{{Short description|Group of Upper Ordovician sedimentary and volcanic rocks in north-west England}} {{Infobox rockunit | name = Dent Group | image = Timley Knott - Dent Group mudstones.jpg | caption = Steeply-dipping calcareous [[mudstone]]s of the Dent Group on Timley Knott near [[Coniston, Cumbria]] | type = [[Group (stratigraphy)|Group]] | age = [[Ordovician]] | period = Ordovician | prilithology = | otherlithology = | namedfor = | namedby = | region = [[England]] | country = United Kingdom | coordinates = | unitof = [[Windermere Supergroup]] | subunits = | underlies = [[Stockdale Group]] | overlies = [[Borrowdale Volcanic Group]] | thickness = ca. {{convert|100|m|ft|abbr=on}} | extent = Southern [[Lake District]], northwest [[Pennines]] | area = | map = | map_caption = }}
The '''Dent Group''' is a [[Group (stratigraphy)|group]] of Upper [[Ordovician]] [[sedimentary rock|sedimentary]] and [[volcanic rock]]s in north-west [[England]]. It is the lowermost part of the [[Windermere Supergroup]], which was deposited in the [[foreland basin]] formed during the [[continental collision|collision]] between [[Laurentia]] and [[Avalonia]]. It lies [[unconformity|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]].<ref name="BGS Lexicon">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=DNT | title=Dent Group | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=14 March 2015}}</ref>
==Distribution== 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, South Lakeland|Dent]] [[Inliers and outliers (geology)|inliers]], the [[Cross Fell]] inlier and the [[Craven in the Domesday Book|Craven]] inliers.<ref name="Fortey">{{cite book | chapter-url=https://books.google.com/books?id=ekD5uKAw_nYC&pg=PA33&dq=%22dent++group%22+stratigraphy+cautley+dent+craven#q=%22dent%20%20group%22%20stratigraphy%20cautley%20dent%20craven | series=Special Reports|volume =24|title=A Revised Correlation of Ordovician Rocks in the British Isles | publisher=Geological Society | editor=Fortey R. | chapter=Northern England|author=Rushton A.W.A. & Ingham J.K.| location=London | pages=33–37 | isbn=9781862390690}}</ref>
===Lake District outcrop=== In the main Lake District outcrop, the group consists of calcareous [[siltstone]]s and [[mudstone]]s of the basal Kirkley Bank Formation,<ref name="BGS_Kirkley">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=KKB | title=Kirkley Bank Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> [[micrite|micritic]] [[limestone]]s of the Broughton Moor Formation<ref name="BGS_Broughton">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BMR | title=Broughton Moor Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> and dark blue-gray [[shale]]s of the Ashgill Formation.<ref name="BSG_Ashgill">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=AHL | title=Ashgill Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> 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.<ref name="Millward">{{cite web | url=http://nora.nerc.ac.uk/3234/1/RR01007.pdf | title=A stratigraphical framework for the upper Ordovician and Lower Devonian volcanic and intrusive rocks in the English Lake District and adjacent areas | publisher=British Geological Survey | work=Integrated Geoscience Surveys (North) Programme Research Report RR/01/07 | date=2004 | accessdate=28 March 2015}}</ref>
===Cautley and Dent inliers=== 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<ref name="BGS_Cautley">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=CMU | title=Cautley Mudstone Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> are overlain by the Ashgill Formation. The Cautley Volcanic Member is a unit of [[Pyroclastic rock|volcaniclastic rock]]s, within the Cautley Mudstone Formation.<ref name="Millward"/>
===Cross Fell inlier=== In the Cross Fell inlier, the basal Dufton Shale Formation<ref name="BGS_Dufton">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=DNSH | title=Dufton Shale Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> is followed by the Swindale Limestone Formation<ref name="BGS_Swindale">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=SWL | title=Swindale Limestone Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> 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]].<ref name="BGS_Keisley">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=KYL | title=Keisley Limestone Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=19 March 2015}}</ref>
===Craven inliers=== The Craven inliers are found to the north of the [[Craven Fault System|North Craven Fault]]. In these inliers, calcareous siltstones and muddy limestones of the Norber Formation<ref name="BGS_Norber">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=NORB | title=Norber Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> are overlain by siltstones and mudstones of the Sowerthwaite Formation.<ref name="BGS_Sowerthwaite">{{cite web | url=http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=SOW | title=Sowerthwaite Formation | publisher=British Geological Survey | work=The BGS Lexicon of Named Rock Units | accessdate=17 March 2015}}</ref> The Dam House Bridge Tuff Member forms the basal part of the Sowerthwaite Formation.<ref name="Millward"/>
==Tectonic setting== 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 [[oceanic crust|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 [[Fold (geology)|folding]], [[Thrust fault|thrusting]] and [[cleavage (geology)|cleavage]] development.
==Depositional environment== The Dent Group was deposited in a shallow water environment.<ref name="BGS Lexicon"/>
==See also== {{Portal|Earth sciences|England|Paleontology}} * [[List of fossiliferous stratigraphic units in England]]
==References== {{Reflist}} * {{cite web|title= Fossilworks: Gateway to the Paleobiology Database|author= ((Various Contributors to the Paleobiology Database))|url= https://www.fossilworks.org/|access-date= 17 December 2021|archive-date= 19 August 2022|archive-url= https://web.archive.org/web/20220819182839/https://www.fossilworks.org/|url-status= dead}}
[[Category:Geological groups of the United Kingdom]] [[Category:Geologic formations of England]] [[Category:Ordovician System of Europe]] [[Category:Ordovician England]] [[Category:Geology of Cumbria]] [[Category:Geology of the Pennines]]