Timing and structural evolution in the limb of an orocline: The Pisuerga–Carrión Unit (southern limb of the Cantabrian Orocline, NW Spain)

• Joint analysis in unconformity bounded strata show 40° of rotation.
• Oroclinal buckling of Variscan belt started at Mychkovian.
• The limb of the orocline underwent out-of-sequence thrusted.
• Syn-orocline rocks deformed passively due to reactivation of former structures.

Oroclines are the largest scale folds on Earth, and the process of oroclinal formation is a key topic in tectonics. However, most studies of oroclines have focused on the hinge areas, where the changes in strike, and therefore the orocline shape, are most obvious. In this paper, we investigate the deformation mechanisms, the timing, and the structural and tectonic evolution of the Pisuerga–Carrión Unit, situated on the southern limb of the Cantabrian orocline at the NW of the Iberian Peninsula. The Cantabrian Orocline located in the Variscan Belt of Western Europe has been recently defined as a secondary orocline, constraining kinematics and deformation timing. Our study in the Pisuerga–Carrión Unit reveals that an out-of-sequence thrust system developed and reactivated existing structures by a flexural-slip mechanism that was diachronous with respect to oroclinal formation. Joint analysis of unconformity-bounded rock sequences provide a late Moscovian age for oroclinal initiation (ca. 308 Ma), at least locally. Additionally, comparing those joint sets found in different series we quantify a minimum of 40° counterclockwise vertical axis rotation for the Pisuerga–Carrión Unit during the Late Pennsylvanian.

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