Computer Code: |
CNE |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Longvillian Substage (OL)
— Longvillian Substage (OL) |
Lithological Description: |
Black hemipelagic mudstones, thinly interbedded with grey turbiditic mudstones and siltstones. |
Definition of Lower Boundary: |
Conformably overlies the main part of the Ceiswyn Formation, the boundary being taken where laminated hemipelagic mudstones become equal or dominant in the sequence. |
Definition of Upper Boundary: |
Conformably overlain by the Nod Glas Formation, the boundary being taken where the turbidite mudstone disappears and the sequence consists wholly of black, graptolitic, pelagic mudstone. |
Thickness: |
200 to 300m |
Geographical Limits: |
Cadair Idris district, North Wales. |
Parent Unit: |
Ceiswyn Formation (CSW)
|
Previous Name(s): |
Upper Ceiswyn Beds [Obsolete Name and Code: Use CNE]
(-150)
|
Alternative Name(s): |
Gelli-Grin Calcareous Ash Formation
|
Stratotypes: |
Partial Type Section |
Craig Hen-gae, 1.5km westnorthwest of Aberllefenni. Pratt et al. 1995. |
Reference(s): |
Bassett, D A, Whittington, H B and Williams, A. 1966. The stratigraphy of the Bala district, Merionethshire. Quarterly Journal of the Geological Society of London, Vol.122, 219-271. |
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp |
Lockley, M G. 1980. The geology of the Llanuwchllyn to Llanmawddwy area, south Gwynedd, North Wales. Geological Journal, Vol.15, 21-41. |
Pugh, W J. 1928. The geology of the district around Dinas Mawddwy (Merioneth). Quarterly Journal of the Geological Society of London. Vol.84, 345-381. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E149
|