| Computer Code: |
WBCO |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Famennian Age (DA)
— Famennian Age (DA) |
| Lithological Description: |
Coarse, unsorted conglomerate containing clasts derived from a Precambrian source. It consists of well rounded pebbles (averaging 2 cm) and cobbles (up to 15 cm), predominately of vein quartz and dark red/brown quartzite, set in a coarse grained sandstone matrix cemented by quartz and calcite. In addition to quartz and quartzite, rare lenses up to 30 cm thick of yellow, coarse grained, cross-bedded sandstone also occur. |
| Definition of Lower Boundary: |
At irregular erosion surface, representing a regional unconformity, where the basal conglomerate rests on the underlying red-brown sandstones of the Black Nore Sandstone Formation. A mature, masssive calcrete extends 1 to 2 m below the contact. |
| Definition of Upper Boundary: |
At top of highest conglomerate bed, where it is overlain by sandstones of the Portishead Formation. |
| Thickness: |
Up to 10 m. |
| Geographical Limits: |
Portishead area, east side of Seven estuary. |
| Parent Unit: |
Portishead Subgroup (POB)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
Woodhill Bay [ST 458 768]. Pick, 1964. |
| 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. |
| Wallis, F S. 1927. The Old Red Sandstone of the Bristol District. Quarterly Journal of the Geological Society of London, 83, 760-789. |
| Pick, M C. 1964. The stratigraphy and sedimentary features of the Old Red Sandstone, Portishead coastal section, NE Somerset. Proceedings of the Geologists’ Association, 75, 199-221. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E264
|
