Variscan olistostrome deposition and synsedimentary nappe emplacement, Valdeon area, Cantabrian Mountains, Spain

In the area of Valdeón and adjacent western Liébana (along the provincial boundary between León and Santander, in northern Spain) Namurian and Westfalian flysch deposits are unconformably covered by a sequence of olistostrome and flysch units, alternating with nappes. This sequence, with a thickness of about 5 km, was built up during the Middle Cantabrian. It is covered in turn by the Picos de Europa nappes with intercalated flyschoid sediments of a slightly younger age. In this paper the discrete lithostratigraphic and structural units are described and analyzed. Special attention is given to the fusulinid biostratigraphy. The contact relations between nappes and olistostrome units and their complementary lithostratigraphy are explained as the result of synsedimentary emplacement of the nappes by gravitational sliding along the earth surface. The palaeogeologic setting prior to the deposition of the nappes and olistostromes is deduced from the stratigraphy and lithofacies of the nappes and the allochthonous elements constituting the olistostromes. The regional geologic setting thus obtained and its consequent sedimentological and structural development, are discussed. An attempt is made to fit these developments in the model of a continental strike-slip system.