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Registros recuperados: 19
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Altered volcanic deposits as basal failure surfaces of submarine landslides ArchiMer
Miramontes, Elda; Sultan, Nabil; Garziglia, Sebastien; Jouet, Gwenael; Pelleter, Ewan; Cattaneo, Antonio.
One of the main concerns regarding the development of submarine landslides is the role played by weak layers in the failure process and, in particular, their impact in terms of volume, shape, and evolution of mass movements. In the present study we identified a weak layer in the eastern margin of the Corsica Trough (northern Tyrrhenian Sea) that formed the basal failure surface of the Pianosa Slump at 42–50 ka. This layer is characterized by high water content, high plasticity, high compressibility, and post-peak strain softening behavior (i.e., strength loss with increasing strain). These specific mechanical and sedimentological properties seem to be related to the presence of analcime zeolites with a concentration of 2–4% in the muddy sediment. Zeolites...
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Ano: 2018 URL: http://archimer.ifremer.fr/doc/00444/55565/57176.pdf
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Focus on sulfur count rates along marine sediment cores acquired by XRF Core Scanner ArchiMer
Cheron, Sandrine; Etoubleau, Joel; Bayon, Germain; Garziglia, Sebastien; Boissier, Audrey.
The aim of this study is to investigate the information provided by sulfur count rates obtained by X-ray fluorescence core scanner (XRF-CS) along sedimentary records. The analysis of two marine sediment cores from the Niger Delta margin shows that XRF-CS sulfur count rates obtained at the surface of split core sections with XRF-CS correlate with both direct quantitative pyrite concentrations, as inferred from X-ray powder diffraction (XRD) and sulfur determination by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry, and total dissolved sulfide (TDS) contents in the sediment pore water. These findings demonstrate the potential of XRF-CS for providing continuous profiles of pyrite distribution along split sections of sediment cores. The...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00346/45731/45376.pdf
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Gas hydrate distributions in sediments of pockmarks from the Nigerian Margin - Results and interpretation from shallow drilling ArchiMer
Wei, Jiangong; Pape, Thomas; Sultan, Nabil; Colliat, Jean-louis; Himmler, Tobias; Ruffine, Livio; De Prunele, Alexis; Dennielou, Bernard; Garziglia, Sebastien; Marsset, Tania; Peters, Carl A.; Rabiu, Abdulkarim; Bohrmann, Gerhard.
A joint research expedition between the French IFREMER and the German MARUM was conducted in 2011 using the R/V Pourquoi pas? to study gas hydrate distributions in a pockmark field (1141 – 1199 meters below sea surface) at the continental margin of Nigeria. The sea floor drill rig MeBo of MARUM was used to recover sediments as deep as 56.74 meters below seafloor. The presence of gas hydrates in specific core sections was deduced from temperature anomalies recorded during continuous records of infrared thermal scanning and anomalies in pore water chloride concentrations. In situ sediment temperature measurements showed elevated geothermal gradients of up to 258 °C/km in the center of the so-called pockmark A which is up to 4.6 times higher than that in the...
Tipo: Text Palavras-chave: Gas hydrate; Pockmark; Chloride profile; Infrared thermal imaging; Fluid flow; Nigerian continental margin; MeBo drill rig.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00213/32382/30846.pdf
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Gas hydrate occurrences and seafloor deformation: investigation of strain-softening of gas-hydrate bearing sediments and its consequence in terms of submarine slope instabilities ArchiMer
Sultan, Nabil; Garziglia, Sebastien; Colliat, Jean-louis.
Published laboratory geotechnical data by Masui and co-authors showed that increase in gas hydrates content tend to increase the peak shear strength and stimulate strain softening of the host sediment. Therefore, development of shear strains may lead to an important degradation of the shear strength (strain softening). In the present work, the strain softening of gas hydrate-bearing sediments was implemented in a 3D slope stability model (SAMU-3D). This was done by adding to the classical limit analysis method a shear strain field compatibility equivalent to the velocity field compatibility. Examples of slope failures related to strain softening behavior documented in the literature were used to test the model formulation. The developed model was then used...
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Ano: 2011 URL: http://archimer.ifremer.fr/doc/00035/14625/11903.pdf
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Geomechanical constitutive modelling of gas-hydrate-bearing sediments ArchiMer
Sultan, Nabil; Garziglia, Sebastien.
In this work and in order to consider theoretically the effect of gas hydrates on the mechanical properties of their host sediments, hydrate fraction was introduced as a state variable in the framework of a Critical State model. For the proposed model, the process of de-structuration and softening of natural clay was considered as a proxy for the gas-hydrate-bearing-sediments behaviour. The developed constitutive model seemed to reproduce the main key behaviours of gas-hydrate-bearing sands observed by Masui and co-authors: i) the elastic properties (Young Modulus, shear modulus) and the strength of the sediment-hydrate medium increase with the hydrate fraction ii) the mechanical softening of the gas-hydrate bearing sediment is amplified with the hydrate...
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Ano: 2011 URL: http://archimer.ifremer.fr/doc/00035/14626/11904.pdf
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High-resolution seismic imaging in deep sea from a joint deep-towed/OBH reflection experiment: application to a Mass Transport Complex offshore Nigeria ArchiMer
Ker, Stephan; Marsset, Bruno; Garziglia, Sebastien; Le Gonidec, Y.; Gibert, D.; Voisset, Michel; Adamy, J..
P>We assess the feasibility of high-resolution seismic depth imaging in deep water based on a new geophysical approach involving the joint use of a deep-towed seismic device (SYSIF) and ocean bottom hydrophones (OBHs). Source signature measurement enables signature deconvolution to be used to improve the vertical resolution and signal-to-noise ratio. The source signature was also used to precisely determine direct traveltimes that were inverted to relocate source and receiver positions. The very high accuracy of the positioning that was obtained enabled depth imaging and a stack of the OBH data to be performed. The determination of the P-wave velocity distribution was realized by the adaptation of an iterative focusing approach to the specific...
Tipo: Text Palavras-chave: Controlled source seismology; Seismic tomography; Acoustic properties; Submarine landslides; Atlantic Ocean.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00044/15510/12959.pdf
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Hydromechanical properties of gas hydrate-bearing fine sediments from in-situ testing. ArchiMer
Taleb, Farah; Garziglia, Sebastien; Sultan, Nabil.
The hydro‐mechanical properties of gas hydrate‐bearing sediment are key in assessing offshore geo‐hazards and the resource potential of gas hydrates. For sandy materials, such properties were proved highly dependent on hydrate content (Sh) as well as on their distribution and morphology. Owing to difficulties in testing gas hydrate‐bearing clayey sediments, the impact of hydrates on the behaviour of such materials remains poorly understood. Hence, to provide insight into the characterisation of clayey sediments containing hydrate, this study relies on a unique database of in‐situ acoustic, piezocone and pore‐pressure dissipation measurements collected in a high gas flux system offshore Nigeria. Compressional wave velocity measurements were used as means of...
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Ano: 2018 URL: https://archimer.ifremer.fr/doc/00466/57746/59974.pdf
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Identification of Shear Zones and Their Causal Mechanisms Using a Combination of Cone Penetration Tests and Seismic Data in the Eastern Niger Delta ArchiMer
Garziglia, Sebastien; Sultan, Nabil; Cattaneo, Antonio; Ker, Stephan; Marsset, Bruno; Riboulot, Vincent; Voisset, Michel; Adamy, J.; Unterseh,.
In a site investigation of the eastern part of the offshore Niger delta, cone penetration tests (CPTU) showed significant drops in tip resistance, associated with decreases in sleeve friction and induced excess pore pressures at the interface between superficial sediments and the underlying deposits of a mass-transport complex (MTC) called NG1. Such signature characteristics of weakened zones are clearly expressed at three sites where the drop in tip resistance reaches more than 40% over 2-3 m-thick intervals. Correlations between CPTU profiles and both 3D and ultrahigh-resolution 2D seismic data suggest that the weakened zones surround syndepositional the within the frontal part of NG1. Hence, weakening appears associated with the remobilization of thrust...
Tipo: Text Palavras-chave: Cone penetration tests; Shear zone; 3D seismic data; Ultrahigh-resolution 2D seismic; Mass-transport complex; Slope stability.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00105/21662/19695.pdf
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In situ characterisation of gas hydrate-bearing clayey sediments in the Gulf of Guinea ArchiMer
Taleb, Farah; Garziglia, Sebastien; Sultan, Nabil.
Increasing needs for energy resources have moved deep offshore developments and research efforts towards regions where high pressure and low temperature conditions allow gas and water to form Gas Hydrates (GH). However, owing to difficulties in sampling and preserving GH under in-situ stability conditions, GH-bearing sediments remain particularly challenging to characterise using conventional laboratory methods. This paper presents the experience gained in the use acoustic and piezocone soundings in characterising gas-hydrate bearing clayey sediments offshore Nigeria. Acoustic measurements of compressional wave velocity are shown to be an expedient means of both detecting and quantifying GH in sediments. Piezocone data and their location in normalised soil...
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Ano: 2018 URL: https://archimer.ifremer.fr/doc/00466/57748/60000.pdf
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Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea) ArchiMer
Ballas, Gregory; Garziglia, Sebastien; Sultan, Nabil; Pelleter, Ewan; Toucanne, Samuel; Marsset, Tania; Riboulot, Vincent; Ker, Stephan.
The geotechnical properties of clay sediments were investigated using laboratory and in-situ measurements as part of the geohazard assessment in the Romanian sector of the Black Sea affected by landslides and seafloor deformation features. The sediments were characterized as predominantly high plastic silty clay of high compressibility, low undrained shear strength, low cohesion and moderate sensitivity. A shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction (e.g. cryptic sulfur cycle) and anaerobic oxidation of methane. Comparison of the compression behaviour of natural and...
Tipo: Text Palavras-chave: Lacustrine clay sediment; Structured material; Sulfur cement; Carbonate cement; Early diagenesis; Weak layer.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00439/55064/56545.pdf
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La géomorphologie des fonds marins et la présence d’hydrates de gaz contrôlent les émissions de gaz dans la Mer Noire au large de la Roumanie ArchiMer
Riboulot, Vincent; Cattaneo, Antonio; Scalabrin, Carla; Gaillot, Arnaud; Jouet, Gwenael; Ballas, Gregory; Marsset, Tania; Garziglia, Sebastien; Ker, Stephan.
The Romanian sector of the Black Sea deserves attention because the Danube deep-sea fan is one of the largest sediment depositional systems worldwide and is considered the world's most isolated sea, the largest anoxic water body on the planet and a unique energy-rich sea. Due to the high sediment accumulation rate, presence of organic matter and anoxic conditions, the Black sea sediments offshore the Danube delta is rich in gas and thus shows Bottom Simulating Reflectors (BSR). The cartography of the BSR over the last 20 years, exhibits its widespread occurrence, indicative of extensive development of hydrate accumulations and a huge gas hydrate potential. By combining old and new datasets acquired in 2015 during the GHASS expedition, we performed a...
Tipo: Text Palavras-chave: Hydrates de gaz; Gaz libre; Panaches de gaz; BSR; Mer Noire; Géomorphologie; Gas hydrates; Free gas; Gas flares; BSR; Black Sea; Geomorphology.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00407/51860/53914.pdf
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Mechanical behaviour of gas-charged fine sediments: model formulation and calibration ArchiMer
Sultan, Nabil; Garziglia, Sebastien.
Multi-phase fluid conditions encountered in geotechnical and geo-environmental problems have led to the development of models that account for the influence of gas solubility and compressibility on the behaviour of soils of various grain sizes. Yet, no consideration has been given to damages related to the nucleation and growth of gas bubbles in fine-grained soils. The purpose of this paper is to present a Cam Clay based constitutive model extended to incorporate such detrimental effects on gassy soils. This is achieved by deriving an analytical expression relating the preconsolidation pressure to a damage parameter dependent on the gas content. That expression is coupled to a deviatoric yield surface accounting for inherent and stress-induced anisotropy....
Tipo: Text Palavras-chave: Compressibility; Constitutive relations; Offshore engineering; Shear strength.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00245/35621/34133.pdf
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MIDAS. Complete geo-mechanical properties of gas hydrate bearing sediments from in situ geotechnical measurements ArchiMer
Garziglia, Sebastien.
The present report aims at providing details about the overall approach, tool and processing techniques deployed to determine geo-mechanical properties of gas hydrate-bearing sediments. It focusses on two piezocone soundings carried out in the Romanian sector of the Black Sea during the GHASS cruise (September 2015). One of them was selected as core sampling at the same site provided ground truth for the presence of gas hydrates in clay sediments. The other sounding was selected to serve as a reference for comparing geo-mechanical properties of sediments with and without gas hydrates. Two distinct classifications were used to identify the behaviour type of sediments during piezocone penetration. Each of them pointed out that, at the reference site,...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00376/48692/49024.pdf
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Morphological control of slope instability in contourites: a geotechnical approach ArchiMer
Miramontes, Elda; Garziglia, Sebastien; Sultan, Nabil; Jouet, Gwenael; Cattaneo, Antonio.
Contourite drifts are sediment bodies formed by the action of bottom currents. They are common features found on continental slopes and are often affected by slope failure. However, processes controlling slope instability in contourite depositional systems are still not well constrained, and it is not clear whether contourites have particular properties that make them more susceptible to slope failure. In this study, we compare sedimentological and geotechnical properties of contouritic and hemipelagic sediments within the Corsica Trough (northern Tyrrhenian Sea) using geophysical data sets and sediment cores in order to get a better understanding of the controlling factors of slope stability. Geomorphological and slope stability analyses reveal that...
Tipo: Text Palavras-chave: Sediment drift; Submarine landslide; Undrained shear strength; Hemipelagite; Mediterranean Sea.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00425/53636/56652.pdf
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New insights into the transport processes controlling the sulfate-methane-transition-zone near methane vents ArchiMer
Sultan, Nabil; Garziglia, Sebastien; Ruffine, Livio.
Over the past years, several studies have raised concerns about the possible interactions between methane hydrate decomposition and external change. To carry out such an investigation, it is essential to characterize the baseline dynamics of gas hydrate systems related to natural geological and sedimentary processes. This is usually treated through the analysis of sulfate-reduction coupled to anaerobic oxidation of methane (AOM). Here, we model sulfate reduction coupled with AOM as a two-dimensional (2D) problem including, advective and diffusive transport. This is applied to a case study from a deep-water site off Nigeria’s coast where lateral methane advection through turbidite layers was suspected. We show by analyzing the acquired data in combination...
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Ano: 2016 URL: http://archimer.ifremer.fr/doc/00339/45068/44493.pdf
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Pockmark formation and evolution in deep water Nigeria: Rapid hydrate growth versus slow hydrate dissolution ArchiMer
Sultan, Nabil; Bohrmann, G.; Ruffine, Livio; Pape, T.; Riboulot, Vincent; Colliat, J. -l.; De Prunele, Alexis; Dennielou, Bernard; Garziglia, Sebastien; Himmler, Tobias; Marsset, Tania; Peters, C. A.; Rabiu, A.; Wei, J..
In previous works, it has been suggested that dissolution of gas hydrate can be responsible for pockmark formation and evolution in deep water Nigeria. It was shown that those pockmarks which are at different stages of maturation are characterized by a common internal architecture associated to gas hydrate dynamics. New results obtained by drilling into gas hydrate-bearing sediments with the MeBo seafloor drill rig in concert with geotechnical in situ measurements and pore water analyses indicate that pockmark formation and evolution in the study area are mainly controlled by rapid hydrate growth opposed to slow hydrate dissolution. On one hand, positive temperature anomalies, free gas trapped in shallow microfractures near the seafloor and coexistence of...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00188/29913/28373.pdf
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Seafloor instabilities and sediment deformation processes: the need for integrated, multi-disciplinary investigations ArchiMer
Vanneste, Maarten; Sultan, Nabil; Garziglia, Sebastien; Forsberg, Carl Fredrik; L'Heureux, Jean-sebastien.
In this paper, we present the current practice of investigations of seafloor instabilities and deformation processes, based on extensive research conducted over the last years, which sets the scene for future research activities in this field. The mapping of the continental margins and coastal areas with ever increasing resolution systematically reveals evidence of instabilities and deformation processes, both active and palaeo-features. In order to properly assess the hazards and risks related to these features, an integrated and multi-disciplinary approach is essential, but challenging. Such an approach consists of combining field data (geophysics, geology, sedimentology, geochemistry and geotechnical data) with numerical simulations constrained by...
Tipo: Text Palavras-chave: Marine geotechnics; Slope stability; Sediment failures; Fluid flow; Shear strength; Marine geophysics; Monitoring; Excess pore pressure; Site investigations.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00173/28378/26692.pdf
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Sea-level change and free gas occurrence influencing a submarine landslide and pockmark formation and distribution in deepwater Nigeria ArchiMer
Riboulot, Vincent; Cattaneo, Antonio; Sultan, Nabil; Garziglia, Sebastien; Ker, Stephan; Imbert, Patrice; Voisset, Michel.
A series of pockmarks observed at the seabed matches well the perimeter of a large submarine landslide, called NG1, located on the outer shelf and continental slope of the Eastern Gulf of Guinea. NG1 extends over 200 km2, is covered by a 120-m thick sedimentary layer which tapers downslope, and has an internal structure clearly identified in 3D seismic data consisting of three adjacent units on the upper continental slope. The pockmarks above NG1 have a diameter of several tens of meters and reveal distinct origins: (1) linked to >500 m deep fluid reservoirs, (2) rooted in NG1 internal discontinuities between NG1 units, and (3) well above NG1, superficially rooted in a regional conformity (D40), which marks the lowest sea level of the Marine Isotope...
Tipo: Text Palavras-chave: Pockmarks; Fluid seepage; Submarine landslide; Sea-level changes; Piezocone; Niger Delta.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00159/27031/31906.pdf
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Soft sediment deformation in the shallow submarine slope off Nice (France) as a result of a variably charged Pliocene aquifer and mass wasting processes ArchiMer
Kopf, Achim J.; Stegmann, Sylvia; Garziglia, Sebastien; Henry, Pierre; Dennielou, Bernard; Haas, Simon; Weber, Kai-christian.
Along the Ligurian slope near Nice, southeastern France, a combination of natural and man-made factors govern slope stability, and contributed to a devastating tsunamigenic landslide near Nice airport in 1979. Based on a total of 72 gravity and Kullenberg cores we characterise the architecture and facies of the subbottom sediment. A total of six sedimentary facies types were observed, three of which represent the Pliocene – Holocene background sediment in the wider Nice area while another three are associated with the 1979 landslide and tsunami. The three primary facies types are soft silty clay/clayey silt, somewhat indurated silt/sand interbeds, and Pliocene conglomerates underlying the former. The three other facies are poorly sorted mass wasting...
Tipo: Text Palavras-chave: Soft sediment deformation; Submarine landslide; Weak zone; Fluidisation.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00343/45397/44894.pdf
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