The BGS Lexicon of Named Rock Units — Result Details

Mercia Mudstone Group
Computer Code: MMG Preferred Map Code: MMG
Status Code: Full
Age range: Early Triassic Epoch (TE) — Rhaetian Age (TR)
Lithological Description: Dominantly red, less commonly green-grey, mudstones and subordinate siltstones with thick halite-bearing units in some basinal areas. Thin beds of gypsum/anhydrite widespread; sandstones are also present.
Definition of Lower Boundary: Gradational on Sherwood Sandstone Group, taken where mudstone and siltstone become dominant over sandstone; incoming of pseudomorphs after halite.
Definition of Upper Boundary: Overlain sharply by Penarth Group (incoming of marine lithologies).
Thickness: 1350m+
Geographical Limits: British Isles.
Parent Unit: New Red Sandstone Supergroup (NRS)
Previous Name(s): Lower Keuper Marl (-1702)
Keuper Marl (-398)
Keuper Marl And Sandstone (-4198)
Middle Keuper Marl (-4199)
Keuper Series (-2942)
Lower Keuper Series (-3553)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Type localities/sections for constituent formations in the Cheshire Basin: Wilson, 1993. 
Type Area  "Mercia" ie the English Midlands; the area south and east of Nottingham is the most suitable part for the type area. (Elliott, 1961; Charsley and others, 1990). 
Reference Section  Type localities/sections for the constituent formations south and east of Nottingham: Elliott, 1961. Modified (but without type sections) by Charsley and others, 1990. 
Reference(s):
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. 
Wilson, A A, 1993. The Mercia Mudstone Group (Trias) of the Cheshire Basin. Proceedings of the Yorkshire Geological Society, 49 (3) pp.171-188. 
Charsley, T J, Rathbone, P A and Lowe, D J, 1990. Nottingham: A geological background for planning and development. British Geological Survey Technical Report WA/90/1. 
Elliott, R E 1961. The stratigraphy of the Keuper Series in southern Notinghamshire. Proceedings of the Yorkshire Geological Society, Vol.33, 197-231. 
Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W, and Taylor, F M. 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No.13. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E084 E075 E062 E124 E140 E216 E183 E184 E043 E263 E262 E234 E047 E037 E199 E139 E154 N35 E017 E279 E102 E055 E065 E064 E072 E080 E081 E089 E090 E091 E058 E018 E023 E027 E103 E114 E115 E127 E128 E158 E172 E187 E201 E202 E217 E142 E048 E235 E236 E237 E250 E253 E264 E265 E141 E280 E326 E340 E281 E341 E342 E343 E400 N28
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