The BGS Lexicon of Named Rock Units — Result Details

Black Rock Group [Obsolete: use BRL]

Computer Code: BPGP Preferred Map Code: notEntered
Status Code: Index Level
Age range: Courceyan Substage (CF) — Courceyan Substage (CF)
Lithological Description: [Obsolete: use BRL] Dark grey to black fine-grained limestones, fossiliferous, massive and thin-bedded, overlain by dolomitised fossiliferous limestone.
Definition of Lower Boundary: Drawn at the base of the Black Rock Limestone where dark grey to black fine-grained limestone conformably rests upon banded dark fossiliferous limestone with the Lower Limestone Shales.
Definition of Upper Boundary: Drawn at the conformable upward passage from dolomitised fossiliferous limestone of the Black Rock Dolomite to coarse bioclastic oolitic facies of the Gully Oolite of the Clifton Down Group.
Thickness: Not defined.
Geographical Limits: From the western Mendips to Chepstow, close to the Bristol Channel.
Parent Unit: none recorded or not applicable
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The Bristol District, Somerset. Sheet 280. 
Reference(s):
Green, G W and Welch F B A, 1965. The geology of the country around Wells and Chedder. Memoir of the Geological Survey of England and Wales, Sheet 280. 
Bright, A. 1816. On the strata in the neighbourhood of Bristol. Transactions of the Geological Society, Vol.4, p.199. 
Cumberland, C, 1819. On the limestone beds in the River Avon near Bristol with a description of the magnesian beds that repose on their basset edges. Transactions of the Geological Society, Vol.5, p.111. 
Kellaway, G A and Welch, F B A. 1955. The Upper Old Red Sandstone and Lower Carboniferous rocks of the Bristol and the Mendips compared with those of Chepstow and the Forest of Dean. Bulletin of the Geological Survey of Great Britain, No.9, p.1-21. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E251 E264 E265 E281 E246