Frequency and timing of landslide-triggered turbidity currents within the Agadir Basin, offshore NW Africa: Are there associations with climate change, sea level change and slope sedimentation rates?

Abstract

Abstract Older sequence stratigraphic models suggested that submarine landslide and turbidite activities are greatest during sea-level lowstands. However, growing evidence indicates that many turbidite systems are also active during sea-level transgressions and highstands. The Moroccan Turbidite System comprises three depocentres, of which Agadir Basin is closest to the Moroccan slope and Canary archipelago. The very large volumes of sediment transported by individual sediment flows in this system suggest that they are triggered by landslides. Extensive core coverage and dating control for the Agadir Basin deposits have provided an excellent opportunity to derive accurate records of turbidite (and associated landslide) frequency for the last 600 ka. Previous studies in the more distal Madeira Abyssal Plain depocentre have indicated that large volume (> 50 km 3 ) turbidites occurred at oxygen isotope stage (OIS) boundaries. This study of Agadir Basin confirms that two major turbidites (beds A5 and A12) occurred during glacial–interglacial transitions associated with OIS4 and OIS6. However, this association is based on just two examples, and two other large-volume turbidites (beds A7 and A11), did not occur at a stage boundary. The main conclusion of this study is that 90% of turbidites and landslides occurred during rising and high sea level, which represents 40% of the total time during the last 600 ka. Only 10% of the turbidites and landslides occurred during glacials (40% of the time), with a paucity of turbidites and landslides at peak glacial lowstands. A comparison to sediment accumulation rates in the source area of the turbidite suggests that landslides did not occur preferentially during periods of more rapid sedimentation rate, although sedimentation rates in this area only varied from 4 to 6 g cm − 2 ka − 1 .