Jordan resides on the northwest flank of the Nubo-Arabian Shield, along the eastern flank of the Dead Sea transform, and on the southern shore of the ancient Tethys Ocean. The transgression-regression of the Tethys resulted in depositing the sediments in different environments. The tectonic evolution of Jordan resulted in the formation of three types of sedimentary basins; these basins have different geological history, which led to the conclusion that two main play concepts exist in the different sedimentary basins.
Oil and gas exploration in Jordan began 50 years ago and can be divided into three overlapping phases.
First, 1947-78, foreign oil companies drilled several exploratory wells, but these were not enough to evaluate the country`s petroleum potential.
Second, 1963-72, a national effort was made. It involved drilling several wells, running seismic surveys, and making stratigraphic studies, but no significant hydrocarbon potential has been registered.
Finally, 1980 to present, 2D and 3D seismic surveys were recorded covering more than one third of the country, and about 100 deep wells have been drilled. Overall these activities led to the discovery of hydrocarbon potential in the northeast part of Jordan.
Jordan is located on the northwestern edge of the Arabian plate and covers about 96,000 sq km (Fig. 1). The country`s landscape is a vast desert or semi-desert plateau in the east; the west is a mountainous region rising to elevations of 600 m to more than 1,200 m.
Between the two mountain areas, west of Jordan and east of Israel, lies one of the strangest landscapes in the world, a north-to-south transform fault from 200 to 400 m below sea level. It is the deepest depression on the face of the earth.
Geologically, Jordan is a part of the Arabian platform, and about 90% of its territory is covered by sedimentary rocks. The section overlying crystalline basement consists of units ranging in age from Late Proterozoic to Holocene (Fig. 2).
Except for the Lisan Peninsula of the Dead Sea and the southeastern part of the Risha area, which attains a thickness of about 10 km of sedimentary rocks, most of the country is thought to be underlain by 4 to 6 km of sediments.1-4 The Paleozoic sediments thicken from the western side of Jordan to the northeastern and southeastern parts of Jordan. In the southeastern corner of Jordan, the sequence is in the order of 2,300 m.
The total thickness of Mesozoic sedimentary rocks increases from the south to the north and to the northeast of Jordan (e.g., the sequence is in the order of 4,000 m on the northwestern side of Jordan). The Paleocene-Eocene portion of the Cenozoic sediments reaches a thickness greater than 700 m in Northeast Jordan. The Oligocene-Miocene sequence is greater than 300 m thick at the east side of the Wadi Araba. In the Plio-Pleistocene, more than 8,000 m of evaporites accumulated in the Dead Sea area. Quaternary clastics reach more than 2,500 m in thickness at the southern end of the Dead Sea. A northern basalt plateau is covered by about 11,000 sq km of thin basalt over a basin believed to contain a thick succession of Mesozoic sedimentary rocks as well as unknown Paleozoic elements.
The stratigraphic column for Jordan (see table) is based mainly on the National Geological Mapping Project reports at 1:50,000 scale of the Geology Directorate, Natural Resources Authority, Jordan, and on the borehole data. Major unconformity is between the Zarqa-Ma`in and Khrayim Groups (Late Permian-Silurian).
Many minor unconformities are identified in local areas in Jordan. For example, an angular and erosional unconformity separates the Paleozoic sequences from Late Proterozoic plutonic rocks in south Jordan. At the Silurian/Ordovician boundary, too, an unconformity developed as observed in oil wells in the Wadi Sirhan area. And in northern Jordan, a period of erosion caused an unconformity during the Early Triassic.
The tectonic framework of Jordan can be divided into different tectonic patterns:
1. N-S trending faults as a result of the consolidation of the Arabian Shield mark the Precambrian rocks;
2. Deep grabens with thick Triassic, Jurassic, Cretaceous, and Tertiary clastics mark the northern areas;
3. Pull-apart Cenozoic basins that contain up to 8 km of Tertiary sedimentary fill are present in the Wadi Araba-Dead Sea-Jordan rift.
Structurally, Jordan can be divided into a series of broad, plateau-like arches and gentle, desert-covered basins. The basic tectonic features, which developed at different times and rates, are intersected by long, essentially linear faults, grabens, and half-grabens along which significant strike-slip movement has occurred. Most of these linear fault zones strike NW parallel to the Red Sea trend (Fig. 2). They are cut off obliquely by the Dead Sea-Jordan transform fault zone. This transform fault zone (Fig. 1) is a Tertiary feature involving over 100 km of left-lateral horizontal displacement that extends for a distance of more than 1,000 km in length. That links the northern end of the Red Sea, where crustal spreading takes place, with the Taurus zone of plate collision. Fig. 3 shows schematic east-west structural cross from Jordan Valley to the Iraqi border.
The nature of this transform is related to the opening of the Red Sea.5-7 According to Frei and Freund,8 the opening of the Red Sea took place in two stages: (a) Late-Early Oligocene and (b) from about 5 million years onward. The northern Red Sea is characterized by its bifurcation into the Gulf of Suez and Aqaba. In terms of plate tectonics, the Red Sea opening is transformed and directly linked to the opening and extension of the Gulf of Aqaba-Jordan-Dead Sea rift.
Middle East reservoirs
Most of the oil fields in neighboring countries occur in sedimentary sequences extending to the east and southeast of the Arabian-Nubian shield, forming a sedimentary platform of Cambrian to Cretaceous rock formations that dips gradually towards the basin of Al Roba`i Al Kha* in Saudi Arabia.
The oil fields in the southeastern part of the Arabian plate are found in anticlinal structures. These structures are formed either by the event of motion in the basement which led to change in the morphology of the basement or as a result of the tectonism. The most important petroleum bearing formations in this part of the Arabian plate are the carbonate rocks of Permian, Jurassic, and Cretaceous ages.
The Syrian and Iraqi oil fields in the north and northeast of the Arabian plate occur where sediment formations reach more than 7,000 m in thickness. The accumulation of hydrocarbon in this part is associated with the edge of the northern folding zone of the Arabian plate. Here, the oil reservoirs occur in domal structures bounded by synclines.
The oil fields in the western part of the Arabian plate in Israel and eastern Egypt are associated with small regional anticlinal structures. Occasionally these reservoirs formed in depositional basins related to the rifted zones, where faults form significant tectonic traps in this part. Reservoir rocks here are limestone and sandstone of Lower and Upper Jurassic and Cretaceous rocks.
Hydrocarbon prospectivity - On the evaluation of the entire country for prospective areas, not enough is yet known of the characteristics of deep structures of the earth`s crust, their dynamics, fault positions, and tectonic activities that control trap formation.
Direct natural evidence for the existence of oil and gas in Jordan has been provided in different areas by surface occurrences of oil and gas seeps, bituminous calcareous sediments, asphalt, and tar sand.
As a result of geological and geophysical exploration, two main play concepts are identified in the different sedimentary basins of Jordan. These are Tertiary and Mesozoic plays and Paleozoic plays. The Tertiary and Mesozoic plays are identified in the Wadi Araba-Dead Sea-Jordan rift, Azraq Depression, Northern Highlands, and Basalt plateau areas (Fig. 1).
Where an anomalous geothermal gradient and some thickening of Tertiary and Mesozoic sediments were recorded in boreholes as well as some indications for hydrocarbon occurrences were found. In addition, the existence of intersected faults of different directions, which divide the areas into blocks of variable sizes make it favorable for the formation of structural traps. Reservoirs at these areas are found in Triassic sandstones, Lower Cretaceous Kurnub sandstones, and Triassic and Jurassic carbonates.
The Paleozoic plays are identified in the Sirhan area, Jafr area, and northeast area (Fig. 1). Prospects in these areas are the Paleozoic successions that reach more than 5 km in thickness of mostly Paleozoic clastics with relatively thin Mesozoic cover.
Numerous attractive structures have been defined in Paleozoic rocks by the existing seismic coverage. Reservoirs are found to be the porous sandstone of the Cambrian Period and the top sand of the Ordovician Period. The indicated source rocks are the thick Cambrian, Ordovician, and Silurian sediments. Trap types are horsts and arches formed by intersecting fault trends, together with the associated drape and rollover features in the overlying beds.
- Abu-Ajamieh, M., Bender, F., and Eicher, R., Natural resources in Jordan, Natural Resources Authority, Amman, Jordan, 1988.
- Al-Zoubi, A., Deep geological structure of Jordan from geophysical data, PhD thesis, Sankt-Petersburg Mining Institute, Russia, 1992, 237 p.
- Batayneh, A., Al-Zoubi, A., and Hassouneh, M., Magnetic and gravity investigation of Lisan Peninsula-Dead Sea (Jordan), J. China University of Geosciences, Vol. 6, 1995, pp. 213-218.
- Batayneh, A., Geophysical data: a tool for studying the tectonic framework of the Risha area, Jordan, and its relation to regional tectonics, Chinese J. of Geophysics, Vol. 40, 1997, pp. 41-50.
- Quennell, A., The structural and geomorphic evolution of the Dead Sea rift, J. Geol. Soc. London, Vol. 114, 1958, pp. 1-24.
- Mart, Y., and Hall, J., Structural trends in the northern Red Sea, J. Geophys. Res., Vol. 89, 1984, pp. 352-364.I> Yossi, M., and David, A., Post-Miocene rifting and diapirism in the northern Red Sea, Marine Geology, Vol. 74, 1987, pp. 173-190.
- Frei, L., and Freund, R., Spatial and temporal relationships between two sets of strike-slip faults in southern Sinai, Tectonophysics, Vol. 180, 1990, pp. 111-122.
Abdallah S. Al-Zoubi has worked since 1989 as an engineer in the Natural Resources Authority of Jordan. In 1997-98 he became the head of research and planning division, and from 1998 to present he has been the director of geophysics division. He was graduated with an engineer diploma of geophysics from Leningrad Mining Institute, PhD degree in geophysics from Sante-Petersburg Mining Institute, DSc degree in geology and mineralogy (geophysics) from Russian Academy of Science, and post doctorate from Tel Aviv University (Dead Sea Research Center).
Awni T. Batayneh has worked as an engineering geophysicist in Natural Resources Authority of Jordan since 1989. His areas of research include archaeology, mineral exploration, geotechnical problems, and groundwater exploration. He has a BSc degree in applied geophysics from Damascus University and an MSc degree in applied geophysics from the University of Jordan. He also holds a PhD degree in engineering geophysics from Chanchun University of Science & Technology. E-mail: [email protected]