The AsturoLeonese Basin is one of the three large palaeogeographical units of the Cantabrian Zone. In the north the basin is bounded by the Asturian Geanticline and the Palencian Basin. In the south the Palaeozoic succession is covered by Mesozoic and Tertiairy deposits. The Upper Devonian to lowermost Carboniferous succession of the AsturoLeonese Basin includes the Nocedo Formation with the Gordón and Millar members, the Fueyo and the Ermita Formation. In these units, eight facies and ten subfacies are distinguished. The sediments of facies a, b, c2, c3, and cr are grouped in an inner shelf cluster, whereas facies cl, e, f, and g are grouped in an outer shelf cluster. With the aid of facies maps and conodont data the palaeogeographic develop ment of the southern part of the AsturoLeonese Basin during the FrasnianFamen nian and earliest Tournaisian is described. Synsedimentary block movements caused very rapid lateral changes in facies and thickness. The SaberoGordón Fault Zone, which is closely related to the IntraAsturoLeonese Facies Line, divided the Asturo Leonese shelf into an outer area, which corresponds with the External Zone, and an inner area, which is subdivided into an Intermediate and an Internal Zone. Each zone