| Computer Code: |
DEL |
Preferred Map Code: |
DEL |
| Status Code: |
Full |
| Age range: |
Caradoc Series (O4)
— Caradoc Series (O4) |
| Lithological Description: |
Dark, blue-black pyritous, slightly calcareous, shelly mudstone, sporadically but richly fossiliferous. |
| Definition of Lower Boundary: |
Not seen, but interpreted as a fault against falsic ash flow tuffs of the Aran Fawddwy Formation (formerly the Llyn Conwy Formation) at its stratotype by BGS mapping in 1993. (Corwen provisional 1:50 000 Sheet 120). Elsewhere considered to be conformable on the Aran Fawddwy Formation. |
| Definition of Upper Boundary: |
Not seen, but appears to be conformable with the mudstones of the Ceiswyn Formation. |
| Thickness: |
1m to 2m. |
| Geographical Limits: |
Corwen and Bala areas. |
| Parent Unit: |
Ceiswyn Formation (CSW)
|
| Previous Name(s): |
Orthis Limestone [Obsolete Name and Code: Use DEL]
(-1496)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
Corwen, Sheet 120. |
| Partial Type Section |
West wall of the gorge of Nant Aber Derfel at Pont Aber Derfel. Bassett, D A, Whittington, H B and Williams, A. 1966. |
| 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. |
| Elles, G L. 1922. The Bala country: its structure and rock succession. Quarterly Journal of the Geological Society of London, Vol.78, 132-175. |
| Whittington, H B and Williams, A. 1955. The fauna of the Derfel Limestone of the Arenig district, North Wales. Philosophical Transactions of the Royal Society, London. Series B, Vol.238, 397-430. |
| Fearnsides, W G. 1905. On the geology of Arenig and Moel Llyfnant. Quarterly Journal of the Geological Society, Vol.61, 608-640. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E120
|
