| Author||B.N. Koopmans|
|Title||The sedimentary and structural history of the Valsurvio Dome Cantabrian Mountains, Spain|
|Journal||Leidse Geologische Mededelingen|
|Abstract||A continuous sequence of about 1000 m of Devonian sediments has been found in the Valsurvio dome, ranging from probable Siegenian to Famennian in age. This sequence of a neritic-littoral facies shows similar characteristics to the Devonian found further west in the province of León.|
North of the Valsurvio dome, a narrow E—W ridge (zone of San Martin—Camporredondo) has been uplifted by a total of 900—1000 m during two periods in the Middle and Upper Devonian. The upheaval of this zone resulted in rapid facies changes, the development of two large hiatuses in the Devonian of this zone and in the totally different facies development north (Rio Arruz area) and south (Valsurvio dome).
During Carboniferous time the San Martin-Camporredondo zone played an important role in sedimentary history. The Carboniferous is subdivided in three groups.
The Ruesga group (Pre-Curavacas folding) is developed in the Valsurvio dome as thick massive limestones of the Caliza de Montaña facies, whereas in the San Martin-Camporredondo zone predominantly clastic, reworked and highly mixed sediments of the Culm facies occur; these lithological differences being due to a subsidence of latter zone during sedimentation of the Ruesga group.
The sediments of the Yuso group (post-Curavacas and Pre-Asturian folding) are very similar to the Culm facies of the Ruesga group.
The Cea group contains at least 1200 m of coal measures, outcropping in a small E—W zone situated at the boundary of the Cantabrian mountains and the meseta of Old Castile.
At least four deformation periods have been distinguished: 1. The Curavacas folding phase which caused isoclinal E—W trending folds and altered the incompetent Devonian shales into slates. In the competent Upper Devonian rocks and limestones of the Ruesga group minor folding has played a less important role. Large isoclinal folds dip 60—40° S. These structures are most typically developed in the Valsurvio dome, but with the facies change into the zone of San Martin-Camporredondo large ESE\u2500WNW tracing lowangle overthrusts developed. The maximum measured thrust movement to the north is about 2.5 km. 2. In the Asturian folding phase contemporaneous E\u2500W and N\u2500S fold directions occur. A crenulation cleavage has been developed in the already cleaved rocks, whereas in the rocks of the Yuso group a slaty cleavage developed, often subparallel to the bedding. A late recrystallization of small unoriented porphyroblasts of chloritoid has been observed. 3. During a Post-Stephanian (and probable Pre-Triassic) folding phase broad open E\u2500W folds developed, which caused the updoming of the Valsurvio dome and a reorientation of first and second generation structures. In the zone of San Martin-Camporredondo this folding is presented by minor folds and crenulation cleavages, often both developed as conjugate systems. 4. Tertiary deformation. The epirogenetic upheaval of the mountainous area along a set of border faults has caused a steepening of the Cea group, the Cretaceous and the lower part of the Tertiary conglomerates in a small E\u2500W running zone in the south of the area.
Together with the development of the WNW\u2500ESE Cotolorno wrench-fault, a flexure like fold has been developed in the Cea group and the Cretaceous. The influence of the Tertiary deformation apart from the wrench faults, is restricted to the southern part of the area.
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