Morphological Quaternary evolution of coastal plain in response to sea-level changes: example from South-East Sicily

Transgressive deposits accumulate during relative sea-level rises and accompanying the landward migration of the coastline can be recognised through gradual or abrupt landward shifts of facies, or deepening-upward facies trends that culminate in a surface of maximum flooding. The offshore area of Marzamemi (SR, Sicily), in the south-eastern portion of the Hyblaean foreland, represents an excellent site for the study of transgressive deposits and their connection with the sea-level changes. From a geomorphological point of view, the study area is part of the Pantani area, a coastal stretch characterized by a series of lagoons, elongated parallel to the actual coastline and separated by the open sea by elevated ridges of Tyrrhenian calcarenites and by coastal sand barriers. In this area, through the integrated interpretation of new multibeam data (MBES) and high-resolution seismic profiles (SPARKER), we have reconstructed the development of deposits connected to the Transgressive System Tract and Highstand System Tract of the last eustatic cycle. Along the northern sector, three submerged lagoonal systems (L1, L2 and L3) mark important steps, of the Late Quaternary sea-level rise, possibly representing periods of lowered sea-level rise. The deepest lagoon L1 is bounded to the west by the 45 m isobath, which identifies a cuspate relief representing a paleo-coastline constituted by the outcropping Tyrrhenian substratum (Calcarenites of Marzamemi), only locally covered with highstand deposits. Southwards, the L1 is characterized by a smooth morphology interpreted to correspond with beach deposits, while in the central portion a system of tidal bars and channels is widespread as imaged in the seismic profiles. Westwards, the lagoon L2 marks a second step of the last sea-level rise, with the development of a paleo-coastline in correspondence of the 35 m isobath. The L2 shows morphological features similar to the L1, with the presence of extensive beach deposits to the south and two cliffs that bounded L2 to the west and to the east. Finally, 20 m isobath corresponds to the third significant step of the sea-level rise, and is associated with the paleo-coastline bounding to the west the lagoon L3. The latter hosted two islets and was confined to the east and west by high cliffs made up by the calcarenite substratum. Only to the south L3 displays a smooth morphology corresponding to beach deposits. Furthermore, a wide delta oriented west-east and characterized by an irregular trend due to the presence of numerous distributary channels is present within L3. In the southern sector, likely due a different inheritance of regressive morphologies the transgressive setting features was significantly different and submerged lagoons did not form. Here the outcropping calcarenite substratum is affected by the development of meandering paleo-rivers and karst structures, such as numerous depressions (poljes), commonly developed along the Mediterranean karst regions.