Penarth Group

The Penarth Group is a Rhaetian age (Triassic) lithostratigraphic group (a sequence of rock strata) which is widespread in Britain. It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed in coastal cliffs southwards to Lavernock Point. This sequence of rocks was previously known as the Rhaetic or Rhaetic Beds.[1]

Penarth Group
Stratigraphic range: Rhaetian
Cut face of Cotham Marble, from the Lilstock Formation, showing the stromatolitic structures resembling a landscape
TypeGroup
Sub-unitsWestbury Formation, Lilstock Formation
UnderliesLias Group
OverliesMercia Mudstone Group
Thicknessfrom 0 to more than 12m
Lithology
Primarymudstone
Otherlimestone, sandstone
Location
CountryGreat Britain, Ireland
Extentwidespread
Type section
Named forPenarth

Stratigraphy

It includes the Lilstock Formation and the underlying Westbury Formation. The Langport and Cotham Members, grey limestones of marine origin with associated mudstones, are recognised within the Lilstock Formation, itself named from Lilstock in west Somerset.[2][1] The Westbury Formation is named from Westbury-on-Severn in Gloucestershire.[3]

Ireland

In 1999, the discovery of an ichthyosaur from Langport Member mudstones exposed at Waterloo Bay, Larne provided the most complete example of this in Northern Ireland.[4]

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References
  1. The BGS Lexicon of Named Rock Units β€” Result Details: Penarth Group
  2. British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 326 Sidmouth
  3. The BGS Lexicon of Named Rock Units β€” Result Details: Westbury Formation
  4. Unearthing the Larne Sea Dragon (2007) National Museums Northern Ireland
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