Impact of the deduced lithospheric architecture on the basin model

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Stratigraphy from seismic reflection

Several seismic reflection surveys and interpretation studies were undertaken for the past years throughout the Levant Basin, the most important of which will be presented in this section. Seismic reflection surveys offshore Tripoli in 1970 and 1971 revealed the compressional Ile du Palmier structure. A later survey, in 1993, detected the presence of pre- Jurassic salt inside this structure (Beydoun, 1977 and Beydoun & Habib, 1995). Studies on shallow coverage seismic from Shalimar cruise detected two basin-wide prominent reflectors named “M” and “N” that correlated well with reflectors identified in different studies (Garfunkel and Almagor, 1985; Vidal et al., 2000a). They separate three different sedimentary sequences, from top to bottom, the Plio-Quaternary turbidites, the Messinian evaporites and the pre-Messinian sequence (Elias, 2006). The uppermost reflector “M” lies between 2.9s and 3s TWT. It has high acoustic reflectivity and represents the base of the Plio-Quaternary sedimentary sequence (Ryan et al., 1971; Ryan and Hsu, 1973). The second reflector “N” (Garfunkel and Almagor, 1985; Tibor et al., 1992) lies around 3.5s TWT below sea level at the base of the 1-1.4 km thick Messinian evaporite layer. Inside this sequence, strong reflectors are visible reflecting facies variations related to environmental change (Elias 2006).
Despite the blanketing effect of this thick Messinian layer, Elias (2006) identified lowamplitude reflectors down to 4.5s TWT corresponding to the Pre-Messinian uniformly stratified parallel layers. Other recent studies (Roberts and Peace, 2007; Gardosh et al., 2008; Steinberg et al., 2011) revealed a thick Cenozoic unit below the Messinian evaporite cover in the Levant Basin. Roberts and Peace (2007), analyzed over 20,000 km-linear of 2-D seismic data from the Levant Basin and adjacent areas and suggested that the Mesozoic and Cenozoic strata deposited above rifted Triassic – Early Jurassic terrain offshore Lebanon is 10,000 m thick, including up to 1500 m of evaporites from the “Messinian Salinity Crisis”. These salts are generally thinner in the northern part of Levant Basin compared to the south and thicker to the west of the Latakia Ridge (Northern part of the Levant Basin) than to the east of the Ridge (Nader, 2011).

Active present deformation and associated seismicity

The geologic history of the Eastern Mediterranean, briefly described above implies a complex tectonic setting, involving the Arabian, African and Eurasian plates. The Arabian Plate colliding with Eurasia in the North, is diverging away from Africa through sea-floor spreading in the Red Sea. At the beginning of the rifting, the Red Sea propagated NNW towards the Mediterranean Sea initiating the Gulf of Suez (Figure 2-13). The rotation of extension in the Gulf of Suez from NNE to NE induced a shift in the rifting from the Gulf of Suez to the Gulf of Aqaba (Figure 2-13) that became the preferred location for the continuation of the Red Sea (Steckler et al., 1988). The majority of this relative movement between the plates have shifted eastward to the Dead Sea transform creating a new plate boundary between Arabia and Africa, accommodating at least 75% of the plate motion north of the Red Sea (Steckler and Brink, 1986). This movement have been transferred to the Levant Fracture System as a strike-slip motion since the onset of the Miocene. Steckler and Brink (1986) explained the creation of this boundary as a result of an increase in the strength of the lithosphere across the Mediterranean continental margin that acted as a barrier to the propagation of the rift.
They based their assumption on an analysis of lithospheric strength variations across the Mediterranean continental margin using the inferred crustal thickness and composition, the geotherm, and thickness of the overlying sediments. The study showed an increase in strength seaward of the hinge zone and a minimum strength landward of the hinge zone [the hinge zone is a feature in the continental margins that marks the beginning of the region affected by substantial extension during rifting] (Figure 2-13).

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Bathymetry and topography

Carton et al. (2009) published a bathymetric map of the Lebanese offshore, outcome of the Shalimar survey as well as a regional bathymetry map of the Levant Basin (Figure 2-21). For a more detailed view, a bathymetric map is represented in Figure 2-20, produced by the National Centre for Geophysical Research, part of the CNRSL.
Onshore, the main features of the topography are Mount Lebanon and Anti-Lebanon that constitute mountainous entities separated by the Bekaa Valley. Physiography of the seafloor also shows three distinct areas of the Lebanese margin, west of Mount Lebanon (Elias, 2006):
-The “shelf” which is the shallowest part of the map. It is wide and shallow south of Beirut and north of Tripoli and separated by a sharp “slope” from the “abyssal plain”. The shelf width narrows from Saida to Jounieh and widens from Tripoli to Akkar (Figure 2-20).
– The continental “slope” is gentle south of Saida and north of Tripoli and extends the shelf while an important increase in steepness is noticed between Beirut and Tripoli and reaches 21-23 at some points and the water depth increases from 100 to 1500 m in less than 5 km. It is the continuation of the elevated topographic gradient onshore where the mountains rise up to 4000 m above the seafloor (Figure 2-20).
– The “abyssal plain” is the sea floor beneath the slope toe. Along the margin, the slope toe is sharply cut by fault scarps and deeply indented by sea valleys, a submarine promontory and submarine flat-floored canyons where water depth can reach 2000 m.

Table of contents :

Acknowledgements
List of figures
List of tables
Chapter 1: Introduction
1.1 General context
1.2 Scientific questions
1.3 Significance of this PhD project
1.4 Flowline of this PhD
Chapter 2: Geological context
2.1 Regional geodynamics
2.2 Tectonic evolution of the Levant and the Palmyra Basins
2.4 Active present deformation and associated seismicity
2.5 Crustal structure
2.6 Mantle structure
2.7 Geophysical data surveying
2.7.1 Bathymetry and topography
2.7.2 Gravity investigations
2.7.3 Heat Flow prediction
2.7.4 Magnetic surveys
Chapter 3: Methods and data
3.1 2D crustal modeling
3.2 3D crustal modeling
3.3 Petroleum system modeling
Chapter 4: Regional crustal modeling
4.1 Lithospheric architecture of the Levant Basin – (Inati et al., 2016)
4.1.1 Abstract
4.1.2 Introduction
4.1.3 Geological settings
4.1.4 Method
4.1.5 The algorithm
4.1.6 Modeling results and interpretation
4.1.7 Discussion
4.1.8 Conclusions
4.2 Paper supplement: Crustal model of a N-S profile
4.3 Strength and elasticity analysis
4.3.1 Rigidity of the lithosphere
4.3.2 Equivalent elastic thickness of the lithosphere
4.4 Regional 3D crustal modeling
4.4.1 The method
4.4.2 Results and interpretation
Chapter 5: Seismic interpretation and crustal modeling offshore Lebanon
5.1 Crustal configuration in the northern Levant Basin based on seismic interpretation and numerical modeling (Inati et al., 2017)
5.1.1 Abstract
5.1.2 Introduction
5.1.3 Geological setting
5.1.4 Methods and data
5.1.5 Seismic interpretation
5.1.6 Time/depth conversion
5.1.7 2D crustal modeling
5.1.8 Discussion
5.1.9 Conclusions
5.1.10 Acknowledgements
5.2 Paper complement: time/depth conversion using refraction data
Chapter 6: Basin modeling
6.1 The context
6.2 The reference model
6.2.1 Data set
6.2.2 Boundary conditions
6.2.3 Calibration well data
6.3 Impact of the deduced lithospheric architecture on the basin model (Scenario 1)
6.3.1 Calibration
6.3.2 Heat Flow Evolution
6.3.3 Geothermal gradient
6.3.4 Burial history and maturity
6.4 Sensitivity analysis
6.4.1 Crustal thinning
6.4.2 Upper mantle thickness
6.4.3 Rifting process
6.4.4 Thermal relaxation
6.4.5 Summary on the sensitivity analysis
Chapter 7: Conclusions and perspectives
7.1 Crustal modeling
7.2 Basin Modeling
7.3 Perspectives
References

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