- Geology of England
The Geology of England is mainly sedimentary. The youngest rocks are in the south east around London, progressing in age in a north westerly direction. [ [http://www.soton.ac.uk/~imw/Geology-Britain.htm Southampton University] retrieved 21/1/07] The
Tees-Exe linemarks the division between younger, softer and low-lying rocks in the south east and older, harder, and generally a higher relief in north west of the line. The geologyof Englandis recognisable in the landscape of its counties, the building materials of its towns and its regional extractive industries.
bedrockconsists of many layers formed over vast periods of time. These were laid down in various climates as the global climate changed, the landmasses moved due to continental drift, 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 eroded and overlain with other layers. To further complicate the geology, the land has also been subject to periods of earthquakes and volcanic activity.
Deposits by glaciers
Overprinted on this
bedrockgeology ("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 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, soil fertility, and many other issues. Glaciationand the resulting glacial and fluvio-glacial depositionhas had a vast impact on the geology of England covering many areas with a veneer of glacial till in the lower lying areas north of a line running from Bristolto London. In the Ribble valley, Lancashirein north west Englandthe resulting drumlinsare clearly visible. Cromer Ridgein East Angliais terminal moraine. Indeed most of East Angliais covered with glacial tillwhich has produced its rich loamy soils. This unconsolidated material (it is not stuck tightly together) is very easily eroded hence the rapid rate of retreat of the coastline.
A similar situation exists in east
Yorkshirein the Holdernessregion. The chalk outcrop at Flamborough Headin the north produces a headland resistant to coastal erosion whilst the coastline south of this at such places as Mappletonand Hornseawith their soft glacial deposits are vulnerable.
Former ice caps did not reach south of the line running from
Bristolto London, so this area has only been impacted by fluvio-glacial depositionwhich is represented in gravel beds around rivers such as the Thames. As the ice caps retreated north wards, more fluvio-glacial depositionoccurred for example in the vale of York
Proterozoic(2,500-542 Mya). The early geological development of the Avalonia terrane, including England, is believed to have been in volcanic arcs near a subduction zoneon the margin of the Gondwanacontinent. [ [http://virtualexplorer.com.au/journal/2001/03/murphy/paper2.html Virtual Explorer] ] Some material may have accreted from volcanic island arcs which formed further out in the ocean and later collided with Gondwana as a result of plate tectonic movements. The igneous activity had started by 730 million years ago and continued until around 570 million years ago, [ Woodcock, N. & Strachan, R., eds, (2000) "Geological History of Britain and Ireland", Blackwell, pp 127-139] resulting in a region of volcanic islands within a shallow sea. The remains of these islands underlie much of central England with small outcrops visible in various places. Dartmoor, Bodmin Moorand the Isles of Scillyin Cornwallwere formed at this time and hence have a significantly different geology to the rest of England. These areas are igneous batholiths and are, therefore, made of granite. The surrounding metamorphic auriolehas produced metamorphic rocks. Hence tinwas mined extensively in the area. The granite tors are important elements in the landscape of Dartmoorand Bodmin Moor. The weatheringby hydrolysisof the granite in these regions has led to deposits of kaolinwhich has been excavated as it is an important source of china clayin the production of such products as porcelainand shiny printing paper. It is due to the resistance of graniteto erosionand weatheringthat these outcrops are considerably higher than the surrounding landscape which produces dramatic and desolate vistas.
Around 600 million years ago, the
Cadomian Orogeny(mountain building period) caused the English landscape to be transformed into a mountainous region, along with much of north west Europe.
Paleozoic(542-251 mya). In the early Cambrianperiod the volcanoes and mountains of Englandwere eroded as the land became flooded by a rise in sea level, and new layers of sediment were laid down. Cambrian shales laid down in a shallow sea are exposed in the Midlands at Nuneaton. Much of central England formed a stable block of crust which has remained largely undeformed ever since.
500 million years ago, in the
Ordovicianperiod, southern Britain, the east coast of North Americaand south-east Newfoundland broke away from Gondwanalandto form the continent of Avalonia. The Skiddaw Slates of the Lake Districtconsist of metamorphosed marine sediments laid down on the northern margin of Avalonia. [ [http://www.northeast-geolsoc.50megs.com/pages/page8ordoviciansilurian1.htm Geological Society of North East England] retrieved 21/1/07]
Large quantities of volcanic
lavaand ash known as the Borrowdale Volcanicscovered the Lake District, still seen in the form of mountains such as Helvellynand Scafell Pike.
Silurianperiod, sandstones and mudstones were deposited in some parts of England. Volcanic ashes and lavas deposited during the period are still found in the Mendip Hills.
Avalonia had now joined with the continent of
Baltica, and the combined landmass collided with Laurentiaaround 425 million years ago, joining the southern and northern halves of the British Islestogether. The resulting Caledonian Orogenyproduced an Alpine-style mountain range. England lay on the southern fringe of this range.
Devonianperiod, northern England was a region uplifted by the Caledonian Orogeny. The uplifted regions were gradually eroded down, resulting in the deposition of numerous sedimentary rock layers in lowlands and seas. The Old Red Sandstonewas deposited across much of central and southern England. Sea levels varied considerably at this time with the coastline advancing and retreating from north to south across England. The Old Red Sandstone of Devongave the period its name. [ [http://www.northeast-geolsoc.50megs.com/pages/page11devonian.htm Devonian period by North East Geological Society] retrieved 21/1/07]
Around 360 million years ago during the
Carboniferousperiod, England was lying at the equator, covered by the warm shallow waters of the Rheic Ocean. During this time carboniferous limestonewas deposited, as found in the Mendip Hills, in the Peak Districtof Derbyshire, north Lancashireand the northern Pennines. The erosion of this landscape by carbonationhas led to a very distinctive scenery. Particularly notable is the area around Malhamin the Yorkshire Daleswith its limestone pavements, sink holesand shake holes. Gaping Gillis a waterfall disappearing underground into the carboniferous limestone.
The formation of
carboniferous limestonewas followed by the deposition of dark marine shales, siltstones and coarse sandstones of the Millstone Grit, notably in the area later uplifted to form the Pennine anticline. This sequence can be seen in the Yorkshire Daleswith Ingleboroughprotruding up above the carboniferous limestone landscape below.
river deltas formed and the sediments deposited were colonised by swamps and rain forest. It was in this environment that the cyclic coal measureswere formed. Coalcan be found as far south as Kentwith deposits stretching northwards to Tyne and Wear; though coal has largely been mined in the Midlandsand northern England. One of the best exposures of the Coal Measuresis on the north east coast between Whitley Bayand Seaton Sluice. [ [http://www.northeast-geolsoc.50megs.com/pages/page12carboniferous.htm Carboniferous review by NE England Geological Society] retrieved 21/1/07]
Throughout the period, south west England was affected by the collision of continental plates. The
Variscan orogeny(mountain building period) around 280 million years ago caused major deformation in south west England. The granite, that had previously been formed beneath the overlying rocks of Devonand Cornwall, was now exposed as Dartmoorand Bodmin Moor. The general region of Variscan folding was south of an east-west line roughly from Avon to Kent. The main tectonic pressure was from the south or south-east, and may have resulted in dextral strike-slip faulting. The Devon- Cornwallmassif may originally have been some distance further east, then to be moved westwards. Lesser Variscan folding took place as far north as Derbyshireand Berwick-upon-Tweed.
By the end of the period, England had a hot arid
desertclimate, with frequent flash floods leaving deposits that formed red beds, somewhat similar to the later, Triassic New Red Sandstone.
After the end of the
Carboniferousperiod (about 280 million year old) intrusion of quartz doleriteforming the Whin Sill. The river Teesflows over this at High Forceon the Alston Block. Whin Sillis also seen again at Hadrian's Wall. The country rock is Lower Carboniferous limestone and shales. [ [http://www.soton.ac.uk/~imw/Geology-Britain.htm Southampton University] retrieved 21/1/07]
Permianperiod was characterised for 30 million years by arid desertand erosion of the areas uplifted in the Variscan Orogeny(southwest England and adjacent areas in the present-day English Channel). Later, much of England was submerged in shallow waters as the polar ice sheets melted and the Tethys Oceanand Zechstein Seaformed, depositing shale, limestone, gravel, and marl, before finally receding to leave a flat desert with salt pans. [ [http://www.northeast-geolsoc.50megs.com/pages/page13permiantriassic.htm Permian times by NE Geology society] retrieved 21/1/07]
Mesozoic(251-65 mya). As Pangaea drifted during the Triassicperiod, England moved away from the equator until they were between 20° and 30° north. Red beds, including sandstonesand red mudstones form the main sediments of the New Red Sandstone. The remnants of the Variscan uplands in Franceto the south were eroded down, resulting in layers of the New Red Sandstone being deposited across central England, and in faulted basins in Cheshire. A basin developed in the Hampshireregion around this time. Rifting occurred within and around England, prior to the breakup of the super-continent in the Jurassic period.
Rock fragments found near
Bristolappear to indicate that in 214 million years ago England was showered with a fine layer of debris from an asteroid impact at the Manicouagan Impact Craterin Canada, although this is still being debated.
Jurassicperiod started, Pangaeabegan to break up and sea levels rose, as England drifted on the Eurasian Plateto between 30° and 40° north. With much of England under water again, sedimentary rocks were deposited and can now be found underlying much of southern England from the Cleveland Hillsof Yorkshireto the Jurassic Coastin Dorset, including clays, sandstones, greensands, oolitic limestoneof the Cotswold Hills, corallian limestoneof the Vale of White Horseand the Isle of Portland. A particularly interesting Jurassicsite is on the North Yorkshirecoast between Staithesand Port Mulgrave. [ [http://www.northeast-geolsoc.50megs.com/pages/page22staithesportmulgrave.htm North east Jurassic coast by NE Geology society] retrieved 21/1/07]
The burial of
algaeand bacteria below the mud of the sea floor during this time resulted in the formation of North Sea oiland natural gas, much of it trapped in overlying sandstone by saltdeposits formed as the seas fell to form the swamps and salty lakes and lagoons that were home to dinosaurs.
After 20 million years during the
Cretaceousperiod, the seas started to flood the land again until much of England was again below the sea, though sea levels frequently changed. Chalkand flints were deposited over much of England, now notably exposed at the White Cliffs of Doverand the 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.
Cenozoic(65 mya-present). In the early Paleogeneperiod between 63 and 52 million years ago, the last volcanic rocks in England were formed. The volcanic Lundy Islandin the Bristol Channeldates from this period.
Alpine Orogenythat took place about 50 million years ago was responsible for the shaping of the London Basin synclineand the Weald anticlineto the south. This orogeny also led to the development of the North Downs, South Downsand Chiltern Hills escarpments, and the near-vertical folds in south Dorsetand the Isle of Wight.
During the period England was uplifted. 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 Channelconsisted of mud flats and river deposited sands. Much of the midlands and north of England may have been covered by Jurassicand Cretaceousdeposits at the start of the Paleogene, but lost them through erosion. By 35 million years ago, the landscape included beech, oak, redwood and palm trees, along with grassland.
Mioceneand Plioceneepochs of the Neogeneperiod, further uplift and erosion occurred, particularly in the Pennines. Plant and animal types developed into their modern forms, and by about 2 million years ago the landscape would have been broadly recognisable today.
The major changes during the
Pleistoceneepoch have been brought about by several recent ice ages. The most severe was the Anglian Stage, with ice up to 1,000 m (3300 ft) thick that reached as far south as Londonand Bristol, took place between about 500,000 to 400,000 years ago, and was responsible for the diversion of the River Thamesonto its present course.
There is extensive evidence in the form of stone tools that southern England was colonised by
humanpopulations during the warm Hoxnian Stageperiod that followed the glaciation of the Anglian Stage. It is possible that the English Channelrepeatedly opened and closed during this period, causing Britain to become an island from time to time. The oldest human fossils in the Isles also date from this time, including the skull of Swanscombe Manfrom 250,000 years ago, and the earlier Clactonian Man.
Wolstonian Stage, between about 352,000 to 132,000 years ago, and thought to have peaked around 150,000 years ago, was named after the town of Wolstonsouth of Birminghamwhich is thought to mark the southern limit of the ice.
The Wolstonian was followed by the
Ipswichian interglacial, during which hippopotamusare 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 Usk valley and Wye valley were eroded by glaciers, with the ice sheet itself reaching south to Birmingham. 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 the British Isles were warmer than they are at present.
Among the features left behind by the ice the glaciated U-shaped valleys of the
Lake Districtand erratics (blocks of rock) that have been transported from the Osloregion of Norwayand deposited on the coast of Yorkshire.
Over the last twelve thousand years during the
Holoceneepoch the most significant new geological features have been the deposits of peatin Irelandand Scotland, as well as in coastal areas that have recently been artificially drained such as the Somerset Levels, The Fensand Romney Marshin England.
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 by 2000 11% of England was covered by roads or buildings.
At the present time, due to Scotland's continuing to rise as a result of the weight of Devensian ice being lifted, England is sinking. This is generally estimated at 1mm (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. A contributary factor is the draining of many stretchs of land.
In addition, rises in sea level thought to be due to
global warmingappear 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.
Recent flooding events leave geological evidence such as the Bristol Channel floods in 1607.
The British Isles continue to be subject to several very minor
earthquakes 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 scale were felt [ [http://www.quakes.bgs.ac.uk/hazard/eqlst.htm Information on Earthquakes] ] , many of them originating within England itself. Notable was the Colchester earthquake in 1884 and the 2002 Dudley earthquake.
Tectonics of Avalonia
Avaloniawas an ancient microcontinentor terranewhose history formed much of the older rocks of Western Europe. The name is derived from the Avalon Peninsulain Newfoundland. England was entirely contained within the Avalonian block, as shown in the map, and thus shares its geolocation chronology.
In the early
Cambrian, the supercontinent Pannotiabroke up and Avalonia drifted off northwards from Gondwana. This independent movement of Avalonia started from a latitude of about 60° South. The eastern end of Avalonia collided with Baltica, a continental plate occupying the latitudes from about 30°S to 55°S, as the latter slowly rotated anticlockwise towards it. This happened at the end of the Ordovicianand during the early Silurian.
In the late
Silurianand lower Devonian, the combined Baltica and Avalonia collided progressively, with Laurentia, beginning with the long extremity of Avalonia which is now attached to America. The result of this was the formation of Euramerica. At the completion of this stage, the site of Britain was at 30°S and Nova Scotiaat about 45°S. This collision is represented by the Caledonian folding or in North America as an early phase in the Acadian orogeny.
Permian, the new continent and another terrane, Armorica which included Iberia, drifted in from Gondwana, trapping Avalonia between it and the continent so adding Iberia/Armorica to Euramerica. This was followed up by the arrival of Gondwana. The effects of these collisions are seen in Europe as the Variscan folding. In North America it shows as later phases of the Acadian orogeny. This was happening at around the Equator during the later Carboniferous, forming Pangaeain such a way that Avalonia was near its centre but partially flooded by shallow sea.
Jurassic, Pangaea split into Laurasiaand Gondwana, with Avalonia as part of Laurasia. In the Cretaceous, Laurasia broke up into North Americaand Eurasiawith Avalonia split between them.
Geological Society of London
British Geological Survey
Geology of the British Isles:* Geology of Ireland:* Geology of Scotland:* Geology of Wales
List of geology of English counties
British Geological Survey
Coal Seams of the South Yorkshire Coalfield
Old Red Sandstone
New Red Sandstone
Geology of Alderley Edge
Geology of Lizard, Cornwall
* [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/ Southampton University Geology of the South Coast]
* [http://www.soton.ac.uk/~imw/jpg/eurogy.jpgGeology map of Europe]
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