The Penarth Group is a

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

age (

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

)

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(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 ...

) 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, Wales, approximately south of Cardiff city centre on the west shore of the Severn Estuary at the southern end of Cardiff Bay. Penarth is a Seaside resort#Brit ...

near

Cardiff Cardiff (; ) is the capital city, capital and List of urban areas in the United Kingdom, largest city of Wales. Cardiff had a population of in and forms a Principal areas of Wales, principal area officially known as the City and County of Ca ...

in south

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

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

Lavernock Point Lavernock () 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 overland tests ...

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

Stratigraphy

It includes the Lilstock Formation and the underlying

Westbury Formation The Westbury Formation is a geological Formation (geology), 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. ...

. 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 in 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, near the Hinkley Point nuclear power statio ...

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 Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

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 ...

Larne Larne (, , the name of a Gaelic Ireland, Gaelic territory)Larne/Latharna
Placenames Database of Ireland. is a to ...

, provided the most complete example of this in

Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...

.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