Cambrian of the Armorican Massif

Abstract

In the Armorican Massif, Cambrian rocks outcrop in the northeast (Normandy and Maine provinces) and to a lesser extent in the south (Vendée province). Brittany was mostly emerged and was only covered during the Arenig or pre-Arenig transgression. This partition roughly reflects the paleogeography (Fig.3). The present geological setting results from a Cadomian structural heritage, and a Cambrian mobility caused by spreading and subsidence. Cambrian sediments unconformably overlie the Cadomian basement; however, the Variscan remobilization is observed in the far north and south. Deposits are mostly detrital with some carbonates in the Lower Cambrian; the sedimentary environments varied from fluvial-deltaic to shallow marine. Unfortunately these sediments contain only rare fossils. A typical Lower Cambrian fauna is known only in North Cotentin; Middle and Upper Cambrian outcrops are identified locally in the Vendée area. The upper parts of Cambrian sections generally contain some red-bed formations which might be Lower Ordovician in age, like those of Central Brittany. Under these conditions, reliable correlations are very difficult to establish between the different basins of the Armorican Massif and also with the other Cambrian rocks of the world. Post-orogenic volcanic activity occurred during the Cambrian, mostly in the eastern and southern parts of the Armorican Massif. Because of the Variscan evolution, the Armorican Massif must be divided into two domains, as was the case for the Cambrian sedimentary evolution.