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.
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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