Sediment transport and turbidite architecture in the submarine Dakar Canyon off Senegal, NW-Africa

The submarine Dakar Canyon incises the continental margin at the transition of the hyperarid Sahara to the semiarid Sahel Zone, and acts as an effective pathway for gravity-driven sediment transport. Four gravity cores recovered directly from the canyon axis were investigated in order to reconstruct the sedimentation processes in the Dakar Canyon during the Late Quaternary. In addition, a hemipelagic record from the northern levee of the canyon was analysed for monitoring background sediment supply, which is dominated by dust input in the area. Coarse terrigenous silt size data and high Ti/Ca ratios reflect overall increased higher dust supply during the last two peak glacials. During these times wide-extensive sand sea covered the exposed shelf almost completely. However, in interglacial periods wind stress diminished considerably and only minor amounts of dust were supplied to the outer shelf and continental slope. Two major periods of turbidite depositions are recorded in intervals from final glacial sea level lowstands to early deglacial sea level rise of the last two glacial/interglacial cycles (i.e. between 141 and 131 kyr BP and from 23.2 to 14.2 kyr BP). These turbidite deposits consist of sandy to silty sediments. Detailed grain size analyses were used to reconstruct the sedimentary characteristics and flow processes of these turbidity currents. A much higher frequency in turbidite activity occur around 135 kyr BP in contrast to the second interval around 18 kyr BP, suggesting a higher sediment budget in the source area. Based on the sedimentological investigation of the turbidites we provide a schematic model for the sedimentation processes in the Dakar Canyon.

Research highlights
► Two intervals of main turbidite activity around the peak glacials are recorded in the Dakar Canyon.
► High aeolian sediment transport during peak glacials forms large dune fields at the shelf.
► Dune fields are the sediment source for turbidity currents in the Dakar Canyon.
► The results we used to create a schematic model for the sedimentation processes in the Dakar Canon.