A refined graptolite biostratigraphy for the late Ordovician-early Silurian of central Wales

Blackett, E. and Page, A. A. and Zalasiewicz, J. and Williams, M. and Rickards, R. B. and Davies, J. (2009) A refined graptolite biostratigraphy for the late Ordovician-early Silurian of central Wales. Lethaia, 42 (1). pp. 83-96. DOI 10.1111/j.1502-3931.2008.00108.x

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Abstract

Morphometric analysis of graptolites from the persculptus and acuminatus biozones of central Wales identifies four successive morphospecies of normalograptids. These graptolites can be used for biostratigraphical subdivision of these strata as follows: (i) an early persculptus Biozone interval containing broad forms with geniculate thecae that have the morphology of Persculptograptus persculptus with an early insertion point for the full median septum (theca 11); (ii) a supra-adjacent level of early persculptus Biozone age, with narrower, parallel-sided forms, that have been referred to as Normalograptus? aff. parvulus and have a slightly later insertion point for the full median septum (theca 12); (iii) a third interval, encompassing the later part of the persculptus Biozone to the early acuminatus Biozone, with Normalograptus? cf. parvulus, which has the full median septum delayed to the level of theca 3–7; and (iv) a younger interval, in the mid-acuminatus Biozone with Persculptograptus cf. persculptus specimens that do not display the median septum on its reverse side. These taxa can be used for refined biostratigraphy and correlation in the late Ordovician and early Silurian of central Wales. The progressive delay in the insertion of the median septum in these taxa may have wider application for the correlation of the interval immediately after the Hirnantian glacial maximum.

Item Type: Article
Uncontrolled Keywords: 08AREP 2008 P IA55
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Lethaia
Volume: 42
Page Range: pp. 83-96
Identification Number: 10.1111/j.1502-3931.2008.00108.x
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:01
Last Modified: 23 Jul 2013 10:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/150

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