Turbidity Currents and Confined Channels: the Case of the Stromboli Slope Valley Bend

Gamberi, Fabiano¹, Michael Marani¹ (1) ISMAR-Sezione Geologia Marina Bologna, Bologna, Italy

Multibeam bathymetric data and MAK deep towed sidescan sonar lines have been interpreted to unravel the sedimentary processes active in the Stromboli Slope Valley bend.

Erosional walls bound the present-day valley floor that is experiencing aggradation and is characterized by braiding thalwegs a and longitudinal bars. The thalwegs are 500-1000 m wide and up to 20 m deep while the bars have a relief of up to 50 m. The upper, more dilute part of the turbidity currents overbank and deposit fines in a marginal depositional terrace and is responsible for trains of megaflutes and for traction over the central bar that is characterized by an almost continuous field of sediment waves. The confinement of the lower, high-density portion of turbidity currents within the floor of the thalwegs can explain their coarser-grained seafloor. Traction features, in the form of coarse-grained sediment waves and smaller scale streaks of alternating coarser- and finer-grained sediments are also widespread in the thalweg floor. However, particularly in the proximal part of some of the thalwegs, patches of homogeneous coarse-grained sediments that do not show any evidence of traction are present. They can indicate that at least the initial deposition from the basal, high-density part of the flows occurs under high rate of suspended load fall-out capable of suppressing bedform development.

The observed architectural elements and seafloor features on the Stromboli slope valley provide an insight into the processes that guide the aggradation of confined sediment gravity flow conduits.