Tidal notches, coastal landforms and relative sea-level changes during the Late Quaternary at Ustica Island (Tyrrhenian Sea, Italy)

Abstract

In this paper we present and discuss data concerning the morphostructural evolution at Ustica Island (Tyrrhenian Sea, Italy) during Late Quaternary. New insights on the relative sea-level changes of Ustica are coming from data collected during a geomorphological field survey around the island, together with the bathymetric analysis of the surrounding seabed and 14C datings on samples of speleothems, flowstones and marine shells found inside three selected sea caves. The survey was mainly accomplished on June 2015 through the first complete snorkel investigation off the about 18 km-long volcanic coast of the island, which allowed to precisely define location, relationship and morphometric features of coastal landforms associated with modern sea level. This study highlights the occurrence, for the first time in the Mediterranean, of tidal notches in correspondence of carbonate inclusions in volcanic rocks. The elevation of the modern tidal notch suggests that no significant vertical deformations occurred in the southeastern and eastern sectors of Ustica in the last 100 years. However, the presence of pillow lavas along the coast demonstrates that Ustica was affected by a regional uplift since the Late Quaternary, as also confirmed by MIS5.5 deposits located at about 30 m a.s.l., which suggests an average uplift rate of 0.23 mm/y. Radiocarbon dating of fossil barnacles collected inside the Grotta Segreta cave indicate an age of 1823 ± 104 cal. BP. The difference in height with respect to living barnacles in the same site suggests that their present elevation could be related to stick-slip coseismic deformations caused by the four earthquake sequences (two of which with Mw = 4.63 ± 0.46) that strongly struck the island between 1906 and 1924.