Geological History of the Picos de Europa
The Carboniferous Period and Variscan Orogeny
During the Carboniferous Period the Picos de Europa, located on the north-eastern margin of the Cantabrian Zone remained a relatively stable province in which carbonate deposition predominated for 55 million years.
At the beginning of the Carboniferous Period uniform marine conditions existed throughout the Cantabrian Zone resulting in the widespread deposition of a sequence of red, nodular limestones with chert and thin shales, the Genicera Formation. At the beginning of the Namurian the black, 'Caliza de Montana' was deposited. Carbonate deposition continued in the Picos de Europa Province however, with intraformational breccias and slump deposits the only indications of tectonic disturbances resulting from the NW movement of the African continental plate towards the Eur-American plate.
The main period of deformation in the Cantabrian Zone occurred at the end of the Moscovian (about 295 Ma). Sediments were thrust into the core of a developing curved mountain chain (i.e. into the Cantabrian Zone) from the northwest, west and southwest. The Picos de Europa Province was the last to be affected by deformation because of it's position at the northeastern margin of the Cantabrian Zone, away from the encroaching thrust sheets. The main phase of deformation within the Picos de Europa Province began in the Kasimovian and continued until the Autunian. Palaeozoic sediments, predominantly Carboniferous carbonates, were thrust from the north-northeast to the south-southwest. The massively bedded limestones moved as a series of competent sheets with very little internal folding. Each thrust sheet was pushed over the one emplaced immediately to the south which greatly increased the total thickness of the carbonate sequence. It has been estimated that the limestones moved at least 20km.
During the Permian, Mesozoic and early Tertiary, a sedimentary sequence was deposited over the Picos de Europa limestones. This is inferred by the presence of Permian deposits within down-faulted regions, as at Sotres, and by the present drainage pattern which must have been superimposed on the Carboniferous limestones from a post-Variscan cover.
Post-Variscan deformation was extensional in character with fault-bounded basins controlling the pattern of sedimentation. In late Eocene and Miocene times, however, northern Spain experienced a further period of north-south compression, this time related to the Pyrenean Orogeny. The compression ended about 38 Ma ago and probably initiated the uplift of the Picos de Europa massifs. The Pyrenean deformation affected the Carboniferous limestones largely by re-activating existing Variscan and post-Variscan fractures. These are particularly important controls on cave development because they are less well 'sealed' by veining and provide the most open routes for water into the massif.