| Computer Code: |
TGN |
Preferred Map Code: |
Tgn |
| Status Code: |
Full |
| Age range: |
Llanvirn Series (OE)
— Llanvirn Series (OE) |
| Lithological Description: |
Mudstones and siltstones with coarse-grained sandstone interbeds containing ferruginous ooids. |
| Definition of Lower Boundary: |
Overlies the sandstones and mudstones of the Bryncroes Formation, possibly with disconformity or non-sequence, the boundary being taken at the base of the first ooidal ironstone within the Tregroes Formation. |
| Definition of Upper Boundary: |
Conformable, gradational boundary where ferruginous sandstones of the Trygarn Formation pass upwards into undivided micaceous siltstones of the Nant Ffrancon Subgroup. |
| Thickness: |
90m |
| Geographical Limits: |
Pwllheli area, northwest Wales. |
| Parent Unit: |
Nant Ffrancon Subgroup (NFR)
|
| Previous Name(s): |
Carw Formation [Obsolete Name and Code: Use TGN]
(-3721)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Partial Type Section |
Bank of small stream 300 m northeast of Ty Ruttan (exposes section of basal part). Young et al., 2002. |
| 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. |
| Beckly, A J. 1988. The Stratigraphy of the Arenig Series in the Aberdaron to Sarn Area, Western Llyn, North Wales. Geological Journal, Vol. 23, 321-337. |
| 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
|
