NEW INSIGHTS INTO THE GELA MASS-TRANSPORT COMPLEX (SICILY STRAIT) FROM 3D SEISMIC REFLECTION DATA

Submarine landslides are a key process for global sediment fluxes and may form some of the largest deposits on Earth, strongly influencing slope morphology. Their sudden emplacement can generate damaging tsunamis, posing a threat to coastal communities and submarine infrastructures. They may originate from a variety of triggers and their deposits often record complex multi-phase deformation patterns. In the Mediterranean Sea, submarine landslides have been recognized in all the different tectonic domains, on both active and passive margin sectors. Within this regional framework, this thesis focuses on the Gela Slide, a large-scale submarine landslide deposit located in the Plio-Quaternary foredeep of the Gela Basin, offshore southern Sicily. Originally interpreted by Trincardi and Argnani (1990) from low-resolution 2D seismic data as a single coherent slide, the deposit is here re-examined using high-resolution 3D seismic reflection data. The new data enable, for the first time, a detailed reconstruction of the internal and external architecture, allowing a new evaluation of the emplacement mechanism, timing and potential controlling factors with respect to the general stratigraphic framework of the basin. Interpretation of 3D seismic data reveals that the Gela Slide is not a single coherent slide, but a mass-transport complex composed of multiple stacked mass-transport deposits intercalated with hemipelagites and turbidites. These MTDs can be traced laterally outside the slide body, indicating that they were emplaced prior to the main failure and subsequently together remobilized along a single, laterally continuous basal shear surface, which acted as a mechanically weak horizon that facilitated large-scale detachment and downslope translation. The kinematic analysis reconstructed using seismic arbitrary lines and time slices reveals that the Gela MTC is made of two main bodies, which we named M1 and M2, separated by an oblique transpressional ramp. Seismic variance and structural mapping indicate that M1 was emplaced first, followed by M2 in a relatively short time or almost simultaneously. We propose that the emplacement of M2 was triggered by the collapse of strata still attached to the shelf edge, which filled the space related to M2’s headscarp and thus generated an additional downslope impulse: this impulse led to M2 and the compartmentalization of the mass-transport complex into two kinematic lobes sharing the same basal detachment surface. The formation of the transpressional structure is interpreted as the structural response to this second impulsive phase, accommodating both compressional and strike-slip components. The overall deformation pattern and preservation of internal stratigraphy indicate that the MTC was ultimately emplaced through a relatively slow, coherent sliding process along a single basal surface. New chronostratigraphic constraints indicate that the Gela MTC was emplaced after the MIS 6 lowstand (~140 ka) and before the Last Glacial Maximum (LGM, ~20 ka), defining a broad Late Pleistocene age range for the failure, with minor reactivation episodes during the final stages of margin instability not to be excluded. The causes of failure may reflect the combined effect of several preconditioning factors, including the presence of gas- and fluid-charged sediments, a buried MTD, and a mechanically weak basal shear surface interpreted as a potential condensed section, which together could have progressively reduced slope stability. We propose that the most plausible trigger for failure was the collapse of a shelf-edge delta during a sea-level lowstand following MIS 6 (~140 ka), or a tectonic and/or volcanic event. Overall, this study revises the previous 2D interpretation of the Gela Slide by investigating its internal structure, stratigraphic architecture, kinematics, age, and possible causes, with the aim of improving the overall understanding of slope failure processes along Mediterranean margins.