Tectonic and Geological Evolution of Syria

GeoArabia, Vol. 6, No. 4, 2001Gulf PetroLink, Bahrain

573

Tectonic and Geologic Evolution of Syria

Graham Brew and Muawia Barazangi, Cornell UniversityAhmad Khaled Al-Maleh, Damascus University

and Tarif Sawaf, Syrian Petroleum Company

ABSTRACT

Using extensive surface and subsurface data, we have synthesized the Phanerozoic tectonicand geologic evolution of Syria that has important implications for eastern Mediterraneantectonic studies and the strategies for hydrocarbon exploration. Syrian tectonicdeformation is focused in four major zones that have been repeatedly reactivatedthroughout the Phanerozoic in response to movement on nearby plate boundaries. Theyare the Palmyride Mountains, the Euphrates Fault System, the Abd el Aziz-Sinjar uplifts,and the Dead Sea Fault System. The Palmyrides include the SW Palmyride fold andthrust belt and two inverted sub-basins that are now the Bilas and Bishri blocks. TheEuphrates Fault System and Abd el Aziz-Sinjar grabens in eastern Syria are largeextensional features with a more recent history of Neogene compression and partialinversion. The Dead Sea transform plate boundary cuts through western Syria and hasassociated pull-apart basins.

The geological history of Syria has been reconstructed by combining the interpretedgeologic history of these zones with tectonic and lithostratigraphic analyses from theremainder of the country. Specific deformation episodes were penecontemporaneouswith regional-scale plate-tectonic events. Following a relatively quiescent early Paleozoicshelf environment, the NE-trending Palmyride/Sinjar Trough formed across central Syriain response to regional compression followed by Permian-Triassic opening of theNeo-Tethys Ocean and the eastern Mediterranean. This continued with carbonatedeposition in the Mesozoic. Late Cretaceous tectonism was dominated by extension inthe Euphrates Fault System and Abd el Aziz-Sinjar Graben in eastern Syria associatedwith the closing of the Neo-Tethys. Repeated collisions along the northern Arabian marginfrom the Late Cretaceous to the Late Miocene caused platform-wide compression. Thisled to the structural inversion and horizontal shortening of the Palmyride Trough andAbd el Aziz-Sinjar Graben.

INTRODUCTION

Since the late 1980s, the goal of the Cornell Syria Project has been to analyze and map the tectonichistory of the structurally deformed areas of Syria. Understanding this rich history can yield a fullerappreciation of the plate-tectonic processes in the eastern Mediterranean region. It can also provide abetter understanding of the likely occurrence and distribution of natural resources. Although notcomparable with the vast hydrocarbon reserves of the Arabian Gulf, the resources of Syria arenonetheless economically important, and there is potential for further significant discoveries.

Much previous work has concentrated on relatively distinct structural provinces within Syria. Thegoal of this paper was to synthesize the tectonic evolution of the entire country by integrating ourprevious interpretations with new regional structural maps, and incorporating significant additionallithostratigraphic knowledge. After outlining the tectonic setting of the area, we provide a briefsummary of previous work. Our regional mapping is then discussed, including a database descriptionand presentation of new lithostratigraphic interpretations, structural maps, and a new tectonic map ofSyria. The result is a Phanerozoic geologic and tectonic model for Syria in a plate-tectonic framework.We conclude by discussing the hydrocarbon habitats in Syria, and their relationship to the tectonicevolution of the region.

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GEOLOGICAL REVIEW

Tectonic Setting

Syria is close to the leading edge of a continent/continent collision where the Arabian Plate is convergingon Eurasia at 18 2 mm/year in a roughly north-northwesterly direction (McClusky et al., 2000). Thiscollision is manifest in the active transform and convergent plate boundaries that are currently proximalto Syria (Figure 1), and have been so for most of the Phanerozoic. The events on these boundaries (andtheir ancient counterparts) have largely controlled the Paleozoic, and particularly Mesozoic-Cenozoic,tectonics of Syria.

The most prominent plate margin at the present-day is the Zagros fold and thrust belt (Figure 1) thattrends northwesterly through western Iran and eastern Iraq. It accommodates the convergence ofArabia with Eurasia by widespread thrusting, folding, and significant crustal shortening. Along the

N

BAHRAIN

Nubian Shield

Arabian Shield

KUWAIT

EGYPT

IRAQ

SYRIA

TURKEY

IRAN

Caspian Sea

CYPRUS

Mediterranean Sea

SAUDI ARABIA

Arabian Gulf

JORDAN

Damascus

Red Sea

0 300

km

QATAR

Palmyride

s

BitlisSuture

East AnatolianFault

North AnatolianFault

LevantineSubplate

Sinai Subplate

AnatolianSubplate

EURASIAN PLATE

ARABIAN PLATE

AFRICANPLATE

Wadi Sirhan

Dead

Sea

Fa

ult S

yste

m

Najd Fault System

Zagros Thrust ZoneZagros Fold Belt

Figure 2

Spreading plate marginMajor thrust faultMajor strike-slip faultCenozoic lava fieldPrecambrian basement

Figure 1: Regional tectonic map of the northern part of the Arabian Plate and adjacent areasshowing the proximity of Syria to several active plate boundaries.

Tectonic and Geologic Evolution, Syria

575

northern Arabian margin, the Zagros belt becomes the Eocene-Miocene Bitlis Suture joining the Eurasianand Arabian plates (Hempton, 1985). To the northwest of the Arabian Plate, the dextral Miocene-Pliocene North Anatolian Fault, and the sinistral East Anatolian Fault accommodate movement on theAnatolian subplate that is escaping westward owing to the Arabian-Eurasian convergence (McCluskyet al., 2000).

Converging with the East Anatolian Fault from the south is the Cenozoic Dead Sea Fault System(Figure 1). This sinistral transform fault accommodates the differential northward motion of the Arabianand African plates (Levantine and Sinai subplates) created by the opening of the Red Sea. Theextensional Red Sea and Gulf of Aden plate boundaries form the southwestern and southern boundariesof the Arabian Plate.

Previous Geologic Studies of Syria

At a gross scale, Syria can be divided spatially (Figure 2) into four major tectonic zones and interveningstructural highs (Barazangi et al., 1993). These zonesthe Palmyride area, the Abd el Aziz-Sinjar area,the Euphrates Fault System, and the Dead Sea Fault Systemhave accommodated most of tectonicdeformation in Syria throughout the Phanerozoic, whereas the intervening stable areas remainedstructurally high and relatively undeformed. The style of structural reactivation is dependent on theorientation of the tectonic zones to the prevailing stress pattern.

Figure 2: Topography of Syria, tectonic zones, and location of various text figures. Shaded reliefimage of topography illuminated from the west.

Bishri Block

km

0 100

Figure 5

Figure 6

Figure 3

Figure 4

Med

iterra

nean

Sea

IRAQ

Aleppo Plateau

LEBANON

Al DawwBasin

Mardin HighTURKEY

EUPHRATES FAULT SYSTEM

DerroHigh

Rawdah High

Anah Graben

Kurd DaghMountains

GhabBasin

Rutbah Uplift

Coas

tal R

ange

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Homs

Depre

ssion Bilas Block

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YRIDE

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Damascus

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MesopotamianForedeep

JORDAN

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Anti-L

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Euphrates

Graben

ABD EL AZIZ-SINJAR UPLIFT

DEAD

SEA

FAUL

TSY

STEM Figure 7

36E 37 38 39 40 41 42

37N

36

35

34

33N

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Neogene

0

1

2

3

4

Jhar Fault, extensive dextral strike-slip feature separating the SW Palmyrides from the Bilas Block

Bilas Block (Upper Cretaceous outcrop)

Abou Rabahfault-bend fold (Upper Cretaceous outcrop)

Paleogene

Triassic evaporite detachment surface,only locally developed

CretaceousUpper Cretaceous strata onlapping anticlineindicating minor LateCretaceous tectonics

Velocity pull-upof imaged horizons

Jurassic and Triassicrepeated sectionOnlapping and thinning

Middle Eocene strata shows Cenozoic structural uplift

Two-w

ay

Tim

e (s

ec)

Paleozoic

Palmyride AreaThe area loosely referred to as the Palmyrides, can be further divided into the SW Palmyrides, andthe Bilas and Bishri blocks of the NE Palmyrides (Figure 2). During most of the Phanerozoic thePalmyride zone was a sedimentary depocenter (the Palmyride/Sinjar Trough). Seismic reflectiondata (Chaimov et al., 1992, 1993) and drilling records show the SW Palmyrides to have been controlledby NW-dipping late Paleozoic and Mesozoic listric normal faults that were structurally inverted in theNeogene. Unfortunately, poor seismic reflectivity of the older section precludes precise documentationof Paleozoic tectonics.

A significant part of the thickening in the Palmyride Trough can be related to broad subsidence ratherthan extensional faulting (Chaimov et al., 1992), particularly during the Triassic. In the Jurassic andLate Cretaceous, however, normal faulting dominated according to Best (1991), Chaimov et al. (1993),and Litak et al. (1997). Since the Late Cretaceous, the Palmyrides have been subjected to episodiccompression leading to folding and the currently observed topographic uplift.

The SW Palmyrides are dominated by a series of short, SE-verging folds controlled by reverse faults.The short-wavelength anticlines have steeply dipping (in some case overturned) forelimbs, and moreshallowly dipping backlimbs, and are progressively steeper toward the southwest. Chaimov et al.(1993) argued that these folds were the result of fault-propagation folding above inverted normalfaults, linked by sinistral transfer faults. This is supported by well data and outcrop evidence whereTriassic strata are thrust over Santonian rocks (Mouty and Al-Maleh, 1983). Reverse faults withsignificantly decreasing fault dip in the shallow section could reconcile the tight fold axes with therelatively low-angle faults seen at the surface.

Chaimov et al. (1992) mapped a locally developed Triassic detachment level that accommodated somefault-bend fold formation, especially in the northern part of the SW Palmyrides (Figure 3). However,on a regional scale, Chaimov et al. (1993) documented similarly deformed Upper Cretaceous andlower Paleozoic strata, thus arguing against a regional-scale Mesozoic detachment in the SW Palmyrides.

Figure 3: Perspective block model of the Abou Rabah anticlinal structure in the northern part of theSW Palmyrides (see Figure 2 for location). Surface is Thematic Mapper imagery draped overtopography. Faces shown are seismic lines CH-36 (dip line) and CH-45. Image is 31x32 km withapproximately no vertical exaggeration.


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In contrast, in the central and northern Palmyrides, Searle (1994) mapped complex folding often in theform of box folds above an Upper Triassic detachment, but only minor reverse faulting. Hence, weinterpret strong along-strike structural variations in the Palmyrides, with thrust faulting becomingless influential toward the northeast. This would agree with the cross-sections of Chaimov et al.(1990) that showed total shortening decreasing from around 20 km in the SW Palmyrides to almostzero in the far northeast.

The extensive low-relief Al-Daww Basin (Figure 2) lies between the SW Palmyrides and the BilasBlock. Dated as a Miocene to Recent depocenter, this intermontane basin contains more than 2,000 mof Cenozoic strata (Chaimov et al., 1992). To the north of the Basin, the Jhar Fault separates the SWPalmyrides from the NE Palmyrides. The Fault has been traced for nearly 200 km in a ENE-directionand shows an average of 1,000 m of uplift on its northern side and significant, but undetermined,amounts of dextral strike-slip (Al-Saad et al., 1992). Well data indicate this was an active extensionalfault at least since the Jurassic. The structural inversion along the Jhar Fault controls the southernedge uplift of the Bilas Block (Figure 2). Deformation within the Block is dominated by strike-slipduplexing where large, relatively undeformed anticlines are bound by steep faults that show verylittle shortening (Chaimov et al., 1990). Along the northern margin of the Palmyrides is the HomsDepression (Figure 2). This large basin shows little or no sign of the structural inversion so prominentin the adjacent Palmyrides, which perhaps suggests a significant fault-controlled detachment of thedepression from the uplifted Bilas Block.

To the north and east of the Bilas Block, the prominent right-lateral Bishri Fault separates the Bilas andBishri blocks. Similar to the Jhar Fault, the transpressional Bishri Fault accommodates uplift of oneblock relative to the other. NE-striking Mesozoic normal faults were more active in the Bishri Blockthan in other parts of the Palmyrides, particularly in Jurassic and Late Cretaceous times (Figure 4).Cenozoic structural inversion of these faults is controlling the present-day NE-plunging anticlinalmorphology of the blocks (McBride et al., 1990; Best, 1991).

Abd el Aziz-Sinjar AreaDuring the late Paleozoic to Late Cretaceous, the Sinjar (Figure 2) and surrounding areas were thenortheastern part of the Palmyride/Sinjar Trough. As in the Palmyrides, accommodation space forlate Paleozoic and Mesozoic clastic sediments several kilometers thick was created largely throughbroad subsidence, although some contemporaneous NE-striking normal faults have been identified(Brew et al., 1999).

Other than this broad trough formation, no significant extension occurred around the Abd el Aziz andSinjar structures until the formation of a network of E-striking faults in the latest Cretaceous. Thesepredominantly S-dipping normal faults and the resulting half grabens formed in the latest Campanianand Maastrichtian and accommodated up to 1,600 m of synrift calcareous, marly sedimentation(Figure 5). The cessation of the extension, as indicated by the termination of faulting, came abruptly atthe end of the Cretaceous.

The currently observed topographic highs (the Abd el Aziz and Sinjar uplifts, Figure 2) are the resultof Cenozoic structural inversion that has been most active in the Late Pliocene to Holocene (Kent andHickman, 1997; Brew et al., 1999). Specifically, the Late Cretaceous E-striking normal faults are beingreactivated in a reverse sense creating fault-propagation folds (Figure 5). Based on limited data, similarand contemporaneous deformation apparently affected the Mesopotamian Foredeep in the extremenortheast of Syria (Figure 2).

Euphrates Fault SystemThe Euphrates Graben (Figure 2) is a fault-bounded failed rift studied extensively by Litak et al. (1998)and de Ruiter et al. (1994). Litak et al. (1997) showed that the Euphrates Fault System is a related butless-deformed zone of extension that extends from the Iraqi border in the southeast to the Turkishborder in the northwest and includes the Euphrates Graben. The lack of widespread inversion limitsthe topographic expression of the Euphrates Fault System (Figure 2).

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A Turonian-Coniacian age unconformityprobably marking prerift upliftis extensively developedin the Euphrates Graben, and the underlying limestone is eroded and dolomitized. Overlying redbedsgrade into progressively deeper water carbonate facies (Litak et al., 1998). Senonian rifting that resultedin about 6 km of extension and an undetermined amount of strike-slip movement was accommodatedby a distributed system of steep normal faults. The synrift carbonate deposition culminated in theCampanian to early Maastrichtian with the deposition of up to 2,300 m of deep-water marly limestoneswithin the graben (Figure 6). Rift-related extension stopped during the Maastrichtian.

The Paleogene was marked by widespread thermal subsidence as the lithosphere reestablished thermalequilibrium after rifting (Litak et al., 1998). The Euphrates Fault System experienced minor dextraltranspression and reactivation during the Neogene. Compressional features are best developed in thenorthwest of the fault zone where reverse and strike-slip movement and some associated minor fault-propagation folding occurred on reactivated Late Cretaceous normal faults. To the south and west ofthe Euphrates Graben is the Rutbah Uplift. The term Hamad Uplift has been used by Mouty andAl-Maleh (1983) to describe the NE-trending paleogeographic high on the northern margin of theRutbah Uplift in Syria (Figure 2).

Dead Sea Fault SystemThe Dead Sea Fault System is a major sinistral transform plate boundary separating Africa (Levantinesubplate) from Arabia, and accommodating their differential movement. Total offset on the southernportion of the fault is well established to be around 105 km (Quennell, 1984). Some authors havesuggested two episodes of strike-slip motion on the Dead Sea Fault System in concert with a two-phase Red Sea openingMiocene slip of 60 to 65 km, and post-Miocene slip of 40 to 45 km (Freundet al., 1970; Quennell, 1984). Other authors (e.g., Steckler and ten Brink, 1986) have advocated a moreconstant Red Sea extension.

Along the northern segment of the fault (from Lebanon northward) the age and rates of faulting areunclear due to a lack of piercing points, although total post-Miocene offset has been reported as lessthan 25 km (Trifonov et al., 1991). These observations and work in the Palmyrides have been combined

0 5

km

Lower Cretaceous and Upper Triassic

NeogenePaleogene

0

54

123

Appr

oxim

ate

dept

h (km

)

Limits of MiddleMiocene outcrop

Strike-slipfaulting

Jebel Abd el Azizelevation 932 m Cretaceous

outcrop Surfacefaulting

Average elevation north of Jebel Abdel Aziz is ~300 m

Two

-wa

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me

(sec

)

0

1

2

Middle Cambrianand older

Lower Paleozoic

Middle and Lower TriassicUpper

Cretaceous

Shiranish(synrift)formation

Maghlouja

Figure 5: Perspective block model of the Abd el Aziz uplift in NE Syria (see Figure 2 for location).Surface is Thematic Mapper imagery draped over topography. Faces shown are seismic linesUN-350 (dip) and SY-48N. Image 29x41 km: topographic exaggeration about x 5; subsurfaceexaggeration about x 2.

Brew et al.

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into a model in which the northern part of the Dead Sea Fault System has been active only during thesecond (post-Miocene) phase of faulting. In this model, 20 to 25 km of post-Miocene sinistral motionhas been accommodated along the northern fault segment, and another 20 km in the shortening of theadjacent Palmyride fold and thrust belt (Chaimov et al., 1990), thus accommodating the full 40 to 45km of post-Miocene slip.

The northern segment of the Dead Sea Fault System strikes parallel to the coast through western Syria,and is clearly defined both topographically and structurally (Figure 2). Along the fault in westernSyria is the Ghab Basin (Figure 7), a deep Pliocene to Holocene pull-apart structure (Brew et al., 2001).The Ghab Basin opened in response to a left-step in the fault, although sinistral motion fails to be fullytransferred across the basin, resulting in the horse-tailing of the fault system observed northwardinto Turkey.

The Syrian Coastal Ranges, in places more than 1,500 m high, occupy most of the Syrian onshore areawest of the Dead Sea Fault and Ghab Basin (Figure 2). An extensive karst terrain, a gently dipping(about 10) western limb, and a chaotic, steep, eastern limb where Triassic strata are exposed, characterizethe area. Stratigraphic relationships indicate that the uplift of the Coastal Ranges is part of the extensiveSyrian Arc deformation (Late Cretaceous and Tertiary compressional folding along the easternMediterranean coast) that has been documented in the Levant (Walley, 2001). The Coastal Rangeshave clearly been affected by the propagation of the Dead Sea Fault System and formation of the GhabBasin, resulting in the steep eastern limb (Figure 7) and the possible rotation of the block (Brew et al.,2001).

Figure 6: Perspective block model of the Euphrates Graben (see Figure 2 for location). Surface isThematic Mapper imagery draped over topography. Faces shown are seismic lines PS-14 (dip) andPS-11. Image 31x20 km.

Dablan

Qahar

Tayyani

Heavily cultivatedQuaternary fluvialdeposits

Very slight Neogenestructural inversion

Miocenecontinental clastics

Euphrates River

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Carboniferousand Silurian

LowerCretaceous

Triassic

Late Cretaceousnormal faults

Upper Ordovician

Lower Ordovicianand older

Appr

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STRUCTURAL AND STRATIGRAPHIC MAPPING

Database

The database available for this work is extensive by academic research standards, and this is the firsttime that all the data have been considered together. The primary data are 18,000 km of hardcopymigrated seismic reflection profiles of various vintages, and drilling records from over 400 wellsmany with comprehensive suites of logs (Figure 8). Supplemental data include 1,000 km of seismicrefraction, remote sensing and topographic imagery, gravity maps, and 1:200,000-scale geologic maps.

Concerning the interpretation of the seismic reflection profiles, the Cenozoic section is fairly unreflectivewith the exception of some Miocene evaporite layers (the Lower Fars and Dibbane formations). Thecarbonate Mesozoic section contains prominent seismic reflectors, and regional unconformities areeasily distinguished. The clastic Paleozoic section is poorly reflective with the exception of severalabrupt facies changes in Cambrian and Ordovician strata that form regionally observed reflectors.Paleozoic reflectors include the Burj limestone between the clastic Zabuk and Sosink formations, andthe Swab shale between the Khannaser and Affendi sandstones (Figure 9). Data quality decreasesmarkedly in areas of complex structure, most notably in the deeper areas of the Euphrates Graben andmost of the SW Palmyrides. Recordings are also very poor in areas of Cretaceous limestone on the

Figure 8: Locations of seismic reflection surveys and exploration and development wells. Wellcolors indicate depth of penetration; symbols show best available knowledge of the status ofwells summarized from various literature sources.

Seismic reflection profiles

TURKEY

IRAQ

JORDAN

LEBANON

Gas showOil showGas wellOil wellDry well

SYRIA

36E 37 38 39 40 41 42

36E 37 38 39 40 41 42

km

0 100

Med

iterra

nean

Sea

Blue wells haveMesozoic terminations

Green wells haveCenozoic terminations

Red wells havePaleozoic terminations

N

37N

36

35

34

33

37

36

35

34

33


583

Bilas Block, and basaltic outcrops (Wadi Sirhan traps) in southwestern Syria. Because the metamorphicbasement does not form a clear event on reflection records, high-quality, multifold refraction datahave been used to determine the depth to basement throughout Syria (Seber et al., 1993; Brew et al.,1997). Well-to-seismic ties are based on synthetic seismograms and associated time-depth curves.

The locations of our data, including all digitally held data, are stored within a Geographical InformationSystem (GIS) for easy retrieval and analysis. Many data interpretations have been conducted withinthe GIS, thus harnessing the power of multiple-dataset visualization, manipulation, and combination(for more details see Brew et al., 2000). As the limitations of a printed journal do not allow a fullappreciation of this digital approach, we have provided downloadable versions of many of our resultsand interpretations via the Internet (http://atlas.geo.cornell.edu/syria/welcome.html).

Lithostratigraphic Evolution

Recent contributions to the understanding of Syrian stratigraphy and paleogeographic evolution arerelatively numerous (e.g., Ponikarov, 1966; Al-Maleh, 1976, 1982; Mouty and Al-Maleh, 1983, 1988,1992, 1994; Sawaf et al., 1993; Mouty, 1998). These workers have concentrated on the extremely well-exposed Mesozoic carbonate section in the Palmyride fold and thrust belt, the Syrian Coastal Ranges,and the Kurd Dagh Mountains (Figure 2). Most recently, Sharland et al. (2001) have provided the firstsequence stratigraphic synthesis of Arabian Plate stratigraphy.

Using extensive drilling records, surface observations, and preexisting studies, we present a newgeneralized lithostratigraphic chart showing the variations of Syrian strata in time and space(Figure 9). The dating of the drilling records was accomplished using the biostratigraphic techniquesof the Syrian Petroleum Company. Clearly illustrated in Figure 9 is the shift from predominantlyclastic Paleozoic deposition to Mesozoic and Cenozoic carbonates. Furthermore, numerous widespreadunconformities showing long-lived hiatuses and erosion occur throughout the section, particularlyduring the Devonian and Late Jurassic. Many of the unconformities that we recognize in Syria arepenecontemporaneous with the boundaries of Arabian Plate (AP) tectonstratigraphic megasequencesof Sharland et al. (2001), denoted AP 1 to 11. These correlations are noted in the text and on Figure 9.Throughout this work we have used the timescale of Gradstein and Ogg (1996), consistent with Sharlandet al. (2001).

Figure 10 is a series of isopach maps of the four major Mesozoic and Cenozoic sedimentary packages,as derived from well and seismic data. The long-lived Rutbah-Rawda Uplift and Aleppo Plateau(Figure 2) show the least complete stratigraphic sections whereas the section is most complete in theprominent Palmyride/Bishri/Sinjar depocenter. For much of the early Mesozoic, the Palmyridedeposition was linked to the Sinjar area (Figures 10a and 10b), whereas for the Late Cretaceous, Sinjarstrata show much closer affinity to rocks of similar age in the Euphrates Graben. This reflects the shiftin subsidence from the Palmyride/Sinjar Trough to the Late Cretaceous fault-bounded extension ineastern Syria (Figure 10c). Furthermore, note the limited Jurassic/Lower Cretaceous section causedby widespread erosion and non-deposition related to regional Late Jurassic/Early Cretaceous uplift.Preserved Cenozoic patterns are dominated by subsidence along the Euphrates Fault System (Figure 10d).

The various formation names used in Syria are often site-specific (Figure 9), leading to a cluttered andconfusing nomenclature. Furthermore, surface and subsurface geologists have historically useddifferent nomenclatures, so compounding the already difficult task of correlating subsurface and surfaceformations. Paleozoic formations in particular are notoriously difficult to distinguish because ofscattered drilling penetrations that compound the often poor differentiation in drill logs, thus renderingdetailed chronology impossible (e.g. Ravn et al., 1994). In rocks of Mesozoic age, confusion involvingthe Kurrachine through Serjelu formations is well-known as they have distinctly different ages inSyria compared to the similarly named formations in IraqMiddle Triassic to Upper Triassic in Syria,versus Upper Triassic to Middle Jurassic in Iraq (see Sharland et al., 2001). In our discussion of Triassicand Jurassic strata we have used traditional formation names (as maintained by the Syrian PetroleumCompany and widely used in the literature) and their modern (e.g. Mulussa Group) equivalents. Thedetailed correlation of Syrian formations, and integration into the regional scheme of Sharland et al.(2001) is of pressing importance.

Brew et al.

584

Figu

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585

The main trends of Phanerozoic thickness changes in Syria (Figure 11) include a southward and eastwardthickening of early Paleozoic strata (illustrated by the East Ratka-101 well), on the Gondwana passivemargin. In the late Paleozoic and Mesozoic, deposition shifted to the west (Abou Zounar section) asthe Levantine passive margin developed (Best et al., 1993). From the late Paleozoic onward, the influenceof the long-lived structural highs of the Rutbah-Rawda Uplift (Tanf-1 well) and Aleppo Plateau(Khanasser-1 well) is apparent. Late Paleozoic and Mesozoic strata are concentrated in the Palmyride/Sinjar Trough, with significant along-strike variation apparent (Bishri-1 and Derro-2 wells). Rapidthickness changes in eastern Syria are associated with Late Cretaceous basin formation (Ishara-101well, Euphrates Graben; Tichreen-301 well, Sinjar Graben), and the influence of Neogene MesopotamianForedeep formation (Swedieh-110 well). Finally, evidence of the uplift and erosion of the Cenozoicsection is seen in the Palmyrides (Balaas-1 well and Abou Zounar section) and Sinjar Uplift(Tichreen-301 well).

Subsurface Structural Maps

We present new subsurface structural maps of four horizons chosen for their geophysical prominenceand tectonic significance (Figures 12a to 12d; stratigraphic positions shown in Figure 9). Each mapshows the present depth to the top of the subject horizon, together with the overlying subcroppingformation, and the current structure.

Areas of highest data density in Syria are invariably those where hydrocarbon production is highest,or where the structure is most complex. Accordingly, these maps show most structure on the EuphratesFault System, parts of the Palmyrides, and in northeastern Syria. However, as data quality and densitydecrease with depth, so does the accuracy of these maps. For example, 460 wells penetrate the topCretaceous horizon whereas only 190 reach as deep as the Paleozoic (Figure 8). The degree of reliabilityin the subsurface mapping of the lower Mesozoic and Paleozoic of the Palmyride region is the lowest,as seismic data are generally not interpretable and well penetrations are few.

In eastern Syria in particularly, the structural mapping was at a much larger scale (typically 1:500,000)than presented in this paper. As a result, there are countless small structures beyond the presentationresolution; conversely, in areas of very low data density, some large faults undoubtedly remainunmapped. The chosen scale of presentation is a compromise.

The maps are not structurally restored. They show present deformation rather than the structure anddepths at the time of deposition of the target horizon. This is why, for example, the Top Triassichorizon demonstrates reverse faulting in the SW Palmyrides although at the time of deposition thesewere normal faults. The symbols on the faults are designed to show the approximate past history offault movement. In addition, present-day depths are shown not those during deposition. For example,the top Paleozoic in the Palmyrides is shown as predominantly uplifted (Figure 12d), whereas it wasa depositional topographic low.

Top Cretaceous

The Top Cretaceous horizon (Figure 12a) illustrates well the effects of Syrian Cenozoic compressionaltectonics. Note the strongly inverted Palmyride Trough (especially the Bilas Block), and the Abd elAziz-Sinjar Uplift. The large sag above the Euphrates Graben is a result of the Paleogene thermalsubsidence. Recent basin formation in western Syria is also illustrated. In general, faulting in easternSyria halted before the end of the Cretaceous. Hence, unless there has been Cenozoic reactivation andfault-propagation of these features, the faulting is not observed at the Top Cretaceous level. The well-developed Al-Daww Basin in the central Palmyrides affected all stratigraphic levels.

Top Lower Cretaceous

The Lower Cretaceous sandstone is a good seismic reflector and forms many hydrocarbon reservoirsin Syria (Figure 12b). Hence it is of particular economic interest. As shown by the subcrop distribution,this sandstone was deposited across most of Syria except on the exposed Rutbah-Rawda Uplift from

Brew et al.

586

37E

37N

N0

km

100

(a)

Thickness (m)

IsopachFault

1,5002,0001,0001,5005001,0000500

2,5003,0003,000+

Outcrop

2,0002,500

(b) 37E37N

Cenozoic

Upper Cretaceous


587

37E

37N

N0

km

100

(c)

(d) 37E37N

Triassic

Lower Cretaceous and Jurassic

Figure 10: Isopach maps of Syriashowing the present thickness ofthe four major Cenozoic andMesozoic sedimentary packages, asderived from well and seismic data;contours at 250 m intervals; coloredunits 500 m thick: (a) Cenozoic, (b)Upper Cretaceous, (c) LowerCretaceous and Jurassic, (d) Triassic.

Brew et al.

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Figu

re 1

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ra-1

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589

which these sands were largely derived (de Ruiter et al., 1994). Later, they were eroded from exposedparts of eastern Syria.

The map shows the full extent of the Euphrates Fault System and Abd el Aziz-Sinjar deformation.Note the distribution of normal faulting in the Euphrates Graben with no major rift-bounding faults.In northeastern Syria, the superposition of the three prominent fault directions is illustrated. Thismap and those on underlying horizons (Figures 12c and 12d), generally show very similar structures.This is because much of the structure in Syria developed on deeply penetrating, high-angle faults.The net sense of offset of any particular horizon changes down section and this is observed on many ofthe mapped faults. However, the locations of the faults remain essentially fixed at this scale ofpresentation. Although some faults only cut the lower portion of the sedimentary column, they areoften either too small or too poorly imaged to be mapped. The biggest difference between Figures12a to 12d is the depth to top of the chosen horizon. Obviously, this is a function of the thickness ofthe strata above it. As we have seen (Figure 11), this can change considerably throughout Syria.

Top Triassic

The Triassic subcrop distribution (Figure 12c) shows the extensive Mulussa F deposition (uppermostTriassic, Serjelu Formation) that covered much of the country. It marks the beginning of a regionaltransgression that continued through the Early Jurassic. Note that some of the Formation was removedby Late Jurassic/Early Cretaceous erosion especially in eastern Syria; thus the original deposition waseven more extensive. The underlying Mulussa Group shows progressively limited extent up-section,again affected by widespread Late Jurassic/Neocomian erosion after regional deposition(Sharland et al., 2001).

Top Paleozoic

Figure 12d has the poorest accuracy of the four maps presented due to a severe decrease in the qualityof seismic reflection data from Paleozoic depths, and fewer well penetrations. As with the overlyinghorizons, the greatest depths are found in the Sinjar Trough and the Euphrates Graben, and in isolatedbasins of western Syria. Note the broader downwarping at this level in the Sinjar area that indicatesthe broad extent of the Triassic Sinjar Trough.

The subcrop pattern is dominated by the widespread Permian Amanous Formation. The map alsoshows the continuation of the Permian Palmyride Trough into the Sinjar area. Note that in the invertedareas of the Palmyrides and Sinjar uplifts, reverse faults are still shown at this level based on well andseismic data showing uplift across these structures. However, associated fault-propagation folds aregreatly subdued or absent (Chaimov et al., 1993). Furthermore, in the southwest of the Palmyride foldand thrust belt, the Top Paleozoic is below the local Triassic-age detachment, and therefore is notsignificantly faulted or folded. However, in the Bilas and Bishri blocks, the thick-skinned deformationhas affected all structural levels. Again, the quality of the mapping is relatively poor for these structures.

Deeper Crustal Structure

The crystalline Precambrian basement in Syria is generally deep (>6 km) and has not been penetratedby drilling. Furthermore, the basement does not form a good seismic reflector. Hence, we have mappedthe basement (Figure 13) using seismic refraction data (Seber et al., 1993; Brew et al., 1997). The depthto the Moho beneath Syria has been estimated from receiver function analysis (E. Sandvol, personalcommunication, 2000). The limits of Moho depths shown on Figure 13 have been calculated fromaverage crustal velocities in the range of 6.2 to 6.8 km/sec. Using the Bouguer gravity anomaly fieldfor Syria (BEICIP, 1975), plus the additional information for basement and Moho depths, we developednew gravity models along two profiles across the Palmyrides (Figure 14).

The first profile crosses the Aleppo Plateau, SW Palmyrides, and the Rutbah Uplift, and shows aclearly dichotomous gravity anomaly on either side of the Palmyrides (Figure 14a). External controlson Moho and basement depths projected along strike into the section, are shown as boxed annotations.

Brew et al.

590

Normal faultReverse faultStrike-slip faultNet normal with oldernormal and reverse motionNet reverse witholder normal motion AnticlineSyncline

Predominant movement on faultsmany with complex history(Unmarked faults have no distinctive sense of motion)

Abd el Aziz Uplift

SinjarUplift

South

west

Palm

yride

s

Ant

i-Leb

anon

CoastalRanges

Top Cretaceous

5001,000+1,000

0500 0 -500

-500 -1,000 -1,000 -1,500-1,500 -2,000-2,000 -2,500-2,500 -3,000-3,000 -3,500-3,500 -4,000-4,000 -4,500-4,500 -5,000

Depth to Top of Unit (m)(in relation to sea level)

Surface Geology

Euphrates Graben

Upper CretaceousLower CretaceousJurassic

37E

37N

(a)

BilasBlock

BishriBlock

Top Lower Cretaceous 37E37N

(b)

Stippled areas indicateextent of no Lower Cretaceous subcrop

In stippled area, Souknhne Formation is the Top of Cretaceous. In all other areas (except eroded parts) Shiranish Formation is Top of Cretaceous.


591

Top Triassic37E37N

(c)

Black contours and labels show the limits of the uppermost subcropping Triassic formations

KA = Kurrachine AnhydriteKD = Kurrachine Dolomite

Top Paleozoic37E37N

(d)

1000

km

N

Black contours and labelsshow the limits of the uppermost subcropping Paleozoic formations

No Triassic

Butm

a

Butma

Butma

Butma

Butm

a

Butma

K.A.

K.A.

K.D.

K. Dolomite

Allan/Mus

s

Allan/MussAllan/Muss

Adaya

Allan

/Mus

s

Affendi

Affendi

Affen

di

Tanf

Tanf

TanfTanf

Marka

da

Markada

Markada

Markada

Markada

Mar

kada

Tanf

Tanf

Swab

Aday

a

Adaya

Adaya

Adaya

K. An

hydr

ite

K. Anhydri

te

K. Anhy

drite

K. Do

lomite

K. Dolo

mite

K. Do

lomite

No Tr

iassic

Allan/Muss

Allan/M

uss

Serjelu

Serjelu

Serjelu

Serjelu

Butm

aSe

rjelu

Allan/Mus

s

K. Do

lomite

Aday

a

Amanus

Amanus

Mark

ada

Aman

us

Figure 12: Depth, structure, andstratigraphy of subsurfacegeological horizons as derived fromseismic and well data (see Figures 8and 9): (a) Top Cretaceous, (b) TopLower Cretaceous, (c) Top Triassic,(d) Top Paleozoic.

Brew et al.

592

N

mgal-100

-75

-50

-25

0

25

50

Seismic refraction profile Depth to metamorphic basementfrom refraction interpretationMinimum depths to basementfrom well data

Gravity profile (Figure 14)Seismograph station

Depths are in kilometers below sea level

Probable Moho depth range usingreasonable crustal velocities (seetext) and receiver functionanalysis from seismological data

6.0 2831

2831

4244

3740

2831

>3.1

>3.1

b

a

Rmahintrusives trend

0 100

km

5.5

8.0

5.05.5

10.0

8.5

>7.0

>7.5

8.0

9.0

6.0

6.0

5.5

>5.3

Using these constraints, we constructed a suitable density model beneath the profile with less thanabout 3 mgal difference between observed and calculated gravity responses. Firstly, we investigatedcrustal-scale effects without concern for the second-order anomalies. The result (black line inFigure 14a) shows a large difference in crustal thickness and density on either side of the Palmyrides,with a discontinuity around the present surface position of the Jhar Fault. A small crustal root, of 2 to3 km, is required beneath the SW Palmyrides to satisfy the receiver-function Moho depth. Speculativemodeling of the second-order anomalies along this transect (dashed pink model and anomaly inFigure 14a) shows that arbitrary, high-density intrusions beneath the Palmyrides can be used to matchthe observed anomalies very closely. These intrusions could perhaps be an extension of the Rmahtrend clearly imaged by the gravity data (Figure 13), and described by Best et al. (1990).

The second gravity profile also crosses the Aleppo and Rutbah highs, but traverses the Bilas Block ofthe Palmyrides (Figure 14b). Large density and thickness differences on either side of an interface ator near the Jhar Fault are again required. There is no requirement for a well-developed crustal root,but a small flexing of the southern block on the southern margin of the Palmyrides improves the fit ofthe model.

Figure 13: Bouguer anomaly map of Syria (BEICP, 1975) together with topographic imagery. Note(1) abrupt along-strike variation in gravity anomalies in the Palmyrides coincident with topographicchange, and (2) contrast between Bouguer anomalies north and south of the Palmyrides.


593

Figure 14: Gravity models on profiles through central Syria (see Figure 13 for locations). Densitiesin g/cm3 in parentheses; boxed comments are constraints other than through gravity modeling;white dots show locations of seismic refraction constraints. (a) Aleppo Plateau, SW Palmyrides,and Rutbah Uplift; anomaly shown with and without two otherwise unconstrained intrusive bodies(striped) that account for second-order gravity anomalies. (b) Bilas Block: note that model does notrequire a significant crustal root beneath the Block.

Distance (km)0 100 200 300

Dep

th (k

m)D

epth

(km)

40

35

30

25

20

15

10

5

0G

ravit

y (m

gals)

-60

-40

-20

0

Gra

vity

(mga

ls)

-60

-40

-20

0

North-northwest South-southeast

North-northwest South-southeast

0 100 200 30045

40

35

30

25

20

15

10

5

0

(b)

With stripedintrusions

Observed

Calculated

Observed

Calculated

(2.99)

Bilas Block

AleppoPlateau

RutbahUplift

RutbahUplift

AleppoPlateau SW Palmyrides

(a)

Seismic-refractionderived basement

Receiver-functionderived Moho

(2831 km)


(4244 km)

Intrusionalso interpreted

on magnetic data

LOWER CRUST (2.92)LOWER CRUST (2.87)

UPPER CRUST (2.70)UPPER CRUST (2.75)

CENOZOIC (2.30)

MANTLE (3.20)

JharFault?

PALEOZOIC (2.60)

INTRUSION(2.98)

INTRUSION(2.99)


(3740 km)

LOWER CRUST (2.92)LOWER CRUST (2.87)

UPPER CRUST (2.70)UPPER CRUST (2.75)

CENOZOIC (2.30)

MANTLE (3.20)


(2831 km)

JharFault?

PALEOZOIC (2.60)

Seismic-refractionderived basement Minimumbasement

depth

Minimumbasement

depth

MESOZOIC (2.40)

MESOZOIC (2.40)

Brew et al.

594

These results support the hypothesis that Syria, like the rest of the Arabian Plate, formed through aProterozoic amalgamation of microplates and island arcsthe Pan-African system (Stoeser and Camp,1985). This left a series of suture/shear zones underlying the continent that have acted as zones ofweakness throughout the Phanerozoic. The difference in basement depth, and crustal thickness anddensity on either side of the Palmyrides could indicate that northern and southern Syria are differentcrustal blocks, sutured along the Palmyride trend. Furthermore, the Jhar Fault, one of the majorstructural features of the Palmyride area, could be marking the position of the suture as first suggestedby Best et al. (1990). Assuming this scenario, crust of Rutbah-Rawda Uplift affinity underlies thepredominantly thin-skinned deformation of the SW Palmyrides, whereas Aleppo Plateau crustunderlies the Bilas and Bishri blocks that exhibit predominantly thick-skinned tectonics. This mightdemonstrate that the Proterozoic architecture of the Arabian Plate is controlling the style, as well asthe location, of Phanerozoic deformation. Walley (1998) argued that this suture zone is traceablewestward through Lebanon. He correlated the deformation style of the northern and southern LebaneseMountains with the NE Palmyrides and SW Palmyrides. Walley (1998) mapped many tens of kilometersof north-south separation between the present locations of his Lebanese and Syrian sutures,presumably suggesting this much translation on the northern part of the Dead Sea Fault System.

The presence of a crustal root appears to follow the leading edge of the southern block. The rootobserved in Figure 14a and the flexure that is observed in Figure 14b could both be interpreted asbending at the leading edge of the southern block. This could be a loading effect created by thePalmyrides themselves preferentially affecting the Rutbah Block, suggesting it may be flexurallyweaker. Alternatively, the increased root formation in the west could be explained by the proximityof profile 14a to the Anti-Lebanon, a crustal load much larger than the Palmyrides.

INTEGRATED TECTONIC MAP

The new tectonic map of Syria (Figure 15: as poster in pocket between p. 596597) shows generaltectonic elements, outcrop distribution, shaded relief imagery, and seismicity. The faults and foldsshown in black were mapped at the surface by Dubertret (1955), Ponikarov (1966), and Searle (1994),or are from our surface observations and limited remote-sensing imagery interpretation. The subsurfacestructure, in red, is modified from the Top Lower Cretaceous structure map (Figure 12b). This levelwas chosen to represent the subsurface as most faulting cuts this horizon, yet it is still relatively closeto the surface. As shown in Figure 12, the sense of motion on these faults may change according to theparticular structural level that is considered.

Figure 15, although relatively accurate at the scale of presentation (1:1,000,000) is undoubtedlyincomplete in some areas. The sense of motion on many of the mapped structures is also ambiguous.In particular, we have mapped many of the reverse faults that core the anticlines of the SW Palmyridesas being reactivated normal faults. Although this is true for many of the faults, some may be thrustfaults detached in the Triassic. Strike-slip activity is also extremely difficult to map accurately in thesubsurface and it is only noted where known with some certainty. Assuredly, many more faults havestrike-slip components than are identified on this map. The map shows again how most deformationin Syria is focused within the four major structural zones of the Palmyrides, the Abd el Aziz-Sinjararea (NE Syria), the Euphrates Fault System, and the Dead Sea Fault System.

Earthquake locations are taken from the International Seismological Center s database(196494), and from the local Syrian seismograph network (199596). Also shown are Harvard CMTfocal mechanisms (197796), supplemented by work at Cornell (Seber et al., 2000). These focalmechanisms are only loosely constrained because of the relatively small size of the events involved.Moreover, the apparent lack of events along the northern Dead Sea Fault System relative to the southernpart of the fault system is a consequence of sparse station distribution in Syria. Nevertheless, there isan obvious concentration of events along the Dead Sea Fault System, some events within the otherSyrian tectonic zones, and very few events in the stable areas of Syria. Also, note the clear alignmentof many events across Syria on the line of the Palmyrides and farther northeast on the trend of thehypothetical suture/shear zone discussed above.


595

GEOLOGICAL EVOLUTION OF SYRIA

Our regional tectonic and geologic evolutionary model presents the interpreted evolution of Syria andSyrian tectonic zones in a regional and global context (Figure 16: as poster in pocket betweenp. 596597). There are many paleoplate reconstructions for the evolution of the Tethys and easternMediterranean, and the issue is still under debate (e.g. Robertson and Dixon, 1984; Dercourt et al.,1986; Ricou, 1995; Stampfli et al., 2001). The reconstruction shown here (Figure 16) is generalized fromStampfli et al. (2001), and is an aid to discussion, rather than an endorsement of validity. Nevertheless,their model is broadly in agreement with our findings. In the discussions below, we refer to present-day polarities. For example, what we refer to as an early Paleozoic E-facing passive margin, waspredominantly N-facing at that time (Figure 16, frame 1a), but was subsequently rotated approximately90. All the frames in Figure 16 are oriented with north roughly toward the top of the page.

Proterozoic (>545 Ma) to End Cambrian (495 Ma)

It has long been accepted that the southern Arabian Plate formed through Proterozoic accretion ofisland arcs and microplates against northeast Africa, most probably between about 950 Ma and 640Ma (Beydoun, 1991) as part of the Pan-African orogeny. Suture zone relics from this accretion, and theNajd-style faults that formed when these sutures were reactivated are well exposed in the ArabianShield (Stoeser and Camp, 1985). Based on geophysical evidence (see discussion above and Best et al.,1990; Seber et al., 1993; Brew et al., 1997) we suggest that the northern part of the Arabian Plate is aresult of a similar concatenation although with a different orientation. Specifically, we find that thecurrent Palmyride fold and thrust belt may overlie the approximate location of a Proterozoic suture/shear zone. Reactivation of this crustal weakness appears to have profoundly affected the tectonicevolution of Syria throughout the Phanerozoic, from the formation of the Palmyride/Sinjar Trough tothe later Palmyride fold and thrust belt.

From about 620 Ma to 530 Ma, continental rifting and intracontinental extension followed the accretion,together with strike-slip movement on the Najd fault system, and Infracambrian and Early Cambriansynrift deposition (Husseini, 1989) (megasequence AP1 of Sharland et al., 2001). Owing to their greatdepth, no direct dating of the oldest sediments in Syria is available. However, from seismic refractioninterpretation we infer Infracambrian to Lower Cambrian strata between 1 and more than 2.5 kmthick across Syria (Seber et al., 1993; Brew et al., 1997). Significant thicknesses of Infracambrian sandstoneand conglomerate are present in SE Turkey (Derik and Camlipinar formations) and in Jordan (SaramujFormation). Husseini (1989) suggested that these synrift and postrift strata resulted from the JordanValley Rift that formed between Sinai and Turkey during the Infracambrian (Figure 16).

The drilled Cambrian rocks of Syria are arkosic sandstones, probably derived from a granitic basementin the south, together with some siltstone and shale (Figure 16, frame 1a). The exception to the clasticCambrian section is the Early to Middle Cambrian Burj limestone formation that is present throughoutSyria (Figure 9), below the maximum flooding surface (MFS) Cm20 of Sharland et al. (2001). Theregional extent of this monotonously carbonate formation on both sides of the Palmyrides suture ismore evidence for the cessation of cratonization and regional intracontinental extension of northernArabia before the Middle Cambrian (about 515 Ma) as discussed above (Best et al., 1993).

An erosional unconformity at the top of the Cambrian (Figure 9), is just one of many unconformitiesthat punctuate the Paleozoic section. This was a time of relatively shallow water over much of Arabia;consequently, relatively minor eustatic variations easily caused hiatuses and erosion.

Ordovician (495 Ma) to Early Silurian (428 Ma)

Ordovician strata were deposited across a wide epicontinental shelf that was especially well developedon the northern and eastern margins of the Arabian Plate. The Syrian Ordovician section increases inthickness from 1.6 km beneath the Aleppo Plateau to more than 3.5 km in the southeast beneath theRutbah-Rawda Uplift (Figure 11), and in eastern Jordan. Wells in the west of Syria penetrated analmost wholly sandy Ordovician section, whereas those in the southeast intersected significant amounts

Brew et al.

596

of siltstone and shale (Figure 9; Figure 16, frame 1b). These facies and thickness trends in the SyrianOrdovician indicate open-marine conditions to the east, and also in Iraq and Turkey (Sharlandet al., 2001). The source areas for the Ordovician, and other Paleozoic clastics, were the extensiveArabian and Indian Precambrian shields exposed to the south and west (Figure 16, frame 1a), and anever-increasing amount of reworked sediments.

The top Ordovician unconformity is the base of megasequence AP3 of Sharland et al. (2001), whoattribute the unconformity to hinterland uplift in western Saudi Arabia. The Rawda-Rutbah High(Figure 16, frame 2b) in the extreme east of Syria and the western part of Iraq was exposed during thisLate Ordovician to Early Silurian regression. The Upper Ordovician Affendi Formation is missing inthe extreme southeast of Syria, and thinned dramatically over the Rawda High (Best et al., 1993).Beydoun (1991) showed that this exposed/structurally high area extended from Turkey to Saudi Arabiaduring the Late Ordovician and Early Silurian, and probably had a tectonic origin.

Polar glaciation of much of Gondwana, including western Arabia, occurred in the Late Ordovician.Deglaciation in the Early Silurian, as Gondwana drifted towards the tropics, caused sea levels to risesharply flooding much of Arabia and depositing what is now an extremely important regionalhydrocarbon source rock (Beydoun, 1991). In Syria, these Early Silurian graptolitic shales (the TanfFormation, Figure 9), were deposited during this transgression (Figure 16, frame 2b). Although nowthickest within the Palmyride/Sinjar Trough (Best et al., 1993), they were probably originally 500 to1,000 m thick across the entire region.

Late Silurian (428 Ma) to Devonian (354 Ma)

The Lower Silurian section in Syria is directly overlain by Carboniferous clastics, demonstrating anunconformity of major temporal and spatial extent. Strong tectonism and volcanism occurredcontemporaneously at many localities in northern Gondwana. Some authors cite two events. Thefirstloosely referred to as Caledonianis of Late Silurian age and the other is of Middle to LateDevonian/Early Carboniferous age, (Husseini, 1992), referred to as Hercynian sensu lato by Sharlandet al. (2001). The absence of preserved strata in Syria prevents such a distinction there. Suggestions ofthe cause of this tectonism include regional compression caused by the obduction of the Proto-Tethyson what is now Iran (Husseini, 1992); uplift on the flanks of the Paleo-Tethys rifting (Stampfli et al.,2001); or a more localized thermal uplifting event (Kohn et al., 1992) (Figure 16, frame 2a).

Whatever the tectonic cause, strata of Late Silurian and Devonian age are almost totally absent fromArabia, and the underlying Early Silurian shales are substantially eroded. The present subcrop patternof Silurian strata in Syria shows an elongate depocenter roughly along the trend of the currentPalmyrides (Best et al., 1993), and a thinned to absent Silurian succession to the north and south. Thiscould be interpreted as evidence for an Early Silurian initiation of the major Palmyride/Sinjar Trough.However, based on a slight angular unconformity observed at the top of the Silurian (Best et al., 1993),we suggest that this subcrop pattern is a result of Late Silurian and Devonian preferential erosion onthe Rutbah-Rawda and Aleppo structural highs southeast and northwest of the Palmyrides, respectively.

During both the Late Ordovician and Late Silurian/Devonian, the Rutbah and Rawda uplifts wereapparently most prominently exposed east of the current structural and topographic high (compareFigure 2 with Figure 16, frame 2b). These highs were then centered near the present location of theEuphrates Graben. Previous publications (e.g. Litak et al., 1997) have examined the possibility thatthe Euphrates Fault System may have formed above a Proterozoic suture/shear zone similar to thatproposed beneath the Palmyrides. However, given little evidence of subsidence or faulting along theEuphrates trend before Late Cretaceous time, this is now considered unlikely. The Rutbah and Rawdahighs (Figure 2) were evidently connected through most of geologic time until Late Cretaceous dissectionby the Euphrates Fault System. Other than a few episodes of minor subsidence after emergence in theDevonian, the basement-cored Rutbah-Rawda Uplift remained structurally high for the rest of thePhanerozoic. The difference in basement depth across the Euphrates Fault System (Brew et al., 1997)(Figure 13) could be explained by a continuation of the Palmyride suture to the east, combined withthe deep-seated Euphrates faulting.

4.7

4.84.95.1

5.0

5.4

4.8

4.7

6.0

4.8

4.5

5.6

?

?

?

?

/

EuphratesRiver

IRAQ

JORDAN

TURKEY

LEBA

NON

PA

LM

YR

I DE

S

PA

LM

YR

I DE

S

MED

ITER

RAN

EAN

SEA

Ghab BasinUp to 3.4 km of

Pliocene / Quaternaryclastics in pull-apart basin

Northern Dead Sea FaultFormed since Late Miocene,

1,600 m of Late Cretaceous

synextensional strata.Site of older Mesozoic trough

A B D E L A Z I Z / S I N J A RU P L I F T S

SW volcanic fieldsNeogene and Quaternary basalterupted from prominent volcanic

centers aligned NNW

Rutbah UpliftBasement-cored crustal block.

Thick (~7 km) Paleozoicsection, thicker crustthan northern Syria

Coastal Ranges~2.5 km of post-

mid Eocene uplift

Coastal Ranges~2.5 km of post-

mid Eocene uplift

Ghab BasinUp to 3.4 km of

Pliocene / Quaternaryclastics in pull-apart basin

Northern Dead Sea FaultFormed since Late Miocene,

Ear

lyE

arly

Ear

lyE

arly

Late

Late

LM

ML

EM

Late

Ear

lyE

arly

Late

Pale

ogen

eN

eoge

ne/

Quat

erna

ryM

Late

Ear

lyLa

teM

Ear

lyL

Carb

onife

rous

Silu

rian

Dev

onia

nO

rdov

icia

nCa

mbr

ian

Perm

ian

Tria

ssic

Jura

ssic

Cret

aceo

usCE

NOZO

ICPR

E-CA

MBR

IAN

100Ma

200Ma

300Ma

400Ma

500Ma

Ear

lyE

arly

Ear

lyE

arly

Late

Late

LM

ML

EM

Late

Ear

lyE

arly

Late

Pale

ogen

eN

eoge

ne/

Quat

erna

ryM

Late

Ear

lyLa

teM

Ear

lyL

Carb

onife

rous

Silu

rian

Dev

onia

nO

rdov

icia

nCa

mbr

ian

Perm

ian

Tria

ssic

Jura

ssic

Cret

aceo

usCE

NOZO

ICPR

E-CA

MBR

IAN

100Ma

200Ma

300Ma

400Ma

500Ma

AP11

AP10

AP9

AP8

AP7

AP6

AP5

AP4

AP3

AP2

AP1

Terminal collision afternorthern Arabian continental

margin shortening

Post-rift unconformity?

Initial final collisionalong northernArabian margin

Subductionin Neo-Tethys

Paleo-Tethyssuture

Paleo-Tethyssuture

EasternMediterranean

opened

Possible EasternMediterranean

openingPalmyride

trough,aulacogen

Hun superterranesutures to Laurussia

IncipientNeo-Tethysformation

Proto

-Tethy

s sutu

re

Axis

of fu

ture

Paleo

-Tet

hys r

iftin

g

Widespread unconformity

Widespread unconformity

Plate-wide unconformity

Regional 'glacial hiatus'

11a

10a

9a

7a

6a

5a

4a

3a

2a

1a

PLATE RECONSTRUCTION KEY

SYRIA TECTONIC/SEDIMENTATION KEY

Annotations in purple

Syrian Arc

a

b

12b

12b

11b

10b

9b

8b

7b

6b

5b

4b

3b

2b

11b

10b

9b

8b

7b

6b

5b

4b

3b

2b

1b

12a

12a

11a

10a

9a

8a

7a

6a

5a

4a

3a

2a

1a

11a

10a

9a

8a

7a

6a

5a

4a

3a

2a

1a

Bishri Block

IRAQ

Aleppo Plateau

LEBANON

Al DawwBasin

Mardin HighTURKEY

EUPHRATES FAULT SYSTEM

DerroHigh

Rawdah High

Anah Graben

Kurd DaghMountains

GhabBasin

Rutbah Uplift

Coas

tal R

ange

s

Homs

Depre

ssion Bilas Block

PALM

YRIDE

S

SW Pa

lmyride

s

Damascus

Hamad U

plift

MesopotamianForedeep

JORDAN

Aman

ous

Mou

ntai

ns

Anti-L

eban

on M

ounta

ins

EuphratesGraben

ABD EL AZIZ-SINJAR UPLIFT

DEAD

SEA

FAUL

TSY

STEM

km

0 100

Med

iterra

nean

Sea

N

Collision withtrench along

northern Arabianmargin

36

35

34

33

Axis o

f futur

e

Neo-Te

thys ri

fting

Pla

te c

onsu

mpt

ion

ATLA

NT

ICPA

LEO

-TE

TH

YS

Des

truc

tion

For

mat

ion

NE

O-T

ET

HY

SO

cean

spre

adin

gR

iftin

gP

RO

TO-T

ET

HY

SH

un s

uper

terr

ane

dock

s w

ith L

auru

ssia

Spr

eadi

ng b

egin

s in

Nor

th th

en S

outh

Atla

ntic

Sub

duct

ion

begi

ns in

Neo

-Tet

hys

Red Sea forms.Africa-Arabia

separate

Afr

ica-

Eur

asia

con

verg

ePa

ngea

Gon

dwan

a

Terminal Eurasia-Arabia collision

34 Ma

63 Ma

92 Ma

149 Ma

182 Ma

255 Ma

295 Ma

364 Ma

445 Ma

520 Ma

Middle Miocene (15 Ma)

Broad subsidencealong Palmyride / Sinjar

Trough; exact timinguncertain, probablyrelated to regional

folding

Palmyride /Sinjar Troughno longer rifting.

Thermal subsidenceand faulting

Uplift, tilting, volcanism and erosion probably mantle-plume related

Widespread reactivation

of normal faults,especially in NE

Palmyrides.Continued subsidence

Inversion alongLate Cretaceous

faults creates current

topography

Trans-pression,inversion

Extension ceases

Uplift and erosion

Uplift and erosion

Rifting esp.in SE;throw

distributed on many

faults

Continued subsidenceand limited fault

reactivation

Widespreadthermal

subsidence

Minortranspressionparticularly in

NW

Wide-spreadvolca-nism

No

dist

inct

tect

onic

act

ivity

in s

epar

ate

Syr

ian

tect

onic

zon

es;

gen

eral

ly m

arin

e co

nditi

ons

on G

ondw

ana

pass

ive

mar

gin

Uplift and erosion

Widespread transgression

Major rifting stage andsignificant deposition inthe Palmyride / Sinjar

Trough

SouthDSFS

Initial upliftof CoastalRanges?

Gen

eral

ly c

ompr

essi

onal

tect

onic

s an

d em

erge

nce

due

to c

ontin

enta

l con

verg

ence

Red Sea rifting;Arabia moves

N. relative to Africa

Anatolianfaults form

Pan-AfricanProterozoicaccretion

Polar glaciationin west Arabia

Trangression

Regional upliftand

erosion

Rifting, extension,synrift deposition

NajdWrench Fault

System

E-facing passive margin on northern Gondwana

No major tectonic events

Regionalfolding

Neo-Tethys Ocean

spreading alongNorth

Gondwana

Rifting along N. African margin, possibleE. Med.

spreading

Glaciation of

southern Arabia

Ophioliteobduction

Terminalsuturing

Cimmeriaseparates

fromGondwana

Subsidencein East

Mediterranean;development

of passivemargin

Ophioliteemplacement

GEOLOGIC EVENTS INARABIAN PLATFORM

ARABIANPLATE MEGA-

SEQUENCEBOUNDARIES(Sharland et al., 2001)

REGIONALPLATE RECONSTRUCTION

SYRIAN TECTONIC ZONES SYRIASEDIMENTATION AND FACIES TECTONIC AND GEOLOGICEVOLUTION OF SYRIA

FIGURE 16

TOPOGRAPHY AND TECTONIC ZONES OF SYRIA

MajorOceans

MajorContinents

PalmyrideFold and

Thrust Belt

NortheastSyria

EuphratesFault

System

DeadSea FaultSystem(DSFS)

Generalcomments

Latitude of central Arabia ~20o N

Latitude of central Arabia ~24o N

Arabia

Late Eocene (35 Ma)Extensive

volcanism

NEO-TETHYS

LYCIAN

End Cretaceous (65 Ma)

NEO-TETHYS

Late Campanian (75 Ma)

NEO

-TETHYS

Latitude of central Arabia ~8 o N

Santonian (84 Ma)

VARDAR

SEMAIL

NEO-TETHYS


Arabia

Aptian (112 Ma)

NEO-TETHYS

ME

LIAT

A

VAR

DA

R

Latitude of central Arabia ~0 o

Arabia

Late Jurassic (156 Ma)

MELIATA

NEO-TETHYS

Latitude of central Arabia ~7 oS

Arabia

Late Triassic (222 Ma)

Apulia

Pelagonia

Cim

merian continent

PALEO-TETHYS

NE

O-T

ET

HY

S

MELIATA


Arabia

Late Permian (~249 Ma)

PALEO-TETHYSCim

merian superterrane


Late Carboniferous (~295 Ma)

Gondwana

Cimmer

ian sup

erterran

e

PALE

O-TET

HYS

Hun s

upert

erran

e


Early Silurian (~435 Ma) Early Silurian (~435 Ma)

Shaly transgressivedeposits

Santonian (84 Ma)

Bishri and Euphratesdepocentersconnected

Minor Syrian Arcdeformation

Accelerated Palmyridesubsidence

RutbahUplift

Aptian (112 Ma)

Marginalmarine

Continued faultreactivation

in Bishri Block

Extensive, marly to marly

limestone deposition

Transtensioncontinues in

Euphrates GrabenUp to 2,000 m

Late Cretaceous synrift deposition

Extension inSinjar / Abd el Aziz,over 1,600 m of fill

AnahGrabenBeginning

of Palmyride uplift,further Syrian arc

deformation

Aafrine Basinforms

Late Permian (~249 Ma)

Slight upliftin SW Palmyrides

Ophioliteemplacement:

affects sedimentationin Aafrin basin

Thermal subsidencebegins above

Euphrates Graben

Northern marginreaches trench:

regional compression

End Cretaceous (65 Ma)

Palmyrides stillgenerally subsiding

Mid Miocene terminal suturing

Palmy

ride tra

nspres

sional

folding

and u

plift

Bishri Blockinversion

No deposition onRutbah and Aleppo uplifts

Dep

ositi

on a

long

subs

idin

g pa

ssiv

e m

argi

n

SinjarTrough

PROT

O-TE

THYS


Early Ordovician (~490 Ma)Gondwana

Middle Miocene (15 Ma)Plio-Quaternary

Abd el Azizand Sinjar uplift

Minor Euphrates

transpressionPlio

cene

DS

FS

SirhanGrabenrifting

BishriBlock, some

faulting

Triassicprogressively

onlappingRutbah Uplift

RutbahUplift

Progressively limitedTriassic deposition

Late Triassic (222 Ma)

Evaporitedeposition

Leva

ntin

e m

argi

nde

posi

tion

as

E M

ed. f

orm

s

Extensiv

e postrift

subsiden

ce, some

faulting,e

specially

in SW

Eastwardtransgression

following emergence

Deeper waterfacies in E

Deltaic sandstonessourced in the

S and SW

Main P

almyrid

e /

Sinjar

rifting

episod

e

Over

1,000

m

of Pe

rmo-T

riassi

c

clastic

s

E. Mediterraneanrifting

Rutbah and Aleppopossible uplifted

rift flanks

>1,700

m of

Carbo

niferou

s

clastic

s

Subsidingincipient

Palmyride /Sinjar Trough

HelezAnticlinorium

Extension stopsin eastern Syria

Late Carboniferous (~295 Ma)

Beginning of riftingin Euphrates Graben

Regional uplift, exposureand extensive erosion in

Late Jurassic / EarlyCretaceous, removed mostMid-Upper Jurassic strata

Jurassic thickenswestward

BishriBlock

Continued subsidence,normal fault reactivation

two depocenters inPalmyrides

Late Jurassic (156 Ma)

Regional transgression

Rut

bah

and

Ale

ppo

high

s up

lifte

d sh

ould

ers

of P

alm

yrid

e/S

inja

r tr

ough

Sub

side

nce

and

over

all e

xten

sion

thro

ugho

ut M

esoz

oic,

exc

ept f

orup

lift a

nd m

antle

-plu

me

activ

ity in

Lat

e Ju

rass

ic/ E

arly

Cre

tace

ous

Collision withtrench along

N. margin

LEGEND

Tectonic Features

Dominant Facies inActive Depositional Areas

Approximate Paleogeography

Approximate Generalized Paleogeography

Rift

Approximate plate boundary

SubductionZone

Spreading platemargin

Sandstone

Shale

Limestone

Marlylimestone

Marl

Ophiolite

Dolomiticlimestone

Dolomite

Tectonic Features

PRINTED AUGUST 2001

Reverse fault

Strike-slip fault showingdirection of movement

Normal fault

Relative major depocenter

Volcanic activity

OCEANIC FEATURES IN UPPERCASEContinental features in lowercase

Predominanttransport direction

Syrian international border

Sedimentary trend

Evaporites

DS

FSM

iocene

Late Campanian (75 Ma)Obduction

on northern margin

Mid-Late Eoceneinitial suturing along

northern margin

Late Eocene (35 Ma)Very minorAbd el Azizinversion

Mid-Eocene upliftin Palmyrides

Syrian Arcdeformation, uplift

of LebaneseMountains

Thermal sagabove Sirhan Graben

Broad thermalsubsidence aboveEuphrates Graben

Syrian tectonic evolution as part of the northern Arabian Plate: plate reconstructions are shown in frames 'a' (left); timelines of significant regional and local tectonic events are central; and Syrian tectonic evolution and sedimentation are shown in frames 'b' (right). Plate reconstructions are simplified after Stampfli et al. (2001) and are not to scale relative to each other; present-day Arabia is highlighted. Gradational coloring of timelines indicates degree of certainty. Relative dates of Arabian Plate (AP) tectonostratigrahic megasequence boundaries (Sharland et al., 2001) have been added for reference. Tectonic/sedimentation frames show elements generalized and in the correct contemporaneous position.

Brew, G., M. Barazangi, A.K. Al-Maleh and T. SawafTectonic and Geologic Evolution of Syria.

GeoArabia, v. 6, no. 4, 2001, p. 573-616.

Published by Gulf PetroLinkP.O. Box 20393, Manama, BAHRAINe-mail: [email protected]://www.gulfpetrolink.com

References:



Arabia

Arabia

Arabia

Arabia

Arabia

EASTERNMEDITERRANEAN

Arabia

36 E 37 38 39 41 42 40

Arabian -NubianShield

37 N

Arabia

Sharland, P.R., R. Archer, D.M. Casey, R.B. Davies, S.H. Hall, A.P. Heward, A.D. Horbury and M.D. Simmons 2001. Arabian Plate sequence stratigraphy. GeoArabia Special Publication 2. Gulf PetroLink, Bahrain, 371 p.

Stampfli, G.M., J. Mosar, P. Favre, A. Pillevuit and J.-C. Vannay 2001. Permian-Triassic evolution of the western Tethyan realm: the NeoTethys/east Mediterranean basin connection. In, W. Cavazza, A.H.F. Robertson and P. Ziegler (Eds.), PeriTethyan rift/wrench basins and passive margins. Memoires du Museum National d'Historie Naturelle, Paris, PeriTethys Memoir 6.

Two-

phas

e S

yria

n A

rc' d

efor

mat

ion

in S

inai

, Lev

ant,

and

Syr

ia

'

EWhalf-grabenformation

Initialuplift

Episodicuplift

North DSFSforms

Pal

myr

ide/

Sin

jar T

roug

h ge

nera

lly

cont

inuo

us e

nviro

nmen

t

Coastal margin

Oceanic

Continental areas and fragments

Very shallow marineor emerged

Deep marine

Shallow marine

South America,

Africaand

Africa-Eurasia diverge

North-South

America diverge

Suturing onN. margin;

margin shortening

Ope

ning

of E

aste

rn M

edite

rran

ean;

exa

ct ti

me

of fi

rst s

ea-f

loor

spr

eadi

ng u

ncer

tain

. E

piso

dic

reac

tivat

ion

of s

prea

ding

and

rift

ing

thro

ugho

ut M

esoz

oicRegional

uplift, tilting, and erosion

Epi

sodi

c M

esoz

oic

volc

anis

m, e

spec

ially

in L

iass

ic a

nd E

arly

Cre

tace

ous

rela

ted

to e

xten

sion

Date post:	03-Sep-2015
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Tectonic and Geological Evolution of Syria

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