Tectono-stratigraphic evolution of the northern Levant Basin (offshore Lebanon)

This paper presents an updated summary of the history and shallow structure of the Dead Sea transform (DST) and its plate tectonic context. The DST formed in the Early Miocene as a transform boundary between the Sinai and Arabian plates. The lateral offset was ca. 105 km near the Dead Sea. Since the DST trace is irregular in map view, the lateral motion led to formation of a 10–80 km wide deformation zone along the plate junction. Thus, the structures along the DST can be interpreted within the framework of the Sinai-Arabia plate kinematics. South of ca. lat. 33° transtension, which increased with time, led to variable oblique separation of the plate edges. This produced an almost continuous ca. 5–25 km wide depression whose structure is dominated by a string of pull-apart basins up to 15–20 km wide and up to ca. 12 km deep. The crystalline crust under the largest basins was appreciably thinned and may have been intruded by basalts. The structural pattern changed over time, the present pattern having been mostly established in the second half of the DST history. North of lat. ca. 33°N transpression dominates and the DST flanks are strongly deformed by folding, faulting, and rotation of fault blocks on vertical axes, which together produce shortening perpendicular to the DST and also left lateral shearing of its flanks, qualitatively compatible with the plate kinematic. The deformation can also account for the observed decrease of the lateral offset along the main fault line from ca. 100 km at ca. lat 33°N to 65–70 km at lat. 36°–36.5°N, and also leads to left lateral shearing along the continental margin near the Galilee and farther north. North of lat. 36.5°N the DST now interacts with the Anatolian plate and the Cyprus arc. This resulted from a rearrangement of the plate configuration in that region when westward extrusion of Anatolia began and the East Anatolian Fault formed, but the details of the kinematic changes are incompletely known. This change obscured the structural relations in this region during the early stages of the DST history.

Lateral Motion and Deformation Along the Dead Sea Transform

Analysis of 5,000 km of multi-client long-offset 2-D seismic data has led to the identification of three sedimentary basins, Levantine, Cyprus, and Latakia, located in offshore Syria. Each basin has a unique structural and stratigraphic history. They are separated from each other by the middle to Late Cretaceous aged Latakia Ridge System that initiated as a compressional fold-thrust belt and was re-activated under a sinistral strike-slip regime that developed during the Early Pliocene in response to a re-organisation of the plate-tectonic stresses. There is significant evidence for a working petroleum system in offshore Syria with numerous onshore oil and gas shows, DHIs (direct hydrocarbon indicators) observed on seismic, and oil seeps identified from satellite imagery. Prospective reservoirs range in age from Triassic to Pliocene – Quaternary and include Lower Miocene deep-water turbidite sands as encountered in recent discoveries in the offshore southern Levantine Basin. The complex structural evolution of each of the three sedimentary basins has produced an array of potential structural and stratigraphic trapping mechanisms.

Regional seismic interpretation of the hydrocarbon prospectivity of offshore Syria

Partitioning of horizontal deformation between localized and distributed modes in regions of oblique tectonic convergence is, in many cases, hard to quantify. Here we use the geometry of river basins and numerical modeling to evaluate modes and rates of horizontal deformation associated with the Arabia-Sinai relative plate motion in Lebanon. We focus on river basins that drain Mount Lebanon to the west and are bounded by the Yammouneh fault, a segment of the Dead Sea fault system that transfers left-lateral deformation across the Lebanese restraining bend. We quantify a systematic counterclockwise rotation of these basins and evaluate drainage area disequilibrium using the χ metric. The analysis indicates a systematic spatial pattern whereby tributaries of the rotated basins appear to experience drainage area loss or gain with respect to channel length. A kinematic model reveals that since the late Miocene, 23%–31% of the relative plate motion parallel to the plate boundary has been distributed along a wide band of deformation to the west of the Yammouneh fault. Taken together with previous, shorter-term estimates, the model indicates little variation of slip rate along the Yammouneh fault since the late Miocene. Kinematic model results are compatible with late Miocene paleomagnetic rotations in western Mount Lebanon. A numerical landscape evolution experiment demonstrates the emergence of a similar pattern of drainage area disequilibrium in response to progressive distributed shear deformation of river basins with relatively minor drainage network reorganization.

/pdf/modes-and-rates-of-horizontal-deformation-from-rotated-river-2y2nzmb7h1.pdf

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

This paper presents an updated review of the Upper Mesozoic and Cenozoic sedimentological and stratigraphic evolution of the Levant margin with a focus on the northern Lebanon. Facies and microfacies analysis of outcrop sections and onshore well cores (i.e., Kousba and Chekka) supported by nannofossil and planktonic foraminifers biostratigraphy, allowed to constrain the depositional environments prevailing in the Turonian to Late Miocene. The “Senonian” (a historical term used to define the Coniacian to Maastrichtian) source rock interval was subdivided into four sub-units with related outer-shelfal facies: (1) Upper Santonian, (2) Lower, (3) Upper Campanian, and (4) Lower Maastrichtian. This Upper Cretaceous rock unit marks the major drowning of the former Turonian rudist platform. This paper confirms the Late Lutetian to Late Burdigalian hiatus, which appears to be a direct consequence of major geodynamic events affecting the Levant region (i.e., the continued collision of Afro-Arabia with Eurasia), potentially enhanced by regressional cycles (e.g., Rupelian lowstand). The distribution of Late Burdigalian–Serravallian rhodalgal banks identified in northern Lebanon was controlled by pre-existing structures inherited from the pulsating onshore deformation. Reef barriers facies occur around the Qalhat anticline, separating an eastern, restricted back-reef setting from a western, coastal to open marine one. The acme of Mount Lebanon’s uplift and exposure is dated back to the Middle–Late Miocene; it led to important erosion of carbonates that were subsequently deposited in paleo-topographic lows. The Late Cretaceous to Cenozoic facies variations and hiatuses show that the northern Lebanon was in a higher structural position compared to the south since at least the Late Cretaceous.

Sedimentological and stratigraphic evolution of northern Lebanon since the Late Cretaceous: implications for the Levant margin and basin

Abstract The Arabian, African and Eurasian plates interact in the Levantine region. Despite numerous studies of the region, many geological issues relating to Mesozoic times remain unresolved. The Lebanon passive margin is a key area for understanding Neo-Tethyan sedimentary history during this period. The Jurassic succession in Lebanon is well exposed and thick (more than 1000 m). It is more or less complete and relatively undeformed. With a few recent exceptions most studies of the area were made in the 1950s and so the sedimentary evolution of the Jurassic is only partly understood. This study provides (1) a new sedimentary and sequence stratigraphic framework, and (2) a new biostratigraphic framework based on benthic foraminifera and calcareous algae. Palaeoenvironmental and geodynamic conclusions are inferred. Jurassic outcrops occur in both the Mount Lebanon and the Anti-Lebanon areas. Here, they were studied essentially in Mount Lebanon. The Jurassic succession can be divided into three parts: (1) the lower part (Kesrouane Formation) is a thick succession of marine limestones or dolomites; (2) the middle part (Bhannes Formation) consists mainly of basaltic eruptive rocks associated with pyroclastic strata; (3) the upper part (Bikfaya Formation) is a succession of marine limestones. During the Bathonian, Callovian, Oxfordian and parts of the Kimmeridgian, a large epicontinental shelf, with very shallow marine environments, extended across Lebanon (Kesrouane Formation). The period was characterized by a stable platform morphology. It was a tectonically quiet period, although intense subsidence allowed the accumulation of a thick sediment package. During the Kimmeridgian, the carbonate platform regime that had dominated Lebanon during the Middle Jurassic came to an abrupt end, as evidenced by a regional unconformity, a regression and block faulting. This rifting phase is associated with a volcanic event (Bhannes Formation) that is recognized from northern to southern Lebanon. During the Lower Jurassic (Kimmeridgian p.p. to Tithonian p.p.) shallow marine carbonate shelf deposits are observed again (Bikfaya Formation), indicating a marine transgression. This last formation exhibits rapid lateral thickness variations, because of active block faulting and erosion, and is overlain by continental sandstones of the basal Cretaceous.

Middle and Upper Jurassic stratigraphy and sedimentary evolution of Lebanon (Levantine margin): palaeoenvironmental and geodynamic implications

Abstract A study carried out on widespread sites of the Aptian–Albian formations in Lebanon led to two palaeomagnetic directions corresponding to the primary magnetization (N=37 sites, D=307.1°, I=23.7°, k=18 and α95=5.5° after tilt correction and to a post-folding remagnetization (N=18 sites, D=346.3°, I=49.2°, k=108 and α95=3.2° before tilt correction). Comparison of these data with previous palaeomagnetic results for the Jurassic age in Lebanon and expected directions from African apparent polar wander path yields evidence of three different counter-clockwise regional rotations, of the order of 33° before Aptian deposition, of 11° during Late Miocene times, and of 18° since Miocene period. The two last rotations are related to the relative displacement of the African and Arabian plates. A model is proposed for the evolution of this particular Middle East area, in which the Dead Sea Transform shows a strong deviation relative to its main north–south orientation.

Rotations in Lebanon inferred from new palaeomagnetic data and implications for the evolution of the Dead Sea Transform system

The Cenomanian-Turonian Boundary Event (CTBE) in northern Lebanon as compared to regional data – Another set of evidences supporting a short-lived tectonic pulse coincidental with the event?

Mustapha Mroueh

Papers

Middle and Upper Jurassic stratigraphy and sedimentary evolution of Lebanon (Levantine margin): palaeoenvironmental and geodynamic implications

Rotations in Lebanon inferred from new palaeomagnetic data and implications for the evolution of the Dead Sea Transform system

The Cenomanian-Turonian Boundary Event (CTBE) in northern Lebanon as compared to regional data – Another set of evidences supporting a short-lived tectonic pulse coincidental with the event?