West Asturian Leonese Zone
The West Asturian Leonese Zone lies to the west and south-west of the Precambrian rocks of the Narcea antiform, and extend east to the Precambrian rocks of the Olle de Sapo antiform. Rocks in this zone are mostly from Cambrian and Ordovician, with few from Silurian to Carboniferous. The Cambrian and Ordovician rocks were formed in shallow water in a subsiding trough. Later deposits were formed in deeper water. They have been metamorphosed to greenschist or low grade amphibolite. Also they mostly have a slaty cleavage. Folds face the centre of the arc. In the west the folds are recumbent and large: Mondonedo and Caurell folds. In the east the folds are asymmetrical. The base of the Mondonedo fold is an overthrust with the same name. Another overthrust forms the edge of this zone where it meets the Narcean Antiform. Crenulation cleavage occurs near these overthrusts. All these structures formed between Lower Devonian and Stephanian B-C.
From the Cambrian Period, the Candana Quartzite is equivalent to the Herreria Formation and is 1 to 2 km thick. The Vegadeo Limestone is equivalent to the Lancara Formation and is 0.1 to 0.2 km thick. The Cabos Series is equivalent to the Oville and Barrios Formations and is 4 km thick.
Black shales, called the Luarca Slates are Llanvirnian to Llandeilian age (middle to upper Ordovician) and are 0.5 to 1 km thick. The Agüeira Formation consists of turbidites of Caradocian age and is 3 km thick. Following a disconformity the Silurian black slates are laid down 0.4 km thick.
There are few outcrops of lower Devonian rocks in the San Clodio area. And in the Carboniferous Period, this was an erosional zone forming the source of material for the Cantabrian Carboniferous deposits.
Read more about this topic: Geology Of The Iberian Peninsula
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