The BGS Lexicon of Named Rock Units — Result Details
Bryncroes Formation
Computer Code: | BRCS | Preferred Map Code: | Br |
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Status Code: | Full | ||
Age range: | Arenig Series (OR) — Arenig Series (OR) | ||
Lithological Description: | A conglomeratic basal division grading upwards into thinly interbedded and interlaminated sandstones and mudstones. | ||
Definition of Lower Boundary: | Unconformable on the metamorphosed and igneous rocks of the Sarn Complex. | ||
Definition of Upper Boundary: | Overlain by siltstones, mudstones and oolitic ironstones of the Trygarn Formation. The boundary, which is possibly a disconformity or non-sequence, is defined by the first oolitic ironstone bed within the Trygarn Formation. | ||
Thickness: | 200m | ||
Geographical Limits: | Pwllheli area, northwest Wales. | ||
Parent Unit: | Nant Ffrancon Subgroup (NFR) | ||
Previous Name(s): | Sarn Formation [Obsolete Name and Code: Use BRCS]
(-4490)
Wig Bach Formation (WGB) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
Partial Type Section | Coastal cliff exposure ar Porth Cadlan, Llyn Peninsula, showing the middle part of the formation. Beckley, A J. 1988. | ||
Partial Type Section | Basal conglomeratic stratotype and unconformity with the Sarn Complex at Mountain Quarry near Coed-y-Gromlech. Young, T P, Gibbons, W and McCarroll, D. 2002. | ||
Reference(s): | |||
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. | |||
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 |