{{Use dmy dates|date=April 2022}} {{Infobox rockunit | name = Holsworthy Group | image =File:Coloured strata on the cliffs on Warren Beach - geograph.org.uk - 1518539.jpg | caption =Chevron folded alternations of sandstone and mudstone of the Crackington Formation, Warren Bay, Hartland Quay | type = Group | age = Namurian to Bolsovian (Carboniferous) | period = Carboniferous | prilithology = mudstones, | otherlithology = siltstones, sandstones, conglomerates | namedfor = Holsworthy | namedby = | region = England | country = United Kingdom | coordinates = | unitof = Culm Supergroup | subunits = Crackington Formation, Bideford Formation, Bude Formation | underlies = Exeter Group | overlies = Teign Valley Group | thickness = 3500 to 4000m | extent = north and east Cornwall to north and east Devon | area = | map = | map_caption = }}
The '''Holsworthy Group''' is a late Carboniferous lithostratigraphic group (a sequence of rock strata) in north and east Cornwall and Devon in southwest England. The name is derived from the Devon town of Holsworthy. The Group comprises (in ascending order i.e. oldest first) 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.<ref>http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=HOWY (BGS on-line lexicon of rock units)</ref>
The ''Crackington Formation'' is over 1km thick in the Exeter area but amounts to only 250m around Bideford. It consists of mudstones with lesser sandstones and siltstones displaying rhythmic bedding, typical of turbidite deposits.<ref>{{cite web | url=https://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=CKF | title=BGS Lexicon of Named Rock Units - Result Details }}</ref> The overlying ''Bideford Formation'' is over 1200m thick in places and consists of interbedded sandstones, mudstones and siltstones with a range of different characters including turbidites, channel sandstones, cross-bedded and slumped sandstones and locally contains burrows and rootlets.<ref>{{cite web | url=https://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BFF | title=BGS Lexicon of Named Rock Units - Result Details }}</ref> The ''Bude Formation'' is calculated to be around 1.3km thick along the north coast and consists of silty sandstones and mudstones. It is fossiliferous and locally contains ironstones and calcareous nodules.<ref>{{cite web | url=https://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BF | title=BGS Lexicon of Named Rock Units - Result Details }}</ref> The ''Bealsmill Formation'' is at least 120m thick and consists of interbedded sandstones, siltstones and mudstones with some conglomerate beds containing chert, lava and limestone clasts.<ref>{{cite web | url=https://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BEAL | title=BGS Lexicon of Named Rock Units - Result Details }}</ref>
==References== {{Portal|Cornwall|Devon}} {{Reflist}}
Category:Carboniferous System of Europe Category:Geology of Cornwall Category:Geological groups of the United Kingdom Category:Geology of Devon Category:Mudstone groups Category:Siltstone groups Category:Sandstone groups Category:Conglomerate groups