This study uses a 1375 km2 3D seismic dataset located in the late Miocene to Pliocene Mississippi River Delta in order to investigate the external characteristics, lithology, and evolution of channelized deposits within the seismic survey. Fluvial thicknesses range from about 11 m to 90 m and widths range from about 100 m to 31 km. Channel fill can be generalized as sandy with low impedance and high porosity (~ 35%), though heterogeneity can be high. Three distinct fluvial styles were recognized: incised valleys, channel-belts, and distributive channel networks. Fluvial styles were interpreted as a result of changes in sea-level and a speculative late Miocene to Pliocene Mississippi River Delta sea-level curve constructed using these relationships. Additionally, a characteristic interval between the major changes in fluvial style was found. These fluvial systems interact with and are affected by other elements in the landscape. Growth faults in particular are common within the survey area; however, the dynamic between fluvial systems and growth fault related subsidence has been poorly understood and so was also a focus of this project. Previous work as well as this study found little evidence that growth faults are able to affect the course or geometry of the majority of small (with most < 500 m in width and < 20 m in depth) channels. However, the relationship between growth faults and larger scale channel-belt systems (between 1 km and 5 km in width and > 25 m in depth) has not been previously evaluated in this area. In contrast to the majority of small distributary channels found within the survey, channel-belts appear to be steered by growth faults. Fluvial response or insensitivity to fault induced subsidence is related to the relative timescales of avulsion and faulting. Channel-belts are longer lived features than more ephemeral small distributary channels. Channel-belts, due to their relatively low mobility compared to small channels, are more likely to experience punctuated faulting events which results in greater apparent sensitivity to faulting than seen in small channels. / text

Recent drilling of deep stratigraphy in subsalt offshore Gulf of Mexico has revealed the presence of thick, amalgamated, Cretaceous siliciclastic reservoirs with the potential to become valid exploration targets. Similar to the Lower Tertiary deepwater play, the significant down-dip distance (> 400 km) from the source deltaics, the data gap across the modern structurally complex salt-tectonics-dominated slope and the difficulties of imaging subsalt stratigraphy pose challenges for the construction of meaningful deepwater system models to aid in exploration and appraisal efforts. A 3D seismic dataset in the Mad Dog field at the basinward end of the modern allochthonous salt canopy and outboard of the Sigsbee Escarpment offers the opportunity to study the nature of the deep stratigraphy at central positions in the basin. The nature of the Cretaceous sedimentary system has been investigated through detailed structural and seismic geomorphologic mapping. An early syndepositional contractional event has been identified and temporally associated with Mesozoic emplacement of a deep salt sheet. These events are masked by the major Neogene-age phase of fold amplification that dominates the present-day subsalt structural framework. Ponded-basin deepwater sedimentation processes control early phases of deposition in the Cretaceous Mad Dog area and sediment-gravity flows are deposited as complexes of low sinuosity amalgamated channelized deposits in roughly-confined sediment pathways. Ponded fills show internal lateral accretion architectures that grow sigmoid in nature as the migrating systems interact with the approaching minibasin margins making evident the structural control on sediment architecture. Later phases of deposition are characterized by slightly sinuous feeder channels with multiple lobe development at their terminus. Variable directions of sediment source pathways indicate a linear-sourced slope apron depositional model for these systems. In addition to the more structured morphologic elements, there were also pervasive mass-transport processes active, presumably triggered by Mesozoic halokinesis. Data in sparse deep wells in the GoM that penetrate the Cretaceous suggest that the Late Cretaceous deepwater depositional system was composed of coarse-grained high density gravity flows. The geometries seen in seismic beneath the Mad Dog area support the existence of such a basinwardly extensive deepwater fan systems developed during the Cretaceous, and the low sinuosity channel geometries and small length:width ratio and amalgamated nature of fan lobes suggest that these systems may have indeed been high-density in nature. / text

This thesis examines the interaction of pre-existing and evolving salt-related topography on the temporal and spatial evolution of depositional systems in deepwater. To achieve this, the thesis integrates stratigraphic and structural analysis of 3D seismic data from the Miocene record of the salt-influenced Lower Congo Basin, Offshore Angola. Observations at multiple scales ranging from the semi-regional (&gt; 50 km) to local, kilometre-scale and covering timescales ranging from the entire Miocene (~ 18 Myr) to &gt; 2 Myr are presented. At the semi-regional scale, results from this study shows that the progressive along-strike linkage of short (&lt;10 km) fault segments and salt diapirs into through-going large scale (&gt; 30 km) faults and elongated saltwalls results in long lived diversion and/or confinement of depositional system fairways. Axial confinement of fairways occurs where structural strike is parallel to sediment input, contrasting with ponding or diversion of deposits oriented at a high angle to structural strike. The orientation of the structures remains relatively static, which in combination with the fixed sediment entry points of the fairways results in recurrence of the major styles of interaction, and long term pinning of fairways throughout the Miocene. The development of large (10's of km) "sediment shadow" zones devoid of coarse clastics downdip of diverted and or confined sediment gravity flows is also observed through the Miocene. At the intraslope basin (10's of km) and sub-basin scale ( < 10 km), the role of confinement by salt-related structures on the temporal evolution and dip-and-strike variability of Late Miocene channelised-lobe complexes in an elongate intraslope basin was also investigated. At both of these scales, the morphology of the recieving basin geometry significantly influences the dimensions, planform morphology and vertical stacking patterns of channelised-lobe complexes. A transition from thick, radial shaped lobe-complexes which are aggradationally stacked and deposited via 'fill-and-spill' of sub-basins within an intraslope basin to thinner, elongate, laterally offset and compensationally stacked channelised-lobe complexes in the intraslope basin is observed. This transition occurs as the salt-related structural template evolves and confinement changes from the sub-basin scale to the intraslope basin scale. At the depositional element scale ( < 5 km), results from this study further shed light on the critical and hitherto neglected role of salt-related topography in controlling the location of channel to lobe transition zones in deepwater depositional systems. The location of the transition zones are documented from four case studies, with the transitions spatially controlled by salt-related reduction in gradient e.g. a break in slope downflow of monoclinal structures, and/or a reduction in lateral confinement of depositional fairways downflow of segment boundaries. Overall, the result of this thesis show the significant influence which evolving saltrelated topography exerts on the stratigraphic development, geometry and sediment routing patterns on salt-influenced continental margins. In particular the study highlights how variable the interaction between evolving salt-related topography and deepwater sedimentation is at a range of temporal and spatial scales.

By examining halokinetics and channel evolution in a deep-water system, we investigate how submarine channel morphology is affected by changing seascape linked to diapirism. The study area is located in Mississippi Canyon, Gulf of Mexico (GOM), situated directly off the continental slope in a prominent salt dome region. Interactions of salt domes with submarine channels in the GOM are poorly documented. Utilizing 3D seismic data and seismic geomorphology techniques, a long-lived Plio-Pleistocene submarine channel system has been investigated to develop a relationship between variable phases of salt movement and plan-form morphology of preserved channels. We suggest that halokinetics acts as a driver for topographic-channel evolution in the study area. We show how submarine channel morphology can be directly controlled by halokinetics, where salt movement can act as a structural control on both location and morphology of meandering channel complexes. Channels are able to move towards an equilibrium state only when holokinetics decreases.

Laurentide Ice Sheet outburst floods to the Gulf of Mexico have been mainly documented based on deep-sea cores, especially the megafloods, only during the last several interglacial episodes in the late Pleistocene. The paleoclimatic significance of giant sedimentary structures developed under unconfined Froude-supercritical turbidity currents in subaqueous settings is considerably under-examined. This research extensively documents >20-km-wide and 200-m-thick Plio-Pleistocene giant sediment waves for the first time on the northern Gulf of Mexico continental slope using 3D seismic data, which show waveform morphology in unprecedented detail. The results suggest that such large-scale bedforms were formed under sheet-like unconfined Froudesupercritical turbidity currents as cyclic steps, based on numerical and morphological analyses. Paleohydraulic reconstruction (e.g., flow velocity, discharge, and unit flux), in association with other evidence like geologic age, stable isotope records, and temporal rarity, points out that the responsible Froude-supercritical turbidity currents were most likely triggered by deglacial catastrophic outburst floods during the late Pliocene to early Pleistocene. These flooding events constitute, by far, the oldest record of the glacial outburst floods during the Quaternary Ice Age. The results propose that such pervasive occurrence of large-scale sediment waves are a proxy for catastrophic megaflood events

No description available.

Une analyse de données de sondeur multifaisceaux, de sondeur de sédiments (Chirp) et de sismique multitraces, présente la morphologie et la dynamique sédimentaire actuelle ainsi que l’évolution architecturale et stratigraphique du Néogène-Quaternaire opérant le long d’une marge leeward, au nord-ouest du Great Bahama Bank. L’analyse morpho-bathymétrique révèle un talus dominé par de la boue aragonitique, et une grande variété de structures sédimentaires, liées à des processus hydrodynamiques diversifiés. Les courants de density cascading associés aux courants de marée et aux vents d’est représentent les mécanismes de transports édimentaire dominant le long de la marge. La zone de Bimini présente localement un talus court et abrupt,stabilisé en bordure de plate-forme par une barrière récifale, ce qui limite l’export off-bank de sédiments.L’architecture stratigraphique montre une évolution complexe du talus au cours du Néogène. La fin du Paléogène est marquée par un talus continu aggradant détaché de la plate-forme par un escarpement sur faille. Ilpasse à un système très peu incliné de type slope-apron, attaché à la plate-forme au Miocène et se termine par un système en accrétion fortement incliné au Pléistocène. Bien que les dépôts de talus soient dominés par de la boue, ils présentent des variations latérales rapides du Sud au Nord tout au long du Néogène (< 30 km) avec la mise en place de tabliers turbiditiques, de nappes de débrites, et de larges Mass Transport Complexes. Ces faciès interagissent depuis le Langhien avec le Santaren Drift qui s’étend et migre progressivement le long du talus jusqu’à aujourd’hui. Le maximum d’empiétement des contourites se produit au Pliocène supérieur et coïncide avec une réorganisation océanographique globale ainsi que des changements climatiques majeurs dans l’hémisphère nord liés à la fermeture de la Central American Seaway. / An analysis of multi-beam echo sounder, sub-bottom profiler (Chirp) and multichannel seismic,highligths the present-day sedimentary dynamics and the Neogene-Quaternary architectural and stratigraphicevolution along the northwestern leeward margin of the Great Bahama Bank.The morpho-bathymetric analysis reveals an aragonite mud-dominated slope, and a broad spectrum ofsedimentary structures, related to various hydrodynamic processes. The density cascading currents associatedwith tidal currents and prevailing easterly winds correspond to the dominant transport mechanisms operatingalong the margin. The Bimini area displays a short and steep slope, stabilized at shelf edge by rimmed reefalbarrier, which constrains the off-bank export of materials.The stratigraphic architecture shows a complex evolution of the slope during the Neogene. The end ofthe Paleogene is marked by a continuous aggrading slope detached from the shelf by a fault escarpment. It passesinto a low angle slope-apron attached to the platform in the Miocene, and ends with an accretionary system witha steepened slope in the Pleistocene. Although the slope deposits are mud-dominated, they show rapid lateralvariations (< 30 km) from South to North throughout the Neogene with the establishment of turbidite aprons,debrite layers and large Mass Transport Complexes. These facies interact since the Langhian with the SantarenDrift which gradually extends and migrates along the slope until today. The maximum extent of the drift occursduring the upper Pliocene and coincides with a global oceanographic reorganization and major climate changesin the northern hemisphere, related to the closure of the Central American Seaway.

La marge provençale, localisée au Nord-Ouest de la Méditerranée, constitue avec la marge du Golfe du Lion et la marge ligure, la bordure septentrionale du bassin Liguro-Provençal. L'objectif principal de ce travail est la reconstitution de l'histoire géodynamique, structurale et géomorphologique de la marge depuis le Tertiaire. Sa structure est principalement le résultat des phases tectoniques anté-miocènes. Sur la marge provençale la transition entre le plateau continental et le bassin est étroite et caractérisée par des pentes abruptes affectées par des phénomènes d'instabilité gravitaire dans l'axe du canyon sous-marin de Cassidaigne. A terre, la marge provençale est caractérisée par une compression pyrénéenne, des fossés oligocènes, et une sédimentation mésozoïque à cénozoïque essentiellement carbonatée propice à l'infiltration des eaux en profondeur. L'origine des cours d'eau de la région est essentiellement karstique, et les sources côtières de Port-Miou et Bestouan constituent des réseaux karstiques noyés développés sur plusieurs kilomètres dans le calcaire urgonien, au droit du canyon de Cassidaigne. Les travaux antérieurs suggèrent que l'absence de réseau fluviatile de surface en amont et la forme de reculée karstique de la tête du canyon de Cassidaigne sont le résultat d'une connexion karstique entre les sources côtières et le canyon, que la marge provençale n'ait pas été affectée par l'érosion messinienne et la transgression pliocène, que certains dépôts transgressifs marins miocènes sont situés à des altitudes anormalement élevées par rapport à leurs niveaux de dépôt théorique. / The Provence Margin is situated in the north-western Mediterranean and constitutes the northern edge of the Liguro-Provençal Basin with the margins of the Gulf of Lion and Ligurian sea. The main objectif of this thesis is the reconstruction of the geodynamic, structural and geomorphologic history of the margin since the Tertiary. This margin is mainly structured by ante-miocene tectonic events. On the Provence Margin, transition between the continental plate and the basin is narrow and characterized by abrupt slopes and associated gravitary instability within the axis of the Cassidaigne canyon. The Provence Margin is characterized by Pyrenean compression and Oligocene extension. The Mesozoïc-Cenozoïc sedimentary pile is dominated by carbonate rocks favorable to water circulation. The origin of the river system in the region is essentially karstic, and the coastal springs of Port-Miou and Bestouan correspond to drowned karstic network that develop along tens of kilometers within the Urgonian limestone, updip of the Cassidaigne Canyon. Previous work suggest (1) that the lack of updip river system and the karst pocket valley shape of the canyon head are the result of an active karstic connexion between the coastal springs and the canyon, (2) that the Provence Margin is not affected by the Messinian erosion and Pliocene transgression, and (3) that Miocene marine transgressions are preserved at higher altitudes than their theoretical level. These facts witness a recent tectonic deformation that is not well understood. This work is based on the integration of geology, geomorphology and hydrogeology with the aim to understand evolution and functioning of coastal karsts