| Computer Code: |
LGAN |
Preferred Map Code: |
Lgn |
| Status Code: |
Full |
| Age range: |
Arenig Series (OR)
— Arenig Series (OR) |
| Lithological Description: |
Dark grey mudstone with thin laminae of sandstone and siltstone. |
| Definition of Lower Boundary: |
Sharply overlies well-bedded muddy sandstones of the St Tudwal's Formation. Boundary is marked by a thin phosphatic conglomerate horizon at the top of St Tudwals Formation, possibly representing a non-sequence or minor disconformity. |
| Definition of Upper Boundary: |
Sharply overlain by oolitic ironstones of the Hen-dy-Capel Ironstone which are succeeded by undivided mudstones of the Nant ffrancon Subgroup. |
| Thickness: |
80m |
| Geographical Limits: |
Pwllheli area, northwest Wales. |
| Parent Unit: |
Nant Ffrancon Subgroup (NFR)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Section |
South of Borth Fawr, near Pwllheli. |
| Reference(s): |
| Nicholas, T C. 1915. Geology of the St Tudwal's Peninsula. Quarterly Journal of the Gelogical Society of London, Vol.71, 83-143. |
| Young, T P, Gibbons, W and McCarroll, D. 2002. Geology of the country around Pwllheli. Memoir of the British Geological Survey, Sheet 134 (England and Wales). |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E134
|
