Sediment partitioning and winnowing in a mixedeolian-marine system (Mauritanian shelf)

摘要

Continental shelf systems are highly dynamicsedimentary environments, where sediments from biogenicproduction as well as from terrigenous sources are redis-tributed in the shelf depositional system, and partlyexported off the shelf to the slope and the deep sea. TheGolfe d'Arguin (Mauritania, NW Africa) is dominated bysuch redistribution processes, involving elastic silt importedas dust from the Sahara desert and biogenic carbonates ofmarine origin. Indeed, surface-sediment grain size andmineralogy show a clear north–south partitioning ofsediment type. Fine material is winnowed from the northernpart of the gulf, and transported toward the southern part offthe Banc d'Arguin, where coarse silt settles on the outershelf and upper slope, at least down to 600 m water depth.Particles of the fine silt fraction, estimated in terms ofeolian material collected aboard the research vessel, arethought to be exported further offshore as they correspondto grain sizes previously reported from adjacent deep-seasediments. These findings suggest that the interpretation ofdust records from the continental slope and rise off NWAfrica must consider reworking and partitioning processesactive on the Mauritanian shelf.