| Mercia Mudstone Group | |
|---|---|
| Stratigraphic range: Early Triassic-Rhaetian | |
| Type | Group |
| Unit of | New Red Sandstone Supergroup |
| Sub-units | Stratigraphy |
| Underlies | Penarth Group |
| Overlies | Sherwood Sandstone Group |
| Thickness | over 1,350 m (4,430 ft) |
| Lithology | |
| Primary | Mudstone |
| Other | Siltstone, sandstone, halite, anhydrite |
| Location | |
| Coordinates | 52°18′19″N 1°41′47″W / 52.3052°N 1.6965°W |
| Region | Scotland, England, Wales |
| Country |  United Kingdom |
| Type section | |
| Named for | Mercia |
 | |
The Mercia Mudstone Group is an early Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands—the name is derived from the ancient kingdom of Mercia which corresponds to that area. It is frequently encountered in older literature as the Keuper Marl or Keuper Marl Series.[1]
The Mercia Mudstone Group is now divided into five formations recognised and mappable across its entire outcrop and subcrop. The formations are a mix of mudstones, siltstones, sandstones and halites. Historically this sequence of rocks has been subdivided in different ways with different names in each of the basinal areas in which it is found. Increasing knowledge of the sequences and the more recent development of seamless electronic mapping by the British Geological Survey (BGS) necessitated a reappraisal of these divisions. A report published by BGS in 2008 recommended the abandonment of previous divisions and naming schemes in favour of a simpler approach which, having now been adopted, is set out below.[2]
- Blue Anchor Formation
- Branscombe Mudstone Formation
- Arden Sandstone Formation
- Sidmouth Mudstone Formation
- Tarporley Siltstone Formation
Older schemes will remain in maps and literature well into the future,[3] providing a source of potential confusion. An example might be the Arden Sandstone Formation which previously enjoyed lower status as a member and also higher status as a group.
- ^ British Geological Survey 1998–2014 (c)NERC. "BGS Lexicon of Named Rock Units - Result Details". bgs.ac.uk. Retrieved 16 March 2014.
{{cite web}}: CS1 maint: numeric names: authors list (link) - ^ Howard, A. S., Warrington, G., Ambrose, K. and Rees, J. G. 2008. A formational framework for the Mercia Mudstone Group (Triassic) of England and Wales. British Geological Survey Research Report, RR/08/04.
- ^ Mercia Mudstone Group at Fossilworks.org