The Penarth Group is a

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

age (

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

) lithostratigraphic group (a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) which is widespread in Britain. It is named from the seaside town of

Penarth Penarth (, ) is a town and Community (Wales), community in the Vale of Glamorgan ( cy, Bro Morgannwg), Wales, exactly south of Cardiff city centre on the west shore of the Severn Estuary at the southern end of Cardiff Bay. Penarth is a weal ...

near

Cardiff Cardiff (; cy, Caerdydd ) is the capital and largest city of Wales. It forms a principal area, officially known as the City and County of Cardiff ( cy, Dinas a Sir Caerdydd, links=no), and the city is the eleventh-largest in the United Kingd ...

in south

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

where strata of this age are exposed in coastal cliffs southwards to

Lavernock Point Lavernock ( cy, Larnog) is a hamlet in the Vale of Glamorgan in Wales, lying on the coast south of Cardiff between Penarth and Sully, and overlooking the Bristol Channel. Marconi and the first radio messages across open sea Following over ...

. This sequence of rocks was previously known as the Rhaetic or Rhaetic Beds.

Stratigraphy

It includes the

Lilstock Formation The Lilstock Formation is a geologic formation in England. It preserves bivalve, insect and other invertebrate fossils, as well as fossil fish of '' Agkistracanthus mitgelensis'' and the basal theropod dinosaur '' Newtonsaurus cambrensis'' dating ...

and the underlying

Westbury Formation The Westbury Formation is a geological formation in England, one of the Penarth Group. It dates back to the Rhaetian.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, Europe)." In: Weishampel, David B.; Dodson, Peter; and ...

. The Langport and Cotham Members, grey limestones of marine origin with associated mudstones, are recognised within the Lilstock Formation, itself named from

Lilstock Lilstock is a hamlet in the civil parish of Stringston within the Somerset West and Taunton district of Somerset, England. It is north-west of Bridgwater, and north-east of Williton. It is on the coast of Bridgwater Bay on the Bristol Channel ...

in west Somerset.The BGS Lexicon of Named Rock Units — Result Details: Penarth Group
/ref> The Westbury Formation is named from

Westbury-on-Severn Westbury-on-Severn is a rural village in England that is the centre of the large, rural parish, also called Westbury-on-Severn. Location The village is situated on the A48 road (between Minsterworth and Newnham on Severn) and bounded by the R ...

in Gloucestershire.

Ireland

In 1999, the discovery of an

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

from Langport Member mudstones exposed at

Waterloo Bay Waterloo Bay is an area of foreshore in Larne on the east coast of County Antrim, Northern Ireland. It is of particular interest to geologists because it provides a clear, complete and accessible example of the sequences from Upper Triassic to ...

Larne Larne (, , the name of a Gaelic Ireland, Gaelic territory) is a town on the east coast of County Antrim, Northern Ireland, with a population of 18,755 at the United Kingdom census, 2011, 2011 Census. It is a major passenger and freight Roll-on/ro ...

provided the most complete example of this in

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

.Unearthing the Larne Sea Dragon
(2007) National Museums Northern Ireland

References

Geological groups of the United Kingdom Triassic System of Europe Geologic formations of England Geology of Wales Geology of Northern Ireland Geologic groups of Europe Geologic formations of Ireland Rhaetian Stage {{UK-geologic-formation-stub