Morpho-sedimentary structure of new mud volcanoes on the Moroccan Atlantic continental margin (Gulf of Cadiz)

Multibeam bathymetry, sub-bottom parametric profiler, multichannel seismic reflection data and sediment cores were used to detail the nature, morpho-sedimentary and internal structure of five newly discovered submarine mud volcanoes (MVs) in the Moroccan margin of the Gulf of Cadiz. The Henriet and Subvent MVs are located at 300–400 m water depth, while Chueca, Demetrio de Armas and Puerto Real MVs are at 1100–1800 m water depth. Two main types of morphologies are identified: regular cone-shaped edifices (Subvent MV) with a pronounced crater (Henriet MV) in the eastern province; and ridge-attached oval-shaped conical edifices (Chueca, Demetrio de Armas and Puerto Real MVs) in the western province. The overall seismic architecture of these MVs is the result of successive events of mud extrusion and outbuilding alternating with periods of dormancy. The Henriet and Subvent MV system is composed of stacked bicones and intrusive complexes, which penetrated upper Miocene-Quaternary sedimentary units rooted in the Gulf of Cadiz wedge. Major phases of mud extrusion and outbuilding took place since the Late Pliocene with re-activation during mid-Pleistocene. Mud breccias interbedded with hemipelagic/contourite sediments were collected for all MVs. Cores attest to recent periods of mud outflows lasting from the Late Pleistocene (180 ky) whereas the end of MV extrusion could date back to historic times (the last 0.6 ky), giving rise to the onset of a new quiescent activity. The most active MV points out to the Subvent MV. These new MVs are formed in response to the extensional and compressional system within the Gibraltar Arc. In the eastern side, MVs are related to extensional faults forming deep sedimentary basins and forcing overpressured fluids to migrate upwards coeval with thick contourite deposits. On the western side, MVs are related to compressional ridges at the front of fold-thrust systems which act, as pathways to deep-seated fluids to ascent to seafloor.