Trace Fossils from the Brioverian (Ediacaran–Fortunian) in Brittany (NW France)

ABSTRACT

The Ediacaran–Fortunian ichnofauna from Central Brittany (NW France) is revised for the first time since the pioneering work by Lebesconte at the end of the 19th century. The study is based on fossils from the type-localities of the historical Brioverian taxa Montfortia (traces from Montfort-sur-Meu) and Neantia (wrinkle surfaces from Néant-sur-Yvel), and on two new outcrops from Saint-Gonlay. The ichnofossil assemblage includes Helminthoidichnites tenuis, Helminthopsis tenuis, Gordia marina, Palaeophycus tubularis, ?Neonereites uniserialis, and ?Spirodesmos archimedeus. Locally, the grazing traces are associated with wrinkle surfaces considered as microbially induced sedimentary structures (MISS). The sedimentological characteristics of these deposits correspond to a shelf marine environment. Both U-Pb datings on detrital zircon and ichnostratigraphic criteria tend toward an Ediacaran age of the fossiliferous deposits, but we cannot exclude the possibility of a Fortunian age at the present state of knowledge.

KEYWORDS:

• Invertebrate ichnofauna
• Ichnosystematic
• Microbial mats
• U-Pb dating
• Brioverian
• Ediacaran–Fortunian
• Brittany
• NW France

Acknowledgments

The authors thank the owners of the quarries for the free access to the outcrops. Moreover, they are grateful to the curators of the ichnological collections of Geosciences Rennes (D. Gendry and J. Plaine, University of Rennes 1) and the Natural History Museum of Nantes (S. Régnault) for the loan of specimens. Y. Lepagnot from Géosciences Rennes is thanked for the sample preparation undertaken for U-Pb geochronology. Finally, the authors are greatly indebted to Simona Saint-Martin for her useful participation during the field trips. This publication is a contribution to the VIBRIO project of the INSU InterrVie program.

Funding

The zircon dating and the field trips were funded by the Observatoire des Sciences de L'Univers de Rennes (OSUR) and the Institut National des Sciences de l'Univers (INSU).