Les interactions " tectonique et sédimentation " entre le front du prisme de la Barbade et le delta de l'Orénoque

This manuscript summarises the research work performed during this thesis, which composed of several parts. The first part, consist of an interpretation of seismic data available documenting the Southern zone of the Prism of Barbados. The second part, consist of an analysis of the deformation (structural study and kinematics) and the last part contains the analysis of the underlying structures.The approach used in this work attempts to analyse geological structures developed underwater and strongly dependent on sedimentation. These structures are formed in compressive and extensive domaines. We tried to define the genetic bonds between the nature and the architecture of the deposits and the geometry and the development of the structures, from data interpretation gathered at the time of CARAMBA survey, of the profiles of surveys VEN and AN, and two drillings located on the platform.The sismostratigraphic analysis enabled us to identify seven seismic units which were located on the platform and in the southern part of the prism of Barbados, and to understand the chronology of the events and the kinematics of deformation. The nature of the deposits (seismic facies), their distribution, and their migration in the course of time appears closely associated with deformation. The development of a network of channels, shale-diapirism, and the localization of the erosion zones constituted other elements to specify the tectono-sedimentary evolution. This permited to identifie deux zones (1 & 2) from seismic facies analysis. Essentially, the majority of the erosion zones were identified in zone 1. These erosion zones are connected to the activation of the internal structures (very strong faults offset). The "chaotic" deposits (mud flows, slips in mass) which mark out fault 5, take part in erosion and feed sedimentation in north. The distribution of the channels is induced by the slopes hydrodynamism (foresets) of the Orenoque delta, and then is controled by the progressive deformation of acretionary prism. From structural study, we proposed that the deformation migrates towards southwest, at a rate of 0.7cm /yr after Pleistocene. In addition, we are noted that structures profonds are independent of the surface structures. According to the focal mechanisms, the underlying structures are opposed to those analyzed on the surface. The thickness of the continental crust tends to abroad towards the SE at the same time as the thickness of sedimentary cover tends to be reduced. The activity of the faults of the cretaceous platform played an important part in space creation for the sedimentary cover.Ce manuscrit résume des travaux de recherche effectués durant mon travail de thèse qui s'est déroulé en plusieurs étapes. La première partie de ce travail a consisté en une interprétation de l'ensemble des données sismiques disponibles documentant la zone Sud du Prisme de la Barbade*. La deuxième partie, a consisté à analyser la déformation (étude structurale et cinématique) du sud du Prisme de la Barbade et la dernière partie a été consacrée à l'analyse des structures profondes. La problématique abordée dans le cadre de cette thèse a porté sur l'étude des structures géologiques développées en domaine sous-marin et fortement dépendantes de la sédimentation. Ces structures concernent à la fois des zones compressives et des zones extensives. Nous avons tenté de définir les liens génétiques entre la nature et l'architecture des dépôts, et la géométrie et le développement des structures, ceci à partir de l'interprétation des données acquises lors de la Campagne CARAMBA, des profils des campagnes VEN et AN, et de deux forages situés sur la plate-forme. L'analyse sismostratigraphique nous a permis d'identifier sept unités sismiques qui ont été repérées sur la plate-forme et dans la partie sud du prisme de la Barbade, et de mieux comprendre la chronologie des événements et la cinématique de la déformation. La nature des dépôts (faciès sismiques), leur distribution, et leur migration au cours du temps apparaissent étroitement associés à la déformation. Le développement d'un réseau de chenaux, le volcanisme de boue, et la localisation des zones d'érosion ont constitué d'autres éléments pour préciser l'évolution tectono-sédimentaire. Ceci a permis de distinguer 2 grandes zones distinctes (1 et 2) à partir de l'analyse des faciès sismiques. L'essentiel des zones d'érosion ont été identifiées dans la zone 1. Ces érosions sont à relier à l'activation des structures internes (jeux des failles très forts) et à l'activité du volcanisme de boue. Les dépôts " chaotiques " (coulées de boue, glissements en masse) qui jalonnent la faille 5, participent à l'érosion et alimentent la sédimentation plus au nord. La distribution des chenaux est induite par l'hydrodynamisme des pentes (foresets) du delta de l'Orénoque, puis contrôlée par la déformation progressive du prisme d'accrétion. A partir de l'étude structurale, nous avons proposé que la déformation migre du nord-est vers le Sud-Ouest à raison d'environ 0.7 cm/an, depuis le Pléistocène. Par ailleurs, nous avons constaté que l'orientation de ces structures superficielles est indépendante des structures profondes. D'après les mécanismes au foyer et l'orientation des contraintes associées, les déformations profondes sont opposées à celles analysées en surface. L'épaisseur de la croûte continentale tend à augmenter vers le SE en même temps que l'épaisseur de la couverture sédimentaire tend à se réduire. L'activité des failles de la plate-forme crétacée a joué un rôle important dans la création d'espace d'accommodation pour les dépôts sédimentaires

Margen norte costa afuera de Venezuela : sísmica marina de alta resolución entre Golfo Triste y Cabo Codera

The continental shelf north of Central Venezuela is partially or completely structurally controlled by major right lateral strike slip active faults (e.g San Sebastian fault), comprising three physiographic provinces, from west to east: The Golfo Triste Playorm, the Choroni Basin and the La Guaira Platform. The two mentioned platforms are of erosional type while the Choroni basin is a deep depression, which is incised by submarine canyons. These canyons seem to be related to turbidity currents with greater flows during the Pleistocene wetter periods. "Wowing several authors, there submarine canyons are partially or completely structurally controlled by major structures present in the north-central coastal range of Venezuela. Five major regional uncon-formities and/or seismostratigraphic limits have been identified GVe propose to correlate the most recent to MIS 2 (Last Glacial Maximum similar to 20 ka) lowstand. The chronological significance of the deepest detected major uncomformity (strong erasion) is tentatively attributed to MIS 6 (similar to 130 ka) lowstand. Based on the present-day position of the later one, we propose an estimation of similar to 1.2 mm.y(-1) of the mean subsidence rate in the La Guaira Shelf; considering that the obtained value may locally represent a minor vertical component of the dominantly horizontal displacement along the San Sebastian Fault. The San Sebastian fault shows a linear deformation in the eastern profiles. In contrast to the west, we observe in some profiles an intense deformation zone

From Subduction to a Compressional transform system: Diffuse Deformation Processes at the Southeastern Boundary of the Caribbean Plate

Geophysical data acquired in the southeastern Caribbean marine area (CARAMBA survey of the French O/V Atalante) provide new information about the deformation processes occurring in this subduction-to-strike-slip transitions zone. The 65 000 km2 of multibeam data and 5600 km of seismic reflection and 3.5 kHz profiles which have been collected evidence that the connection between the Barbados accretionary prism and the south Caribbean transform system is partitioned between a wide variety of recently active tectonic superficial features (complex folding, diffuse faulting, and mud volcanism), which accommodate the relative displacement between the Caribbean and the South America plates. The active deformation within the sedimentary pile is mostly aseismic (creeping) and this deformation is relatively diffuse over a large diffuse plate boundary. There is no direct fault connection between the front of the Barbados prism and the strike-slip system of northern Venezuela. The toe thrust system at the southern edge of the Barbados prism, exhibits clear en-echelon geometry. The geometry of the syntectonic deposits evidence the diachronism of the deformation processes. Notably, it is well evidenced that early folds have been sealed by the recent turbidite deposits, whereas, some of the fold and thrust structures were active recently. Within this active compressional region, extension growth faults develop on the platform and on the slope of the Orinoco delta along a WNW-ESE trending en-echelon fault system that we called the Orinoco Delta Fault Zone (ODFZ). This fault system is clearly oblique with respect to the present-day Orinoco delta slope. These faults are not simply related to a passive gravitary collapse of the sediments accumulated on the Orinoco platform. Though there a decoupling between the shallow deformation processes in the sediments and the deep deformation characterized by earthquake activity, the ODFZ is inferred to be partly controlled by deep structures associated the shearing of the lithosphere at depth (probably at the Continent-Ocean Boundary)

Volcanic influence during the formation of a transform marginal plateau: Insights from wide-angle seismic data along the northwestern Demerara Plateau

International audienceTransform marginal plateaus (TMPs) are submarine seafloor highs located at the continental slope, often at the boundary of two ocean basins of different ages and associated to at least one transform or highly oblique margin. The systematic study of TMPs can, therefore, answer questions about rifting and continental margin development. The Demerara TMP (offshore Suriname and French Guiana) is located at the border between the Central Atlantic, which opened during the Lower Jurassic and the Equatorial Atlantic, which opened during the Lower Cretaceous. This study, based on wide-angle seismic data modeling from the northern and western section of the Demerara Plateau, provides information on both the lower volcanic unit of this TMP and the adjacent oceanic crust. The results confirm that the crust of the Demerara Plateau is around 30 km thick and consists of lava flows possibly mixed with crust of continental origin in its deeper layers. Seismic velocities (exceeding 7 km/s) are compatible with those of volcanic oceanic plateaus. To the west, a relatively wide transition zone separates the plateau from the Jurassic oceanic crust, which is composed of two layers, and is much thicker than normal oceanic crust (∼11 km). During the Cretaceous, the plateau was sharply cut by transform and highly oblique structures, separating the Demerara Plateau from its transform conjugate, the Guinea Plateau. As a result, the Demerara Plateau is flanked to the north by a magma-poor/strongly tectonized Cretaceous oceanic domain with thin (2-3 km) crust, likely partially consisting of serpentinized mantle. In contrast, the oceanic crust located towards the south-east appears to be more characteristic of typical oceanic crust in composition though slightly thinner than normal (4-6 km) thickness. Our analysis allows us to propose a new 3D vision of the crustal structure of the Demerara TMP and its borders

The Orinoco turbidite system: Tectonic controls on sea-floor morphology and sedimentation

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Relations génétiques entre la Ride d'Aves et le bassin arrière-arc de Grenade, Caraïbe orientale

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Geodynamic of the Lesser Antilles Back arc Domain; contributions of the GARANTI cruise, in the Grenada Basin

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Unravelling the genetic relations between the Grenada Basin, the Aves Ridge, and the Lesser Antilles: a structural and stratigraphic analysis

International audienceLocated in the southeastern Caribbean, the Grenada Basin is bounded to the east by the modern Lesser Antillesisland arc, to the west by the Aves Ridge, commonly interpreted as a Cretaceous-Paleocene extinct volcanic arc,and to the south by the transpressive plate boundary with South America. The Grenada Basin has long beenregarded as a classical back-arc basin until recent studies suggest alternative models, such as forearc openingor Wernicke-type simple shear. The genetic relations between the Grenada Basin and its adjacent arcs remaintherefore controversial. Our analysis of seismic reflection and refraction data acquired during the GARANTIcruise (May-June 2017 onboard R/V L’Atalante) sheds light on basement nature and topography, depositionalhistory and deformation of the sedimentary infill, including vertical motions, of the Lesser Antilles back-arc area.Correlations with well logs located on the northern Venezuelan shelf, DSDP sites on the Aves Ridge, and IODPsites off the west coast of Martinique Island, also provide chronostratigraphic constraints.Seismic lines across the Grenada Basin reveal a significant asymmetry: the basement deepens from 5 to 10km southeastwards while flat-lying sediment units thicken from 2 to 7 km. A 6.5 to 7 km thick oceanic crustunderlies the southeastern half of the basin over a width of about 80 km. The Grenada Basin comprises threemajor depositional sequences defined by unconformities and/or changes in the seismic facies, from bottom to top:- Sequence 1: undifferentiated Eocene sediments represented by strong reflectors that drape the acoustic basement,as well as syntectonic deposits.- Sequence 2: Oligocene to Middle Miocene distal turbidites, probably originating from the Orinoco River thatflowed from the south into the Grenada Basin at that time. Sequence 2 lies unconformably over Sequence 1.- Sequence 3: Late Miocene to Recent arc-derived turbidites and pelagic sedimentation, with little detri-tal input from South America, due to the emplacement of the eastward drainage of the Orinoco River southof the northern Venezuelan coastal range during Middle Miocene. Sequence 3 lies unconformably over Sequence 2.Since the oldest syntectonic sediments date from the Eocene, the last tectonic event that shaped the present-daybasement topography dates back from the Eocene. Given the horizontality of Sequences 2 and 3 within the basinand along the Aves Ridge, no differential vertical motions occurred between the Grenada Basin and the AvesRidge since then. This raises questions about the subsidence mechanisms that led to the current depth of theoceanic crust in the southeastern Grenada Basin. By contrast, reflectors in Sequences 2 and 3 are bent upwardsalong the Lesser Antilles slope, reflecting the uplift of the Neogene Lesser Antilles arc. These observations will beintegrated in a future model for the evolution of the Lesser Antilles back-arc area, as part of the ANR GAARAntiproject

Giant seabed polygons and underlying polygonal faults in the Caribbean Sea as markers of the sedimentary cover extension in the Grenada Basin

Based on an extensive seismic and multibeam dataset, 1-5 km wide giant polygons were identified at the bottom of the Grenada basin, covering a total area of ~55000 km². They represent the top part of an active underlying polygonal fault system due to the volumetric contraction of clay- and smectite-rich sediments during burial. To date, this is the widest area of outcropping polygonal faults ever found on Earth. The seabed polygons are bounded by rectilinear ~1000-1500 m wide and ~10-60 m deep furrows, depending on the ESSOAr | https://doi.org/10.1002/essoar.10506638.1 | CC_BY_NC_4.0 | First posted online: Thu, 1 Apr 2021 00:40:54 | This content has not been peer reviewed location in the basin. They are relatively regular in the north Grenada Basin, whereas they are getting longer and more elongated in the south Grenada Basin. The polygonal faults consist in a set of discrete normal faults affecting a 700 to 1200 m thick interval, initiated in the shallow sub-surface at the transition between Early to Middle Pliocene and then having propagated both upward and downward during sedimentation. The centre43 to-centre method has been applied to determine the local ellipse of strains, providing a major orientation for extension needed for polygons to initiate. In the north, the minor axes are oriented N40°, indicating a general NE-SW extension of the upper part of the sedimentary cover consistent with the forearc/backarc regional extension. In the south Grenada Basin, minor axes are progressively turning towards the south, pointing out the actual maximum subsidence point. This implies that seabed polygonal faults could thus be indicative of the present-day (or recent) strain state within the upper sedimentary column