Submarine landslides and canyons: slope degradation and shelf-edge indentation in a tectonically active margin (Finale Basin, Northern Sicilian margin, Tyrrhenian Sea)

Fabiano Gamberi^1*Elena Scacchia²valentina ferrante¹

• ¹Institute of Marine Science, Department of Earth System Sciences and Technologies for the Environment, National Research Council (CNR), Venezia, Italy
• ²Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), Rome, Sicily, Italy

Submarine canyons and landslides are closely related geological features of continental margins. They prevail in the continental slope, but often reach the shelf-edge, indenting also the continental shelf. The character of the linkage between submarine canyons and landslides varies depending on their geological and geodynamic setting. Consequently, a wide range of geomorphologies and processes develop in association with landslides and canyons. They reflect different evolutionary pathways, which ultimately lead to continental margin degradation. The latter is studied in our paper through the analysis of multibeam bathymetric data and seismic lines in the Finale Basin, in the northern Sicilian Margin. We recognize landslides with complex history and character, with main scarpheadwall in the slope or indenting the shelf edge, often associated with debris -flows. More importantly, we recognize that depending on landslide's the style of landslide, two types of canyons develop. The "worm canyons" nucleate in the lower slope and develop through successive small rotational landslides migrating upslope along narrow corridors. The "racket canyons" develop in the depressions created by larger rotational landslides in the upper slope and evolve through further downslope excavation due to debris- -flow processess. Both canyon types can result in shelf-edge indentations. The latter is sometimes enhanced by duck-feetduck-foot bowls, triangular depressions that form the upper reaches of some of the canyons. The observations in our study area suggest that the northern Sicilian margin is reacting through canyon and landslide formation to out-of-grade conditions due to continental margin uplift and tilting. We highlight that canyon nucleation can occur either in the lower or in the upper slope. We also show that whatever the canyon type, debris -flows are the most important processes for slope excavation and canyon enlargement and propagation. Finally, we recognize a hierarchical pattern in various scales of the development of the elements and processes that lead to shelf-edge indentation. Relatively large indentations form in coincidence with the canyon-generating landslide, smaller ones relate to the bowl-shaped source area of channelized debris -flows.