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Journal of Micropalaeontology An open-access journal of The Micropalaeontological Society
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Volume 33, issue 2
J. Micropalaeontol., 33, 165-178, 2014
https://doi.org/10.1144/jmpaleo2014-013
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 4.0 License.
J. Micropalaeontol., 33, 165-178, 2014
https://doi.org/10.1144/jmpaleo2014-013
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 4.0 License.

  01 Sep 2014

01 Sep 2014

Biostratigraphical and palaeobiogeographical implications of Lower Silurian Radiolaria from black cherts of the Armorican Massif (France)

Martin Tetard1, Taniel Danelian1, and Paula Noble1,2 Martin Tetard et al.
  • 1University of Lille 1, Géosystèmes (UMR CNRS 8217), Cité Scientifique, SN5, 59655 Villeneuve d’Ascq cedex, France
  • 2University of Nevada Reno, Department of Geological Sciences, Mackay School of Mines, Reno, NV 89557-0138, USA

Keywords: Radiolaria, Silurian, biostratigraphy, plankton palaeobiogeography, Armorican Massif

Abstract. A moderately well-preserved radiolarian assemblage was recovered from organic-rich black chert in a Llandovery (Lower Silurian) sequence that crops out in southern Brittany (Chalonnes-sur-Loire section, Armorican Massif, France). The assemblage is composed of two families (Rotasphaeridae and Haplotaeniatidae), four genera (?Diparvapila, Secuicollacta, Orbiculopylorum, Haplotaeniatum) and 13 species. Some were identified from whole specimens preserved in silica and extracted following dilute hydrofluoric acid processing, while others were recognized in thin-section preparations, as they are beautifully preserved as ‘carbonized’ microfossils. The age range suggested by conodonts and chitinozoans yielded after HF processing from one of the 27 studied samples is in good agreement with the previously published age based on graptolites. The recovered radiolarians are discussed, documented and compared with known Rhuddanian, Aeronian and lower Telychian assemblages in the literature. The stratigraphic ranges are extended for the species Secuicollacta bipola, S. hexactinia, S. parvitesta, Orbiculopylorum granti and O. splendens based on our new data. A significant number of radiolarians found in our samples occur in Llandovery sections from Alaska, Nevada, Arctic Canada and Sweden. These similarities are used to discuss the palaeodistribution of Lower Silurian Radiolaria and our observations support the hypothesis of a wide geographical distribution for these Palaeozoic species.

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