The BGS Lexicon of Named Rock Units — Result Details
Nant-Y-Big Formation
| Computer Code: | NYB | Preferred Map Code: | NyB |
|---|---|---|---|
| Status Code: | Full | ||
| Age range: | St David's Series (ED) — St David's Series (ED) | ||
| Lithological Description: | Dark grey and blue-grey siltstones with thin beds of pale sandstone/quartzose siltstone in upper part, and local bentonite horizons. | ||
| Definition of Lower Boundary: | Conformably overlies red-brown-green siltstones and subordinate sandstones of the Ceiriad Formation. | ||
| Definition of Upper Boundary: | Unconformity defined by irregular erosion surface, commonly with stromatolites, above which lie conglomeratic sandstones of the Maentwrog Formation. | ||
| Thickness: | At least 110m | ||
| Geographical Limits: | St Tudwal's Peninsula, northwest, Wales. | ||
| Parent Unit: | Mawddach Group (MWG) | ||
| Previous Name(s): | Upper Caered Mudstones [Obsolete Name and Code: Use NYB]
(-3592)
Nant Pig Mudstone [Obsolete Name And Code: See NYB] (NPM) Nant Pig Mudstones [Obsolete Name and Code: Use NYB] (-4818) |
||
| Alternative Name(s): | none recorded or not applicable | ||
| Stratotypes: | |||
| Partial Type Section | Adjacent to faulted contact in Porth Ceiriad. At eastern end of prominent cliff of Pared-mawr, where 110m are exposed in cliff and foreshore. | ||
| Partial Type Section | Foreshore, northwest part of Porth Ceiriad, which exposes the basal contact with the underlying Ceiriad Formation. | ||
| 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). | |||
| Roberts, B and Merriman, R J. 1990. Cambrian and Ordovocian metabentonites and their relevance to the origins of associated mudrocks in the northern sector of the Lower Palaeozoic Welsh marginal basin. Geological Magazine, Vol.127, 31-43. | |||
| 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 | |||