| Computer Code: |
TRGP |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Asturian Substage (CAS)
— Asturian Substage (CAS) |
| 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: |
Warwickshire Group (WAWK)
|
| Previous Name(s): |
Trenchard Group [Obsolete Name and Code: Use TRGP]
(*336)
|
| 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. Cleal and Thomas, 1996. |
| Reference(s): |
| Cleal, C J, and Thomas, B A. 1996. British Upper Carboniferous stratigraphy. Geological Conservation Review Series. No. 11. (London: Chapman and Hall.) |
| Trotter, F M, 1942. Geology of the Forest of Dean and Iron-ore Field. Memoir of the Geological Survey of Great Britain. |
| 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. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E233
E215
|
