| Computer Code: |
AFM |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Aurelucian Stage (OJ)
— Burrellian Stage (OK) |
| Lithological Description: |
Acidic ash-flow tuff. |
| Definition of Lower Boundary: |
Overlies the Pistyllion Formation and oversteps on to the Benglog Formation and also (under the name Llyn Conwy Formation of Lynas, 1973) on to the Allt Lwyd and Dol-cyn-afon formations east of the Ffynnon Eidda fault. |
| Definition of Upper Boundary: |
Overlain by mudstones of the Ceiswyn Formation and equivalents. |
| Thickness: |
Up to 400 m. |
| Geographical Limits: |
none recorded or not applicable
|
| Parent Unit: |
Aran Volcanic Group (AVG)
|
| Previous Name(s): |
Llyn Conwy Formation [Obsolete Name And Code: Use AFM]
(LLNC)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
P Dunkley recommends a section in the south-west of the Aran Fawddwy area [SH 817 190 (base) to 819 185 (top)]. |
| Reference(s): |
| 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. |
| Allen, P M, and Jackson, A A. 1985. Geology of the country around Harlech. Memoir of the British Geological Survey, Sheet 135 with part of Sheet 149 (England and Wales). (London: HMSO.) 112 pp. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E136
E135
E119
E120
|
