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 (Neoproterozoic era) and the Palaeozoic era, namely the Ediacaran, Cambrian, Ordovician, Silurian, Devonian and Carboniferous periods, i.e. between 635 and 299 Ma (million years ago). 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.
A series of late Precambrian rocks which occur around the St Davids peninsula and reaching east almost to Wolf's Castle together with Ramsey Island are assigned to the Pebidian Volcanic Complex or Pebidian Supergroup.
Further south are the diorites, granites and granodiorites of the Johnston Intrusive Complex and the rhyolites of the Benton Volcanic Group which stretch from just northwest of Benton Castle west-northwestwards via Sardis and Johnston in a broken chain to the coast north of Talbenny and include Stack Rocks offshore.
A quarry at Rhydaston works the tuffs of the Ramsey Sound Group whilst another at Boltonhill works the Johnston intrusives.
A series of outcrops of sedimentary rocks from the Early (539-509 Ma), Middle (509-497 Ma) and Late Cambrian (497-485 Ma) are found in the northeast of the county. Unconformably overlying the rocks of the Pebidian, the following sequence has been established (youngest/uppermost at top):
These strata are well-displayed in the coastal cliffs at St Justinian's and between Porthllisky and Newgale though exposures inland are less frequent. The Lingula Flags are encountered intermittently along the north coast between Porthgain and Pwlldawnau to the northwest of St Nicholas. [1]
The various tors scattered about the northwest of the St Davids peninsula such as Carn Llidi, Carn Trelwyd and Penberry are formed of microgabbro intruded into mudstones during the Ordovician period. There are numerous intrusions of dolerite into the Aber Mawr Shales of Mynydd Preseli. That exposed at Carn Goedog has been considered as a source of the 'bluestones' of Stonehenge.
Rocks dating from each of the four epochs of the Silurian period (444-419 Ma) can be found in Pembrokeshire.
Strata dating from the Llandovery Epoch (444-433 Ma) outcrop through the middle of the county. These include the sandstones, mudstones and conglomerates of the Rosemarket Formation which extend west-northwest from Rosemarket. An outcrop including the Portfield, Haverford Mudstone and Gasworks Sandstone formations extends east-west beneath Haverfordwest and out to Narberth.
The Skomer Volcanic Group comprises a succession of extrusive igneous rock dating from the Aeronian stage of the Llandovery. These form the island of Skomer and the northern half of the nearby Marloes peninsula.
The Wenlockian age (433-427 Ma) shales, mudstones and limestones of the Coralliferous Group occur south of St Ishmaels and to the south and west of Marloes. These are overlain by the sandstones and mudstones of the Gray Sandstone Group which outcrop at St Ishmaels and north of Dale along to the Marloes peninsula. A further band occurs as an inlier to the north of St Ishmaels and Marloes.
Ludlovian (427-423 Ma) sandstones extend in a narrow outcrop between Freshwater East and Broomhill Burrows.
Strata of latest Silurian age (Pridoli epoch, 423-419 Ma) form the lowermost units of the Old Red Sandstone which is otherwise Devonian in age. Assigned to the Milford Haven Group, these mudstones and siltstones interbedded with some sandstones underlie the Milford Haven area, extending west to the coast around St Brides and forming the Dale peninsula and the island of Skokholm. To the south they form a band of higher ground from Rat Island at the mouth of Milford Haven waterway, east-southeast via Hundleton to Old Castle Head near Manorbier. A further band extends from Freshwater West via Cheriton Stackpole to Greenala Point and Trwent Point in the east. Pridolian rocks form the southern half of Caldey Island. Another area extends west from Tavernspite to Minwear.
Lying stratigraphically above the Pridolian age strata are those units of the Old Red Sandstone laid down during the Devonian period (419-359 Ma). They include the:
A band runs westwards from Penally to Pembroke Dock and interruptedly to North Hill at Angle. A second band runs parallel to it to the south from Manorbier towards Rhoscrowther and then along the southern shore of Angle Bay. It extends across the southern part of Caldey Island. A major calcrete exposed in the cliffs at the southern tip of the island is named the Chapel Point Limestone Member. Another broader area extends either side of the Daugleddau and underlies Cosheston, Lawrenny Quay, Burton and Houghton.
The Old Red Sandstone sequences differ to the north and south of the Ritec Fault.
The Carboniferous system (equating to 359-299 Ma) is represented by four broadly parallel outcrops of the Carboniferous Limestone in the south and southeast of the county, between the more northerly two of which are outcrops of the Marros Group strata and the lower and middle Coal Measures, extending west to the shores of St Brides Bay.
The most extensive outcrop of the limestone is in the southernmost part of the county where it forms almost continuous coastal cliffs between Stackpole Quay and the south end of Frainslake Sands. Several well-known natural features have been formed by erosion along this coast including the deep chasm of Huntsman's Leap, Elegug Stacks and the Green Bridge of Wales, a natural rock arch. Also of note is the rocky inlet of Hobbyhorse Bay. It has given its name indirectly to a slice of Carboniferous time, the Arundian, ‘arundo' being Latin for hobbyhorse.
The sequence in Pembrokeshire is (youngest/uppermost first):
To the north a band of limestone stretches from the headlands of Lydstep Point and Giltar Point west to Pembroke. It extends from the estuary of Pembroke River west via Rhoscrowther to Angle Bay and again from the village of Angle to West Angle Bay. Offshore, the northern half of Caldey Island is an extension of this band.
A further band extends from St Catherine's Island at Tenby west to Pembroke Dock with an arm extending northwest from Carew to West Williamston and beyond. This band and the one to the south form tracts of low-lying land between east-west ridges of Old Red Sandstone.
The last and most northerly of these bands extends from Gilman Point just east of the county and national park boundary; initially averaging 0.5km in width, it extends via Ludchurch to Templeton beyond which it narrows, finally dying out south of Haverfordwest. [2] [3]
The sandstones and mudstones which make up the Marros Group of south Wales were traditionally known as the Millstone Grit Series. Overlying the limestone, the group comprises three formations, firstly the Twrch Sandstone which is overlain by the Bishopston Mudstone and capped off by the Telpyn Point Sandstone. These strata extend in a band of country from Ragwen Point west-northwest via Marros Mountain (the locality of Marros, after which the sequence is named, is just in Carmarthenshire to the east of the national park) to Picton Park on the Eastern Cleddau and then west and northwest to reach St Brides Bay at Haroldston West. A further band extends from the northern edge of Tenby towards Redberth and via a narrowing outcrop to Llangwm on the western side of the Daugleddau.
The Coal Measures extend from Carmarthen Bay to St Brides Bay, forming the Pembrokeshire Coalfield, the westernmost expression of the South Wales Coalfield syncline. In the east, these strata are seen in sea cliffs and outcrops along the shore between Amroth and Waterwynch south of Monkstone Point. In the west, they are seen in the cliffs around Little Haven and Broad Haven. They are present too in the Newgale area but generally obscured by superficial deposits.
A fault-bounded block of sandstones, mudstones and siltstones of the Pennant Sandstone Formation occurs around Nolton Haven. These are assigned to the Warwickshire Group.
There are no post-Carboniferous rocks known within Pembrokeshire though Permian, Triassic and Jurassic strata are known from offshore. It is possible that the entire area lay beneath sea level during Cretaceous times but any evidence of chalk strata from that period has since disappeared. [4]
The geology of Ramsey Island is complex and comprises a mix of late Cambrian and Ordovician igneous and sedimentary rocks which have traditionally been assigned different names from their mainland counterparts. Skomer and Midland Isle together with the distant Grassholm and the Smalls are formed from extrusive igneous rocks collectively referred to as the Skomer Volcanic Group (formerly ‘Series'). In contrast Skokholm is formed entirely of Old Red Sandstone.
The Bishops and Clerks are formed from intrusive igneous rocks of Palaeozoic age including gabbro (North Bishop and Carreg Rhoson), rhyolite (South Bishop) and microtonalite (Daufraich). [5]
Caldey Island is formed from Devonian and Carboniferous sedimentary rocks.
The Variscan Front defines the northern extent of significant deformation associated with the Variscan Orogeny and is usually drawn on an ESE-WNW alignment through St Brides Bay and Saundersfoot Bay. [6]
Named faults within North Pembrokeshire include the Strumble Head, Newport Sands, Aber Richard, Bronnant, Ogof Cadno, Ceibwr Bay and Penffordd faults all of which have east-west through to ENE-WSW alignments.
In the south are the Ritec and Benton faults which, along with various fold axes affecting the late Palaeozoic succession, have an east-west to ESE-WSW alignment.
Successive glaciations took place within the Quaternary and each one affected Pembrokeshire. Mynydd Preseli did not generate its own icefield but the county was subjected to Irish Sea ice moving southeastwards. There is evidence for glacial lakes in the northeast around the flanks of the Preseli Hills and in the Teifi valley. A major system of glacial meltwater channels extends around the coastal zone between the Teifi estuary and Fishguard, north of the Preseli Hills. Earlier interpretations of these channels as the outflows from glacial lakes have been discarded in favour of a subglacial origin. Of particular note are the Cwm yr Eglwys channel, the Gwaun valley and Esgyrn Bottom. [7]
Head deposits are widespread across the slopes of the Preseli Hills. Elsewhere narrow strips of head occupy the floors of valleys in the northeast of the county.
Tidal flats formed from sand, silt and clay are common within the inner reaches of the Cleddau.
Beaches and shingle bars occur around the back of St Brides Bay.
A quarry at Goodwick produced around 16 million tonnes of rhyolite between 1899 and 1906 for use in the construction of the breakwater at Fishguard. Solva Group sandstones were quarried in the C12th at Caer Bwdy for decorative work in nearby St Davids Cathedral. Slate quarries at Clogeu, Gilfach and Rosebush provided slabs for general building purposes. [8] Locally sourced limestone has been used in the construction of the castles at Carew, Manorbier and Pembroke. Significant coastal limestone quarries were also active at Lydstep and Caldey. [9] Slate was quarried at Caersalem Quarry at Porthgain and exported via the village harbour. Many older buildings and field walls have been constructed from locally sourced stone from riverbeds and hillsides.
Though marketed as 'granite', it was an intrusion of dolerite of Ordovician age which was also formerly worked at Jerusalem Quarry, Porthgain and the legacy of that extraction and of the locally sourced slate and their export from the harbour prior to 1931 is now a visitor attraction. [10] [11]
Coal was formerly extracted on a small scale from contorted seams within the Pembrokeshire Coalfield. [12]
Numerous sites and landscapes within Pembrokeshire are afforded statutory protection for their geological interest. These include SSSIs such as Esgyrn Bottom and RIGS such as Craig Rhos-y-felin in the Preseli Hills. The Pembrokeshire Coast National Park was designated in 1952 principally on account of its spectacular coastal scenery which reflects the diverse geology from which it has evolved. The cliffs, offshore islands and sea stacks (such as Elegug Stacks) provide innumerable nesting sites for seabirds.
The sea cliffs of the Pembrokeshire coast provide numerous venues for rock climbing, particularly on the Carboniferous Limestone in the south and the igneous rocks of the north coast. Coasteering is a sport which has grown popular around the coast of the National Park in recent years which makes use of the abundant coastal cliffs.
Old Red Sandstone, abbreviated ORS, 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 eastern seaboard of North America. It also extends northwards into Greenland and Svalbard. These areas were a part of the paleocontinent 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. The presence of Old in the name is to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain.
St Brides Bay is a bay in western Pembrokeshire, West Wales.
The geology of Shropshire is very diverse with a large number of periods being represented at outcrop. The bedrock consists principally of sedimentary rocks of Palaeozoic and Mesozoic age, surrounding restricted areas of Precambrian metasedimentary and metavolcanic rocks. The county hosts in its Quaternary deposits and landforms, a significant record of recent glaciation. The exploitation of the Coal Measures and other Carboniferous age strata in the Ironbridge area made it one of the birthplaces of the Industrial Revolution. There is also a large amount of mineral wealth in the county, including lead and baryte. Quarrying is still active, with limestone for cement manufacture and concrete aggregate, sandstone, greywacke and dolerite for road aggregate, and sand and gravel for aggregate and drainage filters. Groundwater is an equally important economic resource.
Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 and 325 million years ago. Within England and Wales, the entire limestone succession, which includes subordinate mudstones and some thin sandstones, is known as the Carboniferous Limestone Supergroup.
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.
Gloucestershire is one of the most geologically and scenically diverse counties in England, with rocks from the Precambrian through to the Jurassic represented. These varying rock-types are responsible for the three major areas of the county, each with its own distinctive scenery and land-use - the Forest of Dean in the west, bordering Wales, the Cotswolds in the east, and in between, the Severn Vale.
The geology of Monmouthshire in southeast Wales largely consists of a thick series of sedimentary rocks of different types originating in the Silurian, Devonian, Carboniferous, Triassic and Jurassic periods.
The geology of Lancashire in northwest England consists in the main of Carboniferous age rocks but with Triassic sandstones and mudstones at or near the surface of the lowlands bordering the Irish Sea though these are largely obscured by Quaternary deposits.
The geology of County Durham in northeast England consists of a basement of Lower Palaeozoic rocks overlain by a varying thickness of Carboniferous and Permo-Triassic sedimentary rocks which dip generally eastwards towards the North Sea. These have been intruded by a pluton, sills and dykes at various times from the Devonian Period to the Palaeogene. The whole is overlain by a suite of unconsolidated deposits of Quaternary age arising from glaciation and from other processes operating during the post-glacial period to the present. The geological interest of the west of the county was recognised by the designation in 2003 of the North Pennines Area of Outstanding Natural Beauty as a European Geopark.
The geology of the Isle of Man consists primarily of a thick pile of sedimentary rocks dating from the Ordovician period, together with smaller areas of later sedimentary and extrusive igneous strata. The older strata was folded and faulted during the Caledonian and Acadian orogenies The bedrock is overlain by a range of glacial and post-glacial deposits. Igneous intrusions in the form of dykes and plutons are common, some associated with mineralisation which spawned a minor metal mining industry.
The Tyrone Group is a lithostratigraphical term coined to refer to a particular succession of rock strata which occur in Northern Ireland within the Visean Stage of the Carboniferous Period. It comprises a series of limestones, shales and sandstones which accumulated to a thickness of 2400m in the northwest Carboniferous basin of Ireland. The type areas for the group are the Clogher Valley of County Tyrone and the Fermanagh Highlands of nearby County Fermanagh. The rocks of the group sit unconformably on older rocks of the Shanmullagh Formation of the Fintona Group which are the local representatives of the Lower Old Red Sandstone. The top of the Dartry Limestone, the uppermost part of the group, is a disconformity, above which are the layered sandstones and shales of the Meenymore Formation of the Leitrim Group. The succession continues south and west across the border into the Republic of Ireland, though different names are typically applied.
The geology of national parks in Britain strongly influences the landscape character of each of the fifteen such areas which have been designated. There are ten national parks in England, three in Wales and two in Scotland. Ten of these were established in England and Wales in the 1950s under the provisions of the National Parks and Access to the Countryside Act 1949. With one exception, all of these first ten, together with the two Scottish parks were centred on upland or coastal areas formed from Palaeozoic rocks. The exception is the North York Moors National Park which is formed from sedimentary rocks of Jurassic age.
This article describes the geology of the Brecon Beacons National Park in mid/south Wales. The area gained national park status in 1957 with the designated area of 1,344 km2 (519 sq mi) including mountain massifs to both the east and west of the Brecon Beacons proper. The geology of the national park consists of a thick succession of sedimentary rocks laid down from the late Ordovician through the Silurian and Devonian to the late Carboniferous period. The rock sequence most closely associated with the park is the Old Red Sandstone from which most of its mountains are formed. The older parts of the succession, in the northwest, were folded and faulted during the Caledonian orogeny. Further faulting and folding, particularly in the south of the park is associated with the Variscan orogeny.
The geology of the Gower Peninsula in South Wales is central to the area's character and to its appeal to visitors. The peninsula is formed almost entirely from a faulted and folded sequence of Carboniferous rocks though both the earlier Old Red Sandstone and later New Red Sandstone are also present. Gower lay on the southern margin of the last ice sheet and has been a focus of interest for researchers and students in that respect too. Cave development and the use of some for early human occupation is a further significant aspect of the peninsula's scientific and cultural interest.
The Black Country UNESCO Global Geopark is a geopark in the Black Country, a part of the West Midlands region of England. Having previously been an ‘aspiring Geopark’, it was awarded UNESCO Global Geopark status on 10 July 2020.
The bedrock geology of Carmarthenshire in west Wales consists largely of Palaeozoic age sedimentary rocks. Unconsolidated deposits of Quaternary age in Carmarthenshire include a dissected cover of glacial till, valley floor alluvium and some scattered peat deposits in both upland and lowland settings. There are extensive beach and tidal flat deposits along the Carmarthenshire coast. The exploitation of the county's mineral riches, particularly coal and limestone, was a key part of the local economy through much of the nineteenth and twentieth centuries.
The geology of Anglesey, the largest (714 km2) island in Wales is some of the most complex in the country. Anglesey has relatively low relief, the 'grain' of which runs northeast–southwest, i.e. ridge and valley features extend in that direction reflecting not only the trend of the late Precambrian and Palaeozoic age bedrock geology but also the direction in which glacial ice traversed and scoured the island during the last ice age. It was realised in the 1980s that the island is composed of multiple terranes, recognition of which is key to understanding its Precambrian and lower Palaeozoic evolution. The interpretation of the island's geological complexity has been debated amongst geologists for decades and recent research continues in that vein.
The coastline of Wales extends from the English border at Chepstow westwards to Pembrokeshire then north to Anglesey and back eastwards to the English border once again near Flint. Its character is determined by multiple factors, including the local geology and geological processes active during and subsequent to the last ice age, its relative exposure to or shelter from waves, tidal variation and the history of human settlement and development which varies considerably from one place to another. The majority of the coast east of Cardiff in the south, and of Llandudno in the north, is flat whilst that to the west is more typically backed by cliffs. The cliffs are a mix of sandstones, shales and limestones, the erosion of which provides material for beach deposits. Of the twenty-two principal areas which deliver local government in Wales, sixteen have a coastline, though that of Powys consists only of a short section of tidal river some distance from the open sea. Its length has been estimated at 1,680 miles (2,700 km).
The geology of the Yorkshire Dales National Park in northern England largely consists of a sequence of sedimentary rocks of Ordovician to Permian age. The core area of the Yorkshire Dales is formed from a layer-cake of limestones, sandstones and mudstones laid down during the Carboniferous period. It is noted for its karst landscape which includes extensive areas of limestone pavement and large numbers of caves including Britain's longest cave network.
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.