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Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales

Published online by Cambridge University Press:  26 June 2015

THOMAS STEEMAN ,
THIJS R. A. VANDENBROUCKE ,
MARK WILLIAMS ,
JACQUES VERNIERS ,
VINCENT PERRIER ,
DAVID J. SIVETER ,
JAMES WILKINSON ,
JAN ZALASIEWICZ  and
POUL EMSBO
THOMAS STEEMAN*
Affiliation:
Research Unit Palaeontology, Department of Geology and Soil Sciences, Ghent University, Krijgslaan 281/S8, Belgium
THIJS R. A. VANDENBROUCKE
Affiliation:
Research Unit Palaeontology, Department of Geology and Soil Sciences, Ghent University, Krijgslaan 281/S8, Belgium UMR 8198 du CNRS: Evo-Eco-Paleo, Université Lille 1, Avenue Paul Langevin, bâtiment SN5, 59655 Villeneuve d'Ascq, France
MARK WILLIAMS
Affiliation:
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom
JACQUES VERNIERS
Affiliation:
Research Unit Palaeontology, Department of Geology and Soil Sciences, Ghent University, Krijgslaan 281/S8, Belgium
VINCENT PERRIER
Affiliation:
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom
DAVID J. SIVETER
Affiliation:
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom
JAMES WILKINSON
Affiliation:
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom
JAN ZALASIEWICZ
Affiliation:
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom
POUL EMSBO
Affiliation:
USGS, CMERSC, Denver Federal Center, Denver, CO 80225, USA
*
†Corresponding author: [email protected]
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Abstract

Systematic collecting through the upper Wenlock (upper Homerian) and lower Ludlow (Gorstian and lowermost Ludfordian) Silurian rock succession of the Long Mountain, Powys, Wales, identifies some 48 chitinozoan species that distinguish four biozones, two subzones and an interregnum. Consideration of the chitinozoan biozones together with those of the graptolites enables a local three-fold subdivision of the late Homerian lundgreni graptolite Biozone, and the distinction of lower and upper intervals for the Gorstian incipiens graptolite Biozone. The base of the Ludlow Series in the Long Mountain more or less equates to the base of the Cingulochitina acme chitinozoan Biozone, although no key chitinozoan first or last appearance datums are associated with the series boundary itself. The new graptolite–chitinozoan biozonation allows enhanced correlation between upper Wenlock and lower Ludlow sedimentary deposits of the Lower Palaeozoic Welsh depositional basin and those of the palaeo-shelf in the stratotype Wenlock and Ludlow areas of Shropshire. Chitinozoans seem affected by the phenomena that caused the late Wenlock ‘Mulde extinction’ in graptolites but, with the final disappearance of 9 species and re-appearance of 11 species following an interval of overall low diversity, they seem to have suffered less severely than their macro-zooplanktonic contemporaries.

Keywords

chitinozoansgraptolitesbiostratigraphyWelsh BasinWenlock–Ludlow
Type
Original Articles
Information
Geological Magazine , Volume 153 , Issue 1 , January 2016 , pp. 95 - 109
Copyright
Copyright © Cambridge University Press 2015 

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