Diapiric activity affecting Late Pliocene to Pleistocene sediments under a tectonic compressive regime: an example from the Western Iberian Margin (Srª da Vitória beach, central Portugal)

Abstract

The structural evolution of a folded and faulted Upper Pliocene to Lower Pleistocene sedimentary unit exposed at the coastal cliffs of Sra da Vitoria beach was studied. This sequence is wedged between the S. Pedro de Moel diapir, to the north, and the Pombal–Leiria–Nazare fault zone, to the south, providing striking evidence of neotectonic activity in the Western Iberian Margin and of its role in the triggering of halokinesis. Several deformational events were recognised, related to a regional NW–SE compression that activated halokinesis of underlying Triassic to Lower Jurassic (Hettangian) silty clays and gypsiferous marls. The combined effects of the compression and of the triggered halokinesis generated a NW-verging asymmetric syncline affecting the studied sedimentary unit, where strain was partially accommodated by faulting and crenulation in micaceous horizons of the sandy deposits. This deformation represents the local accommodation on the sedimentary cover of transpression along the S. Pedro de Moel fault, which was intruded by the Triassic to Hettangian evaporitic marls and silty clays, and reactivated with left-lateral reverse movement. This regional fault prolongs offshore, being parallel to other NE–SW trending faults that are located near the upper reach of the Nazare submarine canyon, reinforcing the evidence for neotectonic activity on this major fault system of the Portuguese Atlantic margin.