Architecture et dynamique sédimentaire d'une pente carbonatée moderne : exemple de la pente nord de Little Bahama Bank (LBB), Bahamas

摘要

This study focuses on the architectures and the sedimentary dynamic of a carbonate slope located on the northern part of Little Bahama Bank (Bahamas) using a dataset composed of multibeam echo sounder,subbottom profiler (Chirp) and High-Resolution (HR) multichannel seismic collected during the Carambar 1cruise (2010). A morpho-sedimentary surface analysis defines the physiographic domains and the architectural elements of the slope and investigates the spatial distribution of sediments in the context of the current sea-level highstand. It reveals a slope dominated by periplatform ooze with several levels of induration and incised by numerous slides and submarine canyons. The spatial variability of off-bank transport, combined with the lateral variability of the Antilles Current intensity, are at the origin of a morphological evolution from west to east in the study area. In the western part, the slope is around twice as large as the eastern part and can be considered as a prograding system. The eastern slope is marked by bypass processes. Indeed, numerous submarine canyons are visible on the seafloor and are connected to several shallow distributary furrows feeding confined depositional areas. An integrated study allows a high resolution characterisation of slides and submarines canyons and enables us to propose a model of formation. These architectural elements are initiated by intra-slope destabilisations and their evolution is controlled by phases of retrogressive erosion,pelagic sedimentation and muddy gravity flows. Finally, a seismo-stratigraphic analysis allow to reconstitutethe tectonic and sedimentary evolution of the slope since the Albian to the present-day by establishing a link with the geodynamic context of Caraïbes, relative sea-level changes and the carbonate production on the platform.