Submarine landslides in the Quaternary stratigraphic record of the Campania offshore: case histories based on reflection seismic profiles

Submarine landslides in the Quaternary record of the Campania offshore are investigated based on high resolution seismic reflection profiles. In particular, the case histories of the Ischia island and of the Gulf of Pozzuoli (Naples Bay) have been studied in detail. Here the strong interaction between tectonism and volcanism during Quaternary times has triggered large submarine instabilities. They appear on the seismic sections as acoustically-transparent and/or chaotic wedge-shaped bodies, often interstratified in the deposits of the Late Quaternary Depositional Sequence. A tentative chrono-stratigraphic attribution of slide bodies can be attained dating back the underlying and overlying seismic sequences, in stratigraphic contact with the landslides. Mass gravity transport deposits, varying in nature, internal organization and areal extension have been recognized in the Late Quaternary successions of all the Italian offshore. An extensive, high-resolution bathymetric survey of the continental shelf/slope system of Campania, Southern Italy has been recently carried out. The relative bathymetric data were acquired during the years 1997 and 2002, using Multibeam systems with an everage vertical resolution less than 10 m. The survey data were successively merged with a Digital Terrain Model (DTM) created from topographic maps of the Bay of Naples onshore coastal areas and islands, to produce a Digital Elevation Model (DEM) based on homogeneous grid with cell-spacing of 20 m (D'Argenio et al., 2004). The shaded relief map has make available new and detailed information on the morphology of the Campania coasts. This segment of the Italian continental margin exhibits evidence of the latest Neogene-Quaternary interplays between tectonism and volcanism, as well as of the depositional processes largely developing as a consequence of frequent and large volcaniclastic supply. The major morphological features revealed by the 3D-digital maps are: i) the system of marine canyons (Dohrn and Magnaghi) that cut the continental slope at a depth between 250 m and 1100 m; ii) the continental slope system of the Ischia volcanic structure (Chiocci and de Alteriis, 2006; Aiello et al.. 2009a); iii) the onshore and offshore volcanoes of the Phlegrean Fields volcanic complex (Rosi and Sbrana, 1987; D'Argenio et al., 2004; Aiello et al., 2004; 2005; Milia and Torrente, 2012); iv) the rugged seafloor area of the outer shelf of the city of Naples (Banco della Montagna; Sacchi et al., 2000; D'Argenio et al., 2004); v) the debris flow/avalanche deposits on the inner continental shelf off Mt. Vesuvius (Milia et al., 1998; 2008), laterally grading into the Torre del Greco volcanic structure (Aiello et al., 2010). The DEM of the Bay of Naples (D'Argenio et al., 2004), representing the base of the geologic and morpho-bathymetric interpretations, has a 20x20m cell and has been based on the integration of different grids. This cell is resulted adequate in detecting the most prominent topographic and bathymetric features of the coastal zone, larger than a few tens of meters. Despite the great number of geological and volcanological studies on the Gulf of Naples, among which Latmiral et al. (1971), Finetti and Morelli (1973), Cinque et al. (1997), Pescatore et al. (1984), Fusi et al. (1991), Milia (1996), Milia et al. (1998; 2008), Aiello et al. (2001; 2004; 2005; 2009a; b; 2010; 2011a; b), Bruno et al. (2003), only recently submarine gravity instabilities in the Dohrn and Magnaghi canyons have been investigated in detail by Di Fiore et al. (2011) and the areas of incipient submarine sliding accurately defined. The Dohrn canyon formation was triggered off by the tectonic uplift of both the outer shelf and the fluvial valley mouths, during periods of eustatic fall of