Imaging the seascapes of the Mediterranean

The Mediterranean Sea is a relative newcomer to Earth"s landscape. Due to its complex tectonic history, this mid-latitude sea is composed of a cluster of basins. Their seascape is in most cases dominated by geologically young structures, but also by sedimentary processes. Among the latter, sedimentary processes related to the dynamics of the largest rivers in the Mediterranean (Ebro, Rhône, Po, Danube, and Nile) stand out. This overview article illustrates the main sedimentary processes and their products contributing to shape the Mediterranean seascape within a source-tosink approach. To highlight this approach, this article mainly focuses on one of the EUROSTRATAFORM project study areas: the northwestern Mediterranean

The Role of Canyons in Strata Formation

This paper provides a spatial and temporal multi-scale approach of European submarine canyons. We fi rst present the long-term geologic view of European margins as related to controls on submarine canyon development. Then we discuss the extent to which submarine canyon systems resemble river systems because both essentially form drainage networks. Finally, we deal with the hortest-term, highestresolution scale to get a fl avor of the current functioning and health of modern submarine canyons in the northwestern Mediterranean Sea. Submarine canyons are unique features of the seafl oor whose existence was known by European fi shermen centuries ago, especially for those canyons that have their heads at short distance from shoreline. Popular names given to specifi c canyons in the different languages spoken in European coastal communities refer to the concepts of a"deep" or"trench." In the old times it was also common thinking that submarine canyons where so deep that nobody could measure their depth or even that they had no bottom. Submarine canyons are just one of the seven different types of seafl oor valleys identifi ed by Shepard (1973) in his pioneering morphogenetic classifi cation. Shepard (1973) defined submarine canyons as"steep-walled, sinuous valleys, with V-shaped cross sections, and relief comparable even to the largest of land canyons; tributaries are found in most of the canyons and rock outcrops abound on their walls." Canyons are features typical of continental slopes with their upper reaches and heads cut into the continental shelf

Post-Messinian evolution of the Florence Ridge area (Western Cyprus Arc), Part I: Morphostructural analysis

International audienceThe Florence Ridge, part of the western Cyprus arc, is a compressional relief that was eroded during the Messinian salinity crisis while deposition of salt occurred North (Antalya basin) and South (Herodotus abyssal plain). In order to better assess the impact of salt-tectonics in the Florence Ridge region deformations, we conducted a morpho-structural analysis of available multibeam and seismic data (Simed and Prismed II campaigns). It is indeed a crucial issue to distinguish crustal and gravity driven structures in the compressional to strike-slip belts of the eastern Mediterranean.Along the Antalya basin, we mainly observed multi-directional tectonic rafts typical of gravity gliding above salt. On the Florence Ridge itself, the base of salt evolves laterally to a Messinian erosional surface that erodes a series of stacked nappes. This surface is involved in recent faulting. South of the Florence Ridge, a nearly 100 km wide fold belt characterizes the Herodotus abyssal plain. Three different zones parallel to the Florence Ridge appear within this fold belt. Those are respectively from North to South zones A, B and C. Zone A is characterized mainly by small-wavelength folding and faulting. Approaching Zone B, a long extensional graben deforms the seafloor. Zone B stands ~ 100 to 200 m higher than zones A and C. There, salt welding seems common. In the easternmost zone B deep sub-circular bathymetric depressions are associated with extremely thick and fan-shaped depocenters probably emplaced in relation with active sub-salt thrusts. Many evidences suggest post-Messinian uplift in this zone. Zone C shows medium to high wavelength salt-cored folds. Wavelength of those folds increase approaching the distal Nile deep-sea fan. Within zone C, a nearly undeformed domain exists approaching the Eratosthenes seamount. ‘En echelon’ folds bound this flat domain suggesting lateral salt extrusion at the junction between zone C and the distal Nile deep-sea fan.To conclude, numerous evidences argue for a post-Messinian reactivation of the pre-Messinian Florence Ridge accretionary wedge (numerous folds, uplifted zones). The salt, as on the nearby Mediterranean Ridge, decouples deep and surface deformations and even allow the development of isolated grabens and associated salt ridges in the heart of the Florence compressional zone. We propose in this case that local basal slope of salt increase related to basement fault activity triggered gravity gliding and thus extensional deformation despite the regional compressional regime. Finally, this study shows that the eastern Nile deep-sea fan, submitted to extremely vigorous salt tectonics seems to have collided with the Florence Ridge fold belt and to have generated a “salt extrusion” zone

Imaging the seascapes of the Mediterranean

The Mediterranean Sea is a relative newcomer to Earth"s landscape. Due to its complex tectonic history, this mid-latitude sea is composed of a cluster of basins. Their seascape is in most cases dominated by geologically young structures, but also by sedimentary processes. Among the latter, sedimentary processes related to the dynamics of the largest rivers in the Mediterranean (Ebro, Rhône, Po, Danube, and Nile) stand out. This overview article illustrates the main sedimentary processes and their products contributing to shape the Mediterranean seascape within a source-tosink approach. To highlight this approach, this article mainly focuses on one of the EUROSTRATAFORM project study areas: the northwestern Mediterranean

The role of canyons on strata formation

This paper provides a spatial and temporal multi-scale approach of European submarine canyons. We first present the long-term geologic view of European margins as related to controls on submarine canyon development. Then we discuss the extent to which submarine canyon systems resemble river systems because both essentially form drainage networks. Finally, we deal with the shortest-term, highest-resolution scale to get a flavor of the current functioning and health of modern submarine canyons in the northwestern Mediterranean Sea

Slope Instability on the French Guiana Transform Margin from Swath-Bathymetry and 3.5 kHz Echograms

Although transform margins represent ~30% of rifted margins around the world, few studies have investigated mass-movement processes in such areas and their links with this specific structural context. The French Guiana transform margin and adjacent Demerara abyssal plain have been surveyed during the GUYAPLAC cruise, collecting multibeam bathymetric data, backscatter imagery, 3.5 kHz echograms and 6-channel seismic profiles. The study area is divided into three domains: the shallow Demerara plateau, the Guiana slope and rise, and the Demerara abyssal plain. The Demerara plateau displays multi-scale slope instabilities from huge deep-seated collapses of the whole margin to surficial creeping folds and recent slumps. Giant elongated pockmarks have been also observed for the first time in this area. Fluid escape is common everywhere on the plateau and probably enhances slope instability. On the Guiana slope and rise, large stacked lobate masses have been identified testifying to repetitive failure events. Fluid escape is also ubiquitous there, suggesting a dewatering of debris flows due to sediment loading. Two main types of sedimentary structures are observed on the Demerara Abyssal Plain: small meandering channels of the Amazon Fan at its eastern edge and sediment waves at its western edge, along the foot of Demerara continental slope

Discovery of widespread biogenic methane emissions and authigenic carbonate mound-like structures at the Aquitaine shelf (Bay of Biscay)

International audienc

Mass-transport deposits and fluid venting in a transform margin setting, the eastern Demerara Plateau (French Guiana)

The eastern Demerara Plateau offshore French Guiana was surveyed in 2003 during the GUYAPLAC cruise (multibeam bathymetry and acoustic imagery, 6-channel seismic reflection and 3.5 kHz echo-sounding). The data show the "post-transform" Cenozoic that the series located on the outer part of the plateau (below c. 2000 m) contain at least twelve stacked mass transport deposits (MTDs) that have recorded a history of large-scale slope failure, as well as two main normal fault sets that provide possible pathways for upward fluid migration through the series, reaching at high as the uppermost MTDs. Seabed data show that the area above the failures is characterized by circular-to-elongate (slope-parallel) depressions interpreted as fluid seeps (pockmarks), some of them have been modified by along slope currents. We suggest that the development of the MTDs to results from the combinaiton of the presence of fluid overpressure at depth the geometry of the margin's deep structure, in particular the existence of a 'free borderlateral border' on the outermost plateau. Our results also emphasise the role of stratigraphic decollements within the Cenozoic series