Seafloor Undulations Across the Shelf–Slope Offshore the Sinni River (Ionian Sea, Southern Italy): Depositional, Deformational, or Hybrid Origin?

Seafloor undulations are common on continental shelves and slopes, but their origin is often difficult to determine because similar ridge-and-trough morphologies may originate from depositional processes, post-depositional deformation, or a combination of both. This study investigates seafloor undulations offshore the Sinni River mouth, southern Italy, to assess their depositional, deformational, or hybrid origin, using high-resolution bathymetry, sparker seismic profiles, sub-bottom profiler data, and morphometric analysis. Bathymetric data reveal a seaward-deepening shelf-to-slope system affected by submarine canyons, troughs, slide scarps, crests/ridge, and fields of undulated seafloor. Seismic profiles show that the undulations are mainly developed within the shallow sedimentary wedge, where continuous to gently wavy reflectors pass laterally and downslope into sectors characterized by reduced reflector continuity, local reflector bending, minor reflector offsets, low-angle reflector surfaces, disturbed sediment bodies, vertical to subvertical acoustic anomalies, and locally chaotic to semi-transparent seismic facies. Deeper stratified deposits are generally more continuous, indicating that deformation is mainly confined to the upper sedimentary succession. Morphometric analysis of 65 seabed features distinguishes broader seafloor undulations, characterized by longer wavelengths, low relief, and higher L/H ratios, from shorter, steeper deformation-related sectors with lower L/H ratios. The integrated evidence indicates that the Sinni undulation field is best interpreted as a hybrid depositional–deformational system. Broad, low-relief undulations record depositional accumulation and seabed reworking within the upper sedimentary wedge, whereas shorter, steeper, and more asymmetric sectors indicate localized post-depositional deformation, possibly favored by weak fine-grained deposits, gas/fluid-related acoustic disturbance, slope steepening, and local sediment remobilization.