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The Caledonian orogeny was a mountain-building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the continents and terranes of Laurentia, Baltica and Avalonia collided.
The geology of Wales is complex and varied; its study has been of considerable historical significance in the development of geology as a science. All geological periods from the Cryogenian to the Jurassic are represented at outcrop, whilst younger sedimentary rocks occur beneath the seas immediately off the Welsh coast. The effects of two mountain-building episodes have left their mark in the faulting and folding of much of the Palaeozoic rock sequence. Superficial deposits and landforms created during the present Quaternary period by water and ice are also plentiful and contribute to a remarkably diverse landscape of mountains, hills and coastal plains.
The Widmerpool Gulf is a name given to a sedimentary basin that existed as an area of open water during the Early Carboniferous. It is named after Widmerpool, near Nottingham and was an extension eastwards as far as Lincolnshire, of the North Staffordshire Gulf. It was formed during a rifting event, which began in the Late Devonian, that affected the area between the London-Brabant Massif to the south and the Highland Boundary Fault to the north. It has a large normal fault on its southern margin and has the form of a half-graben.
The geological structure of Great Britain is complex, resulting as it does from a long and varied geological history spanning more than two billion years. This piece of the Earth's crust has experienced several episodes of mountain building or 'orogenies', each of which has added further complexity to the picture.
In geology, a disturbance is a linear zone of disturbed rock strata stretching for many miles across country which comprises a combination of folding and faulting. The British Geological Survey record a number of such features in South Wales including the Neath Disturbance, Pontyclerc Disturbance, Carreg Cennen Disturbance and the Cribarth Disturbance, the latter sometimes also known as the Tawe Valley or Swansea Valley Disturbance. The southwestward continuation of the Carreg Cennen Disturbance is known as the Llandyfaelog Disturbance.
The Bala Fault is a SW-NE trending geological fault in Wales that extends offshore into Cardigan Bay. In the offshore area it is a major normal fault and forms the bounding structure to the Cardigan Bay Basin, with a fill including about 2,500 metres (8,200 ft) of Lias Group. Onshore it is responsible for the lineament which runs through Bala and south of Cadair Idris to the coast at Tywyn. At its northeastern end it links to the similarly orientated Llanelidan Fault.
The Benton Fault is a geological fault in southern Pembrokeshire in Wales that was active as a normal fault during the deposition of the Old Red Sandstone during the Devonian period, forming a thick half graben. During the Carboniferous, the Benton Fault was strongly inverted as part of the Variscan Orogeny.
The Ceibwr Bay Fault is a WSW-ENE trending fault zone that cuts Ordovician rocks of the Ashgill Nantmel Mudstones Formation and the Caradoc Dinas Island Formation. The fault is exposed on the south side of Cardigan Bay in Wales and forms part of the Fishguard-Cardigan Fault Zone. It extends from the coast at Ceibwr Bay at its western end to the coast at Aberporth at its eastern end. The fault zone is thought to have been active as a normal fault throughout the deposition of the Ordovician sequence.
Uriconian rocks are volcanic rocks found in parts of Shropshire, United Kingdom. The name relates to Uriconio, the Latin name for an Iron Age hillfort on the summit of the Wrekin, a hill formed of Uriconian rock.
The Longmyndian Supergroup is a 6,000-metre-thick (20,000 ft) sequence of Late Precambrian rocks that outcrop between the Pontesford–Linley Fault System and the Church Stretton Fault System in the Welsh Borderland Fault System. The supergroup consists of two major geological groups, the Stretton Group and the overlying Wentnor Group. The rocks are a generally regressive sequence from basinal facies to clastic sedimentation. The rocks are thought to be derived from Uriconian mountains that were formed during the southward subduction of an oceanic plate beneath a continental block. The rocks have since been folded due to fault movements and plunge gently to the south.
The Dent Fault is a major fault zone on the boundary between the counties of Cumbria and North Yorkshire in northern England. It is named after the village of Dent in Dentdale, on the western margin of the Yorkshire Dales.
Ceibwr Bay is a bay opening into the Irish Sea in Pembrokeshire, west Wales. It is about 7 km west of Cardigan, and 3 km south of the headland of Cemaes Head. It is owned by the National Trust, and lies within the Pembrokeshire Coast National Park and on the Pembrokeshire Coast Path.
The Welsh Basin was a northeast-southwest aligned back-arc depositional basin during the Cambrian, Ordovician and Silurian periods during which a considerable thickness of marine sediments was laid down in the area. To the southeast lay the Midland Platform and to the northwest, within the Iapetus Ocean, through what is now Ireland and the Lake District, was an island arc; a northeast-southwest aligned Irish Sea landmass which was associated with volcanic activity. Examination of the sediments and associated fossils allows the deeper centre of the basin to be distinguished from shallower 'platform' areas along its southeastern margins. From the middle Silurian onwards, collision of Avalonia with the more northerly continent of Laurentia occurred giving rise to the Caledonian Orogeny. The inversion of the basin occurred at that time i.e. its uplift and deformation.
The Aberystwyth Grits Group is a Silurian lithostratigraphic group in mid Wales. The name is derived from Aberystwyth in northern Ceredigion where the strata are well exposed in coastal cliffs. The Group comprises the Trefechan Formation and the underlying Mynydd Bach Formation. The rocks of the Aberystwyth Grits Group have also previously been known as the Aberystwyth Grits Formation
The Wrekin Terrane is one of five inferred fault bounded terranes that make up the basement rocks of the southern United Kingdom. The other notable geological terranes in the region are the Charnwood Terrane, Fenland Terrane, Cymru Terrane and the Monian Composite Terrane. The Wrekin Terrane is bounded to the west by the Welsh Borderland Fault System and to the east by the Malvern Lineament. The geological terrane to the west is the Cymru Terrane and to the east is Charnwood Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.
The Wentnor Group is a group of rocks associated with the Longmyndian Supergroup of Precambrian age in present-day Wales, U.K.
The Stretton Group is a group of rocks associated with the Longmyndian Supergroup of Ediacaran age, in Shropshire, England. The rocks are located within the tract between two elements of the Welsh Borderland Fault System, the Church Stretton Fault and the Pontesford-Linley Lineament.
The geology of Norfolk in eastern England largely consists of late Mesozoic and Cenozoic sedimentary rocks of marine origin covered by an extensive spread of unconsolidated recent deposits.
References
- ↑ Brenchley, P.J. & Rawson, P.F. (eds) 2006 The Geology of England and Wales. The Geological Society, London (p80)
- ↑ Brenchley, P.J. & Rawson, P.F. (eds) 2006 The Geology of England and Wales. The Geological Society, London (pp14-15)
- ↑ Geology of the Llandovery District - a brief explanation of the geological map sheet 212 ‘Llandovery’
- ↑ Woodock, N.H.; Strachan, R.A. (2000). Geological History of Britain and Ireland. Blackwell Science. p. 187. ISBN 0632036567.