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

ABSTRACT

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).