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A revised sedimentary and biostratigraphical architecture for the Type Llandovery area, Central Wales

Published online by Cambridge University Press:  29 October 2012

JEREMY R. DAVIES ,
RICHARD A. WATERS ,
STEWART G. MOLYNEUX ,
MARK WILLIAMS ,
JAN A. ZALASIEWICZ ,
THIJS R. A. VANDENBROUCKE  and
JACQUES VERNIERS
JEREMY R. DAVIES*
Affiliation:
British Geological Survey, c/o Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, UK
RICHARD A. WATERS
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff, CF10 3NP, UK
STEWART G. MOLYNEUX
Affiliation:
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK
MARK WILLIAMS
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK
JAN A. ZALASIEWICZ
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK
THIJS R. A. VANDENBROUCKE
Affiliation:
UMR 8217 du CNRS: Géosystèmes, Université Lille 1, bâtiment SN5, Avenue Paul Langevin, 59655 Villeneuve d'Ascq cedex, France
JACQUES VERNIERS
Affiliation:
Ghent University, WE13 Palaeontology, Krijgslaan 281 S8, BE-9000 Ghent, Belgium
*
†Author for correspondence: jrdav@bgs.ac.uk
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Abstract

The global standard for the Llandovery Series (early Silurian) in central Wales is re-assessed in the light of detailed geological surveying, biostratigraphical sampling and a rigorous examination of published datasets. A new sedimentary and biostratigraphical architecture is presented. Key graptolite, brachiopod, acritarch and, for the first time, chitinozoan assemblages are critically assessed. Upper Hirnantian to Aeronian strata record events that followed the Late Ordovician glacial maximum and comprise a series of progradational sequences bounded by flooding surfaces, but inferred still to be glacioeustatic in origin. Significant faunal renewals associated with many of the flooding levels underpin their potential for international recognition. Compound non-sequences are a feature of proximal parts of the system where erosion associated with fault footwall uplift was an important process. Extensive slump sheets contribute to further stratal loss and displacement in distal facies. A re-assessment of the Aeronian Stage GSSP reveals shortcomings with the biostratigraphical criteria used in its selection. Telychian portions of the succession display the disrupting effects of intra-Wenlock synsedimentary sliding; hence the relevance of key published fossil assemblages and the criteria used to erect the stage GSSP are undermined. However, the Llandovery area remains one of the best studied early Silurian successions in the world. This, together with regional considerations, supports the retention of the series standard in mid Wales where the contiguous deep-water basinal succession affords internationally cited exposure of richly graptolitic facies for the whole series and, significantly, for the post-sedgwickii Biozone interval.

Keywords

LlandoveryAeronianTelychiansedimentary architecturesequence stratigraphybiostratigraphymicrofossils
Type
Original Articles
Information
Geological Magazine , Volume 150 , Issue 2 , March 2013 , pp. 300 - 332
Copyright
Copyright © Cambridge University Press 2012

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Supplementary material: Image

Davies Supplementary Material

Table part 1

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Supplementary material: Image

Davies Supplementary Material

Table part 2

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Supplementary material: Image

Davies Supplementary Material

Table part 3

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