The contribution of tectonics to relative sea-level change during the Holocene in coastal south-eastern Sicily: New data from boreholes

In order to detect ongoing vertical crustal movement and assess both tectonic instability and marine invasion risk in the south-eastern Sicily coastal area, Holocene sea-level indicators have been compared to the sea-level curve for the same period. A stratigraphical and sedimentological study, accompanied by C-14 AMS dating, has been carried out using seven boreholes in the most depressed coastal sectors, the Catania Plain, the lagoonal environments between Augusta and Siracusa and the Vendicari lagoon south of Siracusa. The distinct boreholes showed irregular transitional successions, represented by infralittoral beach sands, lagoon and brackish marsh deposits. Moreover, C-14 AMS dating on gastropod and bivalves collected at various depths indicated a Holocene age for these deposits that lie directly on the Lower-Middle Pleistocene substratum. Taking into account that the infralittoral and lagoon sediments occurring in the analysed coastal areas were deposited during the Holocene sea-level rise and that the gastropod and bivalve fragments sampled in the boreholes are, with good approximation, sea-level indicators, the short-term vertical motion undergone by this region during the Holocene can be estimated. Comparing the sampling depth below the present sea level of the dated shells to the sea-level rising curve for the central-eastern Sicily coast, the coastal plains between Catania and Siracusa resulted involved during the Holocene in tectonic uplifting with rates varying from about 1 mm/y in the Catania area to 0.5 mm/y in the Siracusa area. Conversely, in the same period the south-eastern most coastal sector of Sicily can be considered tectonically stable. These results are comparable to uplift rates obtained from geomorphologic and archaeological sea-level markers and are consistent with a remote effect of the active normal fault system located in the Ionian offshore between Catania and Siracusa. (c) 2010 Elsevier Ltd and INQUA. All rights reserved.