The BGS Lexicon of Named Rock Units — Result Details

Ceiriad Formation

Computer Code: CRAD Preferred Map Code: Crd
Status Code: Full
Age range: St David's Series (ED) — St David's Series (ED)
Lithological Description: Red, brown and green siltstones with subordinate, similarly coloured fine-grained sandstones.
Definition of Lower Boundary: Conformably overlies coarse-grained, thickly-bedded turbidites of the Cilan Formation (Harlech Grits Group).
Definition of Upper Boundary: Conformably overlain by interbedded grey, blue-grey siltstones and mudstones, with thin beds of pale sandstone, of the Nant-y-big Formation.
Thickness: At least 40m
Geographical Limits: St Tudwal's Peninsula, northwest Wales.
Parent Unit: Not Applicable (-)
Previous Name(s): Lower Caered Mudstones (-4567)
Caered Flags (CAF)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Northwest corner of Porth Ceiriad bay. For upper part of formation. Young, T P, Gibbons, W and McCarroll, D. 2002. 
Partial Type Section  Cliffs immediately west of Trwyn Llech-y-doll. For base and lower part of formation. 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). 
Matley, C A, Nicholas, T C and Heard, A. 1939. Summer field meeting to the western part of the Lleyn Peninsula. Proceedings of the Geologists' Association, Vol.50, 83-110. 
Young, T P, Martin, F, Dean, W T and Rushton, A W A. 1994. Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales. Geological Magazine, Vol.131, 335-360. 
Nicholas, T C. 1915. Geology of the St Tudwal's Peninsula. Quarterly Journal of the Gelogical Society of London, Vol.71, 83-143. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E134