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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.
Skokholm or Skokholm Island is an island 2.5 miles (4.0 km) off the coast of Pembrokeshire, Wales, south of the neighbouring island of Skomer. The surrounding waters are a marine reserve and all are part of the Pembrokeshire Coast National Park. Both islands are listed as Sites of Special Scientific Interest.
Skomer or Skomer Island is an island off the coast of Pembrokeshire, in the community of Marloes and St Brides in west Wales. It is well known for its wildlife: around half the world's population of Manx shearwaters nest on the island, the Atlantic puffin colony is the largest in southern Britain, and the Skomer vole is unique to the island. Skomer is a national nature reserve, a Site of Special Scientific Interest and a Special Protection Area. It is surrounded by a marine nature reserve and is managed by the Wildlife Trust of South and West Wales.
Gateholm or Gateholm Island is a small tidal island off the south west coast of Pembrokeshire, in the community of Marloes and St Brides, in the south west side of Wales, in the west of the UK, and about 8 miles (13 km) west of the port of Milford Haven. It is known for its Romano-British remains. Gateholm is owned by the National Trust as part of their Marloes Sands and Mere estate.
Middleholm, also known as Midland Isle, is a small island lying off southwest Pembrokeshire in Wales, between the island of Skomer and the mainland in the community of Marloes and St Brides. It is roughly circular with a diameter of about 1,210 feet (370 m) and an area of 21.5 acres (8.7 ha). It is separated from the mainland by Jack Sound and from Skomer by Little Sound.
South Wales is an area with many features of outstanding interest to geologists, who have for long used the area for University field trips.
The Cwmystwyth Grits Group is a Silurian lithostratigraphic group in mid Wales. The name is derived from the village of Cwmystwyth near Devil's Bridge in Ceredigion. The Group comprises the Blaen Myherin Mudstones Formation, the Glanyrafon Formation, the Caerau Mudstones Formation, the Rhuddnant Grits Formation and the Pysgotwr Grits Formation.
The Pebidian Supergroup is an Ediacaran lithostratigraphic supergroup in Pembrokeshire, west Wales. The term 'Pebidian' was coined by geologist Henry Hicks in 1876 and published in a scientific paper in the Quarterly Journal of the Geological Society in the following year. It was named for Pebidiauc, an ancient local name for the St Davids area.
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 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 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 Gray Sandstone Group is a late Silurian lithostratigraphic group in west Wales. The strata are exposed in the coast around the Milford Haven area; outcrops occur either side of Marloes Bay. Besides quartzitic sandstones and mudstones, sandy rottenstones are found at outcrop. Fossils within the rottenstone beds include brachiopods and corals. The rocks of this group have also previously been known as the Gray Sandstone Series.
The Red Marl Group is a late Silurian to early Devonian lithostratigraphic group in south Wales and Gloucestershire. The Group which was first established in the early twentieth century, includes the modern-day Temeside Mudstone, Raglan Mudstone and St Maughans formations and forms the lower part of the Old Red Sandstone. The rocks of this group have also previously been known as the Red Marl.
The Dalby Group is a Silurian lithostratigraphic group on the west coast of the Isle of Man in the Irish Sea. The name is derived from the village of Dalby near the west coast of the island. Together with those of the adjoining Manx Group, the rocks of the Group have also previously been referred to as the Manx Slates or Manx Slate Series. The group comprises wacke sandstones with siltstones and mudstones which reach a thickness of about 1200m in the west of the island. It contains only the single Niarbyl Formation which is exposed along the coast between Niarbyl Point and the town of Peel to the north.
Coalbrookdale Formation, earlier known as Wenlock Shale or Wenlock Shale Formation and also referred to as Herefordshire Lagerstätte in palaeontology, is a fossil-rich deposit (Konservat-Lagerstätte) in Powys and Herefordshire at the England–Wales border in UK. It belongs to the Wenlock Series of the Silurian Period within the Homerian Age. It is known for its well-preserved fossils of various invertebrate animals many of which are in their three-dimensional structures. Some of the fossils are regarded as earliest evidences and evolutionary origin of some of the major groups of modern animals.
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 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
- ↑ British Geological Survey 1:50,000 scale geological map (England & Wales) sheet 226/227 Milford
- ↑ Ziegler, A. M.; McKerrow, W. S.; Burne, R. V.; Baker, P. E. (1969-01-01). "Correlation and environmental setting of the Skomer Volcanic Group, Pembrokeshire". Proceedings of the Geologists' Association. 80 (4): 409–439. doi:10.1016/S0016-7878(69)80031-3. ISSN 0016-7878.
- ↑ https://webapps.bgs.ac.uk/Lexicon/lexicon.cfm?pub=SVG (BGS on-line lexicon of rock units)