Structure and Evolution of the Petroliferous Euphrates Graben System, Southeast Syria1
Robert K. Litak,2 Muawia Barazangi,3 Graham Brew,3 Tarif Sawaf,4 Anwar Al-Imam,4 and Wasif Al-Youssef4
ABSTRACT Cenozoic inversion of some structures also is evi- dent. Approximately 30 oil fields have been dis- The northwest-trending Euphrates graben sys- covered in the Euphrates graben system since tem is an aborted intracontinental rift of Late 1984. Recoverable reserves discovered to date Cretaceous age that has subsequently been hidden reportedly exceed 1 billion barrels of oil and less- by Cenozoic burial. Approximately 100 km wide, er amounts of gas. Light oil is primarily found in the system comprises an extensive network of Lower Cretaceous sandstone reservoirs juxtaposed grabens and half grabens extending some 160 km by normal faulting against Upper Cretaceous synrift from the Anah graben in western Iraq to the sources and seals. Palmyride fold belt in central Syria, where it becomes more subdued. The youngest prerift rocks are presently at a maximum depth of about 5 km. INTRODUCTION Based primarily on interpretation of 1500 km of seismic reflection profiles and data from 35 wells, Recent detailed studies on a number of continen- we mapped a complex network of numerous tal rifts have shed considerable light on the archi- branching normal and strike-slip faults, generally tecture and evolution of these types of basins (e.g., striking northwest and west-northwest. Both Rosendahl, 1987; Morley, 1995). Continental rifts branched and single-strand linear normal faults of hosting major hydrocarbon accumulations include generally steep dip, as well as positive and negative the North Sea (e.g., Stewart et al., 1992), Gulf of flower structures, are manifest on seismic sections. Suez (e.g., Patton et al., 1994), and many others. No single rift-bounding fault is observed; instead, a The Euphrates graben system in southeastern Syria major flexure coupled with minor normal faulting is an aborted continental rift that also holds signifi- marks the southwestern edge of the basin, with cant petroleum reserves, but a comprehensive anal- considerable variation along strike. To the north- ysis of its development has been unavailable before east, deformation diminishes on the Rawda high now in the public literature. In this study, we near the Iraqi border. describe the structure of, and interpret the evolu- The Euphrates graben system likely formed in a tion of, the Euphrates graben system. transtensional regime, with active rifting primari- Much of the northern Arabian plate consists of a ly restricted to the Senonian and with an estimat- mosaic of relatively stable blocks, including the ed maximum extension of about 6 km. Minor Rutbah uplift, the Aleppo plateau, and the Rawda (Khleissia) and Mardin highs, bounded by zones of persistent, episodic instability (Figure 1). Deforma- ©Copyright 1998. The American Association of Petroleum Geologists. All rights reserved. tion in many of these unstable zones, including the 1Manuscript received July 22, 1996; revised manuscript received May 29, Palmyride fold belt, Euphrates/Anah fault system, 1997; final acceptance February 3, 1998. Azraq/Sirhan graben, and Sinjar and Abd El Aziz 2Institute for the Study of the Continents, Snee Hall, Cornell University, Ithaca, New York 14853. Present address: 218 Alden Avenue, New Haven, uplifts, can be traced back at least to the Triassic Connecticut 06515-2112. and possibly to the late Proterozoic (e.g., Best et 3Institute for the Study of the Continents, Snee Hall, Cornell University, al., 1993; Litak et al., 1997). Deformation within Ithaca, New York 14853. 4Syrian Petroleum Company, Ministry of Petroleum and Mineral the mobile zones has varied through space and Resources, Damascus, Syria. time, partly dependent upon the orientation of the Seismic and well data for this study were kindly provided by the Syrian Petroleum Company. This research is supported by Amoco, ARCO, Exxon, zones, and apparently has reflected tectonic Mobil, Unocal, and Conoco. D. Seber and W. Beauchamp reviewed a draft of events at nearby plate boundaries (e.g., Chaimov this manuscript. We greatly appreciate the comments of reviewers T. Patton, et al., 1992; Barazangi et al., 1993). Recent studies N. Gorur, P. Yilmaz, and former Elected Editor K. Biddle that helped to improve the manuscript. Institute for the Study of the Continents contribution of the Palmyrides have elucidated much of their number 230. tectonic history, from a possible Proterozoic suture
AAPG Bulletin, V. 82, No. 6 (June 1998), P. 1173Ð1190. 1173 1174 Euphrates Graben System
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