New Insights Into Erosional Processes of Giant Turbidity Currents and Distal Development of Linked Debrites

Wynn, Russell B.¹, Peter J. Talling², Bryan T. Cronin³, Andrey A. K. Akhmetzhanov¹, Michael Frenz¹, Douglas G. Masson¹, UK Taps Group¹ (1) National Oceanography Centre, Southampton, United Kingdom (2) Bristol University, Bristol, (3) University of Aberdeen, Aberdeen, Scotland

As part of the UK-TAPS Agadir Project, an integrated geophysical and sedimentological dataset was collected in autumn 2004 from the modern deep-water Agadir Canyon and Basin off NW Africa. The project aims included 1) quantifying erosional processes of large-volume (125 km3) turbidity currents, and investigating how sinuous canyon morphology, Coriolis and centrifugal forces influence erosional capacity of such flows, and 2) understanding how enhanced proximal erosion can encourage distal flow transformations, particularly the development of linked debrites in a distal basin setting.

Our results highlight the erosive character of the most powerful individual turbidity current (TC 5) to have passed through the system in the last 160,000 years. In the Agadir Canyon, just beyond a sharp right-angled bend some 400 km from source, TC 5 was able to erode >1.0 m of cohesive fine-grained sediment at a height >335 m above the canyon floor. Further downstream, sidescan sonar images reveal the presence of km-scale erosional scours in the canyon mouth, while cores in the proximal Agadir Basin show that TC 5 was still cutting 1.0 m-deep isolated scours at a distance of 550 km from source. Beyond a subtle slope break in the proximal Agadir Basin, TC 5 rapidly switched from being dominantly bypassing to dominantly depositional. Intriguingly, TC5 is the only event in the modern basin fill sequence to develop a linked debrite in its core; we therefore propose a linkage between enhanced proximal erosion and generation of distal linked debrites.