Le Brioverien. Esquisse des caracteres stratigraphiques, metamorphiques, structuraux et paleographiques de l'Antecambrien recent dans le Massif armoricain
The stratigraphic characteristics of the Brioverian from Normandy to the Vendee reflect a complete geosynclinal cycle younger than the Pentevrian (Precambrian) but completed before the Cambrian transgression. The Brioverian is the basement rock of the Armorican massif, and thus has the largest areal extent of any Precambrian formation in France. The lower part consists of epimetamorphic basic rocks (ophiolites). The middle part is feldspathic sandstone, phtanite, quartzite, and phyllitic shale. After a short period of emergence, the upper beds were deposited, consisting of the Saint Germain-le-Gaillard rhyolite, the Granville tillite complex, and shale and sandstone at the top. Cadomian folding and granitic intrusion occurred, forming the Cadomian chain prior to Cambrian transgression, and thereby affecting the structure of the Armorican massif. The Brioverian clearly was a folded and partially granitized sole before the dawn of the Paleozoic, but the exact dates of the deposition of the Brioverian and of the Cadomian orogeny are still hypothetical.