The BGS Lexicon of Named Rock Units — Result Details

TRENCHARD FORMATION
Computer Code: TRGP  Status Code: FORMAL, NATIONAL 
Preferred Map Code:  
Age or Age Range: [ CD ] WESTPHALIAN D  to [  ]  
Lithological Description:
Grey or pinkish grey quartzose sandstone. Quartzose conglomerate beds are common at the base of the formation, increasing in thickness and clast size towards the north. 
Definition of Lower Boundary:
The basal conglomerate of the Trenchard Formation rests unconformably upon the quartzitic sandstone of the Cromhall Sandstone Formation. 
Definition of Upper Boundary:
Taken at the base of the lowermost sandstone of "Pennant"- type (lithic arenite) of the Pennant Sandstone Formation, resting conformably above coarse-grained sandstone of the Trenchard Formation. This is a significant change to the Trotter (1942), who included all strata below the Coleford High Delf as part of his Trenchard Group. 
Thickness:
Up to 120 m thick in the north of the Forest of Dean Coalfield. 
Geographical Limits:
Restricted to the northern part of the Forest of Dean coalfield, approximately north of a line from Mailscott Wood, Coleford (SO 562 142) to Ruspidge, Cinderford (SO 649 119). 
Parent Unit: Parent Unit Code:
WARWICKSHIRE GROUP  WAWK
Previous Name(s): Previous Code(s):
TRENCHARD GROUP  TRGP 
Alternative Name(s):
none recorded or not applicable
Stratotypes:
Partial Type Section  The disused Puddlebrook Quarry, 1 km north of Drybrook: Exposure of the basal conglomerate of the Trenchard Formation. 
Reference(s):
Cleal, C and Thomas, B A. 1996. British Upper Carboniferous stratigraphy. Geological conservation review series No. 11. [London: Chapman and Hall]. 
Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
Jones, P C. 1972. Quartzarenite and litharenite facies in the fluvial foreland deposits of the Trenchard Group (Westphalian), Forest of Dean, England. Sedimentary Geology, Vol. 8, 177-198. 
Trotter, F M. 1942. Geology of the Forest of Dean Coalfield. Memoir of the British Geological Survey. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
Map Code Sheet Name
E  215
E  233

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