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: | |
 Cut face of Cotham Marble, from the Lilstock Formation, showing the stromatolitic structures resembling a landscape | |
| Type | Group |
| Sub-units | Westbury Formation, Lilstock Formation |
| Underlies | Lias Group |
| Overlies | Mercia Mudstone Group |
| Thickness | from 0 to more than 12m |
| Lithology | |
| Primary | mudstone |
| Other | limestone, sandstone |
| Location | |
| Country | Great Britain, Ireland |
| Extent | widespread |
| Type section | |
| Named for | Penarth |
Stratigraphy
editIt 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
editIn 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]
References
edit- ^ a b The BGS Lexicon of Named Rock Units — Result Details: Penarth Group
- ^ British Geological Survey 1:50,000 scale geological map sheet (England and Wales series) 326 Sidmouth
- ^ The BGS Lexicon of Named Rock Units — Result Details: Westbury Formation
- ^ Unearthing the Larne Sea Dragon (2007) National Museums Northern Ireland
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