Morpho-stratigraphic evolution of an offshore portion of the Hyblean plateau eastern flank. Young Researchers in Structural Geology and Tectonics

Transgressive deposits accumulate with rising relative sea-level during the landward migration of a coastline and can be recognised through the evidence of a gradual or irregular landward shift of facies, or a deepening of facies that culminates in a surface of maximum flooding. The offshore area of Marzamemi (SR, Sicily), in the south-eastern portion of the Hyblean foreland, represents an excellent site where to study the development of these 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. Through the interpretation of new morphological data (MBES) and the comparison with 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, the morpho-seismic-stratigraphic analysis highlights the development of three lagoonal systems (L1, L2 and L3) that mark important steps of Late Quaternary sea-level rising. The deepest lagoon L1 is bounded to the west by the contour -45 m, which identifies a cuspited high 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 as beach deposits, while in the central portion a system of tidal bars and channels is widespread and well-imaged in the seismic profiles. Westwards, the lagoon L2 marks a second step of the recent sea-level rising, with the development of a paleo-coastline in correspondence of the contour -35 m. The L2 shows morphological features similar to the L1, with the presence of wide beach deposits to the south and two cliffs that delimited L2 to the west and to the east. Finally, the contour -20 m marks the third significant step of the sea-level rising, and is associated with the paleo-coastline bounding to the west the lagoon L3. The latter hosts within two islets and is confined to the east and west by high cliffs made up by the calcarenite substratum. Only to the south display smooth morphologies attributable to beach deposits. Furthermore, within L3 is present a wide delta oriented west-east and characterized by an irregular trend due to the presence of numerous distributary channels. Along the southern sector, the morphological features are significantly different, and no lagoon systems are observed, probably due to various inherited morphologies of the paleo-coastlines. 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.