The transition from passive to active margin sedimentation in the Cantabrian Mountains, Northern Spain: Devonian or Carboniferous?

In the Cantabrian Mountains of northern Spain, a Cambrian through Pennsylvanian sedimentary succession is preserved that was deformed during the Hercynian orogenic cycle. Within this succession, Silurian and Devonian strata indicate sedimentation on a passive margin. Pennsylvanian deposits are the product of syndeformational uplift and erosion of the newly forming orogen and were deposited in a rapidly filling foreland basin in front of the orogenic belt. The intervening Mississippian succession is strongly condensed and consists of coarse-grained sandstones mantling a regional angular unconformity, crinoidal limestones followed by phosphatic black shales, nodular limestones and siliceous shales. This succession shows abundant erosional surfaces and mass-flow deposits and it is here interpreted as the initial starved foreland basin fill. If this interpretation is correct, the foreland basin system had already developed during the Late Devonian, much earlier than hitherto assumed. Its initiation can be correlated to processes in the internal zones of the Iberian Hercynian orogen where during the Late Devonian there is the change from subduction of oceanic lithosphere to intended continental subduction, its blocking and the subsequent collisional-type deformation. As a direct, long-distance effect of these changes in the plate-tectonic regime, the Cantabrian Hercynian foreland basin was created.