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The Triassic section of the External domain of the Betic Cordillera is rootless and thus allochthonous. The frontal accretionary wedge of the Guadalquivir allochthon consists dominantly of Triassic evaporites and red beds forming a melange with Upper Cretaceous - Paleogene deep-water sedimentary rocks. Throughout the unit, Jurassic rocks are absent. It is here proposed that the widespread Triassic evaporites of the Guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive-margin setting much like the widespread allochthonous salt of the Texas-Louisiana Gulf of Mexico. Thus, on the Betic passive margin, allochthonous evaporites were first emplaced during the Late Cretaceous - Paleogene. Later, during Neogene time, these evaporites were overthrusted as an accretionary wedge to form the Guadalquivir allochthon. A schematic reconstructed position of the Guadalquivir allochthon places the original passive-margin allochthon in its continental-slope setting.

In contractional orogens, a throughgoing basal-detachment system at middle to lower crustal levels or conceivably in the upper mantle detaches the entire crustal section from the underlying lithosphere. The decollement system connects transcurrent faults and coeval thrust belts and allows their motions to be viewed as the resolved components of a regional displacement field largely driven by relative plate motions. The formation of the regional decollement system during contraction may result in subdecollement volume problems and the formation of a lithospheric root in regions where crustal volume is conserved. In regions characterized by large-scale terrane accretion, addition of mass above the basal decollement may result in an essentially balanced system and may not require formation of a lithospheric root.