Ordovician, Silurian, and Devonian of the Medio-North-Armorican Domain

Abstract

During the Arenig, a marine transgression flooded most of the Medio-North-Armorican Domain. To the west, on the southern flank of the Chateaulin Syncline and to the south, in the Martigné-Ferchaud, Segré, and Angers Synclines, the Initial Red Beds, respectively called the Cap de la Chèvre and the Pont-Réan Formations, rest unconformably on the late Proterozoic basement (Brioverian). These formations (Fig. 7) are mainly composed of conglomerates, sandstones, and siltstones which are typically red and were deposited in continental or coarse-grained delta environments. Petrological and geochemical data show that these sediments resulted from the reworking of the underlying Brioverian basement, after a weathering period of unknown duration (Bonjour 1989).