[1] The Ligurian basin, western Mediterranean Sea, has opened from late Oligocene to early Miocene times, behind the Apulian subduction zone and partly within the western Alpine belt. We analyze the deep structures of the basin and its conjugate margins in order to describe the tectonic styles of opening and to investigate the possible contributions of forces responsible for the basin formation, especially the pulling force induced by the retreating subduction hinge and the gravitational body force from the Alpine wedge. To undertake this analysis, we combine new multichannel seismic reflection data (Malis cruise, 1995) with other geophysical data (previous multichannel and monochannel seismic sections, magnetic anomalies) and constrain them by geological sampling from two recent cruises (dredges from Marco cruise, 1995, and submersible dives from Cylice cruise, 1997). From an analysis of basement morphology and seismic facies, we refine the extent of the different domains in the Ligurian Sea: (1) the continental thinned margins, with strong changes in width and structure along strike and on both sides of the ocean; (2) the transitional domain to the basin; and (3) a narrow, atypical oceanic domain. Margin structures are characterized by few tilted blocks along the narrow margins, where inherited structures seem to control synrift sedimentation and margin segmentation. On the NW Corsican margin, extension is distributed over more than 120 km, including offshore Alpine Corsica, and several oceanward faults sole on a relatively flat reflector. We interpret them as previous Alpine thrusts reactivated during rifting as normal faults soling on a normal ductile shear zone. Using correlations between magnetic data, seismic facies, and sampling, we propose a new map of the distribution of magmatism. The oceanic domain depicts narrow, isolated magnetic anomalies and is interpreted as tholeitic volcanics settled within an unroofed upper mantle, whereas calcalkaline volcanism appears to be discontinuous but massive and has jumped in space and time, from the beginning of rifting on the Ligurian margin ($30 Ma), toward the Corsican margin at the end of the Corsica-Sardinia block rotation ($16 Ma). This space and time shift reveals the importance of the rollback of the Apulian slab and of the migration of the Alpine-Apennines belt front toward the E-SE for driving basin formation. We also state that initial rheological conditions and inherited crustal fabric induce important changes in the styles of deformation observed along margins and between conjugate margins. In the NE Ligurian basin the prerift Alpine crustal thickening together with slow rollback velocity likely contribute to distribute strain across the whole NW Corsican margin, whereas farther south the inherited Hercynian structural pattern combined with a faster rollback of the subducting plate tend to focus the extension at the foot of the margin, up to the Sardinian rift which ends within the SW Corsican margin. Therefore the mode of opening and the margin struct...

The Messinian salinity crisis (MSC) [Hsü et al., 1973] has deeply shaped the Mediterranean landscape and triggered large sedimentary deposits (evaporites and clastics) in the deep basins within a short time span. Until recently, the MSC has mainly been analyzed independently, either through outcrops located onshore (e.g. Morocco, Cyprus, Spain, Sardinia, Italy) or through marine seismic profiles in the deep offshore. Each approach bears its own limitations:(1) on the one hand, land outcrops refer to incomplete Messinian successions that are geometrically disconnected from the offshore Messinian deposits owing to tectonics (e.g. Apennines) and/or because they accumulated at an early stage of the crisis in shallow marginal basins (e.g. Spain); (2) on the other hand, seismic profiles from the upper margins down to the deep basins allow to image and explore the entire MSC event as a continuous process, but with a lower resolution and with a lack of stratigraphical and lithological control, in the absence of full recovery of scientific boreholes.We present here a synthesis of a set of modern geophysical data over the Mediterranean and Black seas allowing to image the Messinian markers (erosion surfaces, depositional units and their bounding surfaces) much better than previously and to study the spatio-temporal organisation of these markers from the inner-shelves down to the bathyal plains. The results from thirteen areas located offshore are compared, with common charts and nomenclatures. The comparative and multi-site approach developed here allows to analyse the record of the MSC on margin segments and basins that depict various structural, geodynamical and geological settings, to fix a number of local influencing factors (tectonics, subsidence, inherited topography, sedimentary fluxes...) and to partly assess their influence in facies and geometrical variations of the MSC units. We are thus able to extract from our analysis some recurrent signals related to the MSC ss., allowing us to discuss: (1) the amplitude and modalities of base-level changes during the MSC; (2) the depositional modalities of the MSC units in the deep basins; (3) the location of the erosion product of the margins and to emphasise (4) the major differences between the eastern and western Mediterranean basins. Une meilleure connaissance des enregistrements de la crise de salinité messinienne en domaine marin grâce à l'analyse sismique multi-sitesMots-clés. -Crise de salinité messinienne, Méditerranée, Profils sismiques, Evaporites, Erosion, Clastiques.Résumé. -La crise de salinité messinienne (CSM) [Hsü et al., 1973] a profondément modelé les paysages méditerra-néens et généré d'épaisses accumulations sédimentaires (évaporites et dépôts clastiques) dans les bassins profonds sur une brève période de temps à l'échelle géologique. Jusqu'à présent, la CSM a principalement été étudiée distinctement, à terre, grâce aux affleurements (ex. Maroc, Chypre, Espagne, Sardaigne, Italie…), et en domaine marin, par l'intermé-diaire de profils sismiques. Chacun...

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In the northeast Atlantic, DSDP drilling results, combined with intensive geophysical surveys, permit a proposed model of the structural evolution of a starved, passive continental margin. Environment and tectonics of the rifting phase have been established. Active rifting took place in Early Cretaceous time in a pre-existing marine basin in contrast to many subaerial rift systems. The overall tectonic style is characterized by a series of tilted fault blocks bounded in many cases by listric faults. The rotation of the blocks (20-30°) along listric faults reduced the thickness of the upper continental crust from 6 to 8 km to 4 to 5 km. Close to the near horizontal base of the listric faults, a strong horizontal reflector corresponding to the 6.3 to 4.9 km/s refraction interface has been interpreted as the boundary between the upper brittle and the lower ductile continental crusts. The Moho discontinuity, 25 km deep in the vicinity of the shelf break, is 12 km deep in the lower part of the margin. In this area the ductile part of the crust (6.3 km/s) is only 3 km thick. Drill, dredge, and seismic reflection data allow reconstruction of the topography of the sea floor at the end of rifting in Aptian time. In the axis of the rift system, submarine troughs 2.5 km deep existed. The mechanism of riftingis discussed. The thinning of the continental crust cannot beexplained by the 10 to 15 per cent of extension estimated for the upper brittle part. It is suggested that the ductile part of the crust is thinned by creep in response to tension in the continental plate. Knowing the topography of the sea floor at the end of rifting and the present depth of the Aptian datum, the absolute amount of subsidence can be determined on a transect of the margin after the beginning of accretion (late Aptian time). This value decreases continuously from the oceanic/ continental crust boundary (4000 m) to the shelf break. For each point of the margin, the subsidence versus time curve is an exponential, the time constant of which increases with depth. The post-rifting subsidence is essentially an isostatic adjustment to cooling of the lithosphere in which the continental crust previously has been thinned during the rifting process.