Middle East Geologic Time Scale 2010
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GeoArabia, v. 15, no. 2, 2010, p. 175-204 Miocene Kareem Sequence, Gulf of Suez Gulf PetroLink, Bahrain MIDDLE EAST GEOLOGIC TIME SCALE 2010 Miocene Kareem Sequence, Gulf of Suez, Egypt Moujahed I. Al-Husseini, M. Dia Mahmoud and Robley K. Matthews ABSTRACT The Miocene Kareem Formation in the Egyptian Gulf of Suez, and its equivalent formations throughout the Red Sea (250–550 m thick), contain one of the most important petroleum reservoirs in these highly faulted rift basins. They present a difficult exploration target, particularly over the shelves of the sparsely explored Red Sea for several reasons: (1) water depth exceeds one kilometer, (2) they underlie thick evaporites (including salt exceeding one kilometer in thickness), (3) they are difficult to image by conventional seismic techniques, and (4) their lithology is laterally variable and difficult to predict (anhydrite, carbonate, sandstone, shale and marl). The target Red Sea formations are best controlled by boreholes in the Gulf of Suez, where the Kareem Formation and its members are characterized by various synonymous units. A review of representative data and interpretations shows that the formation and its members are better understood when considered as a third-order, transgressive-regressive (T-R) depositional sequence, named the Kareem Sequence in the Middle East Geologic Time Scale (ME GTS). The Sequence is bounded above by the Belayim Sequence Boundary (Sub- Belayim Unconformity) and below by the Kareem Sequence Boundary (Sub-Kareem Unconformity), both corresponding to major sea-level lowstands. It contains the Arabian Plate Langhian Maximum Flooding Surface Neogene 30 (MFS Ng30) at the top of the Kareem Maximum Flooding Interval (MFI). Its lower Rahmi Member forms the majority of the transgressive systems tract (TST). The Kareem MFI and regressive systems tract (RST or HST) occur within the upper Shagar Member. The paleontology of the Formation is characterized by Planktonic Foraminiferal Zone N9 and in recent papers also N8, and Calcareous Nannofossil Biozone NN5, but the Formation’s assignment to Miocene stages (Burdigalian, Langhian and Serravallian) is unresolved in the literature. In this paper, the Kareem Sequence is interpreted in terms of Kareem subsequences 1 to 6. At semi-regional scales (10s of km), the older three are each represented by an anhydrite bed (Rahmi Anhydrite 1 to 3, each c. 10 m thick) overlain by deep- marine deposits (shale, marl and carbonate, 10s of meters thick). Subsequences 4 to 6 are represented in El Morgan field (Kareem A to C units), and in representative boreholes, by three deep-marine shale/marl units, each of which is overlain by a regressive shallow-marine sandstone unit. The Kareem Sequence is correlated to third-order orbital sequence DS3 1.1 with a depositional period of ca. 2.43 million years between ca. 16.1 and 13.7 million years before present (Ma), or numerically the latest Burdigalian, Langhian and earliest Serravallian (Langhian: 15.97–13.65 Ma in GTS 2004; 15.97–13.82 Ma in GTS 2009). The six subsequences are correlated to the orbital 405,000 year eccentricity cycle (referred to as Stratons 40–35 or DS4 1.1.1 to 1.1.6). The older three subsequences form the transgressive systems tract; the fourth contains the maximum flooding interval MFI (ca. 14.9–14.7 Ma) in its lower part. The regressive systems tract starts in the upper part of the fourth subsequence and encompasses subsequences 5 and 6. The orbital architecture of the Sequence provides a simplified framework for predicting lithology and reservoir development. 175 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/15/2/175/4567369/husseini_megts2010.pdf by guest on 02 October 2021 Al-Husseini et al. The six Kareem subsequences carry the orbital-forcing glacio-eustatic signal. During low eccentricity, Antarctic ice-making and global sea-level drops, the northernmost Gulf of Suez and Bab Al Mandeb Strait restricted marine circulation in the Gulf and Red Sea rift basins. The resulting evaporitic setting was associated with the deposition of the Rahmi Anhydrite 1 to 3 beds and exposure over paleohighs. The deeper-marine deposits above the three Rahmi Anhydrite beds, and those of subsequences 4 to 6 reflect high eccentricity, Antarctic ice-melting, global sea-level rises, pluvial conditions at low latitudes (10–30oN), and open- marine circulation in the Red Sea. During pluvial periods, fluvio-deltaic systems prevailed over the mountainous rift shoulders and coastal plains and carried massive clastics into the Gulf and Red Sea Basins. INTRODUCTION The Upper Oligocene? and Miocene syn-rift succession in the Gulf of Suez and Red Sea basins constitutes a complete petroleum system that extends across the sparsely explored African and Arabian shelves of the Red Sea (Figure 1a; Barakat, 1984, 1990; Barakat and Miller, 1986; Barakat et al., 1997; Miller and Barakat, 1988; Beydoun, 1989; Beydoun and Sikander, 1992; Hughes and Beydoun, 1992; Barnard et al., 1992; Mitchell et al., 1992; Salah and Alsharhan, 1996; Lundquist, 1998; Heath et al., 1998). In the Gulf, the Miocene Kareem Formation houses one of the main petroleum reservoirs, which is sourced from Lower Miocene and older Mesozoic rocks and regionally sealed by massive Miocene evaporites (Lelek et al., 1992; Tewfiq et al., 1992; EGPC, Egyptian General Petroleum Corporation, 1964, 1996; Barakat et al., 1997; Salah and Alsharhan, 1997; Alsharhan, 2003). The lateral equivalents of the Kareem Formation are the most prospective hydrocarbon reservoirs throughout the Red Sea shelves as proven in Saudi Arabia’s Red Sea Burqan and Midyan fields (e.g. Cole et al., 1995a, b; Hughes and Filatoff, 1995; Hughes et al., 1999; Hughes and Johnson, 2005; Alsharhan and Salah, 1997; Polis et al., 2005; Figure 1a). In the Gulf of Suez, the Kareem Formation is extensively sampled by boreholes but is still difficult to correlate because it is highly faulted, lithologically very heterogeneous and inadequately imaged by seismic data (e.g. Abd El-Naby et al., in press). Correlating the Formation beyond the Gulf into the Red Sea is difficult, not only for the same reasons, but also due to very sparse borehole control. These challenges are further compounded by the characterization of the formations in terms of numerous and oftentimes confusing and/or conflicting stratigraphic schemes (Figures 2 to 4). Therefore one of the main objectives of this paper is to reconcile these schemes in terms of a sequence stratigraphic framework that can clarify its reservoir development and lateral distribution. Figure 3 shows one of the first attempts to apply a combined eustatic and structural interpretation for the Gulf’s syn-rift Miocene section (Webster and Ritson, 1984). The study used the sea-level curve of Vail et al. (1977) to distinguish between structural and eustatic unconformities, and recognized the top of the Kareem Formation as a sequence boundary. Subsequent studies of the Gulf of Suez attempted to tie its regional Miocene stratigraphy to the global eustatic cycles of Haq et al. (1988; Figure 4); notably Richardson and Arthur (1988), Evans (1988), Patton et al. (1994), Purser and Bosence (1998), Bosworth et al. (1998) and Bosworth and McClay (2001) and references therein. Several of these schemes are exactly reproduced in Figure 4 to illustrate the many differences that prevail in the literature. In particular, the structural/eustatic interpretation and regional correlation of most hiatuses is not adequately resolved. This paper starts with a literature review of the Kareem Formation covering its lithostratigraphic nomenclature, biostratigraphy and sequence stratigraphy. It shows that the Kareem Formation has been implicitly recognized by many authors as a third-order, transgressive-regressive (T-R) depositional sequence, here proposed as the Kareem Sequence for the Middle East Geologic Time Scale (Al-Husseini, 2008). It then seeks to break its stratigraphic architecture into subsequences, which may be correlated to fourth-order, orbital-forcing eccentricity (405 Ky cycles of Laskar et al., 2004) here named stratons (Matthews and Frohlich, 2002; Al-Husseini and Matthews, 2008). 176 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/15/2/175/4567369/husseini_megts2010.pdf by guest on 02 October 2021 Ankara TURKMENISTAN Azerbaijan 38 Caspian Sea TURKEY 37 36 Alborz Mountains Soltanieh Mountains (Figure 10) Derenjel (Figure 11) Miocene Kareem Sequence, GulfMountains of Suez 35 CYPRUS SYRIA 34 Kashan LEBANON Golpagyan IRAN 33 Med. Sea AFGHA- a b 30° NISTAN PALESTINE 32° Yazd IRAQ 32°30' N Kuh-e-Dina JORDAN Ravar 29°30' 30°N 30° Sinai KUWAIT Zagros Mountains KermaN n Gulf of Suez AL BASHAIR-1H1 North Darag Midyan 32°E PAKISTAN Burqan FARHA-1 Khursaniyah-81 Figure 1b (Figure 5) BAHRAIN Sudr 33° SAUDI ARABIA Ras Matarma QATAR 25° Asl Gulf of Oman EGYPT 29° 29°30 UAE Al' Jabal Fahud al-Akhdar Zaafarana Wadi Salt Arabian Shield Basin Al Bashair-1Gharandal OMAN (Figure 8) Farha-1 Ghaba Salt (Figure 7) Amer North Offshore Basin Red Sea North October 20° Al Huqf Rahmi-2 “J” Ras n Budran SUDAN Issran BabaSouth Plain tern MargiOman s Salt(Figure Basin 5) 32°30' We 28°30' OctoberDhofar Arabian Sea Mountains Abu Rudeis SidriFigure 9 29° North Amer Tanka-3 (Figure 8) Belayim Marine ERITREA Wadi Feiran 46 47 Gharib48 North-249 50 51Ras 52 53 54 55 56 57 58 59 60 Amer Feiran (Figure 7) Belayim Bakr West H Bakr 15° Land N YEMEN Bakr West K Ras Gharib 0 200 Hana Ras Fanar El Ayun SG 300 Km Kareem Bab Al Mandeb July Shagar-1 Ramadan ETHIOPIA Gulf of Gulf of Aden 28° Umm El Yusr SOCOTRA DJIBOUTI Aden Kheir South Ramadan 28°30' Badri 35°E 40° 45° Shukheir Morgan GS 327 Figure 1: (a) The Kareem Sequence (and its lateral Gamma Nessim equivalents) contain producing reservoirs in the GS345 33° SB 339 Gulf of Suez as well as Burqan and Midyan fields in Waly (356) Younis Gebel Zeit Amal Saudi Arabia's Red Sea basin.