The buildup of a continental rise and its morphological patterns depend on sediment transport and deposition via downslope slumps, turbidity currents, along-slope contourites and other deepwater currents. These delivery mechanisms are central to source-to-sink reconstructions, yet untangling their individual roles is not straightforward. The current study focuses on the sink section of the Nile system at the northern Levant continental rise (eastern Mediterranean). During the Pliocene, fluvial systems from northern Africa and the Levant margin supplied sediments to the study area. This supply decreased significantly during the Quaternary because of two processes: (a) The aridification of North Africa made the Nile River the predominant contributor to the basin; (b) the topographic rise of the Levant landmass severely limited fluvial supply. Meanwhile, on-going counter-clockwise marine currents became the prevalent supply system to the Levant margin, and downslope sediment-transport became the only source to the northern Levant continental rise, which became a significant sink of the larger Nile system. These conditions provide an excellent natural laboratory for understanding the individual role of downslope sediment-transport processes in building a continental rise. This research is based on single-channel sparker seismic data, multibeam bathymetry and four 7–8 m long piston-cores collected over the northern Levant continental rise at water depths of 1200–1800 m, together with available multibeam bathymetry and industrial multi-channel seismic reflection data. The results show a major depositional changeover during the Pliocene-Quaternary transition from concordant aggradation to repeated deposition of >12 sediment wave subunits, interpreted as upslope migrating cyclic steps. Quantitative analysis of the sediment wave morphology at the seafloor and subsurface, along with core data, indicates that the immediate sediment source was the nearby shelf. The supply was regulated by basinward-landward shifts of the shore-parallel marine currents during lowstand-highstand conditions (respectively). Hence, this case study highlights the connection between sea-level change and sedimentation patterns on a continental rise.
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© 2021 International Association of Sedimentologists and European Association of Geoscientists and Engineers and John Wiley & Sons Ltd
- continental rise
- seafloor morphology
- sediment waves
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