The BGS Lexicon of Named Rock Units — Result Details

Trwyn Yr Wylfa Member

Computer Code: TWY Preferred Map Code: TW
Status Code: Full
Age range: Arenig Series (OR) — Arenig Series (OR)
Lithological Description: Thickly bedded pale weathering sandstones, bioturbated and fine-grained.
Definition of Lower Boundary: Gradational upward change from coarse-grained sandstones of the underlying Pared Mawr Member.
Definition of Upper Boundary: Conformable contact with the overlying cross-bedded, bioturbated muddy sandstones with granular clasts, of the Penrhyn Du Member.
Thickness: 10-15m
Geographical Limits: Pwllheli area, northwest Wales.
Parent Unit: St Tudwal's Formation (STUD)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  The headland of Trwyn-y-Wylfa. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Reference Section  Porth Bach. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Reference Section  Trwyn Llech-y-doll (upper part) coastal cliff exposure. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Reference Section  Cliff section easy of Cilan Uchaf. Young, T P, Gibbons, W and McCarroll, D. 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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E134