Structuration et dynamique sédimentaire de la plate-forme sous-marine armoricaine : de l’analyse des habitats marins actuels aux processus biosédimentaires fossiles

This manuscript provides an overview of siliciclastic systems in macrotidal and temperate environments. The first section reviews the principles governing sedimentary models in the Armorican submarine platform environment, bordered by the English Channel and the Bay of Biscay. Work carried out over the past 25 years on this geological area has examined the relationships between coastal sedimentation and controlling factors, such as current dynamics and geomorphology, and between sand bedforms dynamics and the available sediment stock. The collected data provides a new perspective on the organisation of sediment transfers in a typical section of the shelf between the Brest estuary and the Iroise Sea. Studies conducted on the north coast of Brittany have revealed a new pattern of residual sediment transport in the context of high sea level, reinforcing geological expertise on this platform and having significant societal implications. The first part also reviews our knowledge of a unique coastal fluid system in a small Tertiary carbonate basin in Concarneau Bay. This is one of the few documented examples that illustrates the simultaneous presence of dense surface colonies of gregarious tubiculous amphipod (Haploops genus) and fluid escape features (pockmarks). The second part examines the relationships between sedimentation and macrobenthic species, particularly those known as 'engineers'. Once characterised, the importance of biological processes in understanding long-term deposition processes on the coast becomes apparent. Crepidula beds transform dynamic sands into subtidal mudflats. Maerl beds provide information on the Holocene history of coastlines and human influence on the environment over several thousand years. Haploops beds demonstrate an opportunistic relationship with a seemingly ‘at rest’ fluid system. Finally, the last section of this thesis presents research prospects for the coming years, focusing on the following four themes: (1) maerl; (2) the Guiana Platform; (3) the geo-biodiversity of the Coral Sea Natural Park seamounts; and (4) the impacts of marine renewable energy on sediment dynamics and biodiversity in the English Channel.