Sediment dynamics and geomorphology of a submarine carbonate platform canyon system situated in an arid climate setting

Changes in neritic carbonate production and sediment transport off platforms are related to climate variations, sea-level fluctuations and tectonic processes. Canyon systems marking the platform slopes represent critical source-to-sink pathways transporting shallow-water sediments basinward. However, these export systems and related processes are primarily studied on platform slopes in humid to tropical climate settings. A newly discovered canyon system on the leeward margin of the Al Wajh platform (north-east Red Sea) represents the ideal laboratory to investigate source-to-sink pathway dynamics in an arid climate that prevailed since the Late Pleistocene. A high-resolution bathymetry map was established to characterize the slope morphology. The system displays a U-shaped, 10 km long main channel dominantly sourced by the north-west/south-east running outer channel and two smaller 2 to 3 km long canyons. The latter are positioned perpendicular to the main canyon. A 4 km wide head scarp at the reef edge and dozens of amphitheatre-shaped scarps along the mid to lower slope suggest significant slope failures over time. The analysis of four sediment cores collected on a profile down the canyon revealed sedimentation rates of 26 cm/ka at the mid-slope to 9.4 cm/ka in the basin. Three main sediment-export processes were identified: (i) sandy and neritic component-poor turbidites; (ii) winnowing of strontium-rich carbonate fines through surface currents; and (iii) remobilized carbonate fines on the upper slope. As of the Last Glacial, turbidites are predominantly deposited during times of significant sea-level instability, both rises and falls, whereas their flat-topped-tropical counterparts show a higher turbidite frequency during highstands. Strontium-rich carbonate fines are exported similarly through time in both climate settings. Overall, sediment export is controlled by: (i) the platform morphology (flat-topped versus rimmed lagoon); (ii) variations in sediment production; (iii) sea-level variations (exposure or flooding of sediment production areas); and (iv) the interaction between the sedimentary system and atmospheric changes (sediment production and delivery).