Accommodation Zones and Tectono-Stratigraphy of the Gulf of Suez, Egypt: a Contribution from Aeromagnetic Analysis

GeoArabia, v. 14, no. 4, 2009, p. 139-162 Aeromagnetics of the Gulf of Suez, Egypt Gulf PetroLink, Bahrain

Accommodation zones and tectono-stratigraphy of the Gulf of Suez, Egypt: A contribution from aeromagnetic analysis

Khamis Farhoud

ABSTRACT

This paper starts with an up-to-date literature review of the pre-rift, syn-rift and post-rift stratigraphy of the Gulf of Suez. The geometry and depth of the Proterozoic basement is not generally known due to poor seismic images below the Upper Miocene evaporites (including massive rock salt) and clastics. The pre- rift Paleozoic to Early Oligocene succession shows that several local basins (c. 10s of km in extent) occur in the Gulf, with thick sedimentary sections (e.g. c. 3,000 m for Paleozoic and 1,000 m for Jurassic and Lower Cretaceous). The origin and distribution of these basins is not well understood and the presence of similar pre- rift basins in the southern Gulf is not known to occur. The syn-rift Late Oligocene to Middle Miocene and post-rift Late Miocene – Pliocene successions are widely distributed within the rift basin and reach a thickness in excess of 5,000 m.

In order to visualize the grain and relative relief of the Proterozoic basement, a series of aeromagnetic images are shown in this paper. The images include Total Magnetic Intensity (TMI), Reduced-to-Pole (RTP), filtered regional and structural RTP, and Second Vertical Derivative (SVD). The paper also shows a three-dimensional visualization image of the magnetic basement that highlights the distribution of the basins in the Gulf. The magnetic lows do not generally trend along the Suez (NNW-trending Clysmic) Fault, but instead show highly variable orientations attributed to a complex pattern of criss-crossing faults. In particular, two areas were selected to interpret the geometry and depth of the basement. The first area covered the northern Zaafarana Accommodation Zone and involved modeling five aeromagnetic profiles. The Zone was interpreted as an EW-trending basement plateau bounded by basins that are c. 8,000 m deep. The second modeled area (four profiles) covered the southern Morgan Accommodation Zone. This zone was interpreted as an ENE-trending plateau of similar relief to the Zaafarana Zone. The Morgan Zone is terminated in the eastern Gulf by the 8,000-m-deep Morgan Basin. The very deep basins surrounding the two plateaus may contain both pre-rift and syn-rift source rocks, from which the numerous surrounding petroleum fields were sourced.

INTRODUCTION

The Gulf of Suez is located in Egypt, between the Sinai Peninsula and the African continent (Figure 1). It originally formed during the Paleozoic as a narrow embayment of the Tethys Ocean, and was rejuvenated as an inter-continental, rift basin in the Late Oligocene (e.g. Robson, 1971; Jarrige et al., 1990; Bosworth et al., 1998; Montenat et al., 1998a, b). The basin contains nearly 100 petroleum fields and has been producing since the early 20th Century (Figure 1; EGPC, 1996). One of the greatest challenges faced by exploration in the Gulf is the poor seismic images obtained from the target reservoir zones below the thick evaporites of the Miocene South Gharib and Zeit formations (Figure 2).

In many frontier basins, geophysical exploration activities generally start with magnetic and/or gravity prospecting. These cost-effective techniques (known as potential methods) estimate the thickness of the sedimentary section above the basement. Once potential methods identify anticlinal basement structures, geophysical exploration continues with seismic prospecting leading to exploratory drilling. In contrast to frontier basins, the Gulf of Suez has been extensively explored with seismic and many 100s of exploration wells. Nevertheless, due to the poor sub-salt seismic images, it continues to hide petroleum fields. The shortcoming of seismic prospecting is precisely why magnetic imaging should

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a 30° b Gebel 30° 32° 32° Ataqa 32°30' 32°30' N N

29°30' 29°30' 30°N 30°N

North Darag E Ayun

32°E 32° Ain Musa Sukhna

Zaafarana Zone Darag Figure 15 Basin Sudr 33° 33°

Ras Matarma Nebwi Asl Basin 29° 29° 29°30' 29°30'

Zaafarana October Basin Hammam Faraun Amer North Offshore North October El Galal El Qibliy “J” Ras a Budran a Zenima Issran Basin

32°30' 32°30' 28°30' October 28°30' Abu Rudeis 29° 29° Sidri North Amer Belayim Marine South Sinai Ras Feiran Issran Massif Amer Basin Hadahid Bakr West H Belayim Bakr Land Bakr West K Ras Gharib South Qaa Hana Ras Fanar Gulf of Belayim Suez Basin El Ayun SG 300 Basin Gebel Araba Kareem July Red Sea and Durba Umm El Yusr Ramadan Hills 28° 28° Kheir South Ramadan 28°30' 28°30' Badri Shukheir El Morgan Morgan Zone Gamma GS 327 Figure 16 GS345 Nessim Zet Bay Basin Gebel Zet 33° SB 339 33° Basin Waly (356) Younis Amal Gebel Ras El Ush GS (356) El Zeit Morgan Sinai/GHM Basin GH (376) 34° 34° Sidki Esh El- Mallaha 27°30' Zeit Bay Ashrafi Zeit East 27°30' Hilal 28° 28° Geisum Gemsa Shoab Ali Tawila

Gemsa-Southeast Esh El-Mallaha

Up Hurghada Fault Strata Red Sea 27°30' structural dip Red Sea 27°30' 0 20 Proterozoic 0 20 Oil fields 27° basement27° 34° km 34° km Figure 1: (a) Landsat Thematic Mapper image showing the basement outcrops and oil fields around the Gulf of Suez region. Satellite image courtesy of GeoTech, Bahrain. Original Copyright Earth Satellite Corporation. (b) Basins and major faults in the Gulf (modified after EGPC, 1996; Amgad and McClay, 2002; updated structural map reproduced by permission of W.M. Meshref).

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be considered as an important tool for exploring this otherwise mature basin. Moreover, in parts of the Gulf, wells do not reach the basement and the deeper stratigraphy is not known.

The present study starts with an up-to-date review of the tectono-stratigraphic setting of the Gulf of Suez. It then shows regional aeromagnetic images of 1981 survey from the Gulf including Total Magnetic Intensity (TMI), Reduced-to-Pole RTP), high-pass and low-pass spatial filters of the RTP image, and Second Vertical Derivative (SVD) of the TMI image. These images provide different ways to see the magnetic basement and a valuable database for explorationists. The final part of the study focuses on using aeromagnetic data to map the basement depth, and in particular the geometry and extent of two major accommodation zones that cross the Gulf.

STRATIGRAPHY OF THE GULF OF SUEZ

The stratigraphy and petroleum geology of numerous oil and gas fields in the Gulf of Suez was published by the Egyptian General Petroleum Corporation (EGPC) in 1964 and 1996. The stratigraphic column in Figure 2 follows with some modifications from these publications as well as numerous papers and books (e.g. Said, 1962, 1990; Saoudi and Khalil, 1986; Richardson and Arthur, 1988; Evans, 1988; Patton et al., 1994; Alsharhan and Salah, 1997; Purser and Bosence, 1998; Bosworth and McClay, 2001; Jackson et al., 2006). The stratigraphy of the Gulf is divided into (Figure 2):

• Proterozoic Basement, • Paleozoic, Mesozoic, and Lower Tertiary pre-rift succession, • Late Oligocene, Early and Middle Miocene syn-rift succession, • Late Miocene, Pliocene, and Pleistocene post-rift succession.

Proterozoic Basement

The Proterozoic Basement of the Arabian-Nubian Shield runs along the margins of the Gulf of Suez. It is represented by a great variety of crystalline and metamorphic rocks, frequently cut by dykes and sills of basic and acidic intrusives (Schurman, 1966). Different types of granites, schists, gneiss and porphyrites are recognized. The youngest intrusive igneous rocks are intermediate and acidic plutons, which yield radiometric ages averaging ca. 570 million years (Ma). Basement rocks crop out along the Gulf Rift shoulders, for example Esh El-Mallaha, Gebel El Zeit, Gebel Araba and Abu Durba, and also throughout the northwestern flank of the Sinai massif (Figure 1). They were uplifted along the coastal ranges most probably in Late Oligocene and Early Miocene time. They are the provenance for clastics deposited in the Gulf throughout the Paleozoic to Quaternary times.

Figure 3a shows an interpretation by Meshref et al. (1976) for the basement from aeromagnetic and geological data. Three major NE-trending shear zones were interpreted to cross the basin. Figure 3b (unpublished map reproduced by permission of W.M. Meshref), shows the basement depth map, which attains a maximum depth of c. 17,000–18,000 ft (c. 5,300 m). Since these pioneering studies, the fault system of the Gulf was interpreted to be more complex (Figure 1b) and as discussed below the basement’s depth to be substantially greater (c. 8,000 m).

Pre-rift Succession

Paleozoic sediments crop out at several localities on both sides of the Gulf and are encountered in numerous boreholes in the offshore Gulf (Abdallah and Adindani, 1963; Al Far, 1966; Issawi and Jux, 1982; see review by Alsharhan and Salah, 1997). On the eastern side (Figure 1), Paleozoic outcrops are found near several gebels (jabals) including Gebel Qibliat, Gebel Durba, Gebel Araba, Gebel Nezzazat, Gebel Umm Bogma, Gebel Nukhul, and Wadi Feiran; along the western-side, outcrops occur at Esh El-Mallaha Range, Gebel El-Zeit, southern and northern Galala plateaus and Wadi Araba.

In the Gulf, the terms Nubia Sandstone, Nubia Group or Nubia Complex are used to describe undifferentiated Paleozoic and Mesozoic sandstones. Alsharhan and Salah (1997) reviewed the

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Type Lithostratigraphy Lithology (meter) Section

LOWER 50 OLIGOCENE Tayiba Formation Upper Tanka Formation Hammam 25 Faraun Kharaba Formation 50 EOCENE Middle Darat Formation 50 CENOZOIC Lower Thebes Formation Luxor 423

PALEOGENE El Egma Group Esna Formation Esna 60 Sudr Formation Wadi Sudr 137 Duwi Formation Gebel Duwi 38

UPPER Matulla Formation Wadi Matulla 170 CRETACEOUS Wata Formation Wadi Wata 64 Abu Qada Fm Wadi Gharandal 25

Nezzazat Group Raha Formation Raha Scarp 120 MESOZOIC LOWER CRETACEOUS Malha Formation Wadi Malha 149 ih Gp

JURASSIC T TRIASSIC El Qiseib Formation Wadi Qiseib 44 PERMIAN Wadi Rod Legend Rod El Hamal 274 Formation El Hamal Mature UPPER source rock CARBONIFEROUS Reservoir Abu Durba Ataqa Group Gebel Durba 122 Formation Seal Conglomerate Umm Bogma LOWER Gebel Nukhul 45 Sandstone CARBONIFEROUS Formation ALEOZOIC Shale P Marl Naqus Formation Gebel Naqus 410 CAMBRIAN- Limestone ORDOVICIAN Araba Formation Gebel Qibliat 133 Dolomite Qibliat Gp Evaporite PROTEROZOIC BASEMENT Volcanics

Figure 2a: Generalized stratigraphic column of the Gulf of Suez for the pre-rift succession (after EGPC, 1996, Alsharhan and Salah, 1997, and Hafez, 2000).

lithostratigraphy, sedimentology and hydrocarbon habitat (reservoirs and source rocks) of the Nubian Sandstone in the Gulf and proposed the following scheme (Figure 2a):

(1) Qibliat Group consisting of the Cambrian – Ordovician Araba Formation (Nubia D member) and Ordovician Naqus Formation (Nubia C member).

(2) Early Carboniferous Umm Bogma Formation (lower part of Nubia B member), which is not assigned to a group.

(3) Late Carboniferous and Permian Ataqa Group consisting of the Abu Durba and overlying Rod El Hamal Formation (upper part of Nubia B member).

The isopach of the Paleozoic succession is shown in Figure 4 (modified after Zahran, 1987, and Hafez, 2000). It shows the NW-trending October Basin contains a Paleozoic section c. 3,000 m

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Aeromagnetics of the Gulf of Suez, Egypt

Post-Rift Succession Post-Rift Succession Syn-Rift Hafez, 1998, al., et Events ransform System T sworth Bo Aqaba 1996, Rapid extentension and subsidence

• Subsidence • Halokenesis • Margin uplift • End of Suez Rift • Start of • Mid-Clysmic Event • Marine transgression • Early rifting and igneous activity EGPC, (after Gulf of System ransition to Low-angle Aqaba Rift high-angle fault blocks Fault Style and rotated T normal faults normal faults 100 75 succession ctonic 50 cm/ky Te 25 Subsidence post-rift 2-12 and 11 pe Section Rudeis-2 Zeit Bay-1 Gharib N-2 Gebel Zeit-2 Ty Abu Zenima-1 South Gharib-2 Belayim syn-rift the for un Musa Formation Ay Suez Gharamul Mbr of Asl Formation Hawara Formation Gulf Mheiherrat Formation Lagia Mbr the Ali Member Ghara Mbr of Sidri Member Baba Member Feiran Member Ras Budran Member Shoab Rahmi Mbr Hammam Faraun Member ardan Formation column W Zaafarana Formation Zeit Formation (940 m) Abu Zenima Formation Upper Member Lower Member South Gharib Formation (700 m) October Mbr Shagar Member Markha Mbr Lithostratigraphy stratigraphic Rudeis Nukhul

(300 m) (460 m) (780 m) (430 m) Kareem Belayim

Formation Formation Formation Formation

Ras Mala'ab Group Mala'ab Ras Group Gharandal Generalized .6 5.3

11 16.0 23.0 28.4

2b: Late Middle Early Oligocene

0 Ma Late Miocene - Pliocene Pleistocene Figure 2000, Alsharhan, 2003, and Jackson et al., 2006).

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30° 30°

32° -1,000 32°30' 32°30' Gebel Ataqa N -2,000 Gebel Ataqa N -3,000 29°30' -4,000 30°N -5,000 30° N -6,000 E -7,000 32° -8,000 Darag -9,000 Basin

Depth (feet) -10,000 r Zone I -11,000 ° Shea 33° -12,000 33 El Galala Nebwi -13,000 El Bahariya Basin -14,000 -15,000

29° 29°30' Zenima 29°30 Basin '

Hammam Faraun Hammam Faraun

El Galal El Galal October El Qibliy El Qibliy a a Basin a a I e I on 32°30'Thin Z 32°30'Thin 28°30' ar 28°30' he S 29° South 29° October South Basin South Sinai Issran Sinai Massif Basin Massif Hadahid Hadahid

Gebel Araba and Durba

Gebel Araba and Durba Red Sea Red Sea South Hills Hills 28° 28° Belayim El Morgan 28°30' Basin 28°30' Zone

III El Morgan e Zone on Gebel Z ar El Zeit e h 33° S 33° Zet Bay Basin Gebel Morgan El Zeit Basin 34° 34° Esh El- Gulf of Esh El- 27°30' Mallaha Suez 27°30 Mallaha 28° ' 28°

Gemsa Trough

Magnetic lineament Hurghada Hurghada Strike-slip Red Sea 27° fault 27°30' 27°30' Proterozoic 0 20 Proterozoic 0 20 basement basement 34° km 34° km Figure 3: (a) Basement fracture/fault map for the Gulf of Suez (after Meshrif et al., 1976). (b) Depth to basement using geological data (unpublished map reproduced by permission of W.M. Meshref).

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30° 30°

32° 32°

32°30' 32°30' Gebel Ataqa N Gebel Ataqa N 1,200 1,400 29°30' 1,600 29°30' 30° 30°N 1,800 N 2,000 Thick 32°E 32°E

100 0 0 500 20 600 300 2,20 400

2,400 33° 33° El Galala El Galala El Bahariya 2,600 El Bahariya 2,800

3,000

Thick 29° 29° 2,600 29°30' 29°30'

2,40 0 Thin 2,200 2,000 1,800 Hammam Hammam 1,600 Faraun Faraun 1,400 1,200 El Galal El Galal El Qibliy a El Qibliy a a a Thick

100 500 200 800 32°30'Thin 32°30'Thin 200 300 1,000

29° 400 600 29° South South Sinai Sinai Massif Massif Hadahid Hadahid 100 300 Gebel Araba and Durba

Red Sea Red Sea Hills Hills 28° 28° 400 28°30' 500 28°30' Gebel Araba 600 800 700 and Durba 900 1,000 El Morgan El Morgan 1,200 Zone Gebel Zone El Zeit 33° 33° Gebel 1,400 El Zeit 1,400

1,000 Gulf of 34° 1,200 34° 800 Esh El- Suez Mallaha 100 m 600 28° 200 Gulf of 400 28° 1,000 m 300 Suez 1,200 400 1,400 500 1,600 600 1,800 700 2,000 800 2,200 900 2,400 Proterozoic 1,000 Proterozoic basement basement 2,600 1,100 Hurghada Hurghada 2,800 1,200 3,000 27°30' 1,300 27°30' 33°30' 0 20 33°30' 1,400 0 20 27° 1,500 34° km 34° km Figure 4: Paleozoic isopach map of Gulf of Figure 5: Isopach of the Late Jurassic and Early Suez (modified after Zahran, 1987, and Hafez, Cretaceous Malha Formation of the Gulf of 2000). Suez (modified after Zahran, 1987, Khalil, 1993, and Hafez, 2000).

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thick, with the North October and giant October fields lying to its northeast. These fields produce oil from the Nubia Sandstone (EGPC, 1996).

(4) El Tin Group (Nubia C member, or Mesozoic Nubian) consisting of the Triassic – ?Early Jurassic Qiseib Formation and Late Jurassic – Early Cretaceous Malha Formation. Triassic rocks are only developed in Arif El Naga in the northern Sinai Peninsula. Jurassic sediments are restricted to the northern part of the Gulf, and exposed in the Maghara Uplift in northern Sinai and Khashm El Galala.

The isopach of the Malha Formation shows several basins in the northern and central Gulf (Figure 5, modified after Zahran, 1987; Khalil, 1993; Hafez, 2000). These basins formed during the Late Jurassic along E-W trending faults (Kerdany and Cherif, 1990), and are associated with Early Cretaceous basaltic igneous activity. The clastics of the Malha Formation are producing reservoirs in several oil fields (Figure 2a; EGPC, 1996).

The Late Cretaceous formations are from base to top, Raha, Abu Qada, Wata and Matulla of the Nezzazat Group, and the Duwi and Sudr formations assigned to the lower part of the El Egma Group (Figure 2a). The lower part of the Sudr contains the Brown Limestone unit, which is an important source rock in the Gulf. Paleogene deposits are widespread in Egypt and represented by the Esna Formation of the El Egma Group (Said, 1962), which was probably deposited in most parts of the Gulf (Figure 6).

In the Hammam Faraun fault block (Figure 1), Jackson et al. (2006) studied the Eocene and Oligocene succession in order to pinpoint the onset of rifting in the Gulf. They reviewed the lithology, biostratigraphy and depositional setting of this succession based on earlier works (see references therein). The Eocene part of El Egma Group consists of four formations (Figure 2a): (1) Lower Eocene Thebes Formation, (2) Middle Eocene Darat Formation, (3) Middle Eocene Khaboba Formation, and (4) Upper Eocene Tanka Formation. In this area, Jackson et al. (2006) identified the Lower Oligocene Tayiba Formation (0–56 m thick) as the youngest preserved pre-rift unit. They also suggested that a regional mid-Oligocene sea-level drop accompanied the onset of rifting.

Syn-Rift Succession

The oldest syn-rift rock unit in the Gulf is represented by the latest Oligocene to earliest Miocene Abu Zenima Formation (0–112 m thick, Figure 2b; Patton et al., 1994; Jackson et al., 2006). This Formation corresponds to the “Red Bed Series of Group A” (Montenat et al., 1988) and in part to the Shoab Ali Member of the Nukhul Formation (Saoudi and Khalil, 1986). The Abu Zenima Formation contains basaltic flows, which have been dated at ca. 24.0–22.0 Ma (Montenat et al., 1988; Evans, 1988).

The Nukhul Formation represents the oldest unit of the Gharandal Group (Figure 2b). Above the Shoab Ali Member, the upper part of this Formation consists of three laterally equivalent Early Miocene members (Saoudi and Khalil, 1986). From the northern to the southern Gulf: (1) continental clastics of the October Member, (2) alternating marls and evaporites of the Ghara Member, and (3) carbonates of the Gharamul Member. The thickness of the Nukhul Formation varies considerably due to syn-depositional faulting and ranges from zero to 800 m. Above the Nukhul Formation, two stratigraphic schemes are used in different parts of the Gulf for the upper part of the Gharandal Group (Figure 2b). The first is characterized by the Lower Miocene Rudeis Formation (100s–2,000 m thick) and Middle Miocene Kareem Formation (250–350 m thick). The Rudies Formation is further divided into Upper and Lower Rudies members separated by the Mid-Clysmic Unconformity. The Kareem Formation is divided into the lower evaporitic Markha or clastic Rahmi members, and upper clastic Shagar Member. The Kareem Formation contains some of the most prolific petroleum reservoirs in the Gulf (EGPC, 1996; Alsharhan, 2003).

In the second scheme (e.g. Wescott et al., 1996; Krebs et al., 1996), the upper part of the Gharandal Group is represented by the Mheiherrat Formation (Lower Rudeis Member), Hawar and Asl formations (in part correlative to Upper Rudies Member). The overlying Ayun Musa Formation consists of the

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30° 30°

32° 32°

32°30' 32°30' Gebel Ataqa N Gebel Ataqa N

29°30' 29°30' 30° 30° N N 0

32°E 200 32°E Limit of Anhydrite 400

600 33° 33° El Galala El Galala El Bahariya 800 El Bahariya 1,000 1,200 29° 29° Limit of 1,400 29°30' Salt 29°30' 1,600 1,800

Hammam Hammam Faraun Faraun

1,800 El Galal El Galal El Qibliy a 1,600 El Qibliy a a a 1,400

32°30' 1,200 32°30'

1,000 29° 29°

800 South South Sinai Sinai Massif Massif 600 Hadahid Hadahid

400 Gebel Araba Gebel Araba and Durba 200 and Durba Gulf of Suez Red Sea Red Sea Hills Hills 28° 28° 28°30' 28°30'

600 El Morgan 400 El Morgan 200 Zone Zone

33° 33° Gebel El Zeit

Gebel

El Zeit 34° 34° Gulf of Esh El- Esh El- Suez Mallaha 27°30' Mallaha 28° 28°

0 m 200 400 600 800 1,000 > 900 m 1,200 Proterozoic Proterozoic basement 1,400 basement Hurghada Hurghada 1,600 1,800 27°30' 27°30' 33°30' 0 20 33°30' 0 20 27° 27° 34° km 34° km Figure 6: Isopach of the Paleogene in the Gulf Figure 7: Northern limits of Miocene salt and of Suez (Farhoud, 2006). anhydrite, Gulf of Suez (modified after Zahran, 1987, Hafez, 2000, and Schütz, 1994).

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evaporitic Lagia Member (in part correlative to the Markha Member of the Kareem Formation) and the clastics of the Ras Budran Member.

Post-Rift Succesion The post-rift Ras Mala’ab Group is mainly composed of evaporites and clastics. It is divided into Middle Miocene Belayim Formation, and Upper Miocene South Gharib and Zeit formations (Figures 2 and 7). The Belayim Formation (c. 300 m thick) consists of the evaporites of the Baba Member (10 to c. 100 m thick), fine clastics of the Sidri Member (several 10 m thick), evaporites of the Feiran Member (c. 100 m thick) and fine clastics and carbonates of the Hammam Faraun Member (c. 50–100 m thick). The overlying Late Miocene South Gharib consists mainly of anhydrite and salt, more than 1.0 km thick in salt domes (Fawzy and Abdel Aal, 1984). The Zeit Formation consists mainly of interbedded anhydrite and shale layers and can attain a thickness of c. 1.0 km in salt withdrawal basins. The post- Miocene succession consists of the Warden Formation and overlying Zaafarana Formation, which together can attain a thickness in excess of 1.0 km in salt withdrawal basins.

TECTONIC SETTING OF THE GULF OF SUEZ

The Gulf basin is characterized as a failed rift system related to the relative movements of the African, Arabian, and Levant plates. The rift was initiated in Late Oligocene (ca. 24.0 Ma) as evident from the volcanic rocks of the Abu Zenima Formation. Several basin-wide unconformities interrupted the Phanerozoic sedimentary record, and according to Dolson et al. (2001) they were primarily in response to regional tectonic adjustments associated with different rift phases. Figure 2b summarizes the tectonic factors that affected the Gulf since the Late Oligocene (Bosworth et al., 1998; Alsharhan, 2003).

Crustal extension and tectonic subsidence of the Gulf’s axial trough reached a maximum during the Early Miocene (ca. 19.0–17.0 Ma; Schütz, 1994), when the syn-rift Rudeis Formation was deposited. The shoulders of the basin may have risen in the Oligocene and Early Miocene due to thermal effects (Steckler, 1985). Moretti et al. (1986) concluded that the rift shoulders were formed as a result of advection in the asthenosphere away from the center of the rift combined with regional stretching of the lithosphere. By Middle Miocene (ca. 15 Ma) strike-slip movements began along the Aqaba-Dead Sea Fault System and the Gulf became less active if not inactive as a spreading center (Abdel Gawad, 1970a, b; Bartov et al., 1980).

Meshref et al. (1976); Moustafa (1976) Moustafa (1996, 1998); Amgad and McClay (2002) concluded that the structural configuration of the Gulf is largely controlled by a complex pattern of faulting with two main trends: (1) NW Suez fault trend (Clysmic), which played the most important role, and (2) NE Aqaba trend. The interaction of the two fault trends resulted in a pattern of en-echelon faulted blocks. The Gulf of Suez basin is generally divided into three structural provinces separated by two accommodation zones (Figure 1b):

(1) Northern Wadi Araba Province with strata dipping regionally to the southwest, (2) Zaafarana Hinge Zone (also Galala–Zenima), (3) Central Belayim Province with strata dipping regionally to the northeast, (4) El Morgan Hinge Zone (also Sufr El Dara), (5) Southern Amal Province with strata dipping regionally to the southwest.

The initial rift fault system was highly segmented with numerous isolated and smaller rift basins developing throughout the three provinces (Amgad and McClay, 2002). Abdel Gawad (1970a, b) noted that three fault systems (trending N, NW, and WNW) appear to have influenced the structure of the Gulf and Red Sea areas. In the western part of the Sinai Peninsula, at Gebels Araba and Abu Durba, he interpreted left-lateral displacements along the N-S faults, and right lateral movements with the WNW faults. Issawi et al. (1981) in their structural study of the Wadi Feiran and Sinai Peninsula concluded that folds are related to faulting in an overall extensional setting rather than to regional compression.

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AEROMAGNETIC SURVEYS OF THE GULF OF SUEZ

The first aeromagnetic survey over the Gulf of Suez was acquired in 1964; it consisted offlights spaced 5 km apart NE-SW and two tie lines over the coasts. In 1981 an aeromagnetic survey was conducted for 10 petroleum companies by Aero-Service; the flight lines were spaced one kilometer apart NE-SW with tie line spaced at 5 km. In 1997 a high-resolution aeromagnetic survey was flown over the southern half of the Gulf with flight-line spacing of 250 m and 400 m tie-line spacing. In 2002 the northern half of the Gulf was covered by another high-resolution aeromagnetic survey with the same specifications as the 1997 survey. The sensitivity and spatial resolution of the cesium vapor magnetometer used in 1997 and 2002, was greater than of that of the proton magnetometer used in the 1981 survey. As a result the later two surveys measured the magnetic field with a spacing of 7–9 m compared with 70–90 m in the 1981 survey.

The present study uses the data acquired by Aero-Service in 1981. It has been interpreted by other authors in different localities in the Gulf (Meshref, 1990; Hammouda, 1986; Zahran, 1987; Said, 1990; Sharafeldin, 1991; Hafez, 2000). The 1997 and 2002 surveys, however, are not available in the public domain. The maps presented here were digitized and compiled by the present author, starting from Total Magnetic Intensity (TMI) readings that were subjected to leveling and joined into one regional map.

ANALYSIS AND INTERPRETATION OF AEROMAGNETIC DATA

The Earth’s magnetic field at its surface arises from four basic sources:

(1) Magnetic basement rocks and basement topography (granitic and basaltic basement rocks either by their varying distances to the surface or by changes in their magnetic properties), (2) Near-surface and surface cultural iron contamination, (3) Local intrusive and volcanic rocks or debris that may lie at semi-shallow depths, (4) Authigenic magnetic alterations in shallow sedimentary formation (sedimentary residual magnetization “SRM”).

Total Magnetic Intensity (TMI) data records the vector sum of all these magnetic bodies. Each body contributes to the total measurement based on the strength of its magnetic susceptibility and its depth of burial. The TMI of the Gulf is shown in Figure 8; it is displayed as an image rather than a contoured map in order to enhance regional geological structural features.

Two major types of anomalies are present in magnetic data. The first is mainly produced by changes in the magnetic susceptibility of the basement’s composition. It results in anomalies (referred to intra-basement anomaly or regional anomaly) that are regionally broad (low frequency or high wave number) and of considerable amplitude (100s of Nanotesla – nT). The second type of anomaly is more sharp (high frequency) and with relatively smaller amplitudes (several 10s nT). It mainly reflects the basement relief, and is referred to as supra-basement anomaly or residual anomaly. Many techniques in the space (wave number) and frequency domains can be applied to aeromagnetic data to enhance regional and residual anomalies or to sharpen subtle anomalies by derivatives and frequency filters.

Reduction to the North Magnetic Pole (RTP)

The inclination of the Earth’s magnetic field varies between 90° to 0° from the Pole to Equator. Magnetic anomalies located at middle latitudes show a dipole nature, which causes difficulties in differentiating and locating their magnetic sources. In order to position the magnetic anomaly directly over its source body, the TMI data (Figure 8) was Reduced-to-Pole (RTP) as shown in Figure 9, assuming a total magnetic field strength of 42,000 nT, inclination of 40.2°, and declination of 02.8°. In the RTP image the magnetic field appears as if the body was situated at the Earth’s magnetic poles, thus simplifying the interpretation procedures. The RTP transformation assumes that all magnetization is induced (i.e. the magnetization direction is parallel to the Earth’s magnetic field), which produces a northward shift of the positive part of each anomaly to a location over the causative body.

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30° 30°

409.0 406.0 32°30' 32°30' 365.0 Gebel Ataqa N 360.9 Gebel Ataqa N 343.0 338.0 322.0 29°30'319.2 304.0 30°N 301.5 30° N 288.0 287.4 277.0 277.1 269.0 268.2 261.0 259.9 254.0 251.8 248.0 243.6 TMI (nT) TMI (nT) 242.0 33° 236.7 33° 236.0 230.9 229.0 224.7 222.0 217.8 213.0 209.6 203.0 29°30' 200.6 29°30' 191.0 186.7 169.0 164.4

Hammam Hammam Faraun Faraun

El Galal Gulf of El Galal Gulf of Suez El Qibliy a Suez El Qibliy a a a

32°30' 32°30' 28°30' 29° 29° South South Sinai Sinai Massif Massif Hadahid Hadahid

Gebel Araba Gebel Araba Red Sea and Durba Red Sea and Durba Hills Hills 28° 28° 28°30' 28°30'

El Morgan El Morgan Zone Zone

33° 33° Gebel Gebel El Zeit El Zeit

34° 34° Esh El- Esh El- Mallaha Mallaha 27°30' 27°30' 28° 28°

Hurghada Hurghada 27° 27° 27°30' 27°30' Proterozoic 0 20 Proterozoic 0 20 basement27° basement 34° km 34° km Figure 8: Digitized Total Magnetic Intensity Figure 9: Total Magnetic Intensity (TMI) field (TMI) field in Nanotesla (nT) of the Gulf of reduced to the north magnetic pole (RTP). Suez (compiled after W.M. Meshref, 1990; Hammouda, 1986; Zahran, 1987; Sharafeldin, 1991; Hafez, 2000).

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Regional - Residual Separation of RTP Data

A magnetic anomaly is composed of a broad spectrum of frequencies, each characterized by an amplitude. If the susceptibility at a certain depth increases, the amplitude of the anomaly will increase and so will its contribution to the corresponding part of the power spectrum. The relationship between wave number and amplitude, for any given depth, may be expressed as a plot of the logarithm of the amplitude power spectrum versus wave number (Spector and Grant, 1970).

Figure 10 shows the power spectra for the Zaafarana and Morgan accommodation zones. The decreasing gradient with increasing wave number reflects shallower sources. The plot can be used to design filters that separate the regional and residual anomalies (Nettleton, 1976). This technique, known as the pseudo depth slice, sets the cut-off for the filter at the intersection of the slopes of the deep and shallow components. It is not however useful for the accurate determination of depth (Spector and Grant, 1970). Figures 11 and 12 compare the residual and regional anomalies after they were separated by a spatial filter.

Second Vertical Derivative (SVD) of RTP data

The second vertical derivative technique is one of the most useful technique for defining the edges of magnetic bodies and amplifying subtle anomalies. The zero contour line is particularly important in identifying the locations of faults (Figure 13) as discussed below.

AEROMAGNETIC INTERPRETATION

The pioneering study by Meshref et al. (1976) interpreted three NE-trending shear zones from the 1964 aeromagnetic data (Figure 3). Figure 14 shows the distribution of magnetic basins derived from the present study as a 3-D visualization image of the low-pass magnetic map of the Gulf. Many of the magnetic lows can be correlated with well-defined basins.

2-D Magnetic Modeling of Accommodation Zones

Depth interpretations were carried out along nine profiles that cross the magnetic anomalies over the Zaafarana and Morgan accommodation zones (Figures 15 and 16). These zones represent the border areas where changes occur in the depth of the basement and for the dips of faults and strata. The objective of the depth modeling is to map these changes along the nine profiles.

Radially Averaged Power Spectrum For Zaafarana Radially Averaged Power Spectrum For Morgan 15 15

10 10

0.5 0.5

0.0 0.0 In (Power) In (Power)

-0.5 -0.5

-10 -10

-15 -15 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Wave number (1/K unit) Wave number (1/K unit) Figure 10: Radially averaged power spectrum of the reduced to the north magnetic pole (RTP) for the Zaafarana and Morgan accommodation zones. See Figure 1b for location of accomodation zones.

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30° 30°

17.4 32°30' 439.0 32°30' 10.1 Gebel Ataqa N 378.0 Gebel Ataqa N 6.8 349.0 4.8 323.0 3.4 30° 30° N 305.0 N 2.5 292.0 1.7 281.0 1.0 270.0 0.4 261.0 -0.3 251.0 -0.9 TMI (nT) TMI (nT) 242.0 -1.6 33° 234.0 33° -2.3 226.0 -3.2 218.0 -4.4 210.0 -6.1 201.0 -8.6 29°30' 191.0 29°30' -13.2 176.0 -28.9 147.0

Hammam Hammam Faraun Faraun

El Galal El Galal El Qibliy a El Qibliy a a Gulf of a Suez

32°30' 32°30'

29° 29° South South Sinai Sinai Massif Massif Hadahid Hadahid

Gebel Araba Gebel Araba Red Sea and Durba Red Sea and Durba Hills Hills 28° 28° 28°30' 28°30'

El Morgan El Morgan Zone Zone

° 33° Gebel 33 Gebel Gulf of El Zeit El Zeit Suez

34° 34° Esh El- Esh El- Mallaha Mallaha 27°30' 27°30' 28° 28°

Hurghada 27° Hurghada 27° 27°30' 27°30' Proterozoic 0 20 Proterozoic 0 20 basement basement27° 34° km 34° km Figure 11: High-pass component of the Total Figure 12: Low-pass component of the Total Magnetic Intensity (TMI) field after it was Magnetic Intensity (TMI) field after it was reduced to the north magnetic pole (RTP, reduced to the north magnetic pole (RTP, shown in Figure 9). shown in Figure 9).

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The RTP magnetic values were digitized along 30° 15.9 the profiles and are shown as the observed points 32°30' in Figures 15 and 16. The geological models are 8.1 Gebel Ataqa N 5.1 two-dimensional (2-D) and shown as Basement 3.3 and Sedimentary Section in the profiles. The 2.1 30° N models included drilled depths to basement, and 1.3 0.6 accounted for measured susceptibility contrasts, 0.1 altitude of outcropping basement, magnetic -0.4 inclination (40.2o), declination (2.8o), and variable -0.9 -1.4 TMI (nT) flight altitude, especially in rugged topographic -1.9 33° areas. -2.5 -3.3 -4.2 For each profile three main parameters were -5.5 considered in building the initial geological -7.2 29°30' model: (1) depth to top of magnetic basement, -10.8 (2) depth to base of magnetic basement, and (3) -26.9

magnetic susceptibility of the basement (constant Hammam in case of regional work like the present study or Faraun can be varied laterally in more detailed work). The GM-SYSTM modeling software (North- El Galal El Qibliy a western Geophysical, Canada) was used because a it allows intuitive and interactive manipulation of the model and real-time calculation of the 32°30' magnetic response. Once the parameters were 29° selected, an iterative technique was used to South Sinai minimize the root mean square (RMS) error Massif between the calculated and observed magnetic Hadahid data. The differences are shown in Figures 15 and 16. Gulf of Suez The inversion procedure applied in this Gebel Araba Red Sea and Durba study is non-linear and does not produce a Hills 28° unique solution in most cases. However, the 28°30' initial models for Profile-1 (Zaafarana area, Figure 15) and Profile-6 (Morgan area, Figure 16) El Morgan were constructed with sufficient depth control to Zone the basement to allow constraining the magnetic 33° Gebel susceptibility of the basement rocks. El Zeit

Zaafarana Accommodation Zone 34° In Profiles 1 to 3 (Figure 15), the magnetic base- Esh El- Mallaha ment depth dips gently from northeast (c. 27°30' 28° 2,500–3,500 m) to the southwest where it reaches 4,500–5,500 m. Profile-4 ties the first three profiles and confirms the depth calculations at their intersections (Figure 15). The first four profiles suggest that the Zaafarana Zone forms a broad plateau in the eastern side of the Gulf. In contrast, Profile-5 provides evidence for the hinge zone along the western flank of the Gulf (Figure Hurghada 15). It shows that the plateau is about 5,000 m 27° 27°30' deep in the western side, the model suggests that Proterozoic 0 20 Zaafarana zone extends c. 25 km EW in the off- basement27° shore Gulf, attains a width of c. 20 km NS and is 34° km bounded to the north and south by basins that Figure 13: Second Vertical Derivative (SVD) of exceed 8,000 m in depth. the Total Magnetic Intensity (TMI) field after it was reduced to the north magnetic pole (RTP, shown in Figure 9).

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Morgan Accommodation Zone and Gebel 30° Ataqa 439.0 Morgan Basin 32°30' 378.0 N Profiles 6, 7 and 9 reveal the deep Morgan 349.0 Basin, which may have a sedimentary section 29°30'323.0 that exceeds 8,000 m in thickness (Figure 16). 305.0 30°N 292.0 The Basin trends along the Suez Rift and is c. 281.0 Ayun

10 km wide near the eastern side of the Morgan 270.0 Ain Musa Accommodation Zone. Surrounding the Basin, 261.0 Sukhna 251.0 Darag the basement is much shallower and ranges in 242.0

TMI (nT) Basin depth between 3,000–4,000 m. Profile 8 (Figure 234.0 33° 226.0 16) shows the northern termination of the Nebwi 218.0 Basin Morgan Accommodation Zone and the limit of 210.0 the Morgan Basin. The model suggests that the 201.0 Morgan Zone extends 18 km into the Gulf and 191.0 29°30' 176.0 ends within it where it attains a width of c. 11 147.0 km. Zaafarana Hammam Zone Faraun IMPLICATIONS FOR PETROLEUM Figure 15 SYSTEM El Galal Zenima Basin El Qibliy a a October In the northern Gulf, the Darag and Nebwi Basin basins occur to the north of the Zaafarana Zone 32°30'

(Figure 14). The models in Profiles 1–5 suggest 29° that the Zone extends across the Gulf and South separates these two basins from the Zenima Sinai Issran Massif Basin in the central Gulf. The RTP and regional Basin Hadahid magnetic images (Figures 8 and 12) show that the Darag and Nebwi basins trend WNW South Belayim Qaa (290o–310o) as suggested by Patton et al. (1994) Basin Basin rather than parallel to the Suez Clysmic trend Gebel Araba o o Red Sea and Durba (310 –350 ) seen in the residual magnetic image Hills 28° (Figure 11) and SVD image (Figure 13). These 28°30' interpretations imply that the Zaafarana Zone El Morgan is a structural high, which separates two deep Zone (8,000 m) broad basins: Darag and Nebwi basins Figure 16 to its north and Zenima Basin to its south. Each Zet Bay Basin Gebel Zet basin may contain a substantial pre-rift and/or 33° Basin Miocene reservoir and source rocks. Gebel El Zeit Morgan Basin 34° In the central Gulf, the Zenima, October, Issran Esh El- Mallaha and South Belayim basins correlate to magnetic 27°30' lows (Figure 14). The Zenima, October and 28° Issran basins trend approximately to the north (350o–030o), whereas the Belayim Basin trends EW. The Belayim Basin is located north of the Morgan Zone, which was modeled with Profiles

Figure 14: Three-dimensional view of regional Fault magnetic component showing the magnetic Strata basins (blue color) correlated with known structural dip 27°30' Proterozoic 0 20 geological basins. The two rectangles are basement centered over the Zaafarana and El Morgan 34° km offshore accommodation zones and modeled in depth (Figures 15 to 16). Faults north of Zaafarana Zone and south of the Morgan Zone (yellow shade) are downthrown to the NE with strata dipping SW. Between the two accommodation zones (gray shade), the faults are downthrown to the SW with strata dipping NE. See Figure 1b.

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6–9 (Figure 16). The Zone forms a plateau that separates the central basins, which contains the July and Ramadan fields, from the southern Morgan and Gebel Zeit basins (Figure 16). The July, Ramadan and Morgan fields are the giants of the Gulf and were probably sourced from these deep basins.

CONCLUSIONS

The Gulf of Suez contains a sedimentary succession that spans the Phanerozoic Era reaching as much as 8,000 m in thickness (Figures 2 to 7). It is segmented into a complex pattern of basins bounded by faults with numerous orientations (Figures 1 and 14). The precise faulting configuration and depth to the basement is difficult to map because of poor seismic data and sparse deep well control. This paper shows that the interpretation of 1980s aeromagnetic data can assist in resolving regional aspects of the basement’s configuration and its relief. Regional aeromagnetic images of the Gulf are shown including Total Magnetic Intensity (TMI, Figure 8), Reduced-to-Pole (RTP, Figure 9), residual structure (high frequency, Figure 11), regional (low frequency, Figure 12) and Second Vertical Derivative (SVD, Figure 13). They show that the Gulf is segmented into numerous magnetic lows that better define the shapes and depths of geological basins (Figure 14).

Two areas were selected to illustrate the contribution of aeromagnetic data to constrain the basement’s configuration in the Gulf. The two areas contain deep geological features that do not run parallel to the Suez Clysmic direction (NNW) and are known as the Zaafarana and Morgan accommodation zones (Figures 15 and 16). Nine aeromagnetic profiles were sampled from the RTP maps and used to estimate the basement depth and thickness of the sedimentary section. The Zaafarana Zone cuts across the northern Gulf as a broad EW-trending plateau. The plateau dips westwards, and its depth is interpreted to increase from c. 2,500–3,500 to 4,500–5,500 m. It extends c. 25 km EW and attains a width of c. 20 km NS. Its western part is bounded to the north and south by deep basins with a sedimentary section exceeding 8,000 m in thickness. The NE-trending Morgan Zone also forms a plateau, c. 11 km wide, which extends c. 18 km across the Gulf. It terminates eastwards at the Morgan Basin, which has c. 8,000 m of sediments. The two zones separate deep basins, which are interpreted to contain the source rocks for many of petroleum fields.

ACKNOWLEDGMENTS

I am grateful to Ahmed El Barkooky, Sharaf El Din Mahmoud and Salah Eldin Abdel Wahab for their thoughtful and constructive reviews. Wafik Meshref encouraged me to collect and interpret all the Gulf’s 1981 aeromagnetic survey data (published by W.M. Meshref, 1990; Hammouda, 1986; Zahran, 1987; Sharafeldin, 1991; Hafez, 2000) and to publish it as part of my PhD thesis at Ain Shams University, Egypt. This paper is based on that thesis. Thanks are also extended to two anonymous GeoArabia reviewers for their comments and suggestions, Dr. Moujahed Al-Husseini for editing the manuscript and Arnoldo Egdane for designing the final graphics.

REFERENCES

Abdallah, A.M. and A. Adindani 1963. Stratigraphy of Upper Paleozoic rocks, western side of the Gulf of Suez, Egypt. Geological Survey and Mineral Research of Egypt, Cairo, Paper no. 25, 18 p. Abdel Gawad, M. 1970a. The Gulf of Suez, a brief review of stratigraphic and structure. Philosophical Transactions Royal Society, London 267(A), p. 41-48. Abdel Gawad, M. 1970b. Interpretation of satellite photographs of the Red Sea and Gulf of Aden. Philosophical Transactions Royal Society, London 267(A), p. 23-48 Al-Far, D.A. 1966. Geology and coal deposits of Gebel El Maghara (north Sinai). Geological Survey and Mineral Research of Egypt, Cairo, Paper no. 37, 59 p. Amgad, I. and K. McClay 2002. Development of accommodation zones in the Gulf of Suez-Red Sea rift, Egypt. American Association of Petroleum Geologists Bulletin, v. 86, no. 6, p. 1003-1026. Alsharhan, A.S. 2003. Petroleum geology and potential hydrocarbon plays in the Gulf of Suez rift basin, Egypt. American Association of Petroleum Geologists Bulletin, v. 87, no. 1, p. 143-187. Alsharhan, A.S. and M.G. Salah 1997. Lithostratigraphy, sedimentology and hydrocarbon habitat of the pre-Cenomanian Nubian sandstone in the Gulf of Suez oil province, Egypt. GeoArabia, v. 2, no. 4, p. 385-400.

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(a) Zaafarana Area, North Gulf of Suez (d) Profile West Profile 3 East 270 406.0 360.9 5 3 338.0 Observed Profile 260 319.2 Error 2 301.5 Profile 287.4 250 277.1 Calculated 1 268.2

Proﬁle 259.9 Magnetics (Gammas) 240 251.8

TMI (nT) 243.6 1.5 236.7 5 4 2.5 230.9

224.7 3.5 Profile Sedimentary Section Profile 217.8 S = 0 209.6 4.5 Proﬁle 200.6 Depth (km) 5.5 186.7 Basement S = 0.001 cgs 164.4 6.5 4 776 778 780 782 784 786 788 790 792 794 796 Distance (km)

(e) West Proﬁle 2 East 312 (b) Observed South Proﬁle 4 North 292 Error 272 300 Calculated Calculated 252 250 Observed

Magnetics (Gammas) 232 Error 200 1.5 5 4

Magnetics (Gammas) 150 2.5

1.5 3.5 Profile Profile 1 2 3 2.5 4.5 Sedimentary Section S = 0

Sedimentary Section Depth (km) Profile Profile Profile Basement 3.5 S = 0 5.5 S = 0.001 cgs 4.5 6.5

Depth (km) 777 779 781 783 785 787 789 791 793 795 797 5.5 Basement Distance (km) S = 0.002 cgs 6.5 710 712 714 716 718 720 722 724 726 728 730 732 734 (f) Distance (km) West Proﬁle 1 East 300 (c) Observed South Proﬁle 5 North 270 260 Error 240 Observed 240 Error Calculated

220 Magnetics (Gammas) 210

Calculated 200 1.5 5 4

Magnetics (Gammas) 2.5 Profile Profile 3 3.5 1 2 3 Sedimentary Section 4.5 5 S = 0 Depth (km) Profile Profile Profile 5.5 Basement Sedimentary Section 7 S = 0.002 cgs S = 0 6.5

Depth (km) 778 780 782 784 786 788 790 792 794 796 798 800 9 Basement Distance (km) S = 0.001 cgs 11 Figure 15: (a) Reduced-to-Pole magnetic image of the Zaafarana Accommodation Zone (see Figure 705 709 713 717 721 725 729 14 for Location). (b to f) Geomagnetic profiles 1 to 5 showing depth model of the basement. Distance (km)

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(a) Zaafarana Area, North Gulf of Suez (d) Profile West Profile 3 East 270 406.0 360.9 5 3 338.0 Observed Profile 260 319.2 Error 2 301.5 Profile 287.4 250 277.1 Calculated 1 268.2

Proﬁle 259.9 Magnetics (Gammas) 240 251.8

TMI (nT) 243.6 1.5 236.7 5 4 2.5 230.9

224.7 3.5 Profile Sedimentary Section Profile 217.8 S = 0 209.6 4.5 Proﬁle 200.6 Depth (km) 5.5 186.7 Basement S = 0.001 cgs 164.4 6.5 4 776 778 780 782 784 786 788 790 792 794 796 Distance (km)

(e) West Proﬁle 2 East 312 (b) Observed South Proﬁle 4 North 292 Error 272 300 Calculated Calculated 252 250 Observed

Magnetics (Gammas) 232 Error 200 1.5 5 4

Magnetics (Gammas) 150 2.5

1.5 3.5 Profile Profile 1 2 3 2.5 4.5 Sedimentary Section S = 0

Sedimentary Section Depth (km) Profile Profile Profile Basement 3.5 S = 0 5.5 S = 0.001 cgs 4.5 6.5

220 Magnetics (Gammas) 210

Calculated 200 1.5 5 4

Magnetics (Gammas) 2.5 Profile Profile 3 3.5 1 2 3 Sedimentary Section 4.5 5 S = 0 Depth (km) Profile Profile Profile 5.5 Basement Sedimentary Section 7 S = 0.002 cgs S = 0 6.5

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Observed 250 Error

200 Calculated

Magnetics (Gammas) 150

0 9

8 2 Sedimentary Section Proﬁle S = 0 Profile 4

Depth (km) 6 Basement S = 0.001 cgs 7 8 Proﬁle Proﬁle 832 837 842 847 852 Distance (km)

9 (d) West Proﬁle 7 East 320

6 TMI (nT) Observed 270 Proﬁle

164.4 186.7 200.6 209.6 217.8 224.7 230.9 236.7 243.6 251.8 259.9 268.2 277.1 287.4 301.5 319.2 338.0 360.9 406.0 Error 220 Calculated

Magnetics (Gammas) 170

0.5 (b) 1.5 9 South Proﬁle 9 North 2.5 240 Sedimentary Section 3.5 S = 0 Profile 4.5 Observed 210 5.5 Error 6.5 Depth (km) 7.5 180 8.5 Basement S = 0.001 cgs Calculated 9.5 834 836 838 840 842 844 846 848 850 852 854 856 858 Magnetics (Gammas) 150 Distance (km)

0 (e) 6 7 8 West Proﬁle 6 East 2 270 Profile Profile Profile 4 240 Observed

6 210 Error Depth (km) 8 Sedimentary Section 180 Calculated S = 0 Basement 10 S = 0.001 cgs Magnetics (Gammas) 150

610 612 614 616 618 620 622 624 626 628 1 Distance (km) 2 Sedimentary Section 9 S = 0 Figure 16: (a) Reduced-to-Pole magnetic image of the Morgan Accommodation Zone (see Figure 14 3 4 Profile for Location). (b to e) Geomagnetic profiles 6 to 9 showing depth model of the basement. 5 6 7 Depth (km) 8 9 Basement S = 0.001 cgs 10 841 843 845 847 849 851 853 855 857 859 861 863 865 867 Distance (km)

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Observed 250 Error

200 Calculated

Magnetics (Gammas) 150

0 9

8 2 Sedimentary Section Proﬁle S = 0 Profile 4

Depth (km) 6 Basement S = 0.001 cgs 7 8 Proﬁle Proﬁle 832 837 842 847 852 Distance (km)

9 (d) West Proﬁle 7 East 320

6 TMI (nT) Observed 270 Proﬁle

164.4 186.7 200.6 209.6 217.8 224.7 230.9 236.7 243.6 251.8 259.9 268.2 277.1 287.4 301.5 319.2 338.0 360.9 406.0 Error 220 Calculated

Magnetics (Gammas) 170

0 (e) 6 7 8 West Proﬁle 6 East 2 270 Profile Profile Profile 4 240 Observed

6 210 Error Depth (km) 8 Sedimentary Section 180 Calculated S = 0 Basement 10 S = 0.001 cgs Magnetics (Gammas) 150

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ABOUT THE AUTHOR

Khamis Farhoud joined Edison International, Egypt, in 2005 where he is currently Exploration Projects Leader. Khamis received his BSc in Geophysics from Cairo University in 1997, and his MSc and PhD from Ain Shams University, Egypt, where he specialized in aeromagnetic techniques. From 1998 to 2002, he worked as Potential Field Geophysicist in the Airborne Geophysics Department of the Nuclear Materials Authority of Egypt. While working with the Authority, he was involved in the planning of acquisition flights, processing and interpretation of aeromagnetic data. His work took him onboard flights over most of Egypt. Before joining Edison, he worked from 2003 to 2005 for ZEITCO as Senior Geophysicist. [email protected]

Manuscript received January 9, 2009 Revised April 21, 2009

Accepted May 10, 2009 Press version proofread by author August 2, 2009

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