| Computer Code: |
BSI |
Preferred Map Code: |
BSI |
| Status Code: |
Pending Upgrade |
| Age range: |
Longvillian Substage (OL)
— Longvillian Substage (OL) |
| Lithological Description: |
Grey silty mudstones, siltstones and fine-grained sandstones (less well bedded than underlying Teirw Formation), tuffaceous sandstones and sporadic coarse-grained feldspathic tuffs and breccias. Includes, at its top, the Pen y Graig Tuff Member. The Formation is very fossiliferous. |
| Definition of Lower Boundary: |
Base of siltstones lie with sharp contact on the Pandy Tuff Formation acid ash-flow tuffs. |
| Definition of Upper Boundary: |
Top of Pen y Graig Tuff Member succeeded by black mudstones of Blaen y Cwm Shale Formation. |
| Thickness: |
180m (120 - 180m) |
| Geographical Limits: |
Not defined. |
| Parent Unit: |
Not Applicable (-)
|
| Previous Name(s): |
Bryn Beds
(-89)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Oswestry, Sheet 137. |
| Reference(s): |
| Brenchley, P J. 1978. The Caradocian rocks of the North and West Berwyn Hills. Geological Journal, Vol. 13, 137-164. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E120
E136
E137
|
