Distinguishing Natural Evolution and Human Impact on Estuarine Morpho-sedimentary Development: A Case Study from the Vilaine Estuary, France

International audienceEstuaries are coastal areas controlled by hydrodynamic factors such as sea-level changes, waves and tidal currents, and river discharge. This study focuses on the Vilaine Estuary which is strongly impacted by human activity after construction of Arzal dam in 1970. The purpose of this research is to differentiate the role of natural from anthropogenic factors on sediment dynamics within the Vilaine Estuary. We are proposing a hypothetical model based on the hydrodynamic modification and morpho-sedimentary development by analyzing the natural estuarine evolution and the impact of human alteration to the natural system by utilizing datasets including river discharge, tidal currents, winds and wave activities to further combine with photographic, bathymetric, topographic and sedimentary surveys. Results show that waves carry sediment from the sea and rework local sediments. The river damming is reducing the tidal prims and leads to the fall of tidal currents. This new situation supports the sediment deposition and reduces at the same time the accommodation space which decrease tidal currents in feed-back. The Vilaine Estuary is therefore coming close to a bay-type functioning which leads to a channel narrowing, a drastic increase of the tidal flat zone, an acceleration of erosional processes affecting the main channel, salt marsh and all associated depositional systems. We propose a hypothetical model showing that this evolution took place in two steps and we show that the dam has an effect to accelerate a natural infilling of the estuary

Status of Coral Reef Communities on Two Carbonate Platforms (Tun Sakaran Marine Park, East Sabah, Malaysia)

International audienceThis study concerns three sites, located on carbonate platforms, east Sabah: Gaya West, Gaya East, and Mantabuan. At each site, the dominant coral shapes and their health were recorded (lagoons and outer slopes). Densities of echinoderms, Tridacna, and nudibranchs were recorded while fish density was estimated. Generally, the coral vitality is low (≤50% living corals). Massive corals dominate all sites, except the Gaya West-outer slope where coral coverage and diversity are the highest. On the Mantabuan-mesh reef, a diverse Acropora assemblage dominates the landscape. On the reef flat of Gaya East, monospecific circa 10 meter coral patches occur. Primary producers are scarce on all sites. Sea urchins, dominated by Diadema, are abundant on the Gaya East-reef flat and the Gaya West-mesh reef. Sea stars and holothurids are the most prevalent in Gaya West-outer slope, although they remain scarce. Crinoids are only abundant in Mantabuan. Stegastes damselfish highly characterizes the sites of Gaya East (reef flat and inner slope) and the Mantabuan-mesh reef. On the Mantabuan-outer slope, parrotfish and other fishes are plentiful. No sign of eutrophication has been detected and natural hypersedimentation and/or eventual ancient bleaching events appear to be the direct principal causes of coral death or coral degradation

2D and 3D seismic simulation for fault modeling: exploratory revision from the Gullfaks field

2D and 3D seismic data have emerged as a key tool in the oil and gas industry to visualize and understand subsurface morphology and boundaries. In addition to providing excellent structural images, the dense sampling of 2D and 3D survey can sometimes make it possible to map reservoir quality and the distribution of hydrocarbon with well-marked limitations. Here we use 2D and 3D seismic data to map and interpret basic structures and fault lines to construct 2D and 3D base fault models of the Gullfaks field, while avoiding common pitfalls. This work also highlights important concepts and principles that allow selection, interpretation and simulation of particular areas containing hydrocarbon traps through the comparison of different maps such as time structure, amplitude and coherence. The field covers an area of approximately 50 km(2) entirely confined within block 34/10 in the Norwegian sector of the North Sea. The area of the seismic lines extends to 4875 m laterally and vertically up to 4.5 s. Based on all the selected horizons, constructed maps and dominant fault construction models (2D and 3D), we show the presence of a major fault that cuts five horizons of the area of interest. The structural features include antiform and a set of extensional faults with master, antithetic and synthetic faults with opposite sense of shear (dip direction and angle similar to 60A degrees). Ductile deformation at the bottom of seismic lines shows the fluctuation of amplitude of acoustic signals in seismic lines. Our results demonstrate uplift along the major fault during extension indicated by chaotic distortion at the bottom, which reveals a gas trap. In the Gullfaks field, termination of fault movement and subsequent deformation appears to have occurred for a long period of time. This illustrates the use of 2D and 3D visualization with horizon attributes that can conveniently provide massive amounts of data which elucidates the trapping mechanism of faults

Cenozoic tectonics of the Western Approaches Channel basins and its control of local drainage systems

International audienceLe domaine des Approches occidentales de la Manche constitue une zone clé pour caractériser l'évolution post-rift des marges continentales NW européennes associées à la collision Afrique/Europe. Malgré les divers témoins des inversions cénozoïques jalonnant le pourtour de la Manche, la structuration et l'amplitude des mouvements demeurent néanmoins incertaines au sein de la partie méridionale française des Approches occidentales. Il en est de même sur le rôle de l'inversion de la mer du Nord dans la mise en place du Fleuve Manche qui drainait un bassin versant bien supérieur à la Manche actuelle durant les grandes régressions plio-quaternaires et alimentait les éventails sous-marins Celtique et Armoricain en bas de pente. La réalisation des campagnes de sismique-réflexion haute résolution GEOMOC et GEOBREST03 dont les résultats font l'objet de cet article permettent de répondre à ces questions en complétant la connaissance géologique de la Manche. Les nouvelles observations soulignent le diachronisme et le contraste de l'amplitude des mouvements du système de failles associées à l'inversion du bassin d'Iroise. Celle-ci se fait en deux épisodes: un épisode paroxysmal paléogène décomposé en deux phases, éocène (Yprésien probable) et oligocène, et un épisode néogène plus modéré réactivant partiellement les structures impliquées antérieurement. Les déformations se concentrent le long de l'accident nord Iroise (NIF) situé dans le prolongement de la faille Médio-Manche et entraîne localement des plissements de la couverture sédimentaire à l'aplomb des accidents profonds. L'inversion induit ainsi un soulèvement de près de 700 m du plateau médian situé au sud de l'accident nord Iroise. La cartographie isochrone des séquences sismiques identifiées démontre également le contrôle majeur des structures tectoniques sur la mise en place des dépôts néogènes. Le soulèvement de la partie orientale du bassin favorise ainsi la mise en place de vastes prismes progradants d'âge miocène supérieur, et contrôle le développement postérieur du réseau des paléo-vallées constituant l'extrémité occidentale du fleuve Manche. Ce réseau présente une géométrie en baïonnette marquée par de brutaux changements de directions variant de N040 à N070, cette dernière direction caractérisant la plus grande partie des failles néogènes associées au bassin d'Iroise. Les paléo-vallées se seraient développées lors d'une chute du niveau marin au-delà du rebord de plate-forme et la stratigraphie établie à travers cette étude amène à placer le début des incisions au Pliocène (Reurévien ou pré-Tiglien). La chute amplifiée par l'inversion du bassin d'Iroise serait suivie d'un basculement tardif de la plate-forme externe à l'instar des observations réalisées sur de nombreuses marges du pourtour nord atlantique

Investigating orphan cytochromes P450 from Mycobacterium tuberculosis : the search for potential drug targets

Tuberculosis (TB) is a disease that the World Health Organisation (WHO) regards as a global pandemic. There is a great need for new drugs to combat this threat. Drug resistant strains of the causative agent, Mycobacterium tuberculosis (Mtb), have increased the urgency of this quest for novel anti-mycobacterial medicines. Publication of the Mtb genome sequence revealed a large number of cytochrome P450 (CYP) enzymes [Cole, S. T. et al. 1998]. These mono-oxygenase enzymes have been studied for many years and are responsible for metabolic functions in every kingdom of life. Research on the Mtb P450s to date has highlighted several of them as having critcal roles within the organism. CYP121 and CYP128 have been implicated as essential through gene knockout studies. It has been demonstrated that CYP125 is not essential for viability. However, it is part of a gene cluster highly important for Mtb infectivity and virulence. Due to the prospective importance of P450s to Mtb, this group of enzymes is under investigation as a source of novel drug targets. CYP142 was discovered as a potential drug target after it was located to a gene cluster involved in cholesterol catabolism during Mtb dormancy. As part of this PhD project, it was demonstrated that CYP142 performs an almost identical role to that reported for CYP125. These enzymes both perform C27 hydroxylation and carboxylation of the cholesterol side chain. However, variations in the level of oxidation have been identified, dependent upon the redox system with which these P450s are associated. A crystal structure of CYP142 showing high similarity in active site architecture to CYP125 supports the physiological role of CYP142 in cholesterol catabolism. Combining this with in vitro data which demonstrates that CYP142 possesses high affinity for a range of azole anti-fungal agents [Ahmad, Z. et al. 2005, 2006] supports the suggestion that it is a candidate target for the next generation of anti-mycobacterial drugs. CYP144 was highlighted as being important during the latent phase of Mtb growth, a phase that is not targeted by any of the current antimycobacterials. Work performed as part of this PhD has shown that many characteristics of CYP144 are highly comparable to those reported for other MtbP450s. CYP144 shows high affinity and specificity towards many azole molecules. Econazole, clotrimazole and miconazole have repeatedly been shown to bind to MtbP450s, including CYP144 and CYP142, with high affinity and are excellent potential candidates as novel anti-mycobacterial agents. An N-terminally truncated form of CYP144, CYP144-T, has been investigated in the pursuit of a CYP144 crystal structure. It is hoped that this will enable the elucidation of a physiological role for CYP144. Both CYP142 and CYP144 have demonstrated biochemical and biophysical characteristics that contribute to our knowledge of P450 enzymes. This PhD has established that CYP142 exhibits an equilibrium between P450 and P420 species in its CO-bound, ferrous form. A conversion from P420, and stabilisation of P450, upon substrate binding was also demonstrated. CYP144 displays unusual azole coordination characteristics when examined by EPR and removal of the CYP144 gene from Mtb increased sensitivity of the strain to clotrimazole. Studies of these enzymes has advanced knowledge of P450 and Mtb redox chemistry, established roles for the MtbP450 cohort and identified the potential of anti-mycobacterial drugs and associated targets.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Campagne océanographique GEOETEL 07

Campagne en mer réalisée du 02/07/2007 au 08/07/2007 par le LABORATOIRE GÉOSCIENCES OCÉAN (LGO) - UMR 6538 à bord du Côtes De La MancheThe South Armorican continental shelf if one of the morphological segments of the North Biscay margin. The current morphology results from two distinct tectonic phases. The first was a rifting and ocean accretion phase linked to the dislocation of the Pangea in the Upper Jurassic. The second was a compression phases linked to the convergence of Iberia towards Europe which began in the terminal Cretaceous which underwent a paroxysm in the Eocene. This is called the Pyrenean phase and it induced the partial closing of the Bay of Biscay, significant deformation of the bedrock and the sediment cover in Northern Iberia and in the ocean domain(uplift of several submarine reliefs). This Pyrenean deformation, with a long wave length and low amplitude, responding to the so called Pyrenean lithospheric buckling, was accompanied by far-ranging topographical, morphological, tectonic and sedimentological modifications both on the South Armorican continental shelf zone and more generally over the entire West European domain. The continental shelf displays prograding prism architecture. With a low rate of subsidence and an exposure to Eustatic cycles, the Quaternary deposits are not well developed there. This means that the current relief of the medial shelf mainly comes from the transgressive sand bodies sealing the former, slightly incised, topographies. The first objective was to obtain high resolution 3-D geometry of the morphological, stratigraphical, sedimentology and structural elements of the extension of South Armor coastal rivers into the sea to the 100-200 metre isobath offshore from Etel and Belle-Île. The second objective was to determine the architecture of the Holocene (10,000 years -today) deposits in the "medial, 70-120 metre" part of the South Armorican shelf, where the current relief is due to transgressive sand bodies. The cruise was related to the regional 'Péri-armor' & 'Cotarmor' programmesLe plateau continental sud-armoricain est l'un des trois segments morphologiques de la marge Nord Gascogne. Cette morphologie actuelle est le résultat de deux phases tectoniques distinctes. La première est une phase de rifting (distension crustale) et d'accrétion océanique liée à la dislocation de la Pangée au jurassique supérieur. La deuxième est une phase de compression liée à la convergence de l'Ibérie vers l'Europe qui débute au Crétacé terminal et qui a une phase paroxysmale à l'Eocène.Appelée phase pyrénéenne, elle induit la fermeture partielle du golfe du Gascogne, une importante déformation du socle et de la couverture sédimentaire Nord-Ibérie et du domaine océanique (surrection de plusieurs reliefs sous-marins). Cette déformation pyrénéenne, de grande longueur d'onde et de faible amplitude, en réponse au flambage lithosphérique "pyrénéen" s'accompagne de profondes modifications topographiques, morphologiques, tectoniques et sédimentologiques en autre sur la plateforme continental sud-armoricaine et plus largement sur l'ensemble du domaine ouest-européen. Le plateau continental présente une architecture en prisme progradant. Avec un faible taux de subsidence et une exposition aux cycles eustatiques, les dépôts quaternaires y sont peu développés. Ainsi le relief actuel du plateau médian est essentiellement hérité des corps sableux transgressifs scellant d'anciennes topographies aux incisions peu marquées. Le premier objectif est d'obtenir la géométrie haute résolution en 3-D des éléments morphologiques,stratigraphiques,sédimentologiques et structuraux de la prolongation à mer des fleuves côtiers sud-armoricain jusqu'à l'isobathe 100-200 mètres au large d'Etel et de Belle-Île. Le deuxième objectif est de préciser l'architecture des dépôts holocène (10000 ans -actuel) sur la partie "médiane,70-120 mètres" du plateau sud-armoricain où le relief actuel est hérité des corps sableux transgressifs. Campagne rattachée aux programmes régionaux 'péri-armor' & 'Cotarmor'

Campagne océanographique GEOSAINTBRIEUC18

Campagne en mer réalisée du 30/03/2018 au 11/04/2018 par le LABORATOIRE GÉOSCIENCES OCÉAN (LGO) - UMR 6538 à bord du ThaliaArchitecture and Morpho-dynamics of the Quaternary sedimentary deposits of the Bay of Saint Brieuc.Architecture et morpho-dynamique des formations sédimentaires quaternaires de la baie de Saint Brieuc

Morphologie et remplissage des vallées fossiles sud-armoricaines : Apport de la stratigraphie sismique

Thèse publiée dans la collection des Mémoires de Géosciences Rennes (ISSN 1240-1498) : Mémoire n° 110 (ISBN : 2-914375-21-2)Recent acquisition of3000 Km ofhigh resolution seismic and morpho-bathymetry EM 1000in south coastal area brittany bring informations which clarify south brittany cenozoic history and comprehension in the genesis of quaternary valleys and estuarines. Studie is based on the cartography of morphologie, stratigraphie and structural elements of the main coastal rivers (Odet, Blavet, Etel, Vilaine). Five hydrographie paleo-network have been caracterised. Studies of longitudinal and transversal profiles evolution, marines abrasions surfaces, the sedimentary evolution of valley fills, and comparaison with cotemporaneous network preserved of the atlantic margin bave allowed to discuss oflithologic, tectonnic and climate impact (role) on the dynamic hydrographie paleo-network.L'acquisition récente de 3000 km de données de sismique sparker haute résolution et morphobathymétriques EM 1000 dans le domaine côtier sud armoricain apporte des éléments qui éclairent l'histoire cénozoïque du Sud Bretagne et notre compréhension de la genèse des vallées et estuaires quaternaires. L'étude est basée sur la cartographie des éléments morphologiques, stratigraphiques et structuraux de la prolongation en mer des principaux fleuves de l'Odet, du Blavet, d'Etel et de la Vilaine. Elle a permis la reconnaissance de cinq paléo-réseaux hydrographiques. L'étude de l'évolution des profils longitudinaux et transversaux de ces réseaux, des surfaces d'abrasion marines qui les recoupent, de l'architecture interne de leur remplissage, et leur comparaison avec les réseaux contemporains préservés le long de la marge atlantique ont permis de discuter l'impact de la lithologie, de la tectonique et du climat sur la dynamique des paléo-réseaux hydrographiques

The Ups-and-Downs of Borneo

International audienc