In sea cliffs along the central zone of the Cantabric coast, near Cabo de Penas, Asturias, the Peran Member of the Candas Limestone (Middle and Upper Devonian) appears in two stratigraphic sections situated near the towns of Peran and Luanco respectively. Faunal assemblages consist of alternations of compact biostromes with units of diversely populated marls. These interbedded deposits reveal that different organisms and morphologies

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have specific roles in one or more of the following phases of reef development: (stage 1) mud trapping; (stage 2) substrate stabilization; and (stage 3) reef building. Important parameters that probably influenced this succession were intensity and periodicity of sedimentation, energy as a function of depth, light availability, and substrate characteristics.

Ideal succession of stages is better developed in the eastern Peran section. Detrital matrix of these reefs is generally grain-supported, whereas interreefal deposits consist of fossiliferous marls. Organic banks of the western Luanco section contain a muddy matrix, and true reef development (stage 3) is rarely attained. Interbank deposits include gray bioturbated mud which contains tentaculitids, trilobites, and clearly transported elements. These observations suggest that the Peran section was formed under very shallow-water conditions on the shelf edge, facing deeper waters toward the west. This shelf edge thins eastward toward a major topographic high in the present-day vicinity of the Picos de Europa. Such a paleogeographic picture is decidedly reversed to that of the now famous evonian reefs of Belgium and Germany.

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