Unveiling the origin of enigmatic seabed morphologies on the Cape Licosa ridge (Italy)

High-resolution marine geophysical surveys have revealed submarine geomorphological features whose origins remain debated offshore Cape Licosa (Tyrrhenian Sea, Italy). Remote and direct data collected within the CORSUB project identified a field of subcircular to polygonal mounded structures distributed between approximately 75 m and 90 m of water depth along a ridge. These bedforms were analyzed using multibeam bathymetry and backscatter data, side-scan sonar, sub-bottom profiling, and video observations. CHIRP profiles indicate that these morphologies occur above a rugged acoustic basement attributed to the Miocene Cilento Flysch, which is draped by a thin, discontinuous Holocene sedimentary cover. Morphometric analysis delineated 565 discrete features with average dimensions of 8.6 × 6.1 × 0.4 m and a prevailing northeast to southeast orientation. The features exhibit a distinctive high-reflectivity ring surrounding a lower-reflectivity core, producing a regular beehive-like seabed texture. Videos document a wavy-profiled seascape characterized by coarse-grained biogenic sediments, including abundant boxwork rhodoliths, and localized encrustations of coralline algae and bivalves on rocky outcrops. The data suggest that an inherited, complex paleo-topography of the Flysch substrate formed during subaerial exposure of the ridge at the Last Glacial Maximum. Holocene sedimentation draped this surface, involving both sediment accumulation driven by intense hydrodynamic activity and benthic colonization of sparse rocky substrates, thereby preserving this complexity and resulting in a wavy seafloor profile. These findings highlight the control of paleo-topography and post-glacial sedimentary dynamics in shaping mesophotic seabed morphology along Mediterranean continental shelves and in distinctive seabed landforms. • Bedforms between 75 and 90 m depth offshore Cape Licosa in the Tyrrhenian Sea, Italy. • They consist of Holocene wavy-shaped sediments over a Miocene flysch ridge. • They drape over a complex paleo-topography generated during the last glacial maximum. • Today they host mesophotic habitats: rhodoliths beds, coralligenous and bivalve reefs. • The interplay of geology, hydrodynamics and biology affects seabed morphology.