Gas-related morphologies and diapirism in the Gulf of Cadiz

Recently developed high-resolution profiling (multibeam, sonar) and surface sampling were used to map seafloor morphology of the Gulf of Cadiz middle continental slope. Multichannel seismic profiling has made it possible to elucidate the geologic origin of these features as well as the main triggering mechanisms of gas-related morphologies, principally mud volcanoes, carbonate mud mounds, pockmarks and slides. Throughout the entire Gulf of Cadiz, from the continental slope to the shelf and even on land, a close correlation between morphology and gas mobility and associated diapirism can be observed. The middle slope area is strongly deformed by several diapiric ridges, named Guadalquivir, Cadiz and Donana. Most of the diapirs identified in this study are related to the Allochthonous Unit of the Gulf of Cadiz, a chaotic body emplaced during the Tortonian, containing salt and shale nappes affected by later gravitational extension collapse and reactivated compression thrusts. It can be proposed that diapirism and related tectonics provided gas migration pathways.