Arquitectura sísmica, olistostromas y fallas extensionales en el norte de la cuenca oeste del Mar de Alborán

Zusammenfassung

A recent acquisition of 3D seismic over a small area in the northern margin of the West Alborán Basin (WAB), at the so called Malaga Basin, allow for much better geological observation than those imagined by conventional MCS profiles. The 3D profiles show new data from the WAB sedimentary infill and demonstrate the presence of Miocene extensional fault-systems in the basin. In the WAB northern margin (Malaga Basin margin) the older extensional detachment system corresponds to the regional contact between the Alborán Domain (Internal Zones of the Betic and Rif Cordilleras) and the Miocene sediment cover, and inserts the metamorphic basement at places. This detachment show rare flat segments and long continuous ramps dipping 28-30º toward SSE. Both, ramps and flats are fossilized by a lower-to-middle Miocene basin onlap seismic configuration initiated during the Late Burdigalian-Early Langhian, at least. This first fault system was eroded in pre-Langhian times and presents big structural antiforms in the external-margin area, close to the present shoreline. In the WAB deep waters, this detachment system show a drastic change in the dip of the major fault-plane and cut the Alborán Domain, consequently created a continuous line of hanging wall anticlines structures parallel to the northern branch of the Gibraltar Arc. The second extensional system, encompassing sin-sedimentary tilting, listric- and grow-faults, and sedimentary wedges, disturbed only the Miocene (Langhian to Tortonian) sequences. This fault system supported intense erosion during the Messinian sea-level fall. The 3D seismic discovers olistostrome bodies. This olistostrome occurred from originally chaotic submarine landslides that evolved to backslide structures through time. The olsitrostome unit sows internal ramps (thrust duplexes) and a frontal ramp (blind thrust fault) thrusting autochthonous Tortonian seismic units. Regional onshore-offshore correlations suggest these olistostrome bodies may derive from the Flysch Units (Alborán Domain) or neighboring lower Miocene olistrostromic unit’s outcropping-out to the W-NW in the Betic Chain. The 3D seismic depicts that the Upper Messinian unit differentiates two seismic sequences that infill incised valleys created during the Messinian sea level fall. Both, well data and the seismic expression allow defining the upper sequence as a turbidity mass-transport deposit (MTD).