Investigating the timing, processes and deposits of one the World¹s largest submarine gravity flows: the 'Bed 5 event' off northwest Africa

Wynn, R.B., Talling, P.J., Masson, D.G., Stevenson, C.J., Cronin, B.T. and Le Bas, T.P. (2010) Investigating the timing, processes and deposits of one the World¹s largest submarine gravity flows: the 'Bed 5 event' off northwest Africa. Mosher, D.C., Shipp, C., Moscardelli, L., Chaytor, J., Baxter, C., Lee, H. and Urgeles, R. (eds.) In Submarine mass movements and their consequences: 4th International Symposium, Austin, Texas, 9th-11th November 2009. Springer. pp. 463-474 . (doi:10.1007/978-90-481-3071-9_38).

Abstract

An extensive dataset of shallow sediment cores is used here to describe one of the World's most voluminous and extensive submarine gravity flows. The Bed 5 event, dated at ~60 ka, originated on the upper slope offshore Atlantic Morocco, in the vicinity of Agadir Canyon. The volume of initial failure was ~130 km³ of sediment, and the failure appeared to rapidly disintegrate into a highly mobile turbidity current. Widespread substrate erosion beneath the flow occurred up to 550 km from the interpreted source, and is estimated to have added a further 30 km³ of sediment. The flow spread upon exiting Agadir Canyon, with deposition occurring across both the Agadir Basin and Seine Abyssal Plain. Evidence for flow transformations and linked turbidite-debrite development can be found in both basins, and there are also indications for sediment bypass and fluid mud behaviour. A portion of the flow subsequently spilled out of the western Agadir Basin, and passed through the Madeira Channels prior to deposition on the enclosed Madeira Abyssal Plain at 5,400 m water depth. The total run-out distance along the flow pathway is about 2,000 km, with only about half of the pathway confined to canyon or channel environments. Our results show that large-volume submarine landslides can rapidly disintegrate into far-traveling fluid turbidity currents, and that depositional processes within such flows may be complex and spatially variable.

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