--> Passive-Margin Allochthonous Salt Canopies Emplaced Within an Alpine Fold-and-Thrust Belt: Example From the Betic Cordillera of Spain

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Passive-Margin Allochthonous Salt Canopies Emplaced Within an Alpine Fold-and-Thrust Belt: Example From the Betic Cordillera of Spain

Abstract

Geological surface data, exploration well log data and seismic 2D data indicate that large volumes of evaporites, mostly salt, but also gypsum and anhydrite, were emplaced during passive-margin development of the Tethys in southern Iberia, today part of the Guadalquivir Allochthon of the Central and Western Betic Cordillera (Southern Spain). Syn-tectonic sediments, remnants of mini-basins, and re-deposited evaporites within deep-water strata suggest that the main emplacement of the salt canopies took place during Upper Cretaceous and Paleocene time. This age results much older than the Miocene to Pliocene emplacement of the Guadalquivir Allochthon. Mostly allochthonous salt bodies occupying the higher and often frontal structural thrust sheet of the Betic Cordillera compose this unit. Late Neogene (Upper Miocene to Pliocene) Alpine compression within the Betic fold-and-thrust belt strongly deformed the allochthonous salt system. During this event, the Guadalquivir Allochthon formed a thrust sheet that was emplaced above the Jurassic-Cretaceous inverted, passive margin (formed by the Pre and Sub-Betic Nappes). The Triassic section of the Guadalquivir Allochthon (>2 km thick salt unit) strongly differs from the underlying sub-autochthonous Triassic section of the Sub-and Pre-Betic units, which is formed by limestone and evaporite strata indicative of pre, syn- and post-rift sabkha type sedimentation. Passive-margin Triassic salt structures can also be found in the antithetic North African margin along the Rif and Tell belts, in Morocco, Algeria and Tunisia. Compared to the Betic Cordillera in Spain, this margin had a less-matured allochthonous canopy system with an older age of emplacement, because it probably occurred during the early Upper Cretaceous.