Spatial Extent of vertical tectonic motions in northern Sicily using Holocene and Last Interglacial sea level markers: a case study between Acquedolci e Capo d'Orlando.

Vertical position of sea-level, related deposits and morphologies (e.g., last interglacial, LIG, 125ka,) provide useful markers to utilize with this purpose (LAMBECK et alii, 2004; FERRANTI et alii, 2006, ANTONIOLI et alii, 2009). Using published (ANTONIOLI et alii, 2006) and new data we provide a review of the northern coast of Sicily uplift rates. The markers used in this study are: terraces inner margin, tidal notches, etc., and, for the last millennia archaeological markers and fossil beaches and vermetid reef. Data on vertical movements calculated for the coastal area developing in the north-Sicilian continental margin indicate that, from East to West, a strong variation of vertical rates of uplift are recognized during both middle-late Pleistocene and Holocene. Uplift rates derived from the LIG markers decrease from east to west from 0.8 mm\yrs (Messina) to 0.2 mm\yrs (Cefalù) The same trend is observed for Holocene markers showing rates still higher (until 2 mm\yrs) than in the LIG. The variations mainly correspond to coastal segments separated by a main regional tectonic feature, the Vulcano-Tindari Fault system (LANZAFAME & BOUSQUET, 1997; BILLI et alii, 2006) with predominantly right-lateral transcurrent (partly extensional and/or contractional) kinematics that dissects transversally the south-western sector of the Calabrian Arc. These structures, which are sub-vertical, cross-cut the whole lithosphere and therefore can act as discontinuities separating crustal blocks characterized by different vertical motion. Here we focus our attention on the eastern sector of the Sicilian northern coast and particularly the area immediately to the west of the Vulcano-Tindari fault system, where several evidences of vertical movements during the Pleistocene-Holocene have been recognized. Here, the occurrence of several oblique and normal fault segments and the alternation of rocks with different competence, that is the Hercynian metamorphic basement, its Meso-Cenozoic carbonate and Oligocene-Miocene terrigenous cover and Pleistocene deltaic sands and gravels (CARBONE et alii, 1998), determine a complex geomorphologic setting. Our analysis was devoted to the coastal sector from Capo d'Orlando to Acquedolci towns, where a well preserved flight of marine terraces occurs. Geomorphologic survey allowed to recognize four orders of marine terraces located at elevations of 200 m, 120-90 m, 60-40 m, and 35-10 m a.s.l.. At Rocca Scodoni, between Acquedolci and Capo d’Orlando, the terrace located between 40 m and 60 m is characterized by the presence of a marine deposit up to 10 m thick, constituted by coarse polygenic conglomerates, microconglomerates and cross-laminated sands in a fining-upward sequence. Here, the inner margin of the terrace has been recognized between 45 m and 50 m a.s.l. and it is constituted by a cliff showing several Lithodomus holes, sometimes preserving fossilized shell inside, and other biological remains. A shell of Spondylus s.p. (Fig. 1) in physiologic position has been collected from this terraced deposit at Rocca Scodonì (Fig. 2) in order to perform geochronological analyses. The preliminary U/Th analysis on Spondylus shell, provides an age (with large error bar) on MIS 5 (between 100 and 125 ka). Based on the eustatic level for Mediterranean sea during Last Interglacial (6 metres ±3), the altitude of the inner margin (50 m) we estimate the tectonic uplift rate between 0.36-0.5 mm/a. Archaeological markers occurring along the coastal area located a few kilometers east of Rocca Scodonì (SCICCHITANO et alii, 2010) suggest similar tectonic uplift rates for the Holocene. The new chronological data allow us to calibrate, with respect to the Stage 5, the distribution of marine terraces recognized in this coastal area at different altitudes.