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Graham Brew Ph.D. Dissertation: Chapter 1


Introduction


This dissertation concerns the tectonic evolution of Syria. Various geophysical and geological data have been interpreted in unison to document and analyze the Phanerozoic structural deformation of several areas within Syria. These interpretations are combined with previous work, and knowledge of regional plate tectonics, to form a complete Phanerozic tectonic model for all Syria.

The work presented here is the latest contribution of the 'Cornell Syria Project'. This academic / industrial collaboration has been active for over twelve years studying the northern Arabian Platform. Interest in Syria and the surrounding areas comes from several geologic and logistic motivations. The primary rationale is to study intracontinental areas that have experienced significant tectonism. Even a casual consideration of Syria shows that it is currently proximal to several active plate boundaries (Figure 1.1), and has been through much of geologic time, especially the Mesozoic and Cenozoic. Previous work of the Cornell Syria Project (e.g. Barazangi et al., 1993), and this dissertation, show how activity on these nearby plate boundaries has affected the deformation within Syria.

A further motivation is the very diverse styles and timing of tectonics within Syria. Tectonism within the country is concentrated in four major tectonic zones. These include a fold and thrust belt, a plate boundary transform fault, inverted basins and an extensive aborted rift. Inspection of the topography of Syria (Figure 1.2) immediately reveals the physiographic provinces that have prominent topographic expression.

The final motivation for the study of Syria is the relevance this work has in the search for hydrocarbons. Although not comparable with the vast reserves of the Arabian Gulf states, the oil and gas reserves of Syria are nonetheless important to the local economy. The maturation of many of Syria's older fields leads impetuous for new discoveries. Many recent efforts have focused on exploration in Paleozoic strata, deeper than most previous discoveries. Our mapping of stratigraphic distributions and structures, as well as regional tectonic elements, can assist in this search.

It is our great fortune that we have access to a very extensive geophysical and geological database that can be used to examine the diverse and interesting tectonics of Syria. Through the generosity of the Syrian Petroleum Company (SPC), the Cornell Syria Project has access to many thousands of kilometers of seismic reflection profiles, data from hundreds of wells, and many other data sets. Detailed descriptions and maps of these data are given in later chapters.

This dissertation is presented as a series of self-contained chapters, each concerned with a certain facet of Syrian tectonic evolution. Chapter 2, 3, and 4 examine the tectonic style and history within three distinct areas of Syria (Figure 1.2). Chapter 5 is concerned with the tectonic evolution of all Syria. In the remainder of this chapter (Chapter 1) a very brief tectonic tour of Syria is undertaken. The direct contributions of this dissertation to the understanding of these tectonics is given with reference to later chapters.

Syria consists of four major tectonic zones separated by less deformed areas. Extending ~400 km northeast from the Lebanese border in the west into central Syria are the Palmyrides, the largest topographic feature, and the first tectonic zone of Syria. The Palmyrides can be further divided, on the basis of topography and structure, into the Southwest Palmyrides (a fold and thrust belt), and the Bilas and Bishri blocks, Mesozoic sub-basins inverted during Cenozoic compression. The Palmyrides have been well studied previously by the Cornell Syria Project including Best et al. (1990; 1993), Chaimov et al. (1990; 1992; 1993), McBride et al. (1990), Al-Saad et al. (1991; 1992), Barazangi et al. (1993), Seber et al. (1993), and Alsdorf et al. (1995). They showed how the Palmyride area was an extensive Permo-Triassic rift, formed under regional extension associated with the opening of the NeoTethys Ocean and the eastern Mediterranean. While this dissertation does not directly add to their understanding, the Palmyrides are included in our discussion of regional tectonic evolution (Chapter 5). This includes structural maps for the Palmyrides, stratigraphic descriptions, isopachs, and seismic reflection examples showing the various styles of deformation.

The subdued topography of the second major tectonic zone, the Euphrates Fault System, belies its complex structure that harbors the greatest oil production in Syria. The Euphrates Fault System (Figure 1.2) extends across Syria from the Iraqi border in the southeast to the Turkish border in the northwest. The southeastern area, the 'Euphrates Graben' is the most intensely deformed part, and most reminiscent of a classic steep-sided graben. The Euphrates Fault System was rigorously studied by Cornell Syria Project researchers (Sawaf et al., 1993; Litak et al., 1997, 1998). They concluded that moderate latest Cretaceous rifting, distributed among many branching faults, was aborted near the end of the Cretaceous. Extensive Paleogene thermal sag above the rift was followed by very minor compression and structural reactivation in the Neogene. The structure, stratigraphy, and evolution of the Euphrates Fault System is detailed in (Chapter 5) in the context of the regional tectonic evolution.

Chapter 2 of this dissertation is an investigation of the deep structure of the Euphrates Fault System and the areas north and south of the rift. This study is based on the interpretation of a seismic refraction profile (see profile location in Figure 1.2). The powerful explosions used in the seismic acquisition and high density of data collection make this a very high quality dataset, unique for Syria. Offsets were long enough to record refracations from sedimentary basement in many places on the profile. These are the best constraints on basement depth available, as metamorphic basement is not penetrated by drilling or imaging on reflection data. The refraction data were interpreted using a ray-tracing approach together with other elements of our database to decrease ambiguity. The results show much deeper basement, and hence a thicker Paleozoic sedimentary section, south of the Euphrates. The interpretation also shows that the faulting in the Euphrates is complex, deep-seated, and steeply dipping.

Two topographically prominent uplifts in northeast Syria, the Abd el Aziz and Sinjar structures, reveal the location of the third major tectonic zone that is considered in Chapter 3 (see Figure 1.2 for location). Almost wholly unstudied in previously published work, the proximity to the northern Arabian margin and topographic expression made this an intriguing target for research. Chapter 3 presents many examples of seismic reflection profiles and maps that show the evolution of this zone. For much of the Late Paleozoic and Mesozoic the area was the northeastern extension of the Palmyride trough. This broad downwarping accumulated many thousands of meters of predominantly clastic Paleozoic strata and Mesozoic carbonates. In the latest Cretaceous this area was affected by the extensional tectonics that created the Euphrates Fault System. East west striking normal faults formed the Abd el Aziz and Sinjar grabens that amassed up to 1.6 km of syn-extensional marly limestone. (Chapter 3) goes on to show how these latest Cretaceous normal faults were structurally inverted from Late Pliocene time onwards. Fault-propagation folding above the structurally inverted latest Cretaceous normal faults has created the topography that is observed in northeastern Syria today.

The fourth and final major tectonic zone is the Dead Sea Fault System, an active transform plate boundary in western Syria. (Chapter 4), the final study of a specific area in this dissertation, examines the Ghab Basin, a pull-apart structure on the Dead Sea Fault System. The Plio-Quaternary age of the Ghab Basin suggests that the Dead Sea Fault System did not propagate through Syria until after the Miocene. This observation fits with previous models of two-phase Red Sea opening and Dead Sea Fault movement. The Late Cretaceous to Recent uplift of the Syrian Coastal Ranges is also documented. This prominent topography directly west of the Dead Sea Fault in Syria is shown to be part of the Syrian Arc deformation, albeit strongly modified on its eastern limb by the Dead Sea Fault System and Ghab Basin formation.

The ultimate result of this dissertation is a new regional tectonic evolutionary model for Syria, presented in (Chapter 5). This brings together many of the observations made in Chapters 2, 3, and 4, together with results from previous research and new interpretations. For the first time, data from all Syria are considered in totality. Adding significantly to this is the incorporation of many stratigraphic observations that refine the timing of many of the tectonic events that are discussed, and set the model into a regional paleogeographic framework. Additional products include a series of subsurface structural maps for the whole country and a new lithostratigraphic chart.

The plates presented in the back pocket of this dissertation are discussed in Chapter 5. Plate 1 is a new tectonic map for Syria. It shows a summary of our mapped tectonic elements, together with Syria geology (Ponikarov, 1966), topography, seismicity and other relevant data. Annotations on the map make it a single primary reference for any researcher concerned with the structure and tectonics of Syria. This mapping clearly shows how the vast majority of tectonic deformation within Syria is focused in the four major tectonic zones as outlined above. Plate 2 is our regional tectonic evolutionary model. It shows two different views of the northern Arabian Platform at twelve time points throughout the Phanerozoic. The first view is of regional plate tectonic reconstruction (modified from Stampfli et al., 2000), and the second is a schematic map of tectonic deformation in Syria. The timelines on Plate 2 show the timing of global, regional, and local tectonic events. In summary, Plate 2 contains the essence of all Cornell Syria Project work concerned with timing and styles of tectonic evolution. This chart shows the contemporaneous evolution of many structures within Syria, and the relationships between this evolution and regional plate tectonic events. To date, this is the single most complete tectonic summary, based on the most data, ever proposed for Syria.


References

Al-Saad, D., T. Sawaf, A. Gebran, M. Barazangi, J. Best and T. Chaimov 1992. Crustal structure of central Syria: The intracontinental Palmyride mountain belt. Tectonophysics, 207, 345-358.

Al-Saad, D., T. Sawaf, A. Gebran, M. Barazangi, J. Best and T. Chaimov 1991. Northern Arabian platform transect across the Palmyride mountain belt, Syrian Arab Republic. Global Geoscience Transect 1, The Inter-Union Commission on the Lithosphere and the American Geophysical Union, Washington, D. C.

Alsdorf, D., M. Barazangi, R. Litak, D. Seber, T. Sawaf and D. Al-Saad 1995. The intraplate Euphrates depression-Palmyrides mountain belt junction and relationship to Arabian plate boundary tectonics. Annali Di Geofisica, 38, 385-397.

Barazangi, M., D. Seber, T. Chaimov, J. Best, R. Litak, D. Al-Saad and T. Sawaf 1993. Tectonic evolution of the northern Arabian plate in western Syria. In E. Boschi, E. Mantovani and A. Morelli (Eds.), Recent Evolution and Seismicity of the Mediterranean Region, Kluwer Academic Publishers, 117-140.

Best, J.A., M. Barazangi, D. Al-Saad, T. Sawaf and A. Gebran 1990. Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian platform in Syria. Geology, 18, 1235-1239.

Best, J.A., M. Barazangi, D. Al-Saad, T. Sawaf and A. Gebran 1993. Continental margin evolution of the northern Arabian platform in Syria. American Association of Petroleum Geologists Bulletin, 77, 173-193.

Chaimov, T., M. Barazangi, D. Al-Saad and T. Sawaf 1993. Seismic fabric and 3-D upper crustal structure of the southwestern intracontinental Palmyride fold belt, Syria. American Association of Petroleum Geologists Bulletin, 77, 2032-2047.

Chaimov, T., M. Barazangi, D. Al-Saad, T. Sawaf and A. Gebran 1990. Crustal shortening in the Palmyride fold belt, Syria, and implications for movement along the Dead Sea fault system. Tectonics, 9, 1369-1386.

Chaimov, T., M. Barazangi, D. Al-Saad, T. Sawaf and A. Gebran 1992. Mesozoic and Cenozoic deformation inferred from seismic stratigraphy in the southwestern intracontinental Palmyride fold-thrust belt, Syria. Geological Society of America Bulletin, 104, 704-715.

Litak, R.K., M. Barazangi, W. Beauchamp, D. Seber, G. Brew, T. Sawaf and W. Al-Youssef 1997. Mesozoic-Cenozoic evolution of the intraplate Euphrates fault system, Syria: implications for regional tectonics. Journal of the Geological Society, 154, 653-666.

Litak, R.K., M. Barazangi, G. Brew, T. Sawaf, A. Al-Imam and W. Al-Youssef 1998. Structure and Evolution of the Petroliferous Euphrates Graben System, Southeast Syria. American Association of Petroleum Geologists Bulletin, 82, 1173-1190.

McBride, J.H., M. Barazangi, J. Best, D. Al-Saad, T. Sawaf, M. Al-Otri and A. Gebran 1990. Seismic reflection structure of intracratonic Palmyride fold-thrust belt and surrounding Arabian platform, Syria. American Association of Petroleum Geologists Bulletin, 74, 238-259.

Ponikarov, V.P. 1966. The Geology of Syria. Explanatory Notes on the Geological Map of Syria, Scale 1:200 000. Ministry of Industry, Damascus, Syrian Arab Republic.

Sawaf, T., D. Al-Saad, A. Gebran, M. Barazangi, J.A. Best and T. Chaimov 1993. Structure and stratigraphy of eastern Syria across the Euphrates depression. Tectonophysics, 220, 267-281.

Seber, D., M. Barazangi, T. Chaimov, D. Al-Saad, T. Sawaf and M. Khaddour 1993. Upper crustal velocity structure and basement morphology beneath the intracontinental Palmyride fold-thrust belt and north Arabian platform in Syria. Geophysical Journal International, 113, 752-766.

Stampfli, G.M., J. Mosar, P. Favre, A. Pillevuit and J.-C. Vannay 2000. Permo-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 margins, PeriTethys Memoir #6, in press, Museum National d'Historie Naturelle, Paris.



Figures

Figure 1.1: Map showing regional setting of Syria, almost surrounded by currently active plate boundaries. NAF = North Anatolian Fault.









Figure 1.2: Map showing topographic contours and general tectonic zones in Syria. The areas investigated in Chapters 2, 3, and 4 of this dissertation are indicated. Chapter 5 concerns the tectonic evolution of all Syria.













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Last updated: January 2001