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
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