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International audience; The numerous processes (superficial and deep) occurring on margins, their origins, consequences, interactions and quantifications are only very partially described and understood. The identification of the relative role of factors is sometimes completely contradictory between authors. Here, we showed the results of a long-term multidecadal and multidisciplinary study (using geophysical, geological, stratigraphic, paleontological, geomorphologic, geochemical, microbiological and numerical models) in the Western Mediterranean Sea that acts as a natural laboratory at many different scales. We showed how sediments efficiently recorded at the same time: variations of glacio-eustatic sea-level changes, variations of sediments yield and sources, and also enabled quantifying vertical movements and geodynamic worldwide events but also detailed regional mass transport, turbidites and contourites deposits. They are also an archive of paleoclimatic, palaeoceanographic and diagenetic processes.

International audience

A multiproxy integrated chronological framework, based on oxygen and carbon stable isotope stratigraphy, biostratigraphy (foraminifera and nannoplankton bioevents and foraminifer assemblage-based climate cyclicity), magnetostratigraphy, sapropel stratigraphy, and C-14 AMS radiometric dates, has been achieved for borehole PRAD1-2, collected in 185.5 m water depth in the central Adriatic. This work was carried out within the European Community project Profiles across Mediterranean Sedimentary Systems (PROMESS1). The 71.2 m long borehole spans a time interval between late MIS 11 and MIS 1 (the last 370 ka), showing a chronological resolution of 500 and 250 years per cm during interglacial and glacial intervals, respectively. At present, this record is the most expanded and continuous marine record available for the Adriatic Basin. Several orbital cycles can be recognized in the PRAD1-2 record: the 100 ka glacial-interglacial fluctuations and the 23 ka precession-related cycles, which in turn control the deposition of sapropel layers. An integrated analysis of short-term oscillations within the Last Glaciation interval (MIS 4–MIS 2) allowed the identification of the Adriatic signature of Dansgaard-Oeschger events, showing the potential to achieve a more refined chronostratigraphic framework for the top part of the PRAD1-2 record. Finally, the age model obtained by this study allowed the chronological integration of the main foraminifera bioevents detected in the borehole as well as of the volcanoclastic layers present in the upper part of the record. Despite its proximal location, PRAD1-2 presents a continuous record and shows the potential to be consistently correlated both with deep-sea and continental records in the Mediterranean region and beyond.

Thick forced regressive units on the wide continental shelf of the Gulf of Lions (western Mediterranean) recorded the composite effect of sea level changes during the Quaternary. They are mostly composed of coastal siliciclastic and bioclastic wedges showing clinoform geometry. These deposits have been intensively explored through high-resolution seismic investigations, but only recently it was possible to ground truth seismic interpretations, based on a long (100 m) borehole that crossed the succession and recovered a large part of the mainly sandy deposits (

The Bourcart–Hérault canyon interfluve in the Gulf of Lions (NW Mediterranean) was the site of very high sedimentation (up to 2.5 m/kyr) around the Last Glacial Maximum, due to the vicinity of major fluvial systems that fed the shelf edge. Shoreface deposits and offshore muds deposited during each glacial/interglacial 100 kyr-cycle, created a repeated motif with high-angle and low-angle clinoforms on seismic profiles. New detailed morphological, sedimentological and paleo-environmental data, constrained by 14C dating, allow us to propose a scenario for the evolution of this critical area between 46 and 15 cal. kyr BP. The major seismic sequence (S5), formed as a forced regression during the overall sea-level fall between MIS-3 and MIS-2, can be sub-divided into several prograding units, which indicate that relative sea-level changes were punctuated by intervals of increased fall or slow-down, or even stillstand. Similarly, the onset of sea-level rise was marked by steps, during which wave-cut terraces formed, and can be tracked all around the Gulf of Lions. Three stillstands or slow-downs of sea-level change are identified and dated by deposits found at 90 m relative sea-level (21 cal. kyr BP), 110–115 m rsl (18–17 cal. kyr BP), and 98–105 m rsl (before 15.9 cal. kyr BP). Cementation of beach rocks, that now form eroded pinnacles culminating at 90 m, occurred during the 21 kyr stillstand. The position of relative sea-level during the maximum lowstand is not known, but should be deeper than 115 m. Periods of increased northwesterly winds favoured transport of coarser sediment at the shelf edge, in relation with deep water cascading: this created a distinct sandy interval during the period of Heinrich event 2 (around 24 cal. kyr BP), at the origin of amplitude anomaly on very high-resolution seismic data. The increased sea-level rise, around 15 cal. kyr BP, resulted in an abrupt decrease of sedimentation.

The PROMESS1 PRAD2 site includes two continuous sediment cores (boreholes PRAD2-4 for stratigraphy and PRAD2-5 for geotechnical studies), in situ cone penetration measurements (CPTU; boreholes PRAD2-3 and PRAD2-6) and spectral gamma ray downhole logging (borehole PRAD2-4) of a stratigraphic succession on the western flank of the Adriatic continental shelf in 56 m water depth. The sedimentary succession is composed mainly of marine silty clay (0 to 27 mbsf) and alternating fine sand and clay (27 to 32 mbsf). The upper 20 m of sediment show seafloor and subsurface undulations on reflection-seismic profiles, representing sediment deformation features with limited displacement, muddy bedforms or a combination, and whose interpretation justified a set of geotechnical measurements. The chronology of the sedimentary succession is based on a regional correlation to stratigraphic units identified on reflection-seismic profiles that were dated in other sediment cores with ecobiostratigraphy of planktic and benthic foraminifera, magnetic parameters (including secular variations in inclination and declination of the Earth magnetic field), oxygen isotope stratigraphy, radiocarbon dating, palynology and tephrochronology. The sedimentary record of the borehole represents the deposit of the last sea level highstand (HST, aged 5.5 kyr to present) and part of the previous transgression. Seismic correlation indicates that: 1) the sandy layers at the base correspond to a progradational unit emplaced during the Bolling/Allerod and Younger Dryas periods culminating in a sharp submarine erosional surface at 27 mbsf; 2) the maximum flood surface (mfs) at the base of the HST is at ca. 21 mbsf; 3) above the mfs there is a seismic unit characterized by discontinuous seismic reflectors at the top, marking a condensed interval between approximately 5.5 and 3.7 kyr; above this condensed unit undulations are present. We show here the result of the direct analysis of the sedimentary succession using integrated stratigraphic techniques and in-situ and laboratory geotechnical tests. Due to the shallow depth of PRAD2 site, we used benthic ecozones to identify the position of the mfs. In particular we noted that from 21 mbsf upwards the benthic association is abundant with frequent E. granosum and B. ex gr. marginata, some V. complanata and C. laevigata carinata, while plankton is rare and composed by G. ruber, G. sacculifer, Orbulina, and G. aequilateralis. Below 21 mbsf, the presence of benthic species U. peregrina, G. laevigatus, and H. balthica suggests a relatively deeper setting, that corresponds to the peak marine ingression at the base of the HST. In-situ measurements and geotechnical tests confirm the existence at 20.5 mbsf of a 1-m thick silty clay layer immediately above the mfs, coarser than the surrounding sediment. This level resulted the most sensitive to earthquake loading in triaxial cyclic tests. Calculation of the potential liquefaction of sediment from PRAD2 site under an earthquake shaking (comparable in magnitude with those measured in this area) shows that sediment liquefaction of the silty clay level above the mfs was possible when its burying was less than 5 m. (Work supported by contract EC EVR1-2001-00041

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.