Dent Group | |
---|---|
Stratigraphic range: Ordovician | |
Type | Group |
Unit of | Windermere Supergroup |
Underlies | Stockdale Group |
Overlies | Borrowdale Volcanic Group |
Thickness | ca. 100 m (330 ft) |
Location | |
Region | England |
Country | United Kingdom |
Extent | Southern Lake District, northwest Pennines |
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 (uppermost Silurian) Coniston Group. [1]
The Dent Group is exposed in four areas, the southern Lake District as a narrow strip across the whole width of the outcrop, in the Cautley and Dent inliers, the Cross Fell inlier and the Craven inliers. [2]
In the main Lake District outcrop, the group consists of calcareous siltstones and mudstones of the basal Kirkley Bank Formation, [3] micritic limestones of the Broughton Moor Formation [4] and dark blue-gray shales of the Ashgill Formation. [5] Locally volcanic formations are developed, including the Yarlside Volcanic Formation at the base of the Kirkley Bank Formation and the High Haume Tuff and Appletreeworth Formations at the base of the Ashgill Formations. [6]
In the Cautley and Dent inliers, rocks of the Dent Group occur in two fault bounded strips next to the Dent Fault. In these inliers, calcareous mudstones of the Cautley Mudstone Formation [7] are overlain by the Ashgill Formation. The Cautley Volcanic Member is a unit of volcaniclastic rocks, within the Cautley Mudstone Formation. [6]
In the Cross Fell inlier, the basal Dufton Shale Formation [8] is followed by the Swindale Limestone Formation [9] and the Ashgill Formation. In the Keisley area, the uppermost part of the Dent Group is represented by the highly fossiliferous Keisley Limestone Formation, exposed in the core of an anticline. [10]
The Craven inliers are found to the north of the North Craven Fault. In these inliers, calcareous siltstones and muddy limestones of the Norber Formation [11] are overlain by siltstones and mudstones of the Sowerthwaite Formation. [12] The Dam House Bridge Tuff Member forms the basal part of the Sowerthwaite Formation. [6]
The early Paleozoic geology of northern England records the convergence and eventual collision of the Avalonia microcontinent with the continent of Laurentia. The underlying Borrowdale Volcanic Group formed in an island arc, caused by the southerly subduction of the crust of the now vanished Iapetus Ocean. At the end of active arc volcanism, the area began to subside, allowing deposition of the shallow marine Dent Group. The final closure of Iapetus occurred during the Devonian Acadian orogeny, with the resulting continental collision causing deformation of the Ordovician rocks, including folding, thrusting and cleavage development.
The Dent Group was deposited in a shallow water environment. [1]
The Howgill Fells are uplands in Northern England between the Lake District and the Yorkshire Dales, lying roughly within a triangle formed by the town of Sedbergh and the villages of Ravenstonedale and Tebay. The name Howgill derives from the Old Norse word haugr meaning a hill or barrow, plus gil meaning a narrow valley.
The geology of the county of Shropshire, England 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.
Bilberry Hill is one of the Lickey Hills in northern Worcestershire, England, 10.3 miles southwest of Birmingham and 24 miles northeast of Worcester. It stands above and to the west of the village of Cofton Hackett, and is part of the Lickey Hills Country Park.
The Mercia Mudstone Group is an early Triassic lithostratigraphic group which is widespread in Britain, especially in the English Midlands—the name is derived from the ancient kingdom of Mercia which corresponds to that area. It is frequently encountered in older literature as the Keuper Marl or Keuper Marl Series.
For the Skiddaw group of hills, see Skiddaw Group
The Drefach Group is an Ordovician lithostratigraphic group in west Wales. The name is derived from the village of Drefach near Meidrim in Carmarthenshire. The Group comprises the Mydrim Shales Formation, the Mydrim Limestone Formation, the Hendre Shales Formation, Asaphus Ash Formation and at its base, the underlying Felin-wen Formation.
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 Clackmannan Group is the name given to a suite of rocks of late Dinantian and Namurian age laid down during the Carboniferous period in the Midland Valley of Scotland.
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 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:
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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 the 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 Loch Lomond and The Trossachs National Park in the southwestern part of the Scottish Highlands consists largely of Neoproterozoic and Palaeozoic bedrock faulted and folded and subjected to low grade metamorphism during the Caledonian orogeny. These older rocks, assigned to the Dalradian Supergroup, lie to the northwest of the northeast – southwest aligned Highland Boundary Fault which defines the southern edge of the Highlands. A part of this mountainous park extends south of this major geological divide into an area characterised by younger Devonian rocks which are assigned to the Old Red Sandstone.
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 Ogwen Group is an Ordovician lithostratigraphic group in Gwynedd, north-west Wales. The name is derived from Ogwen Valley, a locality in Snowdonia where it outcrops.
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The Peak Limestone Group is a Carboniferous lithostratigraphic group in the Peak District of northern England and the north Midlands. The group largely comprises limestones, including biosparite and cherty micrite but also some subordinate mudstones, siltstones and dolomites. Basaltic lava and sills are also found, together with tuffs and volcanic breccia. Though its surface outcrop is present across the White Peak, it is known largely from the subsurface of south Derbyshire, north Staffordshire and north Leicestershire. Its base is generally an unconformity on lower Palaeozoic rocks though rests conformably on Devonian to Carboniferous anhydrites and dolomites in places.
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