The Pembroke Limestone Group is a

stratigraphic unit A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it ...

of Courceyan to Brigantian age (

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

) found in southern

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

and northern

Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lord_ ...

. It forms part of the Carboniferous Limestone Supergroup. These

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

rocks developed in

platform Platform may refer to: Technology * Computing platform, a framework on which applications may be run * Platform game, a genre of video games * Car platform, a set of components shared by several vehicle models * Weapons platform, a system or ...

and ramp environments and are up to 1025m thick in places. The make-up of the Group varies from one part of the basin to another but in south

Pembrokeshire Pembrokeshire ( ; cy, Sir Benfro ) is a Local government in Wales#Principal areas, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and the rest by sea. The count ...

it comprises the following formations: *Oystermouth Formation *Oxwich Head Limestone Formation *Stackpole Limestone Formation *Pen-y-Holt Limestone Formation *Hobbyhorse Bay Limestone Formation *Linney Head Formation *Berry Slade Limestone Formation *Black Rock Limestone Subgroup In the

Tenby Tenby ( cy, Dinbych-y-pysgod, lit=fortlet of the fish) is both a walled seaside town in Pembrokeshire, Wales, on the western side of Carmarthen Bay, and a local government community. Notable features include of sandy beaches and the Pembroke ...

Gower Gower ( cy, Gŵyr) or the Gower Peninsula () in southwest Wales, projects towards the Bristol Channel. It is the most westerly part of the historic county of Glamorgan. In 1956, the majority of Gower became the first area in the United Kingdom ...

and

Vale of Glamorgan The Vale of Glamorgan ( cy, Bro Morgannwg ), often referred to as The Vale, is a county borough in the south-east of Wales. It borders Bridgend County Borough to the west, Cardiff to the east, Rhondda Cynon Taf to the north, and the Bristol C ...

areas, the Stackpole Formation is replaced by the Hunt's Bay Oolite Subgroup which consists of a lower/earlier Cornelly Oolite Formation and an upper/later Stormy Limestone Formation. Likewise the Linney Head to Pen-y-Holt sequence is replaced by a tripartite sequence with the Gully Oolite at its base, unconformably overlain by the Caswell Bay Mudstone Formation and topped with the High Tor Limestone Formation. The Black Rock Limestone is divided into the lower Barry Harbour Limestone Formation succeeded by the Brofiscin Oolite Formation and topped off with the Friars Point Limestone Formation in the Vale of Glamorgan and

Newport Newport most commonly refers to: *Newport, Wales *Newport, Rhode Island, US Newport or New Port may also refer to: Places Asia *Newport City, Metro Manila, a Philippine district in Pasay Europe Ireland *Newport, County Mayo, a town on the ...

areas. The 'North Crop' i.e. the limestone succession exposed to the north of the

South Wales Coalfield The South Wales Coalfield ( cy, Maes glo De Cymru) extends across Pembrokeshire, Carmarthenshire, Swansea, Neath Port Talbot, Bridgend, Rhondda Cynon Taf, Merthyr Tydfil, Caerphilly, Blaenau Gwent and Torfaen. It is rich in coal deposits, espec ...

displays a different sequence and rather more of the succession is absent either through erosion or non-deposition. The Dowlais Limestone Formation is present in place of the Hunt's Bay Oolite, whilst within the Oxwich Head Limestone, the Penderyn Oolite and Honeycombed Sandstones are recognised as

members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

. To the east of the

Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...

, the Pembroke Limestone within the English part of the basin is initiated by an undivided Black Rock Subgroup, overlain except in the

Mendip Hills The Mendip Hills (commonly called the Mendips) is a range of limestone hills to the south of Bristol and Bath in Somerset, England. Running from Weston-super-Mare and the Bristol Channel in the west to the Frome valley in the east, the hills ...

by the Gully Oolite once again. In the

Avon Gorge The Avon Gorge () is a 1.5-mile (2.5-kilometre) long gorge on the River Avon in Bristol, England. The gorge runs south to north through a limestone ridge west of Bristol city centre, and about 3 miles (5 km) from the mouth of the r ...

, the Clifton Down Mudstone Formation is succeeded by the Clifton Down Limestone Formation then by the Oxwich Head Limestone Formation and finally the Upper Cromhall Sandstone. The Gully Oolite, the mudstone and the sandstone are not present in the Mendips. The Oystermouth Formation was formerly known as the Upper Limestone Shales, Rottenstone Beds or Oystermouth Beds. These

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s and

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

s are sometimes

weathered ''Weathered'' is the third studio album by American rock band Creed, released on November 20, 2001. It was the last Creed album to be released until '' Full Circle'' came out in October 2009, with Creed disbanding in June 2004. It is the only Cr ...

at outcrop to

rottenstone Rotten stone, sometimes spelled as rottenstone, also known as tripoli, is fine powdered porous rock used as a polishing abrasive for metalsmithing and in woodworking. It is usually weathered limestone mixed with diatomaceous, amorphous, or crysta ...

and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

References

Geology of Somerset Limestone formations of the United Kingdom Carboniferous Wales Carboniferous System of Europe {{UK-geology-stub

See also

References