Structure and Alpine tectonic evolution of a salt canopy in the western Betic Cordillera (Spain)

Abstract

Surface geology, well data, and seismic profiles confirm the occurrence of an extensive salt canopy in the western Betic Cordillera. Upper Triassic (Keuper) evaporites were emplaced allochthonously in the South-Iberian paleomargin of the Tethys during Upper Cretaceous–Paleogene time. The canopy was later deformed during the Neogene (Miocene–Pliocene) Alpine compression, overthrusting the South-Iberian Mesozoic platform and cover and the Guadalquivir foreland basin. The orogenic advance of the canopy originated a frontal open toe and an accretionary wedge (the Guadalquivir Accretionary Wedge). This wedge, which is a shaly mélange (with blocks of Triassic evaporites) deformed by foreland-directed thrusts with associated piggyback basins and syn-sedimentary listric faults. The structure of the western Betic Cordillera is described through several regional cross sections. The subsalt level involved a Jurassic–Lower Cretaceous thick section, deformed with inverted half-grabens through foreland-directed salt-detached thrusts (northwest vergence). Contraction affects previous salt structures, like Triassic half-grabens, primary minibasins, salt rollers, and a possible large salt pillow. The subsalt deformation shows a thin-skinned subsalt folded belt detached from the Paleozoic section of the Iberian Massif. The salt canopy shows pervasive basal shearing, internal evaporite flow and folding, and brittle thrusting along possible evaporite stringers and preexisting sutures. The suprasalt series consists of secondary and tertiary minibasins and carapaces or rafts. Secondary minibasins are isolated basins infilled with a deepening Upper Cretaceous–Lower Miocene marine sequence. Rotated carapaces or rafts with a condensed Jurassic–Lower Cretaceous sequence, stacked minibasins and welds are the main features of this part of the Betics. The latest stages of the Alpine contraction are accompanied by syn-tectonic (Tortonian–early Pliocene) sedimentation in slightly deformed gentle, marine–to–continental depocenters (referred to here as tertiary minibasins). This salt canopy is comparable in origin to other allochthonous shale sheets, like in the Gulf of Mexico, although as it was later deformed by Alpine compression, it complements observations in other salt-involved orogens like the western Alps, Sivas Basin or the Salina del Istmo Basin, Mexico.