The BGS Lexicon of Named Rock Units — Result Details

Vallis Limestone Formation

Computer Code: VL Preferred Map Code: notEntered
Status Code: Pending Upgrade
Age range: Arundian Substage (CJ) — Arundian Substage (CJ)
Lithological Description: Pale grey coarse-grained crinoidal limestone. Deposited in a shallow shelf/ramp environment.
Definition of Lower Boundary: Taken at the incoming of pale grey coarse crinoidal limestones of the Formation above the dolomitized packstones of the underlying Black Rock Limestone Subgroup. Little is known about this contact, which needs further investigation.
Definition of Upper Boundary: Taken at incoming of ooidal limestones and crinoidal/ooidal limestones of the overlying Burrington Oolite Subgroup above the coarse crinoidal limestone of the Formation. Little is known about this contact, which needs further investigation. At the type locality it is taken at the incoming of calcite mudstones and ooidal/crinoidal limestones of the overlying Clifton Down Limestone.
Thickness: 152m in eastern Mendip, thinning westwards to a feather edge in the central Mendip Hills.
Geographical Limits: Eastern Mendips [ST 70 45]. Passes westwards into the Burrington Oolite Subgroup. The geometry of this Formation is problematical and needs further investigation.
Parent Unit: Pembroke Limestone Group (PEMB)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Crags on the eastern side of Vallis Vale gorge, west of Frome, Somerset. Entire unit exposed, comprising coarse-grained crinoidal limestones. Lower contact with Black Rock Limestone Subgroup not seen but the upper contact with the Clifton Down Limestone is seen. 
Type Section  Vallis Vale, 3km northwest of Frome, Somerset. 
Reference(s):
Kellaway, G A and Welch, F B A, 1993. Geology of the Bristol district. Memoir of the British Geological Survey Special Sheet [England and Wales]. 
Kellaway, G A and Welch, F B A. 1963. 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, 1-21. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E281 E280