The BGS Lexicon of Named Rock Units — Result Details

Bollin Mudstone Member

Computer Code: BOM Preferred Map Code: BoM
Status Code: Full
Age range: Anisian Age (TA) — Anisian Age (TA)
Lithological Description: The upper part is a dominantly laminated reddish-brown and greenish-grey mudstone with siltstones. The lower part is a structureless and laminated, dominantly reddish-brown mudstone. Within the lower part of the member, a unit termed the 'Lower Keuper Sandstone' has been recognised in the Stockport area. This unit closely resembles the Tarporley Siltstone Formation of adjacent areas.
Definition of Lower Boundary: Top of Tarporley Siltstone Formation.
Definition of Upper Boundary: Base of Northwich Halite Member.
Thickness: 1188 ft 6 ins in the Wilkesley Borehole (British Geological Survey; SJ64SW/7) (362.25 m).
Geographical Limits: Cheshire Basin.
Parent Unit: Sidmouth Mudstone Formation (SIM)
Previous Name(s): Bollin Mudstone Formation (-74)
Keuper Marl, Lower [Obsolete Name and Code: Use MMG, SIM] (LKM)
Mercia Mudstone Group (Lower Division) [Obsolete Name and Code: Use BOM] (-3862)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Exposures on banks of River Bollin and its tributaries. 
Type Section  Wilkesley Borehole (British Geological Survey) 4166 ft 8 in to 5355 ft 2 in. (SJ64SW/7). 
Reference Section  Exposures on banks of Wych Brook and its tributaries. 
Reference(s):
Wilson, A A. 1993. The Mercia Mudstone Group (Trias) of the Cheshire Basin. Proceedings of the Yorkshire Geological Society, Vol.49, 171-188. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E123