El Canal de Diego Cao y sus depresiones morfológicas (margen del Banco del Guadalquivir, Golfo de Cádiz). Implicaciones oceanográficas y sedimentológicas

The Diego Cao channel is located on the central-north middle slope of the Gulf of Cadiz. It separates the Bartolomeu Dias and Faro sheeted drift plateaus to the north of the Guadalquivir Bank margin uplift. A striking linear series of circular depressions occur parallel to the channel on the Bartolomeu Dias sheeted drift (western channel flank), while a remarkable amphitheater-shaped escarpment affects the channel eastern flank. Their morphological and high- and medium-resolution stratigraphic analysis allows inferring their origin as the result of a complex interplay between oceanographic (bottom currents), mass-wasting and tectonic processes. All features seem to have a common origin, related to an especially active tectonic phase during the Mid-Pleistocene, probably related to adjustments of the deep structural features. Since then, the action of the bottom currents and the local influence of structural processes have shaped the present-day topography. The Diego Cao channel is re-interpreted as a contourite moat associated to a complex mounded, separated drift that includes the circular depressions. They result from contourite deposition over the erosional surface originated by widespread mass-wasting events during the Mid-Pleistocene.Versión del edito

Origin of morphological depressions on the Guadalquivir Bank uplifted area (Gulf of Cadiz middle slope)

We have investigated the origin of morphological depressions (circular-elliptical depressions, amphitheatre-shaped escarpments and valleys) on the Guadalquivir Bank uplifted area (Gulf of Cadiz middle slope). This work is based on swath bathymetry and high- and mid-resolution reflection seismic datasets. Depressions occur on the distal (depositional) sector of the Gulf of Cadiz Contourite Depositional System, which has been developed under the influence of the Mediterranean Outflow Water (MOW). The Guadalquivir Bank is a NE-oriented relief that was uplifted along the Neogene and Quaternary. It forms the southern limit of the Bartolomeu Dias and Faro Sheeted Drift (SD) plateaus that are separated by the NW-trending Diego Cao Contourite Channel. Circular-elliptical depressions occur on the Bartolomeu Dias SD plateau, aligned parallel to the rim of the Diego Cao Channel. Irregular, crescent-shaped depressions occur to the SE of the study area and a valley surrounds the Guadalquivir Bank. The origin of these features is interpreted as the result of the interplay between oceanographic, mass-wasting, tectonic and fluid-escape processes. Four stages define the development of these features: 1) Onset of a contourite mounded drift associated with a proto-Diego Cao moat originated by a weak MOW circulation as it interacted with the structural features of the Guadalquivir Bank during the Lower Pliocene; 2) Evolution to a more complex multi-crest drift and moat system, probably as a result of an enhanced MOW and increased deformation of the underlying structures during the Upper Pliocene-Early Quaternary; 3) Event of enhanced tectonic activity that provoked widespread mass-wasting events along middle slope sheeted drift plateaus during the Mid Pleistocene. It was recorded in a prominent erosive surface under the present-day Diego Cao channel western rim and numerous slide scars displaying amphitheatre shapes on the limits of the plateaus; 4) Final stage (Late Quaternary) when the Mediterranean Intermediate Branch started flowing towards the N-NW along the deep gateway that was opened as a result of the mass-wasting event and/or structural adjustments. The contourite system evolved, due to tectonic events, to the present-day channel and a complex separated drift that includes circular depressions. They result from the interaction between the bottom current and the irregular basal surface created by the slide scars. During this phase, crescent-shaped depressions were created, probably by the interplay between bottom currents and fluid escape processes, and the marginal valley around the Guadalquivir Bank resulted from current reworking of the irregular topography of contouritic deposits affected by slide scars

Evidencias acústicas de procesos paralelos al talud asociados con depósitos de movimiento en masa en el talud inferior de la Isla de Madeira (Atlántico Central Oriental)

The Madeira Island lower slope has been build-up mostly by along slope-processes associated with mass movement deposits as seen in GEBCO bathymetry, multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles. A plastered contourite drift (Madeira Drift) developed on this lower slope, being composed of seismic units D1, D2 and D3. The most probable water mass responsible for its deposition is the Antarctica Bottom Water (AABW). The youngest sediments of seismic units D2 and D3 are affected by gravity-driven processes, probably slumps and debris flows, which moved downslope towards west. Parasound profiles show evidences of such mass movements on present-day seabottom (e.g. diffraction hyperbolae echoes) but also of past-events buried within the contourite sediments. These older debris flows are recognized by semitransparent/transparent acoustic facies and lenticular shape.Versión del edito

Interacción entre procesos sedimentarios longitudinales y transversales en el Mar de Alborán durante el Plioceno y Cuaternario

Several morphosedimentary signatures produced by the interaction between alongslope and downslope sedimentary processes have been identified in the Pliocene and Quaternary records as well as on the present-day seafloor of the Alboran Sea. The scenarios of interaction move between two-end-members: from bottom currents dominating gravity flows to gravity flows dominating contour currents. In between these extreme cases, the alternation and balancing of both processes can occur; bottom current activity influencing the gravity flows has been also detected. Although interaction occurs in the Spanish and Moroccan margins, it is especially complex and varied on the Spanish margin, with regional and local effects on the turbidite systems. In contrast, the interaction on the Moroccan margin primarily inhibits the formation of canyons and related fan lobe deposits.Versión del edito

Detailed analysis of the interaction between alongslope and downslope sedimentary processes in the Alboran Sea during the Pliocene and Quaternary

This work aims to analyze the interaction between alongslope contouritic and downslope gravitational processes in the Alboran Sea. Recent results (Juan et al., 2012, 2016) demonstrated that the Pliocene and Quaternary stratigraphic architecture is mostly made up the vertical stacking of contourites interrupted by turbidite systems (TSs). The accurate analysis of all available seismic profiles has revealed several morpho-sedimentary signatures produced by the interaction of the Atlantic Water (AW) and Mediterranean waters (MWs) with the gravity flows in the Pliocene and Quaternary sedimentary record, as well as on the present-day seafloor. Different levels of interaction have been identified and they move between two-end-members: from bottom currents dominating gravity flows, to gravity flows dominating bottom currents. In between these extreme cases, a range of possibilities can occur. First, downslope and alongslope processes can alternate, with vertical and cyclic stacking of both types of deposit. Second, these processes can be balanced, allowing the simultaneous outbuilding of contourites and gravity flow deposits. Last, bottom currents can influence gravity flows. This last interaction is the most common in the Alboran Sea, resulting in the migration of the fan deposits in the direction of the dominant current, and also with effects on the architecture of the turbidite fans, and on their sedimentary composition (grain size). The different levels of interaction change in space and time. These changes have controlled the different depositional architecture displayed by the Spanish and Moroccan margins and the lateral changes along the Spanish margin as a consequence of the different architecture of the turbidite systems. Although interaction occurs in both margins, it is especially complex and varied on the Spanish margin, where the alongslope action is related to the AW, the light intermediate and the dense deep Mediterranean waters (LMw and DMw, respectively). This complex interaction has resulted in a depositional architecture that changes laterally as a consequence of the different architecture of the turbidite systems. Contrasting, on the Moroccan margin the alonsglope action is dominant, being mainly governed by the energy of the AW and the WMDW, that primarily inhibits the formation of canyons and related fan lobe deposits. This inhibition has been interpreted to be result of the topographical acceleration of the WMDW core that would favour an intense alongslope sediment transport, preventing deposition, avoiding the convergence of sediment, and thus inhibiting the formation of downslope gravity flows

Seismic architecture of mud volcano systems in the Ceuta

Analysis of a new dataset of high-resolution seismic and swath bathymetry data acquired during the CONTOURIBER-1 cruise in the Ceuta Contourite Depositional System (Western Alborán Sea), reveals the detailed architecture of several mud volcanoes systems that comprises both surface and buried constructional edifices as well as their subsurface feeder complex which pierces the contourite deposits. Seismic characterization, distribution and interpretation of structural elements associated to the mud volcano system promotes a more comprehensive understanding of the processes involved in their genesis and evolution.El análisis de los datos batimétricos y de sísmica de alta resolución durante la campaña CONTOURIBER-1 en el Sistema Deposicional Contornítico de Ceuta (Mar de Alborán occidental) muestran la arquitectura en detalle de varios sistemas de volcanes de fango que comprenden edificios en el fondo marino y edificios enterrados, así como sus complejos de alimentación a través de los depósitos contorníticos. La caracterización sísmica, distribución e interpretación de estos elementos estructurales que componen el sistema de volcán de fango constituyen una importante ayuda para un mejor y mayor conocimiento de su génesis y evolución.Publicado

Contourite drift off Madeira Island (Northeast Atlantic) and implications to Cenozoic bottom-current circulation

EUROPEAN GEOPHYSICAL UNIO