Geomorphology and Sedimentary Processes of A Modern Confined Braided Submarine Channel Belt (Stromboli Slope Valley, Southeastern Tyrrhenian Sea)

Abstract

Abstract The deposits of confined submarine channel belts are important reservoirs for oil and gas, and their study can furnish insight into the behavior of sediment gravity flows. Modern examples of confined channel belts can help in the interpretation of ancient successions in similar settings both on land and in the subsurface. A confined submarine channel belt develops within a bend of the Stromboli slope valley in the southeastern Tyrrhenian Sea. Within the 10-km-wide channel belt, the geometry of the main geomorphic elements and the distribution of smaller-scale seafloor features are reconstructed through geophysical data interpretation. The confined channel belt has a morphology similar to a braided river: a point bar is present in the inner bend side, a mid-channel bar develops in the axis of the channel belt, and a side bar is present in the outside of the bend. Small channels, on average 0.5 km wide, are present in between the bars. Flow stratification results in a coarser-grained seafloor in the channels as compared to the bars. The abundance of sediment waves points to bedload transport associated with concentrated density flows with large thickness and long duration. Hyperpycnal flows are their possible triggering mechanism since tributary canyons to the Stromboli valley, both in the Sicilian and Calabrian margins, have their heads close to the coastline. An autocyclic forcing mechanism can account for both depositional and erosional-bypass features within the channels. Fine-grained deposition in one of the channels results from its abandonment and backfilling following slumping from the wall bounding the confined channel belt. In the point bar, a megaflute erosional surface is formed by repeated flow scouring and represents the first stage of channel development. Successively, a channel evolves through lateral migration accompanied by erosion and bypass and by accretion of the adjacent bars. Finally, due to the establishment of a new channel in another portion of the channel belt the channel infills through vertically aggrading deposits.