The Lower Cambrian deposits of the Le Rozel Formation (Normandy, NW France): Insight into a newly described ichnofossil assemblage
Résumé
The rise of morphological complexity and taxonomic diversity of trace fossils during the Cambrian Period has
been a prominent focus to track the evolution and diversification of early animals. Here, we present a newly
described trace fossil assemblage from the lower Cambrian Le Rozel Formation in Normandy (Northwestern
France) composed of the following ichnogenera: Archaeonassa, Bergaueria, Helminthoidichnites, Helminthopsis,
Nereites, Psammichnites, and Treptichnus. Trace fossils are exquisitely preserved on top of strata (i.e., epirelief),
and are distributed through the entire thickness of the siliciclastic succession of about 200 m. This thick sedi-
mentary succession shows sedimentary environments with ripples generated by unidirectional current processes
or by oscillatory processes, such as hummocky cross-stratification (HCS) storm facies, tidal facies with flaser
stratification, and unidirectional current ripples. In addition, syneresis cracks and microbially induced sedi-
mentary structures (MISS) suggest that the Le Rozel Formation was deposited in a shallow marine shelf envi-
ronment. New U-Pb dating of detrital zircon grains suggests a late Ediacaran maximum deposition age of 549 ±
3 Ma. This dating is supplemented by the substantial preservation of the three-dimensional burrow systems
(Treptichnus pedum) and the large sediment bulldozers (Nereites, Psammichnites). Collectively, our findings suggest
that the trace fossils assemblage was deposited during the Terreneuvian Epoch, beneath the first archaeocyaths
and the first trilobite-bearing facies from both other lower Cambrian Carteret and Saint-Jean-de-la-Rivi`ere
Formation. The ichnofauna described from the Le Rozel Formation complements the worldwide trace fossil re-
cord around this critical time of life history.