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Cambrian–Ordovician boundary age and duration of the lowest Ordovician Tremadoc Series based on U–Pb zircon dates from Avalonian Wales

Published online by Cambridge University Press:  21 November 2000

E. LANDING ,
S. A. BOWRING ,
K. L. DAVIDEK ,
A. W. A. RUSHTON ,
R. A. FORTEY  and
W. A. P. WIMBLEDON
E. LANDING
Affiliation:
Center for Stratigraphy and Paleontology, New York State Museum, The State Education Department, Albany, NY 12230, USA
S. A. BOWRING
Affiliation:
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
K. L. DAVIDEK
Affiliation:
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
A. W. A. RUSHTON
Affiliation:
Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK Formerly British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
R. A. FORTEY
Affiliation:
Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
W. A. P. WIMBLEDON
Affiliation:
Countryside Council for Wales, 4 Castleton Court, Fortran Road, St. Mellons, Cardiff CF3 0LT, UK
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Abstract

Two thin volcaniclastic sandstone beds in the Bryn-llin-fawr road section in North Wales overlie an apparent sequence boundary within the uppermost Cambrian Acerocare Zone and are overlain by lowest Ordovician (lower Tremadoc) Rhabdinopora faunas. U–Pb geochronology of zircons from these sandstones yields a maximum Cambrian–Ordovician boundary age of 489±0.6 Ma. This age indicates both that the Tremadoc Series (lowest Ordovician) may be shorter in duration than was previously thought and that the duration of the Middle and Late Cambrian (c. 22 Ma) was much less than that of the Early Cambrian (c. 33 Ma). Cambrian trilobite zones locally had an average duration as short as 1 Ma.

Type
Research Article
Information
Geological Magazine , Volume 137 , Issue 5 , September 2000 , pp. 485 - 494
Copyright
© 2000 Cambridge University Press

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