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