A large scale lateral spreading, its genesis and Quaternary evolution in the coastal sector between Cogoleto and Varazze (Liguria - Italy)

The results of a study carried out on a coastal area of central western Liguria (Northern Italy), where metamorphosed basic and ultrabasic rocks outcrop, are presented. The study indicates that a wide area (16 km(2)) was involved in a large scale deep-seated gravitational slope deformation (DSGSD). This movement has special features related to the lithology and structure of the involved rock mass, to the Plio-Quaternary uplifting and brittle tectonics, affecting an area where a paleosurface was recognised, and to the continental shelf dynamics. The particular geometry of the DSGSD was recognised on the basis of detailed analyses of the above-mentioned aspects. Due to its characteristics, the deep-seated deformation can be classified as a lateral spreading. The current altitude of the Pliocene marine clay outcrops and their deposition bathymetry allowed estimation of the uplift rate of the coastal area. The altitudinal variations of an ancient marine terrace, which was displaced by the DSGSD, were used to reconstruct the chronology of the gravitational movement. A final issue concerns the very large scale and the particular kind of phenomenon, both of which are certainly new in Liguria. (C) 2011 Elsevier B.V. All rights reserved.