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Hirnantia Fauna from the Condroz Inlier, Belgium: another case of a relict Ordovician shelly fauna in the Silurian?

Pereira, Sofia; Colmenar, Jorge; Mortier, Jan; Vanmeirhaeghe, Jan; Verniers, Jacques; Štorch, Petr; Harper, David Alexander Taylor; Gutiérrez-Marco, Juan Carlos

Authors

Sofia Pereira

Jorge Colmenar

Jan Mortier

Jan Vanmeirhaeghe

Jacques Verniers

Petr Štorch

Juan Carlos Gutiérrez-Marco



Abstract

The end-Ordovician mass extinction, linked to a major glaciation, led to deep changes in Hirnantian–Rhuddanian biotas. The Hirnantia Fauna, the first of two Hirnantian survival brachiopod-dominated communities, characterizes the lower–mid Hirnantian deposits globally, and its distribution is essential to understand how the extinction took place. In this paper, we describe, illustrate, and discuss the first macrofossiliferous Hirnantia Fauna assemblage from Belgium, occurring in the Tihange Member of the Fosses Formation at Tihange (Huy), within the Central Condroz Inlier. Six fossiliferous beds have yielded a low-diversity, brachiopod-dominated association. In addition to the brachiopods (Eostropheodonta hirnantensis, Plectothyrella crassicosta, Hirnantia sp., and Trucizetina? sp.), one trilobite (Mucronaspis sp.), four pelmatozoans (Xenocrinus sp., Cyclocharax [col.] paucicrenulatus, Conspectocrinus [col.] celticus, and Pentagonocyclicus [col.] sp.), three graptolites (Cystograptus ancestralis, Normalograptus normalis, and ?Metabolograptus sp.), together with indeterminate machaeridians and bryozoans were identified. The graptolite assemblage, from the Akidograptus ascensus-Parakidograptus acuminatus Biozone, indicates an early Rhuddanian (Silurian) age, and thus, an unexpectedly late occurrence of a typical Hirnantia Fauna. This Belgian association may represent an additional example of relict Hirnantia Fauna in the Silurian, sharing characteristics with the only other known from Rhuddanian rocks at Yewdale Beck (Lake District, England), although reworking has not been completely ruled out. The survival of these Hirnantian taxa into the Silurian might be linked to delayed post-glacial effects of rising temperature and sea-level, which may have favored the establishment of refugia in these two particular regions that were paleogeographically close during the Late Ordovician–early Silurian.

Citation

Pereira, S., Colmenar, J., Mortier, J., Vanmeirhaeghe, J., Verniers, J., Štorch, P., …Gutiérrez-Marco, J. C. (2021). Hirnantia Fauna from the Condroz Inlier, Belgium: another case of a relict Ordovician shelly fauna in the Silurian?. Journal of Paleontology, 6, 1189-1215. https://doi.org/10.1017/jpa.2021.74

Journal Article Type Article
Acceptance Date Jun 4, 2021
Online Publication Date Aug 16, 2021
Publication Date 2021-11
Deposit Date Sep 14, 2021
Journal Journal of Paleontology
Print ISSN 0022-3360
Electronic ISSN 1937-2337
Publisher Cambridge University Press
Peer Reviewed Peer Reviewed
Volume 6
Pages 1189-1215
DOI https://doi.org/10.1017/jpa.2021.74