A revised age (Emsian-Eifelian) for the Sainte-Anne Formation (Armorican Massif, France): implications for the onset of mountain building in the Variscan belt

Michel Ballevre (1) , Céline Ducassou (1) , Hubert Lardeux (1) , Serge Régnault (2)

1 GR - Géosciences Rennes
2 Muséum d'Histoire naturelle de Nantes

The Sainte-Anne Formation (Châteaupanne Unit, Armorican Massif) consists of immature sandstones conformably deposited upon reefal limestones. Plant debris are abundant in the Saint-Anne sandstones (hence their older name of "Schistes et grès à Psilophytes"), but only rare crinoids and brachiopods have been found. The faunal content is analyzed in detail, consisting of a few columnals of crinoids and brachiopods (Ambocoelia and Plectodonta minor, the most common species). The distribution in space and time of the genus Plectodonta in Europe is analyzed, and allows proposing an Emsian to early Eifelian age for the Sainte-Anne Fm. Consequently, the Sainte-Anne Fm (Armorican Massif) could be the earliest record of the relief created at the beginning of the Variscan orogeny.

Keywords: variscan belt; early to middle devonian; armorican massif; brachiopods; crinoids; mountain building

Domains: Paleontology

Michel Ballevre, Céline Ducassou, Hubert Lardeux, Serge Régnault. A revised age (Emsian-Eifelian) for the Sainte-Anne Formation (Armorican Massif, France): implications for the onset of mountain building in the Variscan belt. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, 2010, 255 (3), pp.237-254. ⟨10.1127/0077-7749/2009/0046⟩. ⟨insu-00600177⟩