Late Oligocene–Early Miocene Nukhul Sequence, Gulf of Suez and Red Sea
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GeoArabia, 2012, v. 17, no. 1, p. 17-44 Gulf PetroLink, Bahrain Late Oligocene–Early Miocene Nukhul Sequence, Gulf of Suez and Red Sea Moujahed I. Al-Husseini ABSTRACT Egypt’s Late Oligocene–Early Miocene Nukhul Formation was deposited during the earliest geological evolution of the Gulf of Suez and Red Sea Rift System. In this paper the formation is cast as a depositional sequence based on published sections, and correlated across the Gulf of Suez and northern Red Sea. The resulting correlations indicate that deposition was initiated in local grabens by the oldest continental clastics of the lower member of the Nukhul Formation, the Shoab Ali Member. The member overlies the Suez Rift Unconformity, a term proposed for the entire Red Sea. Although this member can attain a thickness of ca. 1,000 ft (305 m) locally in grabens, it is generally absent over horsts. Sedimentary facies of the member are interpreted as indicating an initial alluvial-fluvial setting that evolved to an estuarine and coastal setting. The upper part of the Nukhul Formation records a regional shallow-marine transgression, which can be subdivided into three correlative Upper Nukhul members. These sediments are absent over the highest paleo-horsts, but reach up to 900 ft (275 m) in thickness in grabens. In the southern Gulf of Suez the Ghara Member represents the Upper Nukhul members. In places it consists of four cycles, each of which starts with an anhydrite bed and is overlain by deposits of mixed lithology (sandstone, marl, and limestone). The four cycles are interpreted as transgressive-regressive subsequences that can be correlated across ca. 60 km in the Gulf of Suez. The Ghara Member correlates to Saudi Arabia’s Yanbu Formation, which consists of massive salt in wells drilled on the Red Sea coastal plains. The Yanbu Salt is dated by strontium-isotope analysis at ca. 23.1–21.6 Ma (earliest Aquitanian). The Nukhul Formation is capped by the Sub-Rudeis Unconformity or correlative Rudeis Sequence Boundary, and overlain by the Rudeis Formation. The Nukhul Formation is here proposed as the Nukhul Sequence and defined in the Wadi Dib-1 Well, wherein it consists of Nukhul subsequences 1 to 10 (in descending order, ranging in thickness between 33–84 m). The lower six Nukhul subsequences 10 to 5 are characterized by shale-to-sandstone cycles of the Shoab Ali Member, and the upper four are represented by the cycles of the Ghara Member. The 10 subsequences are interpreted as tracking the 405,000 year eccentricity signal of the Earth’s orbit and to span ca. 4.0 million years between ca. 25.0 and 21.0 Ma. INTRODUCTION This paper argues for the proposition that sequence stratigraphy can be used to characterize depositional systems in rift basins (see GeoArabia’s Suez Debate, 2011, v. 16, no. 1, p. 13). It focuses on the oldest syn-rift deposits in Egypt’s Gulf of Suez to understand the earliest structural and depositional evolution of the Red Sea Rift System (Figures 1 to 3). This task is not straightforward because these deposits are named and described in terms of several parallel and oftentimes conflicting stratigraphic schemes that typically apply to local study areas (Figures 1 to 3). Therefore one aspect of this paper is to review some of these schemes so as to resolve synonyms. This simplification of terminology aids in the compilation of an important dataset and the identification of a regional sequence-stratigraphic framework that can be correlated across most – if not all – of the Red Sea Rift System. 17 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/1/17/4568978/al-husseini.pdf by guest on 23 September 2021 Al-Husseini a 35° 40°E 45° b 33°E 34° 35° JORDAN Gulf of Sinai Suez Gulf of JORDAN Sinai Abu Rudeis Aqaba 30°N 29°N Gulf of SAUDI Suez ARABIA Gulf of Aqaba Abu Durba Ras Maqna Gharib Midyan 28° Port Gharamul Safaga Gebel Zeit Gebel Mallaha EGYPT SAUDI ARABIA 25° 25° 27° Hurghada Ras Banas Yanbu Safaga Gebel Arabian Shield Duwi Quseir Jeddah 26° EGYPT Red Sea Mecca Red Sea 20° 20° Marsa’ Alam Port Sudan 25° Ras Honkorab SUDAN Abu Ghusun N 0 100 Ras Banas Jizan 24° ERITREA Km Khartoum Sana’a 15° Asmara Thio-1 15° Figure 1: (a) The Red Sea Rift System YEMEN extends from the northern Gulf of N Suez to the Bab Al Mandeb Strait. 0 200 (b) Locations mentioned in the paper. Bab Al Mandeb ETHIOPIA Gulf of Km DJIBOUTI Aden 35° 40° 45° Saoudi and Khalil (1986) were the first authors to name and define the continental clastics that were deposited in the oldest syn-rift grabens of the Gulf of Suez as the Shoab Ali Member of the Nukhul Formation. The member is overlain by deposits that are more widely distributed and defined in terms of three members; here referred to as the Upper Nukhul members: (1) October Member (mainly clastics), (2) Ghara Member (mainly evaporites and clastics), and (3) Gharamul Member (mainly clastics and carbonates) (Figures 2 and 3). In the paper these members are described in a lexicon style, and the formation is recast as a transgressive-regressive depositional sequence, the Nukhul Sequence. In the final part of the paper the Nukhul Sequence is dated between ca. 25.0–21.0 Ma by the calibration of its subsequence in an orbital-forcing, glacio-eustatic time scale (Matthews and Al- Husseini, 2010). SHOAB ALI MEMBER, NUKHUL FORMATION Nomenclature and Type Section of Shoab Ali Member The oldest syn-rift rock unit in the Gulf of Suez was named the “Shoab Ali Member” of the Nukhul Formation by Saoudi and Khalil (1986). They defined the member in the Well GH 385-1 between log depths 6,980–7,980 ft (1,000 ft, 305 m thick, Figures 2 and 5c). As discussed in this paper their choice of this well for the type section is not considered adequate because its upper contact is not defined in the same well. The Wadi Dib-1 Well is considered a better choice and discussed at the end of the paper. 18 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/1/17/4568978/al-husseini.pdf by guest on 23 September 2021 Nukhul Sequence, Gulf of Suez and Red Sea ISOPACH MAP, SHOAB ALI MEMBER, GULF OF SUEZ 30°N 32°30'E 33° 33°30' 34° 34°30' 30° 0 ft 500 N 1,000 North Darag 0 50 1,500 km 2,000 Sudr Contours in feet City Outcrop 29°30' Ras Matarma Well Asl Oil field Sinai 29°30' Peninsula Hammam Faraun Zaafarana Figure 7 Abu Zenima 29° Wadi Gharandal Ras Wadi Nukhul “J” Budran (Figures 6 and 7) North October 29° (Figure 9) Abu Rudeis Sidri Issran Amer North Offshore October Belayim El Qaa Marine Feiran North Amer Gebel Ekna Belayim Ras Amer Land Ras Fanar 28°30' Proterozoic SG 300 Bakr Bakr West H Basement Hana Bakr West K Ramadan 28°30' Ras Gharib South Ramadan El Ayun GS 327 Kareem July Badri El Tor Umm El Yusr Morgan Kheir Nessim GS345 SB 339 Shukheir Gamma 28° Younis Sinai/GHM Waly (356) Amal GH (376) GH 385-1 Gebel Zeit Ras El Ush GS (356) 28° Gharamul 50 Sidki Shoab Ali 0 1000 Wadi Dib-1 (Figure 12) 1,500 Zeit Bay-1 500 Abu Girfan Hilal Zeit East Zeit Bay 0 Gemsa ? Geisum ? 500 Tawila 27°30' Gemsa-Southeast 1000 Proterozoic Esh El-Mallaha Basement Esh 27°30' El-Mallaha Hurghada 32°30' 33° 33°30' 34° 34°30' Figure 2: Thickness of the Shoab Ali Member as contoured at 500 ft interval by Saoudi and Khalil (1986). In their map the member does not extend north of about 28°N. Also shown are locations mentioned in the paper. 19 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/1/17/4568978/al-husseini.pdf by guest on 23 September 2021 Al-Husseini Wadi Nukhul, Gulf of Suez, Gulf of Suez, Egypt Saudi Arabia Sinai, Egypt Egypt Montenat et Saoudi and Khalil Pooley al. (1998) and Wescott Hughes and (1986) (1947) GENEBASS et al. (1996) Johnson (2005) Group (1996) T50 Shagar Ras Mbr Budran S50 Mbr Kareem T40 Wadi Waqb Middle Fm Formation Rahmi Mbr Lagia un Musa Fm S40 Mbr Ay Not T30 Reviewed Upper Asl Fm Member S30 Burqan Formation Hawara MIOCENE Fm Rudeis Formation T20 Lower Mheiherrat S20 Member Fm T10 Lower Gharandal Group 3 As Ae Nukhul Fm A Nukhul nbu Formation Subgroup Subgroup Marine Unit 23.1–21.6 Ma Ghara Member Formation October Member Ya Musayr Formation Gharamul Member Biosequence ? Group S10 ayran Group Unit T Nukhul Formation Subroup Abu 2 Shoab Ali A1 Al Wajh Zenima Member Red Formation OLIGO- Fm CENE Beds Unit 1 T00 Suez Rift Unconformity Figure 3: Stratigraphic schemes for the Nukhul Formation discussed in the paper. The present study follows Saoudi and Khalil (1986) and Richardson and Arthur (1988) and divides the Nukhul Formation into the continental clastics of the Shoab Ali Member, and the Upper Nukhul members consisting of the October (mainly clastics), Ghara (mainly evaporites) and Gharamul (mainly carbonates) members. The Nukhul Formation (Shoab Ali and Upper Nukhul members), together with the Rudeis and Kareem formations, are assigned to the Gharandal Group (named after Wadi Gharandal, Figure 2) or pre-Evaporite Group (EGPC, 1964, 1996; El-Gezeery and Marzouk, 1974). In some parts of the Gulf, the formations attributed to the Gharandal Group are differently named and defined: Nukhul, Mheiherrat, Hawara, Asl and Ayun Musa formations (EGPC, 1996; Figure 3).