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): |
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). |
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. |
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: |
E134
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