Neogene Tectonic Evolution and Structural Analysis of Offshore Lebanon.
Supervisors: David Iacopini, Giovanni Camanni, Christian Gorini (Univ. Naples)
Offshore Lebanon, located in the easternmost Mediterranean within the Levant Basin, holds geological significance due to its proximity to plate boundaries and extensive sedimentary basins. The region’s plate kinematics, involving r ifting, collision, and strike-slip deformations, have shaped its architecture and sedimentary infill. While previous studies indicated a stable passive margin in northern offshore Lebanon, recent research suggests pre-Messinian thrusting and recent to active strike-slip activity. This study focuses on offshore structures located northwest Lebanon, where deformations had not been mapped in detail, particularly in reference to the Neogene depositional units. In this margin zone, structures exhibit recent and active tectonic activity impacting the Messinian evaporites and the Pliocene-Quaternary turbidite deposits. The study aimed to provide structural evidence of offshore Neogene-recent deformation affecting the seabed and discuss the potential seismic hazards posed by these structures in the northern Levant Basin. To achieve this, using 3D seismic reflection data, a detailed map of the seabed has been produced, as well as both top and base surfaces of the Messinian layers with the associated faults. The study presents evidence of recent compressive deformation affecting the seabed. Most of the thrust faults mapped in the area do not reach the seabed, except for the eastern side of the Rankine-Aabdeh oblique thrust fault (R-AF). This fault trends ENE-WSW, breaching the seafloor at the margin and transitioning into a blind thrust in the basin. It uplifts older units from the Cretaceous/Pliocene to the seafloor, forming a steep NW scarp. A deep seismic line suggests that the R-AF is inherited from Mesozoic extension, and it was reactivated during the late Miocene and remains active, potentially due to the counterclockwise block rotation triggered by the Levant Fracture System (LFS). The surrounding units near the flower structure clearly show signs of deformation. This structure is interpreted as a positive flower structure, characterized by a prominent anticlinal geometry intersected by near-vertical reverse faults. Its activity appears to have been intermittent, with reactivation during the second phase of LFS activity. While its precise formation is difficult to ascertain with the available data, significant uplift may have occurred prior to Messinian. Two kinematic models have been proposed to explain the observed structural variations: one suggesting transpression with strike-slip dominated deformation similar to a pop-up structure, and the other suggesting transpression with thrust-dominated deformation. The mapped faults indicate significant potential for tectonic active deformation, though the seismic activity recorded in the area is relatively low both in magnitude and sparse in distribution. This could imply that these faults are either currently locked, experiencing slow slip events, or creeping aseismically. Evidence of landslides and rockfalls along the slope triggered by the flower or thrust structure has been observed in both the 2D deep seismic section, 3D seismic dataset, and the 3D seabed images. Further detailed monitoring and geophysical surveys are recommended to better understand the ongoing tectonic processes and potential seismic hazards in the region