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Early Neoproterozoic limestones from the Gwna Group, Anglesey

Published online by Cambridge University Press:  16 June 2010

JANA M. HORÁK  and
JANE A. EVANS
JANA M. HORÁK*
Affiliation:
Department of Geology, National Museum of Wales, Cardiff CF10 3NP, Wales, UK
JANE A. EVANS
Affiliation:
NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
*
*Author for correspondence: [email protected]
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Abstract

Limestone megaclasts up to hundreds of metres in size are present within the Gwna Group mélange, North Wales, UK. The mélange has been interpreted as part of a Peri-Gondwanan fore-arc accretionary complex although the age of deposition remains contentious, proposals ranging from Neoproterozoic to Early Ordovician. This paper uses strontium isotope chemostratigraphy to establish the age of the limestone blocks and thus provide a maximum age constraint on mélange formation. Results show that, although the carbonates are locally dolomitized, primary 87Sr/86Sr ratios can be identified and indicate deposition sometime between the late Tonian and earliest Cryogenian. This age is older than that suggested by stromatolites within the limestone and indicates that the limestone did not form as cap carbonate deposits.

Keywords

NeoproterozoiclimestoneAngleseychemostratigraphymélange
Type
Original Article
Information
Geological Magazine , Volume 148 , Issue 1 , January 2011 , pp. 78 - 88
Copyright
Copyright © Cambridge University Press 2010

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