]] together. The resulting [[Caledonian Orogeny]] produced an [[Alps|Alpine]]-style mountain range in much of north and west Britain. The continental collision was probably at an oblique angle rather than a head-on collision, and this probably led to movement along [[Geologic fault#Strike-slip faults|strike-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 collision between continents continued during the [[Devonian period|Devonian]] period, with continuing uplift, and more volcanic deposits such as those now forming [[Ben Nevis]]. Sea levels varied considerably, with the coastline advancing and retreating from north to south across England. The uplifted region was gradually eroded down, resulting in the deposition of numerous sedimentary rock layers in lowlands and seas. The [[Old Red Sandstone]] of [[Devon]] gave the period its name, though deposits are found in many other places, such as the [[Brecon Beacons]], the [[Central Lowlands|Midland Valley]] of Scotland, and the [[Orkney Islands]]. The [[Caledonian mountains]] had largely been [[erosion|eroded]] away by the end of the period during which the country would have experienced an arid [[desert]] [[climate]] and been located between 10° and 15° south of the [[equator]]. ====Carboniferous period==== Around 360 Ma during the [[Carboniferous]] period Great Britain was lying at the equator, covered by the warm shallow waters of the [[Rheic Ocean]], during which time the Carboniferous Limestone was deposited, as found in the [[Mendip Hills]], north and south Wales, in the [[Peak District]] of [[Derbyshire]], north [[Lancashire]], the northern [[Pennines]] and southeast Scotland. Caves have developed more recently in the limestone in some of these areas. These were followed by dark marine [[shales]], [[siltstones]], and coarse sandstones of the [[Millstone Grit]]. Later, [[river delta]]s formed and the sediments deposited were colonised by [[swamp]]s and [[rain forest]]. It was in this environment that the [[cyclic sediments|cyclic]] [[Coal Measures]] were formed, the source of the majority of Britain's extensive [[coal]] reserves that powered the [[Industrial Revolution]]. Coal can be found in many areas of Britain and Ireland, as far north as the Midland Valley of [[Scotland]], as far south as [[Kent]] and in Ireland, though it has largely been mined in the [[Midlands|English midlands]], northern England and Wales. Throughout the period, southwest England in particular was affected by the collision of [[continental plates]]. The [[Variscan orogeny]] (mountain building period) around 280 Ma caused major deformation in south west England. Towards its end [[granite]] was formed beneath the overlying rocks of [[Devon]] and [[Cornwall]], now exposed as [[Dartmoor]] and [[Bodmin Moor]], giving rise to mineralised deposits of [[copper]] and [[tin]]. The general region of Variscan folding was south of an east–west line roughly from south [[Pembrokeshire]] to [[Kent]]. The main [[tectonic]] pressure was from the south or south-east, and may have resulted in [[Geologic fault#Strike-slip faults|dextral strike-slip]] faulting. The [[Devon]]-[[Cornwall]] massif may originally have been some distance further east, then to be moved westwards. Lesser Variscan folding took place as far north as [[Derbyshire]] and [[Berwick-upon-Tweed]]. By the end of the period the various continents of the World had fused to form one super-continent of [[Pangaea]], with [[Great Britain|Britain]] in the interior, where it was again subject to a hot arid desert climate, with frequent flash floods leaving deposits that formed red beds, somewhat similar to the later, [[Triassic]] [[New Red Sandstone]]. ====Permian period==== The [[Permian]] was characterised for 30 million years by arid desert and erosion of the areas uplifted in the Variscan Orogeny (southwest England and adjacent areas in 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]] and [[Zechstein Sea]] formed, depositing [[shale]], [[limestone]], [[gravel]], and [[marl]], before finally receding to leave a flat desert with [[salt pan]]s. ===Mesozoic Era=== ====Triassic period==== As Pangaea drifted during the [[Triassic]], Great Britain moved away from the equator until it was between 20° and 30° north. Red beds, including [[sandstones]] and red [[mudstone]]s form the main sediments of the [[New Red Sandstone]]. The remnants of the Variscan uplands in [[France]] to the south were eroded down, resulting in layers of the New Red Sandstone being deposited across central England, and in [[geologic fault|faulted]] basins in [[Cheshire]] and the Irish Sea. A basin developed in the [[Hampshire]] region around this time. [[Rift|Rifting]] occurred within and around Britain and Ireland, prior to the 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 of debris from an [[impact event|asteroid impact]] at the [[Manicouagan Impact Crater]] in [[Canada]], although this is still being debated. ====Jurassic period==== As the [[Jurassic]] started, [[Pangaea]] began to break up and sea levels rose, as Britain and Ireland drifted on the [[Eurasian Plate]] to between 30° and 40° north. With much of the Isles under water again, [[sedimentary rock]]s were deposited and can now be found underlying much of southern England from the [[Cleveland Hills]] of [[Yorkshire]] to the [[Jurassic Coast]] in [[Geology of Dorset|Dorset]], including [[clay]]s, [[sandstone]]s, [[greensand]]s, [[oolite|oolitic]] [[limestone]] of the [[Cotswold Hills]], [[corallian limestone]] of the [[Vale of White Horse]] and the [[Portland Limestone|Isle of Portland]]. The burial of [[algae]] and [[bacterium|bacteria]] below the mud of the sea floor during this time resulted in the formation of [[North Sea oil]] and [[natural gas]], much of it trapped in overlying sandstone by [[salt]] deposits formed as the seas fell to form the swamps and salty lakes and lagoons that were home to [[dinosaur]]s. ====Cretaceous period==== The modern continents having formed, the [[Cretaceous]] saw the formation of the [[Atlantic Ocean]], gradually separating northern 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 again below the sea, though sea levels frequently changed. [[Chalk]] and [[flint]]s were deposited over much of Great Britain, now notably exposed at the [[White Cliffs of Dover]] and the [[Seven Sisters, Sussex|Seven Sisters]], and also forming [[Salisbury Plain]]. The high sea levels left only small areas of land exposed. This caused the general lack of land-origin sand, mud or clay sediments around this time - some of the late Cretaceous strata are almost pure chalk. ===Caenozoic Era=== ====Palaeogene period==== In the early [[Palaeogene]] period between 63 and 52 Ma, the last volcanic rocks in Great Britain were formed, with the major eruptions that formed the [[County Antrim|Antrim Plateau]] and the [[basalt]]ic columns of the [[Giant's Causeway]]. The volcanic [[Lundy Island]] in the [[Bristol Channel]] also dates from this period. The [[Alpine Orogeny]] that took place about 50 Ma was responsible for the shaping of the [[London Basin]] [[syncline]], the [[Weald-Artois Anticline]] to the south, and also the North Downs, South Downs and Chiltern Hills. During the period the [[North Sea]] formed, Britain was [[uplift]]ed. Some of this uplift was along old lines of weakness from the Caledonian and Variscan Orogenies long before. The uplifted areas were then eroded, and further sediments were deposited over southern England, including the [[London Clay]], while the [[English Channel]] consisted of [[mud flat]]s and river deposited [[sand]]s. Much of the midlands and north of England may have been covered by Jurassic and Cretaceous deposits at the start of the Palaeogene, but lost them through erosion. By 35 Ma the landscape included [[beech]], [[oak]], [[sequoia|redwood]] and [[Arecaceae|palm]] trees, along with [[grass]]land. ====Neogene period==== =====Miocene and Pliocene epochs===== In the [[Miocene]] and [[Pliocene]] epochs of the [[Neogene]], further uplift and erosion occurred, particularly in Wales, the Pennines, and the Scottish Highlands. Plant and animal types developed into their modern forms, and by about 2 million years ago the landscape would have been broadly recognisable today. =====Pleistocene epoch===== The major changes during the [[Pleistocene]] have been brought about by several recent [[ice age]]s. The most severe was the [[Anglian glaciation]], with ice up to 1,000 m (3300 ft) thick that reached as far south as [[London]] and [[Bristol]], took place between about 500,000 to 400,000 years ago, and was responsible for the diversion of the [[River Thames]] onto its present course. There is extensive evidence in the form of stone tools that southern England was colonised by [[human]] populations during the warm [[Hoxnian interglacial]] period that followed the Anglian Glaciation. It is possible that the [[English Channel]] repeatedly opened and closed during this period, causing Britain to become an island from time to time. The oldest human [[fossil]]s in the Isles also date from this time, including the skull of [[Swanscombe Man]] from 250,000 years ago, and the earlier [[Clactonian Man]]. The [[Wolstonian glaciation]], between about 200,000 to 130,000 years ago, and thought to have peaked around 150,000 years ago, was named after the town of [[Wolston]] south of [[Birmingham]] which is thought to mark the southern limit of the ice. The Wolstonian was followed by the [[Ipswichian interglacial]], during which [[hippopotamus]] are known to have lived as far north as [[Leeds]]. During the most recent [[Devensian glaciation]], which is thought to have started around 115,000 years ago, peaked around 20,000 years ago and ended a mere 10,000 years ago, the [[River Usk|Usk valley]] and [[River Wye|Wye valley]] were eroded by [[glacier]]s, with the ice sheet itself reaching south to [[Birmingham]]. The oldest human remains in Britain or Ireland, the [[Red Lady of Paviland]] (29,000 years old) date from this time. It is thought that the country was eventually abandoned as the ice sheet reached its peak, being recolonised as it retreated. By 5,000 years ago it is thought that Great Britain was warmer than it is at present. Among the features left behind by the ice are the [[fjord]]s of the west coast of Scotland, the [[Glaciated valley|U shaped valleys]] of the [[Lake District]] and [[erratic]]s (blocks of rock) that have been transported from the [[Oslo]] region of [[Norway]] and deposited on the coast of [[Yorkshire]]. =====Holocene epoch===== Over the last twelve thousand years (the [[Holocene]] Epoch) the most significant new geological features have been the deposits of [[peat]] in Ireland and Scotland, as well as in coastal areas that have recently been artificially drained such as the [[Somerset Levels]], [[The Fens]] and [[Romney Marsh]] in England. Since humans began clearing the forest during the [[Neolithic|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 by [[2000]] 11% of England was covered by [[road]]s or [[building]]s. At the present time Scotland is continuing to rise as a result of the weight of Devensian ice being lifted. The rest of Britain is sinking, generally estimated at 1 mm (1/25 inch) per year, with the London area sinking at double the speed partly due to the continuing compression 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 land increasingly 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 [[earthquake]]s each month, and occasional light to moderate ones. During the 20th century 25 earthquakes with a magnitude of 4.5 to 6.1 on the [[Richter magnitude scale|Richter scale]] were felt [http://www.quakes.bgs.ac.uk/hazard/eqlst.htm], many of them 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]] *[[Central Lowlands|Midland Valley of Scotland]] *[[Salisbury Plain]] *[[Tees-Exe line]] *[[Whin Sill]] *[[Siccar Point]] in [[Berwickshire]] provided early proof of the immense age of the Earth. *[[Moine Thrust Belt|The Moine Thrust]] was the first thrust belt to be discovered by geologists. *[[London Basin]] *[[Hampshire Basin]] *[[London-Brabant Island]] *[[Dartmoor]] - one of a series of Moors in the South West of England developing [[Tor]]s on a [[granite|granitic]] [[batholith]] ==Geological resources== *[[Coal]] *[[North Sea oil]] *[[Mining in Cornwall|Copper and Tin]] *[[List_of_stone#United_Kingdom|Stone]] ==Events== *[[Storegga Slide]]s, caused a tsunami circa 6100 BC *[[Bristol Channel floods, 1607]] (possible tsunami) *[[1755 Lisbon earthquake]] caused a tsunami that hit [[Cornwall]]. *[[1884 Colchester earthquake|Colchester earthquake]], [[1884]] *[[2002 Dudley earthquake]] ==Institutions== *[[Geological Society of London]] *[[Edinburgh Geological Society]] *[[British Geological Survey]] ==Pioneers of British Geology== *[[Mary Anning]] 1799-1847 *[[Thomas George Bonney]] 1833-1923 *[[William Buckland]] 1784-1856 *[[William Conybeare]] 1787-1857 *[[James Hutton]] 1726-1797 the "Father of modern geology" *[[Charles Lapworth]] 1842&ndash;1920 *[[Charles Lyell|Sir Charles Lyell]] 1797-1875 *[[Gideon Mantell]] 1790-1852 *[[Roderick Murchison|Sir Roderick Murchison]] 1792&ndash;1871 *[[John Phillips (geologist)|John Phillips]] 1800&ndash;1874 *[[Adam Sedgwick]] 1785-1873 *[[William Smith (geologist)|William Smith]] 1769-1839 the "Father of English geology" ==Awards== *[[Wollaston Medal]] [[Image:Geology of UK - Section from Snowdon to Harwich.jpg|thumb|400px|Geology of the UK: Section from [[Snowdon]] to [[Harwich]] showing underlying [[Stratum|strata]].<br> ---- <small>This cross 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 the cutting 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.</small>]] ==See also== *[[Geologic timescale]] *[[Chalk Formation]] *[[Gault Clay]] **[[List of natural disasters in the United Kingdom]] **[[Rock formations in the United Kingdom]] ==References== <references/> ==External links== *[http://www.quakes.bgs.ac.uk/ UK Earthquakes] *[http://www.thepeakdistrict.info/fast/html/peak_district_geology.html UK Peak District Geology] *[http://www.geographyinaction.co.uk/Geology%20files/Geol_index.html Northern Ireland Geology] *[http://www.discoveringfossils.co.uk UK Geology/Fossil locations] *[http://www.soton.ac.uk/~imw/jpg/eurogy.jpg Geology map of Europe] {{Geology of Europe}} {{British Geology}} [[Category:Regional geology|British Isles]]