Transgressive system tract and continental shelf morphology: an example from the Hyblean foreland ramp offshore

In the central Mediterranean Sea, the Messina Strait separates the Italian Peninsula from the Sicily Island, and connects the Ionian and the Tyrrhenian Seas. Tide-dominated oceanographic processes are known to control the sediment distribution and seafloor morphology of the Messina Strait and its northern and southern approaches. In this paper, through the interpretation of multibeam bathymetry and seafloor reflectivity data, and CHIRP sub bottom profiles, we show that they also dominate the north-eastern Sicilian continental shelf to the west of the Messina Strait. Close to the strait, offshore of Capo Rasocolmo, at a depth of about 20 m, a flat area connects seaward to steeper narrow seafloor sectors. The latter corresponds with progradational clinoforms with 30-m-high foresets reaching a depth of about 50 m. Although the lack of any deep-penetrating seismics does not rule out the possibility that the dipping reflectors are merely the results of the draping of an erosional step; a plausible explanation is that they are part of a compound delta. In the latter case, they can be associated to processes of expansion of the flows exiting the Messina Strait constriction and concomitant sediment deposition to form a delta-like subaqueous body. Bottom-currents of tidal origin, control sediment distribution also further offshore, as shown by sediment mounds separated by areas with sediment bypass or erosion. Further to the west along the margin, and away from the Strait, various trains of sediment waves rework the High Stand System Tracts (HST) deposits. The amplitude and wavelength of the bedforms decrease away from the strait. In some cases, two trains of sediment waves interfere and give rise to a complex bedform geometry. In some areas, smaller scale megaripples are superimposed on the larger-scale bedforms. The sediment waves form a belt along the continental shelf, whose width is constrained seaward by the offshore limit of the TST and landward by Posidonia meadows and mattes developed in the shallower water areas along the coast and inhibiting sediment reworking. Further west, and further away from the strait, the seafloor reflectivity data shows very narrow (100 m in width), stripes of alternating higher and lower reflectivity. They indicate an uneven sediment distribution and can correspond with erosional furrows or sediment ribbons that must have a very subdued morphology. In some cases, the area with the longitudinal bedforms interrupt features transverse to the shelf such as prodelta channels. Our work shows an example of the variability of the bedforms’ character in the shelf, furnishing a record of sediment transport pathways away from a strait. It also shows that tide-dominated processes can control the sedimentary architecture of continental shelves even in micro-tidal seas, such as the present-day Mediterranean, as a result of the physiography of the coast. Our contribution also better outline the spatial extent of seafloor features connected with the tidal dynamics of the Messina Strait, thus contributing to better determine the pattern of the currents that are activated by the complex relationships between the Ionian and Tyrrhenian water-masses.