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The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also extends northwards into Greenland and Svalbard. These areas were a part of the ancient continent of Euramerica/Laurussia. In Britain it is a lithostratigraphic unit to which stratigraphers accord supergroup status and which is of considerable importance to early paleontology. For convenience the short version of the term, ORS is often used in literature on the subject. The term was coined to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.
The Borrowdale Volcanic Group is a group of igneous rock formations named after the Borrowdale area of the Lake District, in England. They are Caradocian in age. It is thought that they represent the remains of a volcanic island arc, approximately similar to the island arcs of the west Pacific today. This developed as oceanic crust to the (present) north-west and was forced by crustal movement under a continental land-mass to the present south-east. Such forcing under, as two plates meet, is termed subduction. This land-mass has been named Avalonia by geologists. It is now incorporated into England and Wales and a sliver of North America.
The Fishguard Volcanic Group is an Ordovician lithostratigraphic group in west Wales. The name is derived from the town of Fishguard in Pembrokeshire. This assemblage of rocks has also been referred to as the Fishguard Volcanic Series or Fishguard Volcanic Complex. These rocks are believed to be the source of the 'bluestones' which form a part of the well-known prehistoric monument of Stonehenge in southern England.
The Llanbedrog Volcanic Group is an Ordovician lithostratigraphic group in northwest Wales. The name is derived from the village of Llanbedrog on the Llyn Peninsula where the strata are exposed.
The Snowdon Volcanic Group is an Ordovician lithostratigraphic group in Snowdonia, north-west Wales. The name is derived from Snowdon, the highest peak in Wales where it outcrops. This assemblage of rocks has also been referred to as the Snowdon Volcanic Series.
The Llewelyn Volcanic Group is an Ordovician lithostratigraphic group in Snowdonia, north-west Wales. The name is derived from Carnedd Llewelyn, the highest peak in the Carneddau range where it outcrops.
The Cymru 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 are the Charnwood Terrane, Fenland Terrane, Wrekin Terrane and the Monian Composite Terrane. In this article the definition of terrane is that implying rocks associated with the composition of the Precambrian basement. The Cymru Terrane is bounded to the northwest by the Menai Strait Fault System and to the southeast by the Pontesford Lineament. The geological terrane to the west is the Monian Composite Terrane and to the east is Wrekin Terrane. The majority of rocks in the area are associated with the outcrops that are evident at the faulted boundaries.
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 Caerfai Group is a Cambrian lithostratigraphic group in west Wales. The name is derived from Caerfai Bay on the north coast of St Brides Bay on the Pembrokeshire coast where the strata are well exposed in coastal cliffs. This rock succession has previously been known variously as the Caerfai Series, Caerfai Formation and Caerfai Beds and largely ascribed to the British regional stratigraphic unit Comley Epoch, though these terms are now obsolete.
The Menevian Group is a Cambrian lithostratigraphic group in west Wales. The name is derived from Menevia, the Roman name for the St Davids area north of St Brides Bay on Pembrokeshire’s west coast where the strata are well exposed in coastal cliffs. This rock succession has previously been known variously as the Menevian Series and Menevian Beds and largely ascribed to the British regional stratigraphic unit St David’s Epoch, though these terms are now obsolete.
The Dent Group is a group of Upper Ordovician sedimentary and volcanic rocks in north-west England. It is the lowermost part of the Windermere Supergroup, which was deposited in the foreland basin formed during the collision between Laurentia and Avalonia. It lies unconformably on the Borrowdale Volcanic Group. This unit was previously known as the Coniston Limestone Group or Coniston Limestone Formation and should not be confused with the significantly younger Coniston Group.
The Cosheston Group is an early Devonian lithostratigraphic group in west Wales. The name is derived from the village of Cosheston in south Pembrokeshire. The Group comprises the Llanstadwell, Burton Cliff, Mill Bay, Lawrenny Cliff and New Shipping formations. The strata are exposed in the Milford Haven area of southern Pembrokeshire where several partial type sections are defined. The outcrop extends around the northern and southern shores of the Haven. It is bounded to the north by the Benton Fault between the villages of Rosemarket and Lawrenny, and extends east to New Shipping and west almost to the town of Milford Haven itself. The rocks of this group have also previously been known as the Cosheston Beds.
The Milford Haven Group is a late Silurian to early Devonian lithostratigraphic group in west Wales. The name is derived from the estuary and town of Milford Haven in south Pembrokeshire. The Group comprises calcareous marls with occasional sandstones along with conglomerates and breccias.
The Exmoor Group is a late Devonian to early Carboniferous lithostratigraphic group in southwest England whose outcrop extends from Croyde in north Devon east across Exmoor to Minehead in west Somerset. The group comprises the following formations the:
The Eycott Volcanic Group is a group of volcanic rock formations of Ordovician age named after the locality of Eycott Hill in the English Lake District. The group overlies the Skiddaw Group and is unconformably overlain by a variety of different Devonian and Carboniferous age rocks.
The geology of England's Lake District is dominated by sedimentary and volcanic rocks of mainly Ordovician age underpinned by large granitic intrusions. Younger sedimentary sequences outcrop on the edges of the Lake District area, with Silurian to the south, Carboniferous to the north, east and west and Permo-Triassic to the west and east. The entire area was covered by a Mesozoic sequence that was eroded off during Paleogene uplift related to the opening of the North Atlantic. During the Quaternary the area was affected by repeated glaciations, which sculpted the current mountainous landscape.
The geology of the Peak District National Park in England is dominated by a thick succession of faulted and folded sedimentary rocks of Carboniferous age. The Peak District is often divided into a southerly White Peak where Carboniferous Limestone outcrops and a northerly Dark Peak where the overlying succession of sandstones and mudstones dominate the landscape. The scarp and dip slope landscape which characterises the Dark Peak also extends along the eastern and western margins of the park. Although older rocks are present at depth, the oldest rocks which are to be found at the surface in the national park are dolomitic limestones of the Woo Dale Limestone Formation seen where Woo Dale enters Wye Dale east of Buxton.
The geology of Pembrokeshire in Wales inevitably includes the geology of the Pembrokeshire Coast National Park which extends around the larger part of the county’s coastline and where the majority of rock outcrops are to be seen. Pembrokeshire’s bedrock geology is largely formed from a sequence of sedimentary and igneous rocks originating during the late Precambrian and the Palaeozoic era, namely the Ediacaran, Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods, i.e. between 635 and 299 Ma. The older rocks in the north of the county display patterns of faulting and folding associated with the Caledonian Orogeny. On the other hand, the late Palaeozoic rocks to the south owe their fold patterns and deformation to the later Variscan Orogeny.
The Skomer Volcanic Group is a Silurian lithostratigraphic group in Pembrokeshire, Wales. The name is derived from the island of Skomer off the west coast of Pembrokeshire. It was traditionally known as the Skomer Volcanic Series. The rocks are exposed across the island of Skomer and along the northern half of the nearby Marloes peninsula as far east as St Ishmaels.
The Benton Volcanic Group is an Ediacaran lithostratigraphic group in Pembrokeshire, Wales. The name is derived from the locality of Benton Castle in mid Pembrokeshire. It has previously been known as the Benton Volcanic Series or simply the Benton Series. They include lavas of trachytic and rhyolitic composition together with lesser amounts of red and green silicic tuffs and are found as apparently faulted blocks between the Daugleddau and west to Talbenny.
References
- ↑ Sissingh, W. 2012 Rocky Roads from Firenze: History of Geological Time and Change 1650-1900 Utrecht Studies in Earth Sciences 020 ISSN 2211-4335 Utrecht University Chapter 9 Main sequences of rocks p533 The ISBN printed in the document (978-6266-305-7) is invalid due to an incorrect number of digits. retrieved 9 Oct 2013 from http://igitur-archive.library.uu.nl/geo/2012-1003-200424/Rocky-roads-Sissingh_USES-20120814-part%20III.pdf
- ↑ British Geological Survey 1:50,000 scale geological map sheets (England and Wales series) 209 St David's and 210 Fishguard.
- ↑ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=PN (BGS on-line lexicon of rock units)