Provenance study of Pliocene–Pleistocene sands based on ancient detrital zircons (Alvalade Basin, SW Iberian Atlantic coast)

Abstract

Pliocene–Pleistocene sand of the Alvalade basin was taken from the sea-cliffs of SW Iberia coast for a provenance study using radiometric dating. The U–Pb ages obtained revealed a wide interval ranging from Cretaceous to Archean, with predominance of Paleozoic, Neoproterozoic and Cretaceous zircon ages. Cretaceous ages interpreted to indicate a Sines Massif provenance are dominant in sands close to Cape Sines but are absent in sand sampled 12 km north. Carboniferous ages younger than ca. 315 Ma suggesting a possible contribution from the Central-Iberian Zone originally; however, these zircons may be multi-cyclic, having been reworked from Eocene–Miocene siliciclastic deposits related to transport from central Iberia (Lower Tagus basin drainage evolution). These signatures provide important constraints on the location and extent of the Pliocene–Pleistocene topography and drainage system that were probably controlled by: i) Miocene to Pleistocene landscape rejuvenation driven by Alpine movements along major faults; and ii) residual reliefs related to inherited Variscan structure. The U–Pb ages obtained also trace the pre-Cenozoic paleotectonic evolution of SW Iberia recorded in their sources: i) the North Gondwana accretion and breakup; ii) the Gondwana and Laurussia collision; and iii) the Pangea breakup and opening of the Atlantic Ocean.