Paleogeographic imprint of a piggy-back basin rotation. The Ainsa Basin (South-central Pyrenees)

Sedimentary geometries and paleocurrent distribution from the Ainsa basin support the paleomagnetic data about its rotation and chronology. The Ypresian foreland platform margin, folded in the Boltaña anticline, predates thrusting and related piggyback basin transport. An early Lutetian initiation for the thrust–fold of the Boltaña – Balces system is consistent with the onlap geometries on the east limb of the Boltaña anticline. In the mid Lutetian, growth strata followed by an angular unconformity in the carbonate west limb of the Balces anticline postdates the fault-propagation folding in the Boltaña-Balces system. The forced deltaic progradation that filled the Ainsa basin following the syncline geometry during the mid to late Lutetian (Sobrarbe Fm) track this mid-Lutetian unconformity. The Campodarbe Group, including the Escanilla Fm (Bartonian – middle Priabonian), is connected to the hinterland tectonic uplifting by the Gavarnie thrust with a new palaeogeography and basin configuration. Sedimentary data reinforce a post Lutetian (Bartonian – middle Priabonian) main event of rotation.