Abstract

In the northern part of the Picos de Europa Unit (Cantabrian Zone), near the village of Arenas de Cabrales (Cantabrian Mountains, Asturias - Northern Spain), a stratigraphic succession of Carboniferous age has been studied. The goal of the investigation is to show the evolution of the Upper Carboniferous environment under the influence of the progressing Variscan orogenic front. The study is based on geologic mapping in an area of 15 km2 around the Sierra Dobros. A geologic map of a scale of 1 : 10 000 has been produced. Biostratigraphic data of fusulinids are available from Upper Bashkirian to Middle Kasimovian. The data are restricted to a part of the succession (Villa & Martínez García 1989), wherefore the age of the overlaying units can not be established. Hence, new samples of fusulinids have been collected and dated as young as Gzhelian. Investigations of the palynomorpha yield no further biostratigraphic details because of the destruction by bacterial activity, and crystallization of Pyrite.

Mapping and biostratigraphy of fusulinids provide a continuous section during the Upper Carboniferous.

A sandstone of Ordovician age comprise the lowermost sediments of the Sierra Dobros (Barrios Formation). The Barrios Formation is directly overlain by carbonate and later siliciclastic deposits, at some locations more than 1000 m in thickness. The Carboniferous deposits of the Barcaliente Formation start with micritic black limestones of Serpukhovian age (Lower Carboniferous). The sequence continues with massive bright-colored limestones (Valdeteja Formation) followed by grey bedded, and bright-colored massive limestones of the Picos de Europa Formation. An interval of detritic limestones occurs in an erosive channel within the Picos de Europa Formation (Dobros beds). An erosive discordance separates the younger Puentelles Formation from the older calcareous dominated deposits. A terrigeneous and calcareous unit, as well as a stadium of mud mound development, comprise the Puentelles Formation. Terrigeneous shales with some intercalations of sand- or limestones predominate the Cavandi Formation.

The sequence of the Sierra Dobros represents the evolution from a stable carbonate platform (Barcaliente Formation) to unstable carbonate platform (Valdeteja- and Picos de Europa Formation including the Dobros beds). The Puentelles Formation displays the change of the sedimentary conditions due to the progression of the Variscan orogenic front. The change from marine to terrigeneous sedimentation occurs in a cyclic evolution (stadium of mud mound development) as the result of transgression and regression. The Cavandi Formation is dominated by Flysch-sedimentation.

Villa, E. & Martínez García, E. (1989): El Carbonifreo Superior marino de Dobros (Picos de Europa, Asturias, NW de España) y su contenido en fusulinaceos.- Trab. Geol. Univ. Oviedo, 18, 77-93, Oviedo.

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Last updated 21-08-1998