| Computer Code: |
GCO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Arundian Substage (CJ)
— Arundian Substage (CJ) |
| Lithological Description: |
Pale grey to grey, thick-bedded to massive, medium- to coarse-grained oolite and ooidal limestone with lenses of crinoidal limestone. Deposited in a barrier environment. |
| Definition of Lower Boundary: |
In the Bristol area and Broadfield Down it is taken at the incoming of ooidal limestones of the Formation above the dolomite and calcite mudstones and mudstones of the underlying Clifton Down Mudstone Formation. In the Weston-super-Mare area and Steepholm it is taken at the incoming of massive, coarse crinoidal and ooidal limestones of the Formation above the grey to dark grey, medium-bedded skeletal limestones of the High Tor Limestone Formation. |
| Definition of Upper Boundary: |
In the Weston-super-Mare area it is taken at the incoming of the calcite mudstones of the Clifton Down Mudstone Formation above the ooidal limestones of the Formation. In the Bristol area it is taken at the incoming of calcite mudstones and skeletal limestones of the Clifton Down Limestone Formation above the ooidal limestones of the Formation. |
| Thickness: |
15m in the Bristol area (Avon Gorge) thickening to 70 m at Weston-super-Mare. |
| Geographical Limits: |
Bristol [ST 60 74], Broadfield Down [ST 50 65] and Weston-super-Mare [ST 30 60] areas. Passes northwards into the Clifton Down Mudstone Formation and southwards into the Burrington Oolite Subgroup. |
| Parent Unit: |
Pembroke Limestone Group (PEMB)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
North side of Goblin Combe, north east of Congresbury, Broadfield Down, Somerset. Entire unit exposed [38m], which comprises oolites and oolitic limestones. Lower contact with Clifton Down Mudstone Formation and upper contact with Clifton Down Limestone Formation exposed. |
| Reference(s): |
| 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. |
| 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]. |
| Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E279
E264
E265
|
