Juxtapositions of Load-and-Flames, Clastic Diapirs and Deformation Bands as Diagnostic Tool for Earthquake-induced Liquefaction in Mixed Siliciclastic-Carbonate Successions of the Finale Ligure Basin (NW Italy)

The mixed siliciclastic-carbonate successions of the Finale Ligure Basin (NW Italy) features a terrigenous basal complex and a superimposing carbonate wedge. In wide parts, the siliciclastic and carbonate successions are characterized by heteropic sedimentation patterns. Moreover, individual sedimentary units are lithologically heterogeneous, as they display abrupt changes of lithofacies distributions and associated interpreted depositional environments. Essentially the interface between the terrigenous base and the carbonate wedge features a diverse suite of soft sediment deformation structures (SSDS). In the course of this study we identified several deformed parts of stratigraphy, ranging from small size (cm- to dm-scale) load-and-flame structures, pseudonodules and ball-and-pillow structures, mini-slumpings to outsized (several meters in height) chaotic contorted and folded stratigraphic intervals, diapiric sand intrusions and tree-shaped water escape structures. Many of the SSDS are related to fast injection of overpressurized fluids after sand liquefaction. Arrays of deformation bands such as disaggregation and phyllosilicate dilational shear bands, carbonate filled veins and sandy dykelets accompany the cyclic repetition of these SSDS. In the case of the Finale Ligure basin the stratigraphic distribution and cyclic repetitions of SSDS-prone intervals indicate an earthquake-induced origin. We can also sustain that the contemporaneous presence of both dykes and disaggregation bands, moreover related to cyclicity and SSDS, serves as a reliable diagnostic tool for seismite identification in the field. Since these particular SSDS reflect seismic activity in the area, they provide compelling evidence of previously unreported seismic activity in the Finale Ligure basin during the Miocene banding of the Ligurian area and the associated Corsica-Sardinia drift during the late stages of the opening of the Liguro-Provençal Basin.