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Tessier, B.; Poirier, C.; Weill, P.; Dezileau, L.; Rieux, A.; Mouaze, D.; Fournier, J., and Bonnot-Courtois, C., 2019. Evolution of a shelly beach ridge system over the last decades in a hypertidal open-coast embayment (western Mont-Saint-Michel Bay, NW France). In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 77–88. Coconut Creek (Florida), ISSN 0749-0208.The behavior of the shelly beach ridge system forming a more or less continuous barrier lying along the southern coast of the hypertidal Mont-Saint-Michel bay (NW France) is examined using a set of various data including aerial photographs since 1947, sediment cores collected in back-barrier salt marshes, ground penetrating radar profiles, and differential digital elevation models (DEMs). The latter shows that since the middle of the 20th century, the tidal flats extending in front of the ridge system experience erosion and accretion that alternate spatially according to cross-shore corridors. The shelly ridges are better developed on line with the erosional bands. The reasons for this erosion/accretion compartment pattern are not totally elucidated. It probably results from the combined influence of shellfish farms, tidal channels and reef present on the tidal flats on wave and current dynamics. At the decadal to pluri-decadal scale, the shelly beach ridge system behavior as well as its internal organization can partly be related to the fluctuations of hydrodynamic conditions controlled by the 18.6 years nodal tidal cycle. Periods of intense landward migration alternate with periods of relative stability during the peak and the trough of the cycle respectively. This general scheme is complicated due to variations in storm wave dynamics. The most morphogenic events happen potentially during coinciding nodal cycle peaks and enhanced storminess. Such conditions actually occurred around 1995-2000, resulting in the most prominent washover fan deposit preserved within the back-barrier infilling successions. These sediment successions evidence as well that no beach ridge system older than the 19th century is preserved in front of the Medieval dike built during the 11th century on a relict beach ridge, and on which the present-day system is backed. We suggest that the enhanced storminess conditions of the Little Ice Age provoked the reworking of beach ridges formed between the 11th and 19th centuries. Changes in quantity and type of mollusk shells, related to the shellfish farming development during the 20th century are also thought to have had positive consequences on the barrier building and stability.

Due to its exceptional tidal range and the immensity of its intertidal zones, Mont-Saint-Michel is a favored model for research on coastal hydro-sedimentary processes, present-day sedimentary dynamics and the reconstruction of coastal paleo-environments. The purpose of this article is to analyze the erosion/sedimentation processes which govern the sedimentary dynamics and the recent evolution of the characteristic sedimentary environments of the bay. The western bay head is made up of tidal sand and silt deposits, where the extent of the surface sediment reworking is less than 10 cm and linked to the nature of the substrate and the wind direction. Added to these tidal dynamics are the dynamics of the swell, which set coarse bioclastic sands in motion as the waves wash away the shore. These sands migrate on the tidal flat at rates of several dozen m/year and accumulate on the upper tidal flat, forming a relatively stable non-continuous coastal barrier of large shell banks. The eastern part of the bay is an estuarine zone, where the morpho-dynamics of the sandy tidal flat are constrained by shifting channels. Studies of the interaction between vegetation and sedimentation around Mont-Saint-Michel show sedimentary accretion rates varying from 0.2 to 10 cm/year, depending on the morpho-dynamic context of the salt marsh front. The volume of sediment deposited by the tide leads to cyclical deposition of calcareous muds followed by the steady advance of salt marshes at a rate of about 17 ha/year between La Chapelle Sainte-Anne and the Roche Torin point. The bay has filled for thousands of years to the rhythm of sea level oscillations, leading to the gradual infilling of the Dol marsh and the advance of the shoreline. In addition to this natural evolution, human activities have developed in the bay, both on the western tidal flat (fixed fisheries and shellfish farming) and on the eastern estuarine side (polder formation, construction of dikes and a dam) and have altered the landscapes, the historical evolution of which was reconstructed from old documents.

In order to define and quantify the rhythm and amplitude of the processes of erosion and sedimentation on broad tidal flats, in situ measurements of sediment elevation have been performed in the western part of the Mont-Saint-Michel bay. The amplitude of reworking is generally low (< ± 5 cm), and variable from west to east. The wind influence on tidal currents and surficial reworking emphasizes erosion phases rapidly followed by accretion of similar amplitude on the whole tidal flat. A numerical model for hydrodynamics and sediment transport is applied to Mont Saint Michel Bay, where ecological concerns are related to sediment transfers., Les rythmes et l'ampleur des processus « érosion-sédimentation » ont été suivis, à trois échelles de temps, sur le vaste estran sablo-vaseux de la partie occidentale de la baie du Mont-Saint-Michel. Les mesures in situ du niveau de l'interface eau-sédiment montrent que l'amplitude générale des remaniements est généralement inférieure à 5 cm et variable d'ouest en est. L'influence du vent sur les remaniements superficiels souligne des phases d'érosion rapidement suivies par des phases de sédimentation de même amplitude sur l'ensemble de l'estran. Un modèle numérique hydro-sédimentaire, validé par des mesures sur l'estran, permet de simuler les courants et les transferts de sédiments en zone intertidale.

Tidal environments in the western part of Mont-Saint-Michel Bay, reputed for its large tidal range, comprise numerous shore-parallel bars and banks consisting of coarse biogenic sands rich in well-preserved shells. The shell banks can be grouped into three morphological types according to their size and their position within the tidal environments: salt marsh banks, upper tidal flat banks and mid- to upper tidal flat banks. The mid- to upper tidal flat banks migrate shoreward, at rates of several tens of m/year, from the lower tidal flat towards the Duchess Anne dyke, which forms the present shoreline, and which was built in the 11th century to protect a coastal marsh, the Dol Marsh, from marine influence. The salt marsh banks are relatively stable, their migration rates not exceeding a few cm/year. The morphodynamic study of these sedimentary bodies highlights various stages of evolution from the western to the eastern part of the bay, depending on exposure to wave action which drives bank migration. The oldest, almost fossil salt marsh banks, are situated in the western part of the bay, while recent dynamic tidal flat banks develop in the more exposed eastern part. The upper tidal flat banks are gradually forming an almost continuous barrier located a few hundred metres in front of an old shell barrier on which the Duchess Anne dyke was built., Résumé Dans la partie occidentale de la baie du Mont-Saint-Michel, le haut estran est caractérisé par la présence de nombreux bancs coquilliers, alignés parallèlement au trait de côte et dont la morphologie et la dynamique sont liées à l'action des houles. Selon leur position sur le haut estran et leur taille, trois types morphologiques de bancs peuvent être reconnus depuis les parties les plus hautes du schorre jusqu'à la haute slikke. Ces accumulations calcaires migrent depuis le bas estran jusqu'à la digue qui marque le trait de côte à des vitesses qui varient de quelques dizaines de cm parlan pour les bancs de schorre, presque stables, à plusieurs dizaines de m/an pour les bancs ď estran qui viennent conforter les bancs de haute slikke qui forment la bordure du schorre. L'étude morpho-dynamique de ces corps sédimentaires met en évidence différents stades d'évolution depuis les bancs les plus anciens, presque fossiles, de la partie occidentale jusqu'aux bancs récents et très mobiles de la partie orientale. Les bancs de haute slikke constituent progressivement une barrière littorale presque continue, située à quelques centaines de mètres en avant des anciens cordons littoraux, sur lesquels a été édifiée au xi' siècle la digue de la Duchesse Anne afin d'isoler le marais de Dol des influences marines., Bonnot-Courtois Chantal, Fournier Jérôme, Dréau Alain. Recent morphodynamics of shell banks in the western part of the Bay of Mont-Saint-Michel (France) / Morphodynamique actuelle des bancs coquilliers dans la partie occidentale de la baie du Mont-Saint-Michel (France). In: Géomorphologie : relief, processus, environnement, Janvier-mars, vol. 10, n°1. pp. 65-79.

Due to its exceptional tidal range and the immensity of its tidal flat, the Mont-Saint-Michel bay is a favored model for research on coastal hydro-sedimentary processes, reconstruction of the depositional wedge during the Holocene, and landscape evolution. The western tidal flat consists of a large muddy to sandy embayment, whereas the eastern intertidal domain consists of estuarine deposits characterized by finely laminated muddy sand, enriched in biogenic carbonate. The present-day morphology and sedimentary dynamics are the result of a complex balance between tide-dominated sediment supply and erosive processes under wave action and tidal channels migration. The bay has been filled for thousands of years to the rhythm of sea level oscillations, leading to the gradual progradation of the shoreline. In addition to this natural evolution, human activities have developed in the bay, both on the western tidal flat (fixed fisheries and shellfish farming) and on the eastern estuarine side (polder formation, dikes, and dam construction), and have progressively changed the landscapes. In 1884, Victor Hugo issued an appeal for the protection of the Mont-Saint-Michel in these terms: “The Mont-Saint-Michel is to France what the Great Pyramid is to Egypt. It must be protected from any damage. The Mont-Saint-Michel must remain an island. This combined work of nature and art must be conserved at all costs.” Since that time, salt marshes have progressed, the land reclamation and man-made developments to facilitate the access to the mount also continued, so the maritime character of Mont is still endangered.

Dans le cadre de la rehabilitation et de l'amenagement du polder de Ploubalay (Cotes d'Armor), des etudes geomorphologiques, sedimentologiques et hydrologiques ont ete menees afin de definir les possibilites de developper les potentialites de ce secteur. La fragilite de certaines parties de la digue, ancien ouvrage en terre, et l'analyse des niveaux de submersion soulignent les risques d'inondation de l'ensemble du polder. Une remise en eau partielle par creation de mares peut etre envisagee dans des conditions topographiques strictement definies afin de restaurer les caracteristiques ecologiques de cette zone humide littorale.

Some antique maps (manuscripts, or prints ranging from 1680 to 1836) are kept in various french libraries. The reliability of three groups of maps, exactly surveyed at large scale, provides satisfying reconstitution of the shoreline evolution. The related historical background and the critical analysis of the maps enhances various aspects of the shoreline variations up to present time., Parmi les sources (manuscrites et imprimées), versées dans plusieurs fonds d'archives, trois types de cartes détaillées levées avec exactitude et à grande échelle entre 1680 et 1836, permettent de retracer l'évolution de l'estran entre Tréveneuc et Plurien. Une analyse critique de chaque document, replacé dans le contexte historique de sa rédaction, fait ressortir les traits majeurs de l'évolution du rivage., Bousquet-Bressolier Catherine, Bonnot-Courtois Chantal. Reconstitution historique de l'évolution d'un littoral depuis la fin du XVIIe siècle : la baie de Saint-Brieuc. In: Norois, n°177, Janvier-Mars 1998. pp. 33-49.

International audience; The relationship between short-term morphodynamics and internal structure of shelly chenier ridges is investigated using ground-penetrating radar and core X-ray analysis, complemented with a comparison of aerial photographs. These cheniers are located on the uppermost part of a macrotidal flat in Mont-Saint- Michel bay (North-Western France). They actively migrate landward over the salt-marshes by washover processes when they are submerged during the coincidence of spring tides and enhanced wave activity. The architecture of the cheniers is imaged using high-frequency radar antennas (400 MHz to 2.6 GHz). Three types of cheniers are recognized, featuring differences in morphology and internal structure. The altitude of the banks on the tidal flat relative to the level of tidal flooding, as well as local sediment supply, seem to be important forcing parameters in chenier development and stages of evolution. On a multi-annual time scale, evolution of this chenier system is influenced by a combination of the 18-year and the 4-year tidal cycles, superimposed on wave activity. During minima of the 18-year cycle, spring tide level is globally lower on the tidal flat, allowing salt marsh progradation and chenier ridge development. During peak periods of the tidal cycle, former barriers are reworked by wave action and experience onshore migration associated with salt marsh erosion. The 4-year tidal cycle coupled with enhanced wave activity is probably responsible for the deposition of large washover units, observed in GPR reflection profiles.

Leaching with 1 N HCl, 1 N NH4Cl, acetone, humic acid extracts, cation-exchange resin and NH4-EDTA have negligible effects on the RbSr and KAr systems of different size fractions (< 0.4 and 0.8–2 αm) of a 1M diagenetic illite. None of these treatments, including the 1 N HCl treatment, induced preferential removal of radiogenic 87Sr and 40Ar from mineral structures. However, the 1 N HCl treatment removed significant amounts of Sr and REE, as compared to the treatments by NH4-EDTA and cation-exchange resin. However, much of these HCl-derived elements resided in non-clay minerals such as carbonate and Fe-oxide phases. The KAr and RbSr ages of the samples were not affected by the HCl treatment any more than by the NH4-EDTA or the cation-exchange resin. Because of potential loss of solid material during elutriation of differentially treated samples, the HCl treatment is preferred over other methods allowing sufficient controls on the isotopic and mass balances between the leachate and the corresponding residue of an untreated sample. For RbSr isotopic dating purposes of clay minerals from sedimentary and metasedimentary rocks, leaching experiments give information about the ambient environment of crystallization. Analysis of both the leachate and residue under carefully controlled conditions is recommended.

Bonnot-Courtois C. Le laboratoire de géomorphologie de l'E.P.H.E. en 1991 et 1992. In: Norois, n°160, Octobre-Décembre 1993. pp. 673-685.

International audience

The Lancieux Bay and the Arguenon estuary are located in the Saint-Malo Gulf, along the southern part of the normand-breton Gulf, at places where coastal dynamics are conspicuously efficient. As being protected from the dominant eastward longshore currents by headlands such as cape Fréhel, these sheltered inlets are the site of a fine-grained sedimentation. At the mouth of Arguenon estuary, the mudsilty sedimentation is favoured by the presence of shellfish farming settings which enhance a natural tendancy for tidal-flat enrichment. Sediment deposition due to calm marine conditions and organic detrital excretion are both responsible for the mud intertidal accretion., RÉSUMÉ L'estuaire de l'Arguenon et la baie de Lancieux sont situés dans le Golfe de Saint-Malo, au sud du Golfe normand-breton dans une région où les agents dynamiques sont particulièrement efficaces. Cependant, la position d'abri qu'offre le cap Fréhel à ces baies les protège de la circulation dominante d'ouest, d'où une sédimentation essentiellement constituée de vase et de sables fins. Dans l'estuaire de l'Arguenon, la sédimentation fine est renforcée par la présence d'installations conchylicoles à son embouchure, ce qui, en freinant la propagation des agents hydrodynamiques, accentue la tendance à l'envasement déjà sensible dans la partie amont de l'estuaire ; à ce premier impact, purement mécanique, s'ajoute un impact biologique dû aux rejets des mollusques., Vaucourt C, Bonnot-Courtois C. Dynamique sédimentaire dans les baies de Lancieux et de l'Arguenon (Côte-d'Armor). In: Norois, n°153, Janvier-Mars 1992. pp. 29-44.

The aim of this study concerns the understanding of the littoral risks along the entire coastline of the Cotes d’Armor county (northern Brittany coast, France). Coastal hazards were characterized and classified into several types according to the different geomorphological features. All the different types of coastal geomorphology occur in this area : igneous or sedimentary-rock cliffs, shingle bars, sandy beaches, muddy embayment, estuaries, coastal dunes, dykes and seawalls. The present-day status of the erosion was mapped overall the coastline. Different types of hazards were recognized and recommendations can be applied for the coastline management. Mots Cles : Erosion cotiere Aleas Enjeux Cartographie Bretagne Nord. 191 Xemes Journees Nationales Genie Cotier – Genie Civil, 14-16 octobre 2008, Sophia Antipolis

Mineralogical (XRD), morphological (transmission electron microscopy), chemical (major, rare-earth elements, and scanning-transmission electron microscopy), and isotope (Sr, O, H) measurements were made of marine detrital smectite from shales to study their reactions during early diagenesis. Albian, Aptian, and Palaeogene smectite samples were selected from Deep Sea Drilling Project drill cores taken in the Atlantic Ocean and from outcrops and drill cores from Belgium and northern France. Detrital, fake-like smectite particles seem to have adapted to their depositional environment by isochemical dissolution and subsequent crystallization of authigenic, lath-like particles. The major-element and rare-earth element compositions of both types of particles are similar. The Sr isotope chemistry suggests that the dissolution-crystallization process occurred soon after deposition in an almost closed chemical system. Except for slight changes in the amount of Fe and the oxygen isotope composition, the reaction took place without noticeable chemical exchange with the interstitial or marine environment. Such closed-system recrystallization of clay minerals may be a common diagenetic process if the water/rock ratio is small, as in shales.

Resume Le loch Sunart constitue le receptacle d’une sedimentation importante, propice a l’enregistrement des variations climatiques sur la marge nord-est de l’Atlantique. Les resultats d’une campagne de prospection sismique tres haute resolution (Boomer Seistec) permettent de mettre en evidence cinq facies acoustiques qui ont ete correles a certaines caracteristiques des sediments d’une carotte profonde (de grande section). Des analyses granulometriques, morphoscopiques et palynologiques, completees par trois datations au 14C, permettent de retracer l’evolution de la sedimentation et des paleoenvironnements depuis le debut de la deglaciation, mettant en evidence les refroidissements de 8200, 5500 et 3500 ans cal. BP, ainsi que le petit âge glaciaire.

The western part of the Mont Saint-Michel Bay is characterized by very extended mud- to sand-flats, predominantly subject to tidal currents, episodically to wave action. In order to define and quantify the rhythm and amplitude of the processes of erosion and sedimentation on such broad tidal flats, measurements of sediment elevation have been performed along three cross-shore profiles. Each profile, few kilometers long, is representative of the different sedimentary environments of the western bay. Monthly measurements, realized during high spring tides, evidence that the amplitude of reworking is generally low (< ± 5 cm), and variable from west to east : relatively high at Cancale and Vilde-Hirel, it is much lower at Cherrueix. During storm events, especially during winter season, the whole flat experiences severe erosion of decimetric scale, which is however

International audience; This study presents a combinated approach of the coastal area of the "Sables-d'Or" with acoustic and optical data. A sand spit, covered by dunes, which isolates a lagunal system behind it, constitutes this coastal portion. The acoustic imageries of the sedimentary structures, identified on the aerial photographs (optical imageries), show: seagrasses meadows which grow in shallow waters on sandy substratum near lowest tide sea level; a sandy ridges system of large extension from the middle to the lower beach; a flood delat developed at the internal extremity of the sand spit and, eventually, the internal mud flats colonized by the halophile vegetation (salt marsh) with external edges invaded by sands. Thus, the combination of sonar data, aerial pictures and field work observation allows a very precise description of the different morpho-sedimentary structures. This double approach constitutes a fast and relliable survey method, perfectly adapted to follow the evolution of the coastal area.; Etudié selon une double approche, acoustique et optique, le littoral de Sables d’Or est formé d’une longue flèche sableuse surmontée d’un massif dunaire, qui isole en arrière d’elle une lagune côtière. Les images acoustiques des unités morpho-sédimentaires identifiées sur les photographies aériennes (images optiques) révèlent : * les herbiers de zostères qui se développent au niveau des plus basses mers sur les petits fonds sableux de l’avant-côte ; * le système de rides sableuses de grande extension qui occupent la basse et la moyenne plage; le delta de flot qui s’étend à l’extrémité interne de la flèche littorale; * et enfin les vasières internes de la lagune, colonisées par la végétation halophile (le schorre) dont la bordure externe est envahie par les sables. Ainsi, la combinaison des images sonar et des photographies aériennes – validée par des observations de terrain - permet une description qualitative et quantitative (amplitudes et longueurs d’onde) des différentes unités morpho-sédimentaires. Cette double approche permet une reconnaissance rapide et fiable, donc parfaitement adaptée, pour un suivi d’évolution du littoral

Etudie selon une double approche, acoustique et optique, le littoral de Sables d’Or est forme d’une longue fleche sableuse surmontee d’un massif dunaire, qui isole en arriere d’elle une lagune cotiere. Les images acoustiques des unites morpho-sedimentaires identifiees sur les photographies aeriennes (images optiques) revelent : * les herbiers de zosteres qui se developpent au niveau des plus basses mers sur les petits fonds sableux de l’avant-cote ; * le systeme de rides sableuses de grande extension qui occupent la basse et la moyenne plage; le delta de flot qui s’etend a l’extremite interne de la fleche littorale; * et enfin les vasieres internes de la lagune, colonisees par la vegetation halophile (le schorre) dont la bordure externe est envahie par les sables. Ainsi, la combinaison des images sonar et des photographies aeriennes – validee par des observations de terrain - permet une description qualitative et quantitative (amplitudes et longueurs d’onde) des differentes unites morpho-sedimentaires. Cette double approche permet une reconnaissance rapide et fiable, donc parfaitement adaptee, pour un suivi d’evolution du littoral

The dynamics of the upper tidal flat is the most important factor which determines the nature of sediments and their accumulation rate at the schorre edge. The supply of suspended matter depends on the width and the slope of the tidal fiat in front of the schorre. The sediment trapped in the upper tidal fiat is directly related to submersion levels and decreases from the lower to the upper part of the schorre. Sedimentation rates vary from 1-2cm/year at the schorre edges evolving in a calm environment, to 8-12cm/year at schorre edges in dynamic situation.

From geomorphology and coastal evolution, three units can be distinguished in the Bay of Saint-Brieuc. A previous study, based on the comparison of geomorphical characters obtained from historical analysis of the shoreline after antique maps, emphasized continuity or discontinuity of the shoreline evolution up to present day. Main geomorphological features of the Bay of Saint-Brieuc are described and equilibrium weakness zones are pointed out and related to marine, continental or anthropic erosion processes., A l'échelle de la baie de Saint-Brieuc, la géomorphologie des rivages fait ressortir de grandes unités dont l'évolution diffère. La comparaison avec les résultats d' un précédent article sur l'évolution des estrans à l 'échelle historique, fait apparaître des continuités et des discontinuités importantes pour l' interprétation de l'évolution actuelle. Les principales caractéristiques géomorphologiques du littoral de la baie sont mises en évidence ainsi que la vulnérabilité du trait de côte aux divers processus d'érosion marine, continentale ou anthropique., Bousquet-Bressolier Catherine, Bonnot-Courtois C. Géomorphologie et vulnérabilité des rivages de la baie de Saint-Brieuc. In: Norois, n°179, Juillet-Septembre 1998. pp. 495-506.

In the western sector of the bay of Mont Saint-Michel, the upper tidal zone consists of large tidal flats covered by numerous shell-ridges that move toward the coastline and extended salt marshes that present a specific morphology at the drainage channel outlets. The natural sedimentological behaviour of this area consists of a progressive and continuous sedimentation that guides the human activities in the littoral zone. Calcareous sediments and shellbanks exploitation, salt-marsh grazing, oyster and mussel farming have been developed from the specific characteristics of this very large tidal area. Although there has been no abrupt break, a change in the ideas concerning the occupance and utilisation of the upper tidal flats can be observed which has shifted towards a greater consideration of the natural factors in the environnement., Le haut estran de la partie occidentale de la baie du Mont Saint-Michel comprend de vastes zones de slikkes accidentées de nombreux bancs sableux coquilliers qui progressent vers la côte et viennent border un schorre peu développé qui présente une géomorphologie particulière au débouché des canaux de drainage du marais. La dynamique sédimentaire naturelle de cet espace littoral consiste en un colmatage progressif qui s'effectue avec une continuité qui a orienté l'utilisation humaine du littoral. L'exploitation de la tangue et des bancs coquilliers comme amendement calcaire, le pâturage des prés salés, la conchyliculture et la vocation du port mytilicole du Vivier-sur-Mer sont autant d'activités qui se sont développées à partir des potentialités et des particularités de cette vaste zone intertidale. Sans qu'il y ait une rupture brutale, on observe un changement dans les conceptions de l'occupation et de l'utilisation de l'estran qui s'orientent vers une meilleure prise en compte des données naturelles du milieu., Bonnot-Courtois Chantal, Verger Fernand, Le Vot Monique, Ghirardi Raymond. Cartographie et évolution du haut estran dans la partie occidentale de la baie du Mont Saint-Michel (France) / Cartography and evolution of the upper tidal zone in the western sector of the bay of Mont Saint-Michel (France). In: Cahiers du Centre nantais de recherche pour l'aménagement régional, n°47-48, 1997. Littoral 95 - Actes du Colloque International Continuités et ruptures sur les littoraux européens. pp. 281-288.

L'estuaire de la Rance est un exemple unique d'implantation d'une usine maremotrice mise en service il y a trente ans dans un secteur a tres fortes marees et sur un fleuve a faible debit. La construction du barrage puis l'exploitation de l'usine ont entraine des modifications hydrologiques qui ont eu des consequences sur la sedimentation et l'environnement du milieu estuarien. Les premiers resultats des analyses sedimerttologiques et micropaIeontoIogiques, ainsi que des essais de datation sur quelques carottes prelevees a l'interieur et a l'exterieur du bassin de retenue mettent en evidence les changements intervenus dans les conditions de sedimentation des vases estuariennes.

Located on the eastern coast of St Brieuc bay, the Sables d’Or les Pins beach is formed by a sand spit, covered by dunes, isolating an internal lagoon from the sea. Morphological, topographical and sedimentological surveys emphasize the coastal evolution : erosion processes occur at the eastern part of the spit whereas longshore current produces sand drifting towards the western head of the spit., La plage des Sables d'Or les Pins, située sur la côte Est de la baie de Saint-Brieuc, est adossée à une flèche littorale sableuse surmontée de massifs dunaires. La flèche s'étend d'Est en Ouest sur une longueur de près de 2 km et subit des érosions importantes dans sa partie centrale, tandis que son extrémité progresse vers l'Ouest, isolant derrière elle une lagune en voie de colmatage. L'analyse morphologique, topographique et sédimentologique du site permet de mettre en évidence la dynamique sédimentaire qui y règne et de suivre son évolution. L'érosion des massifs dunaires et le recul du trait de côte observé depuis plusieurs années nécessitent des aménagements en vue de protéger l'environnement et les installations de la station touristique des Sables d'Or., Bonnot-Courtois Chantal, Lafond Louis-Robert. Dynamique sédimentaire du littoral de Sables d'Or les Pins (Côtes d'Armor). In: Cahiers du Centre nantais de recherche pour l'aménagement régional, n°41-42, 1994. Défense des côtes ou protection de l'espace littoral, quelles perspectives ? Actes du colloque international (17-20 octobre 1991) pp. 106-115.

Bonnot-Courtois C, Verger Fernand, Lafond Louis Robert, Le Rhun Jeannine. Le laboratoire de géomorphologie de l'Ecole Pratique des Hautes Etudes en 1989-1990. In: Norois, n°151, Juillet-Septembre 1991. pp. 315-322.

The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, δD, δ18O) and chemical (REE, H2O+) compositions of biotite has been studied on a suite of migmatitic biotites from the Chad Republic. During the early stages of weathering the Rb-Sr system is strongly affected, the hydrogen and oxygen isotope compositions change markedly, the minerals are depleted in light REE, the water content increases by a factor of two, and the K-Ar system is relatively little disturbed. During intensive weathering the K-Ar system is more strongly disturbed than the Rb-Sr system. Most of the isotopic and chemical modifications take place under nonequilibrium conditions and occur before newly formed kaolinite and/or smectite can be detected. These observations suggest that 1. (a) “protominerals” may form within the biotite structure during the initial period of weathering, and 2. (b) only when chemical equilibrium is approached in the weathering profile are new minerals able to form.

Hydrothermal deposits “sensu stricto” have been recovered during the FAMOUS cruise and Leg 54 of the Deep Sea Drilling Project near the Galapagos Spreading Centre. The studied sediments, mainly composed of clay material, have very poor REE concentrations, below about ten ppm. The shale-normalized patterns are characterized by a significant enrichment in heavy rare earths and show a negative Ce anomaly. The magnitude of this anomaly fluctuates but is generally lower than the seawater Ce anomaly. The geochemical characteristics of these hydrothermal deposits are in contrast with those of metalliferous sediments which are more enriched in trace elements, especially in REE.

In central Baja California (Vizcaino Peninsula, and Cedros and San Benito Islands) two distinct radiolarian bedded chert sequences of late Triassic and late Jurassic/lowermost Cretaceous age, can be differentiated on lithostratigraphic and geochemical criteria. These bedded chert sequences are part of the conformable sedimentary cover of more or less dismembered ophiolites, which are overthrusted by the San Andres-Cedros volcanic arc system of middle late Jurassic age. Major and trace elements permit paleogeographic zonation of the late Jurassic/lowermost Cretaceous radiolarites lying conformably upon ophiolites considered as fragments of an oceanic basin floor which developed westward of the San Andres volcanic arc. Progressive accretion of this oceanic basin floor, along the continental margin is supported by the fact that the more distal radiolarian chert sequences belong to the lowermost structural units of this area.

The pyroclastic deposit drilled at site 123 is a rhyodacitic material. Major and rare-earth element abundances in these volcanic rocks suggest that they are the result of a differentiation process by fractional crystallization from a calc-alkaline magma. The vertical variation of mineralogy and chemistry of this deposit is the result of three superposed stages of weathering. The first is aerial weathering, the second is the product of alkaline brines, and the third is a hydrothermal alteration. The K Ar age of the pyroclastic deposit is 23.8 ± 1.2 m.y.; this age is not disturbed by the presence of phillipsite; consequently, the first two alteration stages are very early. The existence of these two stages implies that the age of opening of the Valencia Trough begins at the Oligocene—Aquitanian boundary after the eruptive stage.

Rare-earth element (REE) distributions in altered basalts and glasses collected during some Legs of the Deep Sea Drilling Project show that a fractionation of these elements occurs during submarine weathering. When the alteration is well-marked, the REE distribution in altered glasses shows an enrichment in light rare-earths relative to the fresh glass. In particular, Ce is selectively enriched in palagonitized glasses that comprise, besides polymetallic nodules, another phase liable to explain the Ce depletion in seawater. Taking in account these processes of submarine weathering of the oceanic crust, a geochemical balance of Ce between authigenic phases of the marine environment is attempted.

The major element chemistry and the rare earth element (REE) distribution of sedimentary smectite and diagenetic clinoptilolite from the lacustrine volcanic-sedimentary succession near Bigadic in northwestern Anatolia, Turkey, suggest a constant influx of volcanogenic material into the basin with, especially, a systematic negative Eu anomaly. This is supported by the Sr isotope chemistry which shows slight differences in the 87 Sr/ 86 Sr of the sedimentary phases (carbonates and smectites) with values between 0.70835±7and0.70859±9 and the diagenetic clinoptilolite with values between0.70861±8and0.70893±17. This lacustrine volcanic-sedimentary succession is Early to Middle Miocene in age, with K Ar values for the biotite and hornblende of the basal volcanic rocks showing an average age of ∼22 Ma. The K Ar data of the clinoptilolite are strongly dependent on the permeability of the tuffaceous host rocks. They suggest an age of ∼14 Ma for the end of the diagenetic recrystallization of the clinoptilolite in impermeable rocks, and further chemical exchange with the interstitial fluids in the permeable rocks. This latter process induced a loss of radiogenic 40 Ar and REE out of the zeolites from the permeable tuffs, and might have had an influence on their chemical composition.

Resume Dans une serie de hyaloclastites et dans des basaltes de l'ocean Indien, les progres de l'alteration sous-marine de materiel volcanique se manifestent par l'introduction ou l'augmentation relative du fer dans le reseau des smectites. Au depart, les smectites magnesiennes, parfois accompagnees de smectites alumineuses, dominent puis sont progressivement remplacees par des smectites ferriferes. La distribution des terres rares dans ces mineraux varie en fonction de la composition des verres originels. Elle est identiqueacelle du verre frais dans les premiers stades de l'alteration, mais, lorsque les smectites ferriferes se developpent, le cerium a un comportement specifique qui peuteˆtre relieadifferents modes de formation de ces mineraux. Il presente une anomalie positive dans les smectites ferriferes formees precocement dans les verres palagonitises et une anomalie negative dans les smectites ferriferes neoformees plus tardivementapartir de solutions enequilibre avec l'eau de mer.

The French coastline has suffered from maritime pollution since the 1960's (Torrey Canyon, Amoco Cadiz, Erika, Ievoli Sun, Prestige, etc.). Has management developed by French authorities to cope with maritime pollution been adapted to risks? How have the means allowed to crisis management developed? Does contingency planning fulfill its objectives? The study deals with an evaluation of maritime pollution risks along the French coastline, an analysis of the evolution of crisis management from Torrey Canyon to Prestige, the main current changes since 2002 and the potential improvements. Thanks to many current changes, this study is a topic question (Civil Safety Modernization Law, local contingency planning, new stakeholders involved, etc.). Beyond a strong bibliographic analysis, the study is based on several surveys concerning local and national authorities. As project manager in Vigipol (local authority focused on maritime safety), the author gives her research an operational approach, especially through the creation of local contingency plans and management of several crises (Prestige and MSC Napoli). Finally, two foreign systems of maritime pollution management (Great Britain and Alaska) are compared to the French one in order to find potential improvements based on exchange of good practices., Le littoral métropolitain a subi de nombreuses pollutions maritimes de grande ampleur depuis les années 1960 (Torrey Canyon, Amoco Cadiz, Erika, Ievoli Sun, Prestige, etc.). L'organisation mise en place par la France pour gérer les pollutions maritimes accidentelles est-elle, et fut-elle, adaptée aux risques présents sur les façades maritimes françaises ? Comment et pourquoi les moyens mis en œuvre ont-ils évolué en France depuis les années 1960 ? Cette organisation est-elle capable de gérer efficacement une pollution maritime accidentelle depuis les années 1960 ? L'étude repose sur un diagnostic des risques de pollution maritime accidentelle au large des côtes françaises, sur l'analyse de l'évolution de la gestion des pollutions maritimes en France du Torrey Canyon au Prestige, sur le suivi des mutations en cours depuis le Prestige en 2002 et les perspectives d'amélioration. D'importantes mutations en cours au niveau national et européen donnent au sujet une forte actualité (loi de modernisation de la sécurité civile du 13 août 2004, mise en place des Plans Communaux de Sauvegarde, émergence de nouveaux acteurs). Cette étude, au-delà d'une vaste analyse bibliographique, se fonde sur des entretiens avec l'ensemble des acteurs de la gestion des pollutions maritimes et sur plusieurs enquêtes menées auprès des élus locaux du littoral nord de la Bretagne et des préfectures de département littoraux. Son rôle de chargée de mission à Vigipol (syndicat mixte de protection du littoral breton) a permis à l'auteur de donner un caractère directement opérationnel à ses recherches, notamment au travers de la mise en place de plans Infra POLMAR et la gestion de plusieurs pollutions (Prestige et MSC Napoli). Enfin, deux modèles étrangers (Royaume-Uni et Alaska) ont été comparés au plan POLMAR français afin de dégager de potentielles améliorations issues de l'échange de bonnes pratiques.