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The evolution of deformation structures and associated past fluid flow is a key to better appraise both the reservoir properties of a rock and the regional evolution of an area. Indeed, the meso-scale fracture network often develops over a long period of time, granting access to a long term evolution of a past fluid system (i.e. the temperature, origin and migration pathways of the fluids) on the one hand. On the other hand, major thrusts are believed to enable episodic fluid migrations on larger spatial scales, in relation to their activity calendar, whether this activity is over or ongoing. It is seldom however to reconstruct both the past fluid flow and the present-day fluid flow on the same structure, yet it can be very enlightening about the evolution of the thrust connectivity at depth since before a fold developed over it.In this study we reconstructed the deformation pattern and associated past fluid system related to the development of the Sierra de Orba Anticline (Spain), and we compare it to the current-day fluids resurging in the vicinity of the fault. The Sierra de Orba anticline is part of a fault-propagation fold system that developed in the northern part of the Jaca Basin, Southern Pyrenean foreland, Spain. This fold affects the sedimentary succession including the Triassic decollement level, the Upper Cretaceous to Paleocene carbonate strata and the Middle Eocene marls. The N110 striking major thrust, where the Upper Cretaceous Marboré Fm. lies unconformably onto the Eocene marls, was sampled, along with the fracture network in the hangingwall and the footwall of the thrust. The fracture network includes a sequence of prefolding sets of joints and veins, striking E-W and N060 and flexural-slip related reverse faults. Then, the network encompasses the orogeny history since likely the forebulge development until the strata tilting during folding. Syn-kinematic calcite cements were characterized petrographically in both joints and faults, then studied by means of oxygen and carbon isotopic measurements coupled with fluid inclusion microthermometry. Results highlight that the fluid system recorded an alternation between meteoric fluids (δ18O signature of the fluid: -5‰ SMOW) heated up at 70-80°C, and evolved seawater (δ18O signature of the fluid: +5 to +10‰SMOW) heated up at 70-100°C. That past fluid system around the main thrust did not record any deep-sourced fluids, unlike similar structures in the southern Pyrenean foreland. The major gas content of current day fluids was analysed from a resurgence in the footwall of the thrust. This gas is especially nitrogen-rich (>86%), and is characterized by an heavy δ13C signature of the methane content (4‰PDB). Both these features could relate to deep processes, such as an oxidation of a potential abiotic carbon that can be related to a serpentinization process. This hypothesis needs to be further evaluated by means of a study of noble gas content. Beyond regional implications, this case study illustrate how a combination of geochemical proxies can help to unravel the evolution of a fluid system at a fold-thrust scale, from its onset to today.

Helium-rich gases (up to 6%) upwell along a fault that bounds the western edge of the granitic Morvan Massif (northeastern part of the French Massif Central) and the sedimentary rocks of the southeastern edge of the Paris Basin. The sampled gas is mainly composed of nitrogen (90 %.). The radiogenic 3He/4He (0.02 Ra, where Ra is the atmospheric ratio) and nucleogenic 21Ne/22Ne (0.031) imply that the gas is basement-derived, in good agreement with the presence of granite in the area. The high radiogenic He concentration can be explained by a rock/ water system isolated over geological time scales and might be linked with the presence of a close-by fluorite ore deposit, dated 130 Ma, located above the fault and at the basement/sediment unconformity in Pierre-Perthuis, formed by leaching of granite (Gigoux et al., 2015).The possible link between the fluorite ore and the He-rich gases should imply that groundwater in which He released from U and Th in granite was trapped for several millions of years in the granite or in the permeable basement/sediment unconformity reservoir, below the sedimentary cover probably reaching 1.5 km in the area at the end of the Cretaceous. Deep groundwaters trapped in the reservoir accumulated helium before tectonic exhumation of the Morvan Massif and remobilization of fluids to the surface through the Bazois fault, whose onset began 40 My ago (Lenoir et al., 2021). Mixing between old deep crystalline-water with superficial water is evidenced by the presence of high amount of atmosphere-derived nitrogen.The high chloride content of the waters may originate from the marine water trapped in the Early Jurassic clays, and released by faulting, or by water-rock interaction and hydrolysis of minerals, reinforcing the link between chlorine, fluorine, and water from granite.This geological example shows that in quiescent area, inactive fault can act as a fluid pathway over long time scale.

Noble gases are ideal natural tracers to characterize the storage, migration and origin of fluids in geological environments. They are chemically and biologically inert and therefore are only partially separated by physical processes including the one related to the molecular diffusion phenomenon, so called kinetic fractionation. However, its precise quantification is difficult to achieve and its modeling is still open for debates. Thus, in this work, we have investigated the capability of simple and predictive models to estimate elemental and isotopic fractionation of noble gases in various geological fluids. To do so, molecular dynamics simulations on noble gases in water, gas and oil under sub-surface conditions were performed. These numerical results were found to be consistent with previous ones including experiments and molecular simulations when available, i.e. in water. Interestingly, it appeared that the widely used square-root law is able to provide a good prediction for elemental fractionation between noble gases in all solvents, except for helium. Such unexpected result from the theoretical point of view is explained by a peculiar relationship between the molecular mass and the molecular size of noble gas elements. Regarding the noble gas isotopic fractionation, the square-root law is shown to be unable to provide reasonable results, confirming recent experimental and numerical works. As expected, it has been noticed that the kinetic theory relation provides a reasonable estimate of the isotopic fractionation in gas whereas it deteriorates in water and in oil. Finally, using the previous findings, we propose a simple and predictive scheme for the isotopic fractionation of noble gases in all studied geo-fluids which is noticeably better than both the square-root and the kinetic theory relations.

The Haiti region – bounded by two strike-slip faults expressed both onshore and offshore – offers a unique opportunity for an amphibious drilling project. The east–west (EW)-striking, left lateral strike-slip Oriente–Septentrional fault zone and Enriquillo–Plantain Garden fault zone bounding Haiti have similar slip rates and also define the northern and southern boundaries of the Gonâve Microplate. However, it remains unclear how these fault systems terminate at the eastern boundary of that microplate. From a plate tectonic perspective, the Enriquillo–Plantain Garden fault zone can be expected to act as an inactive fracture zone bounding the Cayman spreading system, but, surprisingly, this fault has been quite active during the last 500 years. Overall, little is understood in terms of past and present seismic and tsunami hazards along the Oriente–Septentrional fault zone and Enriquillo–Plantain Garden fault zone, their relative ages, maturity, lithology, and evolution – not even the origin of fluids escaping through the crust is known. Given these unknowns, the Haiti-Drill workshop was held in May 2019 to further develop an amphibious drilling project in the Haiti region on the basis of preproposals submitted in 2015 and their reviews. The workshop aimed to complete the following four tasks: (1) identify significant research questions; (2) discuss potential drilling scenarios and sites; (3) identify data, analyses, additional experts, and surveys needed; and (4) produce timelines for developing a full proposal. Two key scientific goals have been set, namely to understand the nature of young fault zones and the evolution of transpressional boundaries. Given these goals, drilling targets were then rationalized, creating a focus point for research and/or survey needs prior to drilling. Our most recent efforts are to find collaborators, analyze existing data, and to obtain sources of funding for the survey work that is needed.

International audience; The Mozambique and Madagascar margins present major rivers that are responsible for the discharge of large amounts of terrestrial organic matter (OM) which can influence carbon cycling in marine environments. Therefore, the Mozambique channel represents a unique case to study the fate of the organic carbon in deepwater domains. Using a new and extensive data set of sedimentary OM collected from sediment traps, seafloor sediments and core sediments, we address the origin of the OM that is transported and deposited in the Mozambique Channel, its degradation state and preservation conditions. A Rock-Eval 6 survey allowed us to characterize the origin and amount of OM from shallow to deep-water turbidite systems, between 500 and 4400 m water depth. Rock-Eval 6 performed on suspended sediments within particle traps at 47 m above the seabed show that the OM is transported into the deep-water domain with relatively high TOC (between 1.5 and 2.5%). However, the OM is largely oxidized close to the water-sediment interface (Oxygen Index >300 mg CO 2 /g TOC). Seafloor sediments sampled to a maximum depth of 40 cm show lower TOC values compared to those collected from particle traps suggesting that the degradation of the OM is mainly active at the water-sediment interface. Small concentrations of OM are preserved within the recent sediments of the distal area of the Zambezi turbidite system below 2500 m water depth (TOC < 0.5%). Rock-Eval results show that core sediments from the Majunga slope (NW margin of Madagascar) and the Zambezi slope (Mozambique margin) contain the highest concentration of terrestrial OM (TOC between 1 and 2%). However, the OM within core sediments from the deep-water domain is largely oxidized and degraded, probably due to the conjugate effect of low sediment accumulation rates (SARs) and high permeabilities of the coarse-grained sediments. Consequently, the deep-water domain of the Mozambique Channel does not seem to be an important sink of terrestrial OM. This process is reinforced by important bottom water currents which induce the remobilization and transport of seafloor sediments that lead to higher oxygen exposure time in the uppermost centimeters of sediments.

International audience; Evidences for active fluid seepages have been discovered along the Zambezi continental slope (offshore Southern Mozambique). These seepages are mostly associated with pockmarks which are aligned along a trend parallel to the slope and running closely upstream of the headwall scarp of a wide zone of slope destabilization. Fluid seepages are interpreted as a potential trigger for the slope destabilization. Acoustic anomalies within the water column have been interpreted as related to moderate bubble seepages mostly located outside and only punctually inside the destabilization zone. Exploration with the SCAMPI towed camera system in the widest pockmark (diameter 200 m wide) has shown fluid seepages associated to authigenic carbonate crusts and possibly bacterial mats. These fluid seepages are also associated to the presence of chemiosynthetic organisms (Vesicomyidae and Thyasiridae bivalves, Siboglinidae tubeworms). The sampled gas in the sediment corresponds mainly to CH4 of microbial origin, generated by hydrogenotrophic methanogenesis from a substrate of organic origin, i.e. a conventional process of genesis of microbial gas in the marine domain. No evidence for thermogenic gas was detected. Another type of pockmarks has been observed within the core of the slope destabilization zone. Most of these pockmarks are inactive in terms of fluid seepage at present time and are associated to carbonate buildups forming chimney geometries. They probably correspond to diagenetic chimneys of former fluid migration pathways that have been exhumed during the mass sliding and the surrounding depression are related to recurrent activity of strong lateral slope currents which have scoured the sediments around. The spatial organization of the slope destabilization features is considered as representative of the temporal evolution of the landslide giving information about the dynamics of slope instability processes. This proposed evolution started by scattered seepages of formation water with dissolved gas. Then free gas seepages appeared notably in the upper part of the slope. This was followed by progressive shallow deformation in the sediments downslope of the main gas seepages. Finally, the whole slope was destabilized forming imbricated landslides exhuming locally former diagenetic chimneys.

The back arc extensional area of Tuscany is characterized by anomalously high heat flow as a result of lithospheric thinning facilitated by locally intruded granite, which ultimately led to the occurrence of numerous fumaroles and other manifestations of geothermal activity. The present study builds up on molecular and isotopic geochemical analyses of fumarolic gases discharging near Larderello geothermal field in order to report on their origin and generation mechanisms. The fumarole gases are rich in CO2 (15.65–92.5 vol%), poor in CH4 (0.08–3.70 vol%) and highly-depleted in C2+ ( −4.2‰VPDB) reflect thermo-metamorphic of CO2, however magmatic-volcanic contribution cannot be ruled out. This work tests various hypotheses of the origin of H2: the intruded granite, the ophiolite and/or a deeper source. Petrographic and electron microbeam investigations performed on the Ligurian ophiolite and plutonic granite, which outcrops in the vicinity of the study area, revealed serpentinization of ophiolite (in contact with geothermal fluids at 200 °C) as the most probable source of the measured H2. Hydrogen that forms deeper, potentially near or within the granitic intrusion, at higher temperatures, is likely consumed to form abiotic methane.

15 pages, 8 figures, 1 table, supplementary data http://dx.doi.org/10.1016/j.margeo.2019.106064, The Western Mediterranean basin has been formed by Miocene back-arc extension and is underlain by a thin and young lithosphere. This young lithosphere is warm, as testified by an overall elevated offshore heat flow. Heat flow within the Western Mediterranean is, however, highly variable and existing data are unevenly distributed and poorly studied in the central part of the Liguro-Provençal and Algero-Balearic basins. This central part is floored by a young oceanic crust, bordered by different continental margins, cut by transform faults, and filled by up to 8 km of sediments. We present a total of 148 new heat flow data collected during the MedSalt and WestMedFlux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin-scale, but also locally on the margins. A new heat flow map for the Western Mediterranean outlines the following regional features: (1) a higher average heat flow in the Algero-Balearic basin compared to the Liguro-Provençal basin (94 ± 13 mW/m2 and 78 ± 16 mW/m2, respectively), and (2) a regional thermal asymmetry in both basins, but with opposed heat flow trends. Up to 20% of this heat flow difference can be explained by sediment blanketing, but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint. Estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger West Algerian basin (16–23 Ma) compared to the East Algerian basin and the West Sardinia oceanic floor (31–37 Ma). On the margins and ocean-continent transitions of the Western Mediterranean the new heat flow data point out the existence of two types of local anomalies (length scale 5–30 km): (1) locally increased heat flow up to 153 mW/m2 on the Gulf of Lion margin results from thermal refraction of large salt diapirs, and (2) the co-existing of both low (110 mW/m2) heat flow areas on the South Balearic margin suggests a heat redistribution system. We suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread Plio-Pleistocene volcanism on the South Balearic margin, This work was also supported by the “Laboratoire d'Excellence” LabexMER (ANR-10-LABX-19) and co-funded by a grant from the French government under the program “Investissements d'Avenir”, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

International audience; In this paper, we present an overview of the SiteChar workflow model for sitecharacterisation and assessment for CO2 storage. Site characterisation and assessment is requiredwhen permits are requested from the legal authorities in the process of starting a CO2 storageprocess at a given site. The goal is to assess whether a proposed CO2 storage site can indeed beused for permanent storage while meeting the safety requirements demanded by the EuropeanCommission (EC) Storage Directive (EU, 2009, Storage Directive 2009/31/EC). Many issueshave to be scrutinised, and the workflow presented here is put forward to help efficiently organisethis complex task.Three issues are highlighted: communication within the working team and with the authorities;interdependencies in the workflow and feedback loops; and the risk-based character of theworkflow. A general overview (helicopter view) of the workflow is given; the issues involved incommunication and the risk assessment process are described in more detail. The workflow asdescribed has been tested within the SiteChar project on five potential storage sites throughoutEurope. This resulted in a list of key aspects of site characterisation which can help prepare andfocus new site characterisation studies.

International audience; Hydrothermal circulation affects heat and mass transfers in the oceanic lithosphere, not only at the ridge axis but also on their flanks, where the magnitude of this process has been related to sediment blanket and seamounts density. This was documented in several areas of the Pacific Ocean by heat flow measurements and pore water analysis. However, as the morphology of Atlantic and Indian ridge flanks is generally rougher than in the Pacific, these regions of slow and ultra-slow accretion may be affected by hydrothermal processes of different regimes. We carried out a survey of two regions on the eastern and western flanks of the Mid-Atlantic Ridge between Oceanographer and Hayes fracture zones. Two hundred and eight new heat flow measurements were obtained along six seismic profiles, on 5 to 14 Ma old seafloor. Thirty sediment cores (from which porewaters have been extracted) have been collected with a Kullenberg corer equipped with thermistors thus allowing simultaneous heat flow measurement. Most heat flow values are lower than those predicted by purely conductive cooling models, with some local variations and exceptions: heat flow values on the eastern flank of the study area are more variable than on the western flank, where they tend to increase westward as the sedimentary cover in the basins becomes thicker and more continuous. Heat flow is also higher, on average, on the northern sides of both the western and eastern field regions and includes values close to conductive predictions near the Oceanographer Fracture Zone. All the sediment porewaters have a chemical composition similar to that of bottom seawater (no anomaly linked to fluid circulation has been detected). Heat flow values and pore fluid compositions are consistent with fluid circulation in volcanic rocks below the sediment. The short distances between seamounts and short fluid pathways explain that fluids flowing in the basaltic aquifer below the sediment have remained cool and unaltered. Finally, relief at small-scale is calculated using variogram of bathymetry and compared for different regions affected by hydrothermal circulation.

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated 4He porewater contents. Shallower levels show lower and lower 4He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.

We explored the submarine portions of the Enriquillo–Plantain Garden Fault zone (EPGFZ) and the Septentrional–Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high-resolution multibeam echo-sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate-boundary structures are a series of strike-slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50–100 km long cut across pre-existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike-slip regime. Along the most recent trace of the SOFZ, we measured a strike-slip offset of 16.5 km, which indicates steady activity for the past ~1.8 Ma if its current GPS-derived motion of 9.8 ± 2 mm a−1 has remained stable during the entire Quaternary.

Carbon Capture and Storage (CCS) is one of the solutions that can significantly reduce CO 2 during the transition from fossil fuel-based energy to an energy system based on renewable energy sources. Recent studies point out that sufficient storage capacity in saline aquifers and depleted gas fields is available to permanently store several decades worth of current CO 2 emissions. Nevertheless, a significant hurdle for the post-demonstration phase of CCS development is the lack of proven and tested storage reservoirs. One of the goals of the EU FP7 SiteChar project is to develop an efficient site characterisation workflow, to support the development of the numerous storage sites that will be needed for large-scale deployment of CCS. The workflow is designed to address all aspects of safe and secure storage required by the EU Storage Directive. The links between the Storage Directive requirements and the site characterisation workflow are described in detail. The workflow is currently being applied to five sites suitable for CCS across Europe. A final version of the workflow will be published early 2014.

The Makran accretionary prism developed in the north-western part of the Indian Ocean as a consequence of the subduction of the Arabian Sea since Late Cretaceous times. It extends from southern Iran to the Baluchistan region of Pakistan where it joins the Chaman-Ornach-Nal left-lateral strike-slip fault systems to the north and the Owen Fracture Zone-Murray Ridge transtensional (right-lateral) system to the south in a complex triple junction near the city of Karachi. In September to October of 2004, we surveyed most of the accretionary complex off Pakistan with R/V Marion Dufresne. We achieved a nearly continuous bathymetric mapping of the prism and the subduction trench from 62°30′E to the triple junction near 62°30′E together with nearly 1000 km of seismic reflection (13 lines) and we took 18 piston cores in different geological settings. One of the main results is that the frontal part of the Makran accretionary prism is less two-dimensional than previously expected. We interpret the along-strike tectonic variation as a consequence of lateral variations in sediment deposition as well as a consequence of the under-thrusting of a series of basement highs and finally of the vicinity to the triple junction.

Hydrothermal processes affect all oceanic domains therby controlling their thermal regime. At global scale, heat flow studies may lead to different interpretations than local studies. Comparing hydrothermal effects in different local contexts is essential to overcome this scale- issues. To do so, we studied the hydrothermal impact on the thermal regimes of a young oceanic domain (Atlantic Ocean) and a young margin (South Balearic). We quantified heat and matter transfers and heat losses with heat flow measurements and pore water chemical analyses. The young oceanic domain is situated on the first segment south of Oceanographer transform fault in the Atlantic Ocean. The low heat flow values indicate that hydrothermal circulations, conveyed by numerous outcrops, extract a lot of crustal heat. The composition of water in pores is similar to that of seawater. This points to a short residence time of water in the basement. We identified that the ruggedness of the seabed is one of the key parameters that control the fluid circulation efficiency. This small scale relief was compared to others regions where hydrothermal processes have already been debated. We deduced an empirical relation which links the fraction of the conductive heat flow to this relief. On the Southern Balearic margin, hydrothermal processes appear to be more limited because of their more local thermal impact. On the continental slope, great heat flow contrasts are highlighted. They suggest that hydrothermal circulation is controlled by numerous volcanic mounts. On one hand, pore fluid chemistry remains close to seawater composition and does not allow confirming these observations. On the other hand, hydrothermal processes in the basin are limited by thick sediment deposits and pore fluid chemistry indicates residual brines and their diffusion towards the surface. Heat flow values along the Southern Balearic margins are perturbed by thermal conductivity contrasts induced by salt diapirs or basement topography. In both study areas, fluid circulations are linked to fractured basaltic structures with a much larger permeability than the surrounding sediments. The seabed’s initial ruggedness and the sedimentation rate control the age range during which the crust is connected to ocean. Nevertheless, fluid circulations cease quickly due to important sediment flows from the nearby continent. This conclusion is partially offset by other events that may occur on the margins such as volcanism or active tectonic.; Résumé Les processus hydrothermaux affectent l'ensemble des domaines océaniques et contrôlent efficacement leur régime thermique. Cependant, les études de flux de chaleur à l'échelle globale conduisent à des interprétations parfois en contradiction avec les études locales. Il est donc essentiel de comparer les effets de l'hydrothermalisme dans différents contextes régionaux. Dans cette optique, nous avons étudié le rôle de l'hydrothermalisme sur le régime thermique d'un domaine océanique jeune (en Atlantique) et d'une marge continentale jeune (Sud Baléares). Pour cela, nous avons quantifié les transferts et pertes de chaleur et de matière en utilisant des traceurs thermiques (mesures du flux de chaleur) et des traceurs chimiques (analyse des fluides interstitiels). Le domaine océanique jeune se situe dans l'océan Atlantique sur le premier segment au sud de la faille transformante Oceanographer. Les faibles valeurs du flux de chaleur indiquent que les circulations hydrothermales, induites par les nombreux affleurements, extraient d'importantes quantités de chaleur de la croûte. La composition de l'eau interstitielle est similaire à l'eau de mer, indiquant un temps de résidence faible de l'eau dans le socle. Nous avons identifié que la rugosité du plancher océanique est un des paramètres majeurs qui contrôlent l'efficacité de ces circulations de fluides. Ce relief à petite échelle a été comparé à d'autres régions où l'efficacité des processus hydrothermaux avait préalablement été discutée. Nous en avons déduis une relation empirique qui relie la fraction du flux de chaleur à ce relief. Sur la marge Sud des Baléares, les processus hydrothermaux semblent plus restreints car leur impact thermique est plus local. Sur la pente continentale, des contrastes importants du flux de chaleur ont été mis en évidence. Ils suggèrent des circulations hydrothermales controlées par la présence de nombreux monts volcaniques. Cependant, la chimie des fluides reste proche de celle de l’eau de mer et ne permet pas de confirmer ces observations. En revanche, les processus hydrothermaux sont limités dans le bassin par les épais dépôts de sédiments. La chimie des fluides indique la présence de saumures résiduelles et leur simple diffusion vers la surface. Les valeurs du flux de chaleur sont perturbées par les contrastes de conductivité thermique induits par la présence de diapirs de sel ou du socle. Dans les deux zones d’étude, les circulations de fluides sont liées à la présence de structures basaltiques fracturées dont la perméabilité est supérieure de plusieurs ordres de grandeur à celle des sédiments alentours. La rugosité initiale du plancher océanique et le taux de sédimentation contrôlent la tranche d’âge durant laquelle la croûte reste connectée à l’océan. En revanche, les circulations sont rapidement inhibées sur les marges par les apports importants de sédiments venant du continent proche. Cette conclusion est contrebalancée par d’autres événements pouvant survenir sur les marges telles que le volcanisme ou la tectonique active.