From platform top to adjacent deep sea: New source-to-sink insights into carbonate sediment production and transfer in the SW Indian Ocean (Glorieuses archipelago)

Over the past ten years, a huge amount of source-to-sink studies have aimed to unravel the tectonic, climatic and other processes that shape the landscape from mountains to the deep ocean. Interestingly, these studies have been mainly dedicated to siliciclastic or mixed systems, for which the connection between drainage basins, continental shelves, slope and basin environments are often well constrained. Here we present a study focusing on a source-to-sink study dedicated to a pure carbonate system, located in the SW Indian Ocean (Glorieuses archipelago). Extensive field sampling and geophysical acquisition across the carbonate platform have allowed us to estimate the composition, the lateral variability, and volumes of neritic sands deposited on the platform top. Additional seismic and bathymetric surveys across the platform interior illustrate the presence of plurimetric sandy bodies deposited along the leeward platform edge, corresponding to the export of carbonate sediments from the platform top toward the platform edge, under the influence of dominant currents and winddriven processes. High-resolution seismic, bathymetric data and sediment cores acquired along the leeward slope and basin adjacent to the carbonate platform highlight the presence of channel-levee complexes and turbiditic lobes, which have accumulated on the seafloor on top of a 250 m-thick sedimentary basin at 2000-3400 m water depth. Our study points out that carbonate sands and aragonitic mud produced on the platform top during the Holocene have been shed to the adjacent basin. We also demonstrate that this routing system was active at least throughout the last three glacial/interglacial cycles. This study has important consequences for our understanding of carbonate sedimentation processes occurring in the vicinity of isolated carbonate platforms: 1 - it highlights the role of oceanographic conditions in the distribution of sediment on a platform top and its export along the platform edge and the adjacent basin; 2 - it contributes to quantify the productivity of a carbonate platform as well as its sediment storage capacity; 3 - a first estimate of a carbonate source-to-sink system is proposed, demonstrating that 0,57 km(3) of sediments have been produced during the Holocene, 0,3 km(3) being presently stored on the platform, and the remaining having been exported to the deep basin.