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Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales

Published online by Cambridge University Press:  01 May 2009

T. Young ,
F. Martin ,
W. T. Dean  and
A. W. A. Rushton
T. Young
Affiliation:
Department of Geology, University of Wales College of Cardiff, P.O. Box 914, Cardiff CF1 3YE, UK
F. Martin
Affiliation:
Département de Paléontologie, Institut royal des Sciences naturelles de Belgique, rue Vautier 29, B-1040 Brussels, Belgium
W. T. Dean
Affiliation:
Department of Geology, University of Wales College of Cardiff, P.O. Box 914, Cardiff CF1 3YE, UK
A. W. A. Rushton
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
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Abstract

Lithostratigraphic units of early to late Cambrian age established by T. C. Nicholas in 1915 in the St Tudwal's Peninsula are revised. They comprise, in ascending order: Hell's Mouth Formation (> 190 m); Trwyn y Fulfran Formation (37 m);Cilan Formation (400 m); Ceiriad Formation (40 m seen); Nant-y-big Formation (> 110 m seen); Maentwrog Formation (in part, 50 m seen, an estimated 250 m concealed); Ffestiniog Flags Formation (in part, c. 120m seen). The ‘calcareous grit’ at the top of Nicholas's Nant-pig Mudstones spans the unconformable boundary between the Nant-y-big and Maentwrog formations. Previously described limestone clasts in the ‘grit’ are probably erosional remnants of an in situ bioclastic limestone bed; their contained trilobites include genera and species found in the Andrarum Limestone (late Middle Cambrian) of Scania, Sweden. Acritarchs are documented and compared particularly with those from eastern Newfound-land. Those from the highest part of the ‘calcareous grit’ include Cymatiogalea sp. and are of late Cambrian age. One new species, Heliosphaeridium? llynense Martin, comes from the lower part of the Nant-y-big Formation (middle Middle Cambrian), where it appears a little earlier than the Adara alea Biozone.

Type
Articles
Information
Geological Magazine , Volume 131 , Issue 3 , May 1994 , pp. 335 - 360
Copyright
Copyright © Cambridge University Press 1994

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