Rushton, A.W.A., Owen, A.W., Owens, R.M. & Prigmore, J.K. 2000. British Cambrian to Ordovician Stratigraphy. Geological Conservation Review Series No. 18, JNCC, Peterborough, ISBN 1 86107 4727. The original source material for these web pages has been made available by the JNCC under the Open Government Licence 3.0. Full details in the JNCC Open Data Policy
Tables
(Table 3.1) General stratigraphical successions proposed for the Arfon area
|
Llanberis |
Nantlle |
|
Wood, 1969; Reedman et al., 1984 |
Morris and Fearnsides, 1926 |
| (Arenig |
Graianog Sandstone) |
|
| Merioneth |
Marchlyn Formation (with Carnedd y Filiast Grit at top) |
|
| age uncertain |
Bronllwyd Grit |
Cwmffrch Grit |
| Comley |
Llanberis Slates |
Llanberis Slates |
|
Fachwen Formation |
Glog Grits |
|
|
Cilgwyn Conglomerate |
|
|
Tryfan Grits |
| Cambrian or Precambrian |
Padarn Tuff |
Padarn Tuff |
(Table 5.1) The trilobite faunas recognized by Illing, correlated with Scandinavian zonal succession (Rushton, 1979)
| Horizons |
Faunas |
Biozones |
| G1–G3 |
Upper Paradoxides davidis Fauna |
Ptychagnostus punctuosus |
| F1–F3 |
Lower Paradoxides davidis Fauna |
Hypaagnostus parvifrons |
| E1–E3 |
Hartshillia (passage) Fauna |
? |
| D1–D3 |
Upper Paradoxides hicksii Fauna |
|
| B1–C3 |
Lower Paradoxides hicksii Fauna |
Tomagnostus fissus |
| A4 |
Paradoxides aurora Fauna |
Ptychagnostus gibbus |
(Table 7.1) Divisions of the Tremadoc in Wales, showing their approximate correlation
| Fearnsides (1910) |
Howells and Smith (1997) |
Fearnsides (1905) |
|
| (Tremadoc or Ynyscynhaiarn) |
|
(Arenig area) |
|
| Garth Hill Beds |
Upper Mudstone |
— |
Migneintian |
| Penmorfa Beds |
Amnodd Beds |
| Portmadoc Flags |
Upper Sandstone |
Tai-hirion Flags |
Cressagian |
| Moel-y-gest Beds |
Lower Mudstone |
Nant-ddu Beds |
| Tyn-llan Beds |
Lower Sandstone |
Niobe Beds |
| (Dolgelly Beds |
Dolgellau Formation Dolgelly Beds |
|
Merioneth) |
(Table 15.1) Stratigraphy devised by Lapworth (1878, slightly modified)
| Formation |
Graptolite zone |
|
|
| Birkhill Shale (Part |
acuminatus |
|
Silurian (part) |
| perscultus |
|
Ordovician |
| Upper Hartfell Shale (= 'Barren Mudstones') |
extraordinarius |
|
| anceps |
pacificus |
| complexus |
| complanatus |
|
| Lower Hartfell Shale |
linearis |
|
| clingani |
morrisi |
| caudarus |
| wilsoni |
|
| Glenkiln Shales |
'peltifer' |
|
| (gracilis — not seen at Dob's Linn) |
|
References