| Computer Code: |
AFO |
Preferred Map Code: |
AFO |
| Status Code: |
Index Level |
| Age range: |
Tremadoc Series (O1)
— Tremadoc Series (O1) |
| Lithological Description: |
[Obsolete: use DYN] Grey, blocky to slightly fissile mudstones and sporadic thin, discontinuous silty laminae. Bioturbated. Fossiliferous. Includes a siltstone member - the Tai-herion Member. |
| Definition of Lower Boundary: |
Succeeds black pyritous mudstones. |
| Definition of Upper Boundary: |
Marked by base of massive grits although this boundary may be gradational locally and where the grit is absent by incoming of streaky mudstones and siltstones. |
| Thickness: |
500 metres. 20-500 metres. |
| Geographical Limits: |
Not defined. |
| 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 |
Snowdon, Sheet 119. |
| Reference(s): |
| Lynas, B D T, 1973. The Cambrian and Ordovician rocks of the Migneint area, North Wales. Journal of the Geological Society, London, Vol.129, 481-503. |
| Rushton, A W A and Howells, M F. 1998. Stratigraphical framework for the Ordovician of Snowdonia and the Lleyn Peninsula. British Geological Survey Research Report, RR/99/08. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E120
|
