Slope instability and erosional features of the Ligurian Margin

The recent conclusion of the Magic Project (Marine Geohazards along the Italian Coasts) (Chiocci & Ridente, 2011), the MALISAR Cruises (Migeon et. Al., 2011; Migeon et al., 2012) and the contribution of the data available at the Universities of Genoa (IT) and Trieste (IT) allowed us to identify and study the large series of erosional and gravitative phenomena along the Ligurian continental margins. The dataset allowed us to relate the structural evolution of the Ligurian Basin, the characteristics of the sedimentation, the erosive action of a dense canyon network and the gravitational phenomena (Corradi et al., 2002). The Ligurian Sea is the northwestern portion of the Mediterranean Sea. It originated from the roto-translation of the Corsica-Sardinia Block and is connected to the Apennine orogenic dynamics (Fanucci & Morelli, 2000). The complex geological evolution of the Liguran Sea brought to the division of this basin in different physiographic domains. The main one is the Valley of Genoa that separates the margin of the Alpine area from the Apennines one, which developped in a portion of the newly formed chain. The evolution of the two margins, mainly controlled by extensional tectonics processes, was interrupted by compressional and/or transpressive reactivations, which gave particular characteristics to the margins (Fanucci & Morelli, 2013; Sage et al., 2013; Sage et al., 2014). The Alpine margin is characterized by high seismicity, high sedimention rate and steepness of the margin, determining massive and unstable sedimentary masses along the slope, which are carved by a dense network of canyons. It is in the western Liguria sector that these erosive features are extensively represented until the "Dorsal of Imperia", a structural element that runs parallel to the margin for about 50-60 kilometers. Its genesis can be attributed to the effects of a compressive deformation and this structure isolated an intra-slope basin in which huge quantities of sediments were accumulated and drained by canyons and conveyed in the Valley of Genoa, through the Canyon of Vado. The continental margin between the City of Genoa and the Portofino Promontory is characterized by the two main canyons of the Ligurian Gulf: the Polcevera and the Bisagno canyons. These are in continuity with their respective rivers and almost entirely eroded a thick Plio-Quaternary sequence. The Apennine margin presents a less complex structure than the Alpine one (Fanucci & Morelli, 2006); however, large gravitative phenomena are present. The most important is the Portofino Landslide, located in front of the corresponding promontory. It is mainly characterized by rotational slips and incipient detachment niches, stimulated by the erosion at the base by the Levante Canyon. This last, oriented along the Apennine tectonic lineations, produces significant erosion, both on the head than along its way, which is almost parallel to the coast until its confluence in the Bisagno Canyon. References Chiocci F.L. & Ridente D. 2011. Regional-scale seafloor mapping and geohazard assessment. The experience from the Italian project MaGIC (Marine Geohazards along the Italian Coasts). Mar. Geophys. Res., 32 (1-2), 13-23. Corradi N., Cuppari A., Fanucci F. & Morelli D. 2002. Gravitative instability of sedimentary masses on the Ligurian Sea margins. GeoActa, 1, 37-44. Fanucci F.,& Morelli D. 2000. Caratteri e cronologia della deriva del Blocco Sardo-Corso. Atti Ass. It. Oceanol. Limnol., 13 (2), 167-181 Fanucci F.,& Morelli D. 2006. Assetto strutturale ed evoluzione polifasica del Margine appenninico tra Portofino e La Spezia. Rend. Soc. Geol. It., http://hdl.handle.net/11368/1693875 Fanucci F.,& Morelli D. 2013. Rapporti tra morfologia e tettonica sul margine continentale ligure. http://hdl.handle.net/11368/2768328 Migeon S., Cattaneo A., Hassoun V., Larroque C., Corradi N., Fanucci F., Dano A., Mercier de Lepinay B., Sage F. & Gorini C. 2011. Morphology, distribution and origin of recent submarine landslides of the Ligurian Margin (North-western Mediterranean): some insights into geohazard assessment. Mar. Geophys. Res., 32 (1-2), 225-243. Migeon S., Cattaneo A., Hassoun V., Dano A., Casedevant A. & Ruellan E. (2012). Failure Processes and Gravity-Flow Transformation Revealed by High-Resolution AUV Swath Bathymetry on the Nice Continental Slope (Ligurian Sea). Advances in Natural and Technological Hazards Research, 31, 451-461. Sage F., Beslier M.O., Gaullier V., Larroque L., Dessa J.X., Mercier de Lepinay B., Corradi N., Migeon S., Katz H., & Ruiz Constan A. 2013. Partitioning of deformation along a reactivated rifted margin:example of the northern Ligurian margin. Geophys. Res. Abs. Vol. 15. http://hdl.handle.net/11567/692573. Sage F., Beslier M.O., Dessa J.X., Schénini L., Watremez L., Mercier de Lépinay B., Gaullier V., Larroque C., Béthoux N., Corradi N., Bigot A., Migeon S., & Ruiz Constan A. 2014. Inversion of back-arc basins: example of the LigurianBasin, Western Mediterranean. Geophys. Res. Abs. Vol. 16, EGU2014¬15668, http://hdl.handle.net/11567/692574.