engleski

Stratigraphic-structural interpretation of SE Palmyrides (Syria)

The territory of Syria is divided into the following four major tectonic units: the Palmyrides fold-thrust belt, the Euphates Graben or Depression, the Abd el Aziz – Sinjar Uplift and Dead Sea Fault System. The Palmyrides fold-thrust belt is the most extensive and topographically prominent tectonic zone in Syria. It represents a 400 km long, NE-SW trending intracontinental fold-thrust belt, formed in between the two relatively undeformed tectonic blocks known as the Allepo Plateau on the north and the Rutbah Uplift on the south. To the east and west the Palmyrides are bounded by the Euphrates and Dead Sea fault systems, respectively. This fold-thrust belt is usually subdivided into SE (or Frontal) Palmyrides and the NW (or Central) Palmyrides, separated by Jhar fault located at the northern edge of the Al Daww Depression in between the SW and NE Palmyrides. During most of the Phanerozoic the Palmyrides belt was a sedimentary depocenter, with several kilometres of Palaeozoic and Mesozoic sediments accumulated in the period of episodic rifting and broad subsidence (e.g. BREW et al., 2001 ; CHAIMOV et al., 1992). Since the Late Cretaceous the Palmyrides have been subjected to episodic compression leading to folding and faulting of sedimentary pile, which resulted in formation of the modern NE-SW trending mountain range evident in topography. The Palmyrides represent the object of special interest because of the Hayan block, the most important exploration/ production privilege of INA Industrija nafte d.d. in Syria. This concession occupies the northern part of Palmyrides, the northeastern part of the Al Daww Depression and the part of the SE (Frontal) Palmyrides. The SE (Frontal) Palmyrides represents the NE-SW trending fold-thrust belt, which extends from Damascus for more then 200 km due northeast. They are divided into two areas with sum of five INA’s exploration wells. The Palmyra Area occupies northeastern part with wells Palmyra-1, -2 and -3. The Khnifes – Al Bahra Area, the main topic of this study, where Khnifes-1 and Al Bahra-1 exploration well are located, occupies their central part. The subsurface geology of the Khnifes – Al Bahra Area was in more detail examined by analysing the rocks samples and relevant well data obtained during drilling the Al Bahra-1 and Khnifes-1 wells in the years 2004 to 2006. Regardless on tectonics, the idealized succession of sediments in the vertical exploration well Al Bahra-1 (see abstract: Paleozoic and Mesozoic succession of sediments in Al Bahra-1Well) starts with the Tanf Formation of the Silurian. Subsequently to regionally determined emergence phase at the Silurian-Carboniferous boundary came the Markada Formation of the Carboniferous in age. The Permian Amanus Sand Formation and Scythian Amanus Shale Formation, although probably alienated by local unconformities, are due to a lack of information declared jointly. After a new emergence phase at the Scythian-Upper Anisian boundary, the Kurrachine Dolomite Formation of the Middle to Upper Triassic (Late Anisian to Carnian) follows. The significant tectonic activity at the end of the Triassic resulted in major regional emersion of the greater part of the Palmyrides. In the Al Bahra-1 well this stratigraphic hiatus lasted (app. 130 MY) from the Carnian to the Upper Cenomanian. Consequently, the Judea Formation of the Upper Cretaceous, Late Cenomanian to Turonian in age unconformably overlies the Triassic sediments. After most likely an additional undefined local unconformity The Soukhne Formation of the Coniacian (Santonian) to Early Campanian in age follows. The Shiranish Formation of the Upper Cretaceous, Late Campanian to Maastrichtian in age ends the borehole series of deposits. The vertical exploration well Khnifes-1 (see abstract: Paleozoic and Mesozoic succession of sediments in Khnifes-1 Well) has drilled 3022mof sediments ranging from the Upper Cretaceous to the Carboniferous, and not considering abnormal contacts caused by faults the basic lithostratigra-phic column begins with the Carboniferous deposits of the Markada Formation. The next is Amanus Sand Formation of the Permian age overlied with the Amanus Shale Formation of the Scythian age. After the regional emergence phase, first the Kurrachine Dolomite Formation and than the Kurrachine Anhydrite Formation of the Middle to Upper Triassic proceed behind. The Butmah Formation of the Upper Triassic, Carnian in age follows. The recognized Palmyrides regional emersion at the end of the Triassic in the Khnifes-1 well began in Carnian and lasted to the Lower Cretaceous with lengthened duration of stratigraphic hiatus (app. 117 MY). The Rutbah Formation of the Lower Cretaceous precedes the Hayane Formation of the Lower to Upper Cretaceous, Upper Albian to Middle Cenomanian in age. The Judea Formation of the Upper Cenomanian to Turonian age follows. The Soukhne Formation of the Late Santonian to Early Campanian in age unconformably overlies previous deposits. The Shiranish Formation of The Upper Cretaceous, Late Campanian to Maastrichtian in age ends this succession of sediments. The Khnifes – Al Bahra Area is morphologically characterized by a set of en echelon arranged NE-SW trending anticlines largely composed of Cretaceous deposits. The surface geologic features were observed around the Khnifes-1 well by field campaign in November, 2005. We proved that geological and structural relations shown on geological map of PONIKAROV (1966), as well as mapped and reconstructed by SALEL & SEGURET (1994) are in a good correlation with our field observations, except for the Triassic age of the oldest outcropping sediments that are incorrectly indicated on geological map of PONIKAROV (1966) as Jurassic. The Khnifes-1 well is located at the northwestern margin of the valley covered by Quaternary sands and silts, which unconformably rest over Paleogene limestones and marls. These sediments are nicely exposed in a huge phosphate mine at the southwestern entrance into the valley. The Kneffes valley is bounded on both sides byNW-SE trending hills where Mesozoic sediments crop out. Ahill slope at the northwestern valley margin (i.e. to the northwest from the Khnifes-1 well) is composed of well layered dolomites and micrites (with chert nodules) of Cretaceous Judea Formation. Sediments moderately dip to the southeast (150/30) and going upslope pass into red-coloured ferruginous sandy dolomite of the lower part of Judea Formation. Next are the sediments of the upper part of Judea Formation, but with dipping in an opposite direction (300/10) which suggests that sediments are folded in a form of an anticline. To the northwest, layers become steeper and dip between 45 to 60° due NW into the Al Daww depression below Paleogene and Quaternary series. The sediments of Judea Formation cropout again along the hill on the opposite side of the valley (i.e. to the southeast from the Khnifes-1 well) with layers dip at about 20–30° due northwest. Consequently, sediments of the Judea Formation are expected to be penetrated by the Khnifes-1 well first close to the surface and then again at depth of ca. 400 m. Down the slope, the Judea Formation is underlain by the Hayan, Rutbah and Butmah Formations and finally by evaporites of the Kurrachine Anhydrite Formation exposed at the toe of the slope. Further eastward Paleogene and Cretaceous sediments appear again on the surface, gently dipping due northwest, i.e. structurally below the evaporites of the Kurrachine Anhydrite Formation. The repetition of Upper Triassic to Upper Cretaceous sediments, geological relations at the surface and on assembled reflection seismic section which extends from the Al Daww depression across the Khnifes anticline and to the Al Bahra-1 well indicate a complex internal structure.

SE (Frontal) Palmyrides; fold-thrust belt; Khnifes-Al Bahra Area; Syria

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