Sedimentary processes are critical geological phenomena in the evolution of continental margins. Environmental forces from various temporal and spatial scales control these processes. Due to the fast increase of anthropogenic activities in marine environments, these studies on sedimentary processes and their products are becoming increasingly necessary. In this context, geophysical data, such as high-resolution 2D seismic reflection profiles, are efficient tools to characterize sedimentary processes and deposits. This study aimed to map and interpret different types of echo character on the continental shelf of the São Paulo Bight to increase the knowledge of the spatial variability of sedimentary processes in current-dominated shelf settings. With this aim, 120 seismic lines, almost 3200 km in length, have been analyzed in conjunction with 451 surficial sediment samples. Based on the broad-scale seafloor morphology, microtopography and seismic characteristics (e.g., sharpness, amplitude, continuity) of sub-bottom reflections, seven echo types distributed in three echo classes were identified in the study area. Type 1-1 is a flat seafloor with either no or low-amplitude sub-bottom reflectors, mainly observed in the middle shelf; type 1-2 is a flat sea floor with medium to high-amplitude sub-bottom reflectors also found in middle shelf settings; type 1-3 is defined by a transparent acoustic response below the seafloor evolving downsection into a highly reflective pattern that covers most of the inner shelf; type 1-4 presents a flat seafloor molded by regularly spaced undulations, and it is restricted to the outer shelf; type 2-1 consists of mounds with no internal reflectors also located on the outer shelf; type 3-1 is an irregular echo with prolonged internal reflectors found around the São Sebastião Island; finally, type 3-2 is a broad irregular echo with high relief variations mainly found in the outer shelf. The analysis of the seismic survey allowed recognizing that the distribution of the echoes reflects not only the composition of the seabed but also the sedimentary processes that acted during the deposition of the material. In the inner shelf and middle shelves, the Brazilian Coastal Current and the action of waves are the main processes responsible for the echo types found, while the outer shelf echo types are strongly influenced by the Brazil Current. / Processos sedimentares são fenômenos importantes na evolução das margens continentais. Esses processos são controlados por forçantes de várias escalas espaciais e temporais. Devido ao rápido crescimento das atividades antropogênicas em ambientes marinhos, estudos sobre processos sedimentares e seus produtos tem se tornado cada vez mais necessários. Nesse contexto, dados geofísicos, como perfis de sísmica de reflexão de alta resolução, são ferramentas importantes na caracterização desses processos e depósitos. O objetivo do estudo foi mapear e interpretar os tipos de caráter de eco na plataforma continental do estado de São Paulo visando aumentar o conhecimento a respeito da variabilidade espacial dos processos sedimentares em plataformas dominadas por correntes. Para alcançar esse objetivo 120 linhas sísmicas totalizando quase 3200 km em extensão foram analisadas em conjunto com 451 amostras sedimentares. Baseados na morfologia de macro e microescala e características sísmicas do sinal acústico de fundo como nitidez, amplitude e continuidade dos refletores, foram identificados 7 tipos de caráter de eco distribuídos em 3 classes (fundo plano, monticular ou irregular). O tipo 1-1 apresenta fundo plano com refletores de sub fundo ausentes ou de baixa amplitude localizado principalmente na plataforma média; o tipo 1-2 refere-se a um fundo plano com refletores internos com amplitudes médias a altas também presente na plataforma média; o tipo 1-3 é definido por uma camada superficial transparente que é substituída em profundidade por uma camada altamente refletiva que cobre grande parte da plataforma interna; o eco 1-4 apresenta fundo moldado por ondulações com localização restrita na plataforma externa; o tipo 2-1 consiste em montes sem refletores internos localizado próximo a quebra da plataforma; o tipo 3-1 é irregular com refletores internos prolongados e é encontrado ao sul da Ilha de São Sebastião; finalmente, o eco 3-2 é um eco irregular que apresenta grandes variações de relevo presente em grande parte da plataforma externa. A análise dos dados sísmicos permitiu o reconhecimento de que os ecos respondem não somente a composição sedimentar superficial, mas também os processos sedimentares que atuaram durante a deposição do material. Nas plataformas interna e média, a Corrente Costeira Brasileira e a ação de ondas geradas pelos ventos são os principais processos responsáveis pela geração dos ecos encontrados, enquanto na plataforma externa, os tipos de eco são fortemente influenciados pela Corrente do Brasil.

Determining the relative importance of processes that control the generation and preservation of continental margin stratigraphy is fundamental to deciphering the history of geologic, climatic and oceanographic forcing imprinted on their sedimentary record. The Northern Carnarvon Basin (NCB) of the North West Shelf of Australia has been a site of passive margin sedimentation throughout the Neogene. Cool-water carbonate sedimentation dominated during the early-middle Miocene, quartz-rich siliciclastics prograded over the shelf during the late-middle Miocene, and carbonate sedimentation resumed in the Pliocene. Middle Miocene to Pliocene siliciclastics were deposited as clinoform sets interpreted as delta lobes primarily based on their plan-view morphology and their relief of 40-100 m. Shelf-edge trajectory analysis suggests that part of this stratigraphic succession was built during a long-term, third order, regressive phase, producing shelf-edge deltas, followed by an aggradational episode. These trends appear to correlate with third-order global eustatic cycles. Slope incisions were already conspicuous on the slope before deltas reached the shelf-break. Nevertheless, slope gullies immediately downdip from the shelf-edge deltas are wider and deeper (>1 km wide, ~100 m deep) than coeval incisions that are laterally displaced from the deltaic depocenter (~0.7 km wide, ~25 m deep). This change in gully morphology is likely the result of greater erosion by sediment gravity flows sourced from shelf-edge deltas. Total late-middle to late Miocene margin progradation increased almost three times from 13 km in the southwest to 34 km in the northeast, where shelf-edge deltas were concentrated. Flat-topped carbonate platforms seem to have initiated on subtle antecedent topographic highs resulting from these deltaic lobes. A reduction of siliciclastic supply to the outer paleo-shelf during the Pliocene combined with the onset of a southwestward-flowing, warm-water Leeuwin Current (LC) most likely controlled the initiation of these carbonate platforms. These platforms display marked asymmetry, likely caused by an ancestral LC, which created higher-angle, upcurrent platform margins, and lower-angle, downcurrent clinoforms. The along-strike long-term migration trend of the platforms could be the result of differential subsidence. These platforms constitute the first widespread accumulation of photozoan carbonates in the Northern Carnarvon Basin. They became extinct after the mid-Pleistocene when the LC weakened or became more seasonal. / text

Dans le contexte des nouvelles exigences en termes de qualité des eaux du surface, les modèles hydro-écologiques s'avèrent être des outils indispensables pour compléter notre compréhension du fonctionnement du milieu ou prévoir l'impact sur la qualité de l'eau de nouvelles mesures. L'objectif de cette recherche est de tirer parti de l'outil de modélisation ProSe, et de le faire évaluer afin de compléter la compréhension du fonctionnement biogéochimique de la Seine. Dans une première étape, différents processus biogéochimiques sont implémentés, calibrés et validés indépendamment, grâce à des jeux de données disponibles sur un linéaire de 220 km (de Paris jusqu'à l'estuaire), à différents pas de temps, pour la période 2007-2012. Ces améliorations sont réalisées grâce à l'utilisation directe de résultats expérimentaux, à l'extrapolation de résultats de couplage entre expériences de laboratoire et modélisation biogéochimique, ou encore grâce à l'analyse de mesures haute fréquence in-situ. Le modèle ProSe est ensuite utilisé pour établir un bilan du fonctionnement biogéochimique de la Seine dans cette zone fortement anthropisée. L'effet des processus pélagiques et benthiques sur les différents cycles biogéochimiques (carbone, azote, phosphore) est quantifié, pour différentes conditions hydrologiques, en amont et en aval de la plus grosse station d'épuration de l'agglomération parisienne, qui traite les effluents de plus de 5 millions équivalent habitants. La précision spatio-temporelle du modèle est ensuite utilisée pour évaluer l'effet de la fréquence d'échantillonnage sur l'estimation des critères de qualité de l'eau au sens de la Directive Cadre sur l'Eau. Les résultats soulignent l'importance d'une représentation précise des processus physiques (hydrodynamique et processus hydro-sédimentaires) dans les modèles de qualité de l'eau pour parvenir à une simulation fiable des flux biogéochimiques dans le milieu et des échanges entre compartiment benthique et colonne d'eau. Ce travail illustre enfin toute l'utilité des modèles hydro-écologiques pour venir en appui au suivi du milieu dans le cadre des objectifs actuels d'amélioration de la qualité des milieux aquatiques. / Hydro-ecological models are essential to complete our knowledge of the functioning of aquatic systems. They can moreover be used to forecast the impact of new management strategies on the future water quality. The aim of this thesis is to use the hydro-ecological ProSe model to improve our understanding of the biogeochemical functioning of the Seine River downstream the Paris urban area. Simulated biogeochemical processes are first implemented, calibrated, and validated independently for the 2007-2012 period. For each one of these processes, appropriate methodologies are used. These methodologies include the direct use of experimentally obtained parameters, the upscaling of results from coupled laboratory experiments and stand-alone biogeochemical modelling, or the analysis of high frequency in-situ measurements. Different datasets, which are available at various time steps, allow the validation of these processes along the whole 220 km simulated stretch (from Paris to the entrance of the Seine River estuary). Once validated, the ProSe model is then used to assess the biogeochemical functioning of the Seine River along this highly anthropized stretch. The impact of pelagic and benthic processes on the different biogeochemical cycles (carbon, nitrogen, and phosphorus) is quantified for different hydrological conditions, up- and downstream the major waste water treatment plant of the Paris urban area, which treats the effluents of over 5 million population equivalent. The model is then used to assess the effect of the monitoring frequency on the estimation of the water quality as defined by the European Water Framework Directive. The results highlight the importance of a detailed representation of physical processes in hydro-ecological models for a reliable simulation of in-river biogeochemical fluxes and of exchanges at the sediment-water interface. Having in mind the present targets of the improvement of the quality of water bodies, this work illustrates the importance of hydro-ecological modelling as an essential complement to water quality monitoring strategies.

Cette étude présente une reconstruction du fonctionnement sédimentaire au Quaternaire de deux pentes carbonatées des Bahamas (leeward et windward). Elle est basée sur les analyses stratigraphique et sédimentaire de 34 carottes principalement collectées lors de la mission CARAMBAR (2010). Une étude stratigraphique à haute résolution a été développée à partir de plusieurs outils stratigraphiques, dont l’écostratigraphie basée sur les assemblages de foraminifères planctoniques qui a permis de dater l’ensemble des séquences sédimentaires en s’affranchissant des problèmes liés à la diagenèse précoce. L’analyse sédimentaire des carottages a permis de proposer une nouvelle classification des sédiments carbonatés meubles qui caractérise les fractions dominantes du sédiment au moment du dépôt. Elle permet notamment de discriminer les dépôts fins et d’identifier les processus de transport off-bank, les dépôts contouritiques, gravitaires ou légèrement diagenétisés. Les processus de transport off-bank permettent l’accumulation de boue carbonatée de plate-forme (aiguilles d’aragonite et silts) au niveau des pentes des Bahamas lorsque la plate-forme est ennoyée. Les derniers 4ka cal BP, le MIS 5e et le début du MIS 11 sont les principales périodes d’accumulation sédimentaire au cours des derniers cycles climatiques. L’érosion intra-pente, l’action des courants de fond et les processus de diagenèse précoce ont également été mis en évidence. La pente leeward se caractérise par une sédimentation très importante (wackestone) alors que la pente windward a conservés a morphologie pliocène avec localement des accumulations sédimentaires quaternaires de faible épaisseur (wackestone à packstone). / This study proposes a reconstruction of the quaternary sedimentary history of two Bahamian slopes (leeward and windward). This work is based on the stratigraphicand sedimentary analysis of 34 marine cores recovered mainly from the CARAMBAR oceanographic cruse (2010). A high-resolution stratigraphic study was conducted by coupling several tools including ecostratigraphy based on planktonic foraminifera assemblages, which allowed dating all sedimentary sequences despite early diagenesis processes. The sedimentary analysis of the marine cores proposes a new classification for carbonate sediment. It characterizes the dominant particle distributions at the time of deposition and allows for discriminating the fine sediments and for determining the depositional processes such as off-bank transport, contouritic or gravity deposits, and slightly altered sediment. Off-bank transport is the mainprocess responsible for high-accumulation of platform carbonate ooze (aragonite needles and silt) on the Bahamian slopes. It predominates during major flooding of the platform, so during the last 4 ka cal BP, the MIS 5e and at the on set of the MIS11. Intra-slope erosion, bottom currents, and early marine diagenesis processes have also been highlighted. The leeward slope is characterized by a high accumulation of wackestone sediment where as the windward slope preserved its Pliocene morphology with local quaternary sediment accumulation (wackestone to packstone).

The steep forearc slope along the northern sector of the obliquely convergent Hikurangi subduction zone is characteristic of non-accretionary and tectonically eroding continental margins, with reduced sediment supply in the trench relative to further south, and the presence of seamount relief on the Hikurangi Plateau. These seamounts influence the subduction process and the structurally-driven geomorphic development of the over-riding margin of the Australian Plate frontal wedge. The Poverty Indentation represents an unusual, especially challenging and therefore exciting location to investigate the tectonic and eustatic effects on this sedimentary system because of: (i) the geometry and obliquity of the subducting seamounts; (ii) the influence of multiple repeated seamount impacts; (iii) the effects of structurally-driven over-steeping and associated widespread occurrence of gravitational collapse and mass movements; and (iv) the development of a large canyon system down the axis of the indentation. High quality bathymetric and backscatter images of the Poverty Indentation submarine re-entrant across the northern part of the Hikurangi margin were obtained by scientists from the National Institute of Water and Atmospheric Research (NIWA) (Lewis, 2001) using a SIMRAD EM300 multibeam swath-mapping system, hull-mounted on NIWA’s research vessel Tangaroa. The entire accretionary slope of the re-entrant was mapped, at depths ranging from 100 to 3500 metres. The level of seafloor morphologic resolution is comparable with some of the most detailed Digital Elevation Maps (DEM) onshore. The detailed digital swath images are complemented by the availability of excellent high-quality processed multi-channel seismic reflection data, single channel high-resolution 3.5 kHz seismic reflection data, as well as core samples. Combined, these data support this study of the complex interactions of tectonic deformation with slope sedimentary processes and slope submarine geomorphic evolution at a convergent margin. The origin of the Poverty Indentation, on the inboard trench-slope at the transition from the northern to central sectors of the Hikurangi margin, is attributed to multiple seamount impacts over the last c. 2 Myr period. This has been accompanied by canyon incision, thrust fault propagation into the trench fill, and numerous large-scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in down-slope length from a few hundred metres to more than 40 km. The indentation is directly offshore of the Waipaoa River which is currently estimated to have a high sediment yield into the marine system. The indentation is recognised as the “Sink” for sediments derived from the Waipaoa River catchment, one of two target river systems chosen for the US National Science Foundation (NSF)-funded MARGINS “Source-to-Sink” initiative. The Poverty Canyon stretches 70 km from the continental shelf edge directly offshore from the Waipaoa to the trench floor, incising into the axis of the indentation. The sediment delivered to the margin from the Waipaoa catchment and elsewhere during sea-level high-stands, including the Holocene, has remained largely trapped in a large depocentre on the Poverty shelf, while during low-stand cycles, sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope. The formation of the indentation and the development of the upper branches of the Poverty Canyon system have led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision. Sediment has also accumulated in the head of the Poverty Canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes. Prograding clinoforms lying seaward of active faults beneath the shelf, and overlying a buried inactive thrust system beneath the upper slope, reveal a history of deformation accompanied by the creation of accommodation space. There is some more recent activity on shelf faults (i.e. Lachlan Fault) and at the transition into the lower margin, but reduced (~2 %) or no evidence of recent deformation for the majority of the upper to mid-slope. This is in contrast to current activity (approximately 24 to 47% shortening) across the lower slope and frontal wedge regions of the indentation. The middle to lower Poverty Canyon represents a structural transition zone within the indentation coincident with the indentation axis. The lower to mid-slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east-facing thrust-propagated asymmetric anticlines separated by early-stage slope basins. North of the canyon system, sediment starvation and seamount impact has resulted in frontal tectonic erosion associated with the development of an over-steepened lower to mid-slope margin, fault reactivation and structural inversion and over-printing. Evidence points to at least three main seamount subduction events within the Poverty Indentation, each with different margin responses: i) older substantial seamount impact that drove the first-order perturbation in the margin, since approximately ~1-2 Ma ii) subducted seamount(s) now beneath Pantin and Paritu Ridge complexes, initially impacting on the margin approximately ~0.5 Ma, and iii) incipient seamount subduction of the Puke Seamount at the current deformation front. The overall geometry and geomorphology of the wider indentation appears to conform to the geometry accompanying the structure observed in sandbox models after the seamount has passed completely through the deformation front. The main morphological features correlating with sandbox models include: i) the axial re-entrant down which the Poverty Canyon now incises; ii) the re-establishment of an accretionary wedge to the south of the indentation axis, accompanied by out-stepping, deformation front propagation into the trench fill sequence, particularly towards the mouth of the canyon; iii) the linear north margin of the indentation with respect to the more arcuate shape of the southern accretionary wedge; and, iv) the set of faults cutting obliquely across the deformation front near the mouth of the canyon. Many of the observed structural and geomorphic features of the Poverty Indentation also correlate well both with other sediment-rich convergent margins where seamount subduction is prevalent particularly the Nankai and Sumatra margins, and the sediment-starved Costa Rican margin. While submarine canyon systems are certainly present on other convergent margins undergoing seamount subduction there appears to be no other documented shelf to trench extending canyon system developing in the axis of such a re-entrant, as is dominating the Poverty Indentation. Ongoing modification of the Indentation appears to be driven by: i) continued smaller seamount impacts at the deformation front, and currently subducting beneath the mid-lower slope, ii) low and high sea-level stands accompanied by variations on sediment flux from the continental shelf, iii) over-steepening of the deformation front and mass movement, particularly from the shelf edge and upper slope.

La sédimentation marine récente dans les fosses de subduction est caractérisée par l'interstratification de sédiments hémipélagiques et de turbidites localement intercalées avec les coulées de débris, qui peuvent résulter de la destabilisation des pentes continentales par de tremblements de terre. La marge d’Equateur est constituée par une forte érosion tectonique qui contribue à la formation d'une fosse profonde remplie d'une suite complexe de faciès sédimentaires. La sédimentation par écoulements gravitaires est omniprésente le long de la marge et les faciès vont de dépôts de transport de masse d'épaisseur métriques latéralement continus à des turbidites d'épaisseur centimétriques isolées intercalées avec des couches d'hémipélagites, de volcanoclastiques et de téphras. Nous présentons l'interprétation de la bathymétrie, des profils sismiques à haute résolution et des données pétrophysiques des carottes sédimentaires. L'objectif de cette étude est de décrire la complexité morphologique à la frontière équatorienne de la plaque de Nazca où un ensemble d'aspérités marines profondes ont subducté à différentes échelles, et ses conséquences sur la distribution latérale des sédiments dans les différents sous-bassins. La marge équatorienne comprend trois segments géomorphologiques: Le segment nord, situé au nord de la crête Carnegie, est caractérisé par une large (5-10 km) et profonde fosse (3800-4000 m), une pente continentale ravinée et une plate-forme (10-40 km de large) avec subsidence active. Le segment central en face de la crête de Carnégie montre une fosse étroite (0-5 km de large) et peu profonde (3100-3700 m), la pente escarpée et ravinée, sans canyons, et plateau continental étroit de 15 à 40 km de large caractérisé par des zones d'affaissement et de soulèvement actifs. Enfin, le segment sud, situé au sud de la crête Carnegie, présente une large (5-10 km) et profonde fosse (4000-4700 m), une pente continentale pauvre en sédiments avec des systèmes de canyons bien définis et une large plate-forme de subsidence (20-50 km). La dynamique sédimentaire le long de la marge est évaluée par l'analyse de 15 carottes sédimentaires dont la description visuelle, les photographies à haute résolution, l'imagerie par rayons X, les données XRF et les propriétés pétrophysiques conduisent à l'identification de 11 faciès sédimentaires caractérisant 7 processus sédimentaires: dépôts de turbidite, hémipélagites, téphras, dépôts de coulées de débris, homogénites, des slumps et des dépôts de carbonate de ooze. Les âges des dépôts sont définis par la datation au radiocarbone des sédiments hémipélagites. Les âges vont de 500 à 48000 ans BP. Les profils sismiques à haute résolution permettent de définir 3 echo-faciès: transparent, stratifiés et chaotiques. Le facies transparent est principalement associé aux dépôts d'homogénites, le facies stratifié est associé aux dépôts interstratifiés turbiditique-hémipélagique et le facies chaotique est associé à des dépôts gravitaires grossiers. Le remplissage de la fosse représente un enregistrement lacunaire mais important de l'histoire de la marge de subduction. De grandes coulées de débris se déplaçant vers l'est dans les deux séquences inférieures du remplissage de la fosse sont initiées le long de la paroi extérieure de la fosse, le long de grandes failles normales dues à la flexion de la plaque océanique subductante. Les sédiments de la séquence supérieure du remplissage qui nappent la fosse sont plus largement fournis par la paroi interne de la fosse mais avec un fort contrôle de la ride de Carnegie. En conséquence, la profondeur, la fréquence, l'épaisseur, la composition et la disposition latérale des dépôts sédimentaires varient grandement entre le nord et le sud. Les grands méga-lits simples, les slumps, les coulées de débris et les homogénites sont situés dans les segments nord et sud. Ils sont déclenchés par de grands escarpements de failles régionales, dans le Nord / Recent deep marine sedimentation in subduction trenches is characterized by the inter-stratification of hemipelagic and turbidite sediments locally interbedded with debris flow, which can result from continental slope shaking triggered by earthquakes. The active margin of Ecuador comprises tectonic erosion that contributes to the formation of a deep trench filled by a complex suite of sedimentary facies. Gravity flow sedimentation is ubiquitous along the margin and facies range from laterally continuous m-thick mass transport deposits to isolated cm-thick turbidites intercalated with hemipelagite, volcanoclastics and tephra. In this study we show interpretation of swath bathymetry, high-resolution seismic profiles and petrophysical data from cores. The objective is to describe the morphologic complexity on the Ecuadorian border of the Nazca plate where a set of deep marine asperities is subducting at different scales, and their consequences on the distribution of sediments in the different sub-basins. Ecuadorian margin comprises three geomorphological segments: The northern segment, northward of the Carnegie Ridge, is characterized by a wide (5-10 km) and deep trench (3800 – 4000 m), a gentler gullied continental slope and a shelf (10-40 km wide) with active subsidence. The central segment facing the Carnegie Ridge, is strongly influenced by the subduction of the Carnegie ridge which induces a narrow (0–5 km wide) and shallow trench (3100 – 3700 m depth), a steep and gullied slope with no canyons and a 15–40 km wide shelf characterized by areas with active subsidence and uplift. Finally, the southern segment, southward of the Carnegie Ridge, presents a wide (5–10 km) and deep (4000–4700 m) trench, a starved continental slope with well-defined canyon systems and a wide subsiding shelf (20–50 km). The sedimentary dynamics along the margin is evaluated by the analysis of 15 cores. Visual description, high-resolution photographs, X-Ray imagery, XRF data and petrophysical properties led to the identification of 11 sedimentary facies that characterize seven sedimentary processes: turbidites, hemipelagites, tephras, debris flows, homogenites, slumps, and ooze carbonate deposits. Age of the deposits is defined by radiocarbon age dating of hemipelagic sediments. Ages range from 500 to 48,000 years BP. High-resolution seismic profiles allow definition of three echo-facies: transparent, layered and chaotic. Transparent echo-facies is mainly associated to homogenite deposits, layered echo-facies is associated to the turbiditic-hemipelagic interbedded deposits and chaotic echo-facies is associated to reworked gravity flow deposits. The trench fill represents a lacunar but important record of the subduction margin history. Large eastward debris flows in the lower two sequences of the trench fill are provided by the trench outer wall as a results of slope failures along normal faults due to the downward bending of the oceanic plate. The sediment of the upper sequence of the trench fill draping the trench floor, are largely provided by the inner trench wall strongly controlled by the Carnegie Ridge. As a result, depth, frequency, thickness, composition and lateral disposition of the deposits vary greatly from those at north and south. The large, simple mega-beds like slump, debris flows and homogenites are located at the northern and southern segments. They were triggered by large regional faults in the North and enhanced by the activity of sets of splay faults in the South overhanging the seafloor at the slope toe. Small-size, fluid rich events were triggered by subduction of isolated seamounts at the edges of the Carnegie Ridge due to frequent but small destabilizations of an inner trench wall preconditioned by the impacts of successive seamounts. Sets of partly volcanoclastic turbidites in central segment might have been triggered by the complex interaction of slope and continental shelf deformation by seamount subduction