Middle-Upper Ordovician conodonts from the Ffairfach and Golden Grove groups in South Wales, United Kingdom

ABSTRACT

The conodont fauna of the reference succession of the regional British Llandeilian Stage of the Llanvirn Series was first described in a classical study by Rhodes more than 65 years ago using single element (form) taxonomy. Although several subsequent authors have recorded a substantial number of conodont taxa from the Llandeilo area, the present study is the first to present a modern taxonomic review of these late Darriwilian-early Sandbian faunas that include approximately 20 multielement species. Most prominent are representatives of Amorphognathus, Baltoniodus, Eoplacognathus, and Plectodina. The study faunas have their own biogeographical character. The distinctive genera Complexodus, Protopanderodus, and Pygodus, which are common in coeval Baltoscandic faunas, are not present, but the occurrence of Amorphognathus, Baltoniodus, and Eoplacognathus provides a link to age equivalent Baltoscandic faunas. The presence of abundant specimens of Plectodina and less common representatives of Erismodus and Icriodella are reminiscent of North American Midcontinent faunas. This type of faunal assemblage is in some respects similar to those of the early Caradoc Series of the Welsh Borderland. Biostratigraphically diagnostic species indicate that the Llandeilo study succession ranges from the Eoplacognathus lindstroemi Subzone of the Pygodus serra Zone to the Baltoniodus variabilis Subzone of the Amorphognathus tvaerensis Zone.

KEYWORDS:

• Llandeilian
• taxonomy
• biostratigraphy
• biogeography
• Darriwilian
• Sandbian

Acknowledgments

The authors would like to thank Massimo Tonelli (Scientific Instruments Facility–CIGS, University of Modena and Reggio Emilia, Modena, Italy) and Simona Marchetti Dori (Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, Modena, Italy) for the skilled assistance during the SEM investigations. We greatly acknowledge useful comments on the manuscript by Chris Barnes and John Repetski.

AF acknowledges grant support from Project FAR 2020, University of Modena and Reggio Emilia. This paper is a contribution to the IGCP Projects IGCP 652 “Reading geologic time in Paleozoic sedimentary rocks”, IGCP 653 “The onset of the Great Ordovician Biodiversity Event” and IGCP 735 “Rocks ‘n’ ROL: Rocks and the Rise of Ordovician Life.”

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Project FAR 2020, University of Modena and Reggio Emilia.