Seismic evidence for Neogene and active shortening offshore of Lebanon (Shalimar cruise)

Abstract

Lebanon, located on a 160‐km‐long transpressional bend of the left‐lateral Levant (Dead Sea) fault system (LFS), has been the site of infrequent but large earthquakes, including one submarine, tsunamigenic event. The main objective of the Shalimar marine survey was to characterize and map active deformation offshore of Lebanon using a range of geophysical techniques, particularly seismic reflection profiling. The cruise results clearly establish the presence of young submarine thrust faults and folds and clarify the structure of this part of the Levant margin. A submarine fold belt, bounded by thrusts and lateral ramps and extending up to 30 km from the shoreline, is interpreted as the foreland thrust system of the actively growing Mount Lebanon range. There is no large fault extending into the Levant basin toward Cyprus, which indicates that thrusting only absorbs local transpression resulting from the Lebanese restraining bend. Both the Miocene and Plio‐Quaternary sedimentary sequences are affected by shortening, with landward dipping blind thrusts and associated growth strata. The presence of the Messinian evaporites creates complex deformation patterns, including normal faults due both to folding accommodation and to gravity spreading, all well imaged in the seismic reflection profiles. Because the evaporite layer acts as a décollement level, shortening extends farther out seaward through a series of thrust imbricates or duplexes. The strongest shortening, observed between Beirut and Batroun, decreases toward the south between Saida and Tyre. North of Tripoli, the passive margin is not affected by Neogene deformation and is well preserved. We propose that since the Miocene, the northward propagating LFS interacted with margin structures inherited from the Mesozoic rifting phase and was deviated along the more rigid oceanic crust flooring the Levant basin, a process which led to the formation of the Lebanese restraining bend of the LFS and consequently to the offshore shortening we document here. Such coastal transpression has resulted in local (∼100 km) inversion of the passive margin, which might eventually evolve into a new subduction zone.

Deformed Messinian markers in the Cyprus Arc: tectonic and/or Messinian Salinity Crisis indicators?

“…The velocity-to -thickness conversion law used to calculate the thickness of the MSC deposits is based on a constant velocity of 4 km s À 1 , following Mart & Ben Gai (1982). Carton et al (2009) used a 3.8 km s À 1 velocity. However, Hˇbscher et al (2008) recently calculated interval velocities up to 4.5 km s À 1 for the transparent upper layer of the MSC deposits; the layered units would appear to have a lower velocity.We assume that the 2 km maximum thickness we found for the MSC evaporites is a minimum value, which is nevertheless consistent with other studies (Gradmann et al, 2005;Netzeband et al, 2006b).…”

“…The velocity‐to‐thickness conversion law used to calculate the thickness of the MSC deposits is based on a constant velocity of 4 km s −1 , following Mart & Ben Gai (1982). Carton et al . (2009) used a 3.8 km s −1 velocity.…”

“…5a). Similar structures have been observed in the Levantine basin, such as north-directed intra-MU thrusts in the central Levantine Basin (Netzeband et al, 2006a, b) and in the Levantine margin (Bertoni & Cartwrigth, 2007) and north-west-directed intra-MU thrusts on the Lebanon margin (Carton et al, 2009). Although those structures are located 200 km to the south of our study area, we correlate them with B2 deformation.…”

Modes and rates of horizontal deformation from rotated river basins: Application to the Dead Sea fault system in Lebanon

“…By contrast, the Beirut-Tripoli thrust system offshore of Lebanon accommodates mainly dip-slip motion (Elias et al, 2007;Carton et al, 2009).…”

Early-to-mid Pleistocene Tectonic Transition Across the Eastern Mediterranean Influences the Course of Human History

“…Seismic data reveals a succession of incised channels that drained land area during its tectonic uplift however today has no trace on the shelf seabed. Offshore, several fault systems re-activated the northern Levant continental margin during the Pleistocene (Schattner and Ben-Avraham, 2007) from the marine extension of the Carmel fault , along the Lebanese continental slope (Daëron et al, 2001Carton et al, 2007Carton et al, , 2009Elias et al, 2007), and were traced to a possible juvenile triple junction with the easternmost part of the Cyprus Arc (Butler et al, 1998;Schattner et al, 2006). These along-margin fault systems originate as westward branches of the Dead Sea fault, which dissect the uplifted folds of the Sinai plate.…”