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The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, shales, marls and clays.
The Whitby Mudstone is a Toarcian geological formation in Yorkshire and Worcestershire, England. The formation, part of the Lias Group, is present in the Cleveland and Worcester Basins and the East Midlands Shelf.
The Claerwen Group is a Silurian lithostratigraphic group in mid Wales. The name is derived from Claerwen in Powys where the strata are exposed. The Group comprises the Rhayader Mudstones Formation and the underlying Derwenlas Formation which outcrop across the region. The rocks of the Rhayader Mudstone Formation have variously been known as the Rhayader Pale Shales, Rhayader Pale Shales Formation and Cwmsymlog Formation.
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 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 Lulworth Formation is a geologic formation in England. It dates from the late Tithonian to the mid Berriasian. It is a subunit of the Purbeck Group. In Dorset, it consists of three members, which are in ascending order, the Mupe Member, the Ridgway Member, and the Warbarrow Tout Member. The Mupe Member is typically 11 to 16 m thick and largely consists of marls and micrites with interbeds of calcareous mudstone. The Ridgeway Member is about 3 to 7 m thick and consists of in its western portion carbonaceous muds, marls and micrites, in the east the muds are replaced by micritic limestone. The Warbarrow Tout Member is 17 to 39 m thick and consists of limestone at the base and micrite and mudstone for the rest of the sequence, this member is the primary source of the vertebrate fossils within the formation. Elsewhere the unit is undifferentiated.
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 Holsworthy Group is a late Carboniferous lithostratigraphic group in north and east Cornwall and Devon in southwest England. The name is derived from the Devon town of Holsworthy. The Group comprises the Crackington, Bideford and Bude formations. In the Launceston area the group is represented by the Bealsmill Formation. It was formerly known as the Upper Culm Group.
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 Pembroke Limestone Group is a stratigraphic unit of Courceyan to Brigantian age found in southern Wales and northern Somerset. It forms part of the Carboniferous Limestone Supergroup. These carbonate rocks developed in platform and ramp environments and are up to 1025m thick in places.
The Craven Group is a lithostratigraphical term referring to the succession of mudstone and limestone rock strata which occur in certain parts of northern and central England and northeast Wales in the United Kingdom within the Chadian to Yeadonian sub-Stages of the Carboniferous Period. Other lithologies including sandstones, siltstones and chert occur within the group. The Group is subdivided into numerous formations, some of which previously enjoyed group status. In stratigraphic order, these are:
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 Leitrim Group is a lithostratigraphical term coined to refer to the succession of rock strata which occur in Northern Ireland within the Visean and Namurian stages of the Carboniferous Period. The group disconformably overlies the Dartry Limestone of the Tyrone Group.
The Broad Vein Mudstone Formation is an Ordovician lithostratigraphic group in Mid Wales. The rock of the formation is silty mudstone, intensely bioturbated in places. It varies in colour from a pale to a medium blue. This formation has been commercially quarried as slate in several locations along its length. The formation is between 400 metres (1,300 ft) and 560 metres (1,840 ft) thick and runs from Dinas Mawddwy south-west to Cardigan Bay at Tywyn.
The Narrow Vein Mudstone Formation is an Ordovician lithostratigraphic group in Mid Wales. The rock of the formation is silty, homogeneous or finely-laminated mudstone. It generally a medium blue colour. This formation has been commercially quarried as slate in several locations along its length. The formation is between 400 metres (1,300 ft) and 560 metres (1,840 ft) thick and runs from Dinas Mawddwy south-west to Cardigan Bay at Tywyn.
The Nod Glas Formation is an Ordovician lithostratigraphic group in Mid Wales. The rock of the formation is made up of pyritous, graptolitic mudstone that is generally black in colour. It weathers to a soft, very well cleaved and coal-like material. The formation runs from Conwy in the north, down to Cardigan Bay in the area around Aberdyfi and Tywyn, though it is not a continuous over this area.
The Garnedd-Wen Formation is an Ordovician lithostratigraphic group in Mid Wales. The rock of the formation is a mixture of mudstones, siltstones, fine- to coarse-grained sandstones, greywackes and conglomerates. The formation extends from Dinas Mawddwy in the north-east to Tywyn in the south-west.
The geology of Exmoor National Park in south-west England contributes significantly to the character of Exmoor, a landscape which was designated as a national park in 1954. The bedrock of the area consists almost wholly of a suite of sedimentary rocks deposited during the Devonian, a period named for the English county of Devon in which the western half of the park sits. The eastern part lies within Somerset and it is within this part of the park that limited outcrops of Triassic and Jurassic age rocks are to be found.
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.
References
- ↑ http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=DRE (BGS on-line lexicon of rock units)
- ↑ British Geological Survey 1:50,000 scale geological map (England & Wales) sheets 210, 211, 212, 228, 229