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Theses

Dynamique de comblement d'un bassin sédimentaire soumis à un régime mégatidal : Exemple de la baie du Mont Saint-Michel

Abstract : Search carried out falls under a convention DRET/CNRS relating to the problems of sedimentary dynamics in a bay dominated by the currents of tide. It combines the descriptive study of the units morphosdimentaires the modeling of the phnomnes with the surface of the bottom. Located at the South of the Norman-Breton Gulf, the bay of the Mount-Saint-Michel considered for his exceptional marlings extends as a whole, between the archipelago of the Chausey Islands at North and the coast made up of cliffs briovriennes in the South. One distinguishes thus on both sides from the archipelago two broad master keys. The presence of shallow waters and rocky outcrops locally disturb the gradient decreasing of the currents of tide broad towards the estrans. The flood shorter than the ebb is also more intense. The rivers which are thrown in bay have low flows trs compared to the oscillating volume which penetrates and which is withdrawn with each tide of this vast system in the process of filling. The tidaux currents, temporarily opposed or reinforced by the swells, remain the principal engines of the construction of the Holocene sedimentary prism. The analysis of the sets and the sedimentary bodies of bay is based on a groundwork of sedimentary taking away dense and corings sub-surfaces, on the prospection by sonar with side sweeping, sounder and video camera, like on the installation of courantologic and hydrological stations. The coarse sedimentary cover made up of elements of levelling base, gravel and gravels occupies the central part of bay subjected to the strongest currents of tide. These hard funds of type "gravel lag " are not very mobile but are the seat of a strong surface sedimentary dynamics organized in the form of a hairy network of rectilinear sandy ribbons. The limits of the sandy prism begin around 10 m of depth. The influence of the rock courses of Grouin, Granville and Champeaux on the propagation of the tidal wave is the origin of modelled sound and advanced gravelly tablecloth until the intertidal field in certain sectors. Thus three broad sandy corridors put in contact the delta of tide, vast mobile fine sand trap and these coarse funds. The coastal banks of maritime bay are connected to the littoral prism. Their morphology as that of the associated dunes tidales is controlled by the currents of tide chenalized between the depressions dug around the point of Grouin. The sandy prism which rests between Granville and the point of Champeaux is also modelled banks and large dunes tidales. More open towards the West, it is also more subjected to the action of the oceanic swells. The conditions of weak bathymetry and the agitation of the water level destabilize the morphology of these structures. in this environment where the sequence sedimentary maintain well establish be organize according to the intensity of current of tide, the proliferation of crepidule for 30 year be a element new and significant in the distribution of facies sedimentary. The alive and dead biomass is estimated 214 000 T. between 0 and 10 m of depth. The production of bioagregats and their trapping in the colonies support the installation of mudholes in mediums hitherto unfavorable to the deposits of the muds and their stabilization. the convergence of result of various method indirect of determination of direction and of direction of transit sedimentary show the existence with scale of bay of vast corridor of transit of sediment since the broad towards the field intertidal, the presence of area source bus potentially rodables and close of zone with strong assessment sedimentary and of trap sedimentary mobile be useful of relay the dynamics of sediment which come himself accumulate in the bay Eastern. the volume of sand calculate by the code numrique and penetrating in the system pre-estuarien starting from tide of VE average, have be evaluate with 500000 m3/an, the volume of suspension cross the radial nozzle of Andaine-Hermelle with 900000 m3/an. These computed values under conditions of null agitation recut former work but are probably undervalued. They stress the importance of the hydrodynamic phenomena controlled by the currents of tide in this area of the Sleeve.
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Contributor : Axel Ehrhold <>
Submitted on : Tuesday, January 27, 2004 - 9:33:41 AM
Last modification on : Monday, April 27, 2020 - 4:26:29 PM
Long-term archiving on: : Wednesday, September 12, 2012 - 12:55:18 PM

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  • HAL Id : tel-00004311, version 1

Citation

Axel Ehrhold. Dynamique de comblement d'un bassin sédimentaire soumis à un régime mégatidal : Exemple de la baie du Mont Saint-Michel. Minéralogie. Université de Caen, 1999. Français. ⟨tel-00004311⟩

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