ABSTRACT

The onshore and offshore Saudi Arabian Red Sea region contains a series of lithostratigraphic units that have not previously been formally defined and described. Based on an intensive study of the succession, a lithostratigraphic scheme is proposed in a lexicon format that integrates biostratigraphic, sedimentological, seismic and field studies from the Midyan Peninsula in the north, to the Jizan Coastal Plain in the south. In view of the economic aspect of the Neogene succession and greater accessibility to Neogene subsurface samples, emphasis has been placed on a revision of the Neogene lithostratigraphy. Resting upon Proterozoic Basement, the sedimentary succession was deposited during the Cretaceous to Pleistocene times. The oldest pre-rift Suqah Group nonconformably overlies the Proterozoic Basement and consists of Upper Cretaceous shales of the Adaffa Formation and Cretaceous to Palaeogene sandstones, shales and thin limestones of the Usfan Formation. A series of volcanics includes the early to middle Oligocene Matiyah Formation and the late Oligocene-early Miocene Jizan Group.

The Neogene succession displays a great lithological diversity. The Tayran Group (Al Wajh, Musayr and Yanbu Formations) includes marginal marine siliciclastics of the Al Wajh Formation, and represents the earliest rift-associated sediments deposited during the earliest Miocene. These are conformably overlain by lower Miocene shallow-marine carbonates of the Musayr Formation. In some of the central Red Sea onshore basins, thick lower Miocene submarine evaporites of the Yanbu Formation were deposited under locally restricted conditions and form the third formation of the Tayran Group. Rapid subsidence during the early Miocene caused deposition of deep-marine, planktonic-foraminiferal mudstones and thick submarine fan sandstones of the Burqan Formation. Carbonates, marine mudstones and submarine evaporites of the Maqna Group (Jabal Kibrit and Kial Formations) unconformably overlie the Burqan Formation and were deposited during latest early Miocene to earliest middle Miocene. The Jabal Kibrit Formation consists of an anhydrite-carbonate facies, of which the carbonates form the Wadi Waqb Member. Siliciclastic facies of the Jabal Kibrit Formation are termed the Umm Luj Member. Above the Jabal Kibrit Formation, the Kial Formation is typified by interbedded anhydrites, calcareous siltstones and carbonates, and includes the Sidr, Nakhlah, Yuba, Rayaman and Sabya Members. Within the region, thick evaporites of the Mansiyah Formation were deposited extensively during the middle Miocene, and are overlain by poorly exposed sands, shales and thin anhydrite beds of the middle to upper Miocene Ghawwas Formation. The Lisan Group unconformably overlies the Ghawwas Formation and consists of coarse alluvial sands and gravels of possible Pliocene to Holocene age.

INTRODUCTION

Between 1967 and 1976, ten deep exploratory wells were drilled in the Saudi Arabian Red Sea by international oil companies, and between 1982 and 1986 six shallow stratigraphic wells were drilled in the Yanbu coastal region (Figure 1). The sedimentary successions penetrated by these wells were readily equated with the standard lithostratigraphy of the well-explored Gulf of Suez in Egypt, but no systematic attempt was made, at that time, to establish a formal stratigraphic succession. Between 1990 and 1994 (Figure 1), Saudi Aramco undertook an intensive exploration program in the Red Sea and drilled 14 exploratory wells (1992–1994); an additional four wells were drilled in 1998.

During the Saudi Aramco exploration program, detailed field observations were made in the Midyan (Figure 1a), Al Wajh (Figure 1b), Yanbu (Figure 1c), Jiddah (Figure 1d), Ghawwas (Figure 1e), and Jizan (Figure 1f) coastal areas. Fieldwork was focused on the Midyan coastal area where the most complete range of lithostratigraphic units is extensively exposed and easily accessed. Supplementary fieldwork in the Midyan region was carried out in 1997 by Saudi Aramco and the King Fahd University of Petroleum and Minerals Research Institute (KFUPM-RI) to investigate the stratigraphy of additional exposures of the Wadi Waqb Reservoir equivalent carbonates (1998, KFUPM Report). This project also provided a new geological map and structural synthesis for the Midyan region, incorporating satellite images derived from the Landsat Thematic Mapper (TM). A new technique for imaging the pre-Mansiyah fault blocks in the Midyan region was discussed by Mougenot and Al-Shakhis (1999). The results of the Saudi Aramco work have been documented as Saudi Aramco unpublished reports (A.M. Afifi, T.C. Connally, M. Senalp and G.W. Hughes, 1993; G.S. Ferguson, 1993a, b; G.S. Ferguson and M. Senalp, 1993; G.S. Ferguson, M. Senalp and A.M. Afifi, 1993; G.W. Hughes and R.A. Kamal, 1993a, b, c; R.A. Kamal and G.W. Hughes, 1993 a, b; R.S. Johnson, D. Rodgers and G.R. Savage, 1995) and published by Hughes and Filatoff (1995), Kamal and Hughes (1995), Filatoff and Hughes (1996), and Hughes et al. (1998a, b; 1999).

Various informal lithostratigraphic schemes have been applied to the Saudi Arabian Red Sea succession (Karpoff, 1956; Skipwith, 1973; Remond and Teixido, 1980; Bokhari, 1981; Le Nindre, 1981; Dullo et al., 1983; Moltzer and Binda, 1984; Schmidt and Hadley, 1984; Clark, 1986; Le Nindre et al., 1986; Jamal, 1991; Srivastava and Binda, 1991). The similarity of the Saudi Arabian succession to the well-studied Gulf of Suez and to the Red Sea drilled or exposed successions, enabled Beydoun (1991) and Hughes and Beydoun (1992) to suggest a regional Red Sea lithostratigraphic scheme (Figure 2). The aim of the present study is to establish, for the first time, a formal lithostratigraphic scheme and depositional history for the Saudi Arabian Red Sea region (Figures 1 and 3). This scheme incorporates pre-1990s stratigraphic nomenclature together with the results of the recent Saudi Aramco studies of outcrop and subsurface data (Hughes and Filatoff, 1995; R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report; Hughes et al., 1999).

STRATIGRAPHIC CONVENTIONS

The terms ‘early’ and ‘late’ are restricted to indicate relative time designation whereas ‘lower’ and ‘upper’ are applied to equivalent time-stratigraphic units (Hedburg, 1961; Bates and Jackson, 1980; Haile, 1987). As none of these designations is formal for the Cenozoic (GTS 2004, Gradstein et al., 2005), lower case lettering is used. Due to the many rock unit definitions in the Red Sea, the words Member, Formation and Group are capitalized to imply formal definitions as consistent with the present study. Also, in order to avoid confusion, the plurals of these three words are also capitalized where the units are formal. The status of rock units (member, formation, group) that are not considered compatible with the present study are not capitalized. In addition, the word Basement as in “Proterozoic Basement” is capitalized. The following summary provides a list of the rock units and their status.

The wells that are discussed in this study are listed in Table 1 and Figure 1. Where the depths are quoted in wells, they are in feet below sea level. Various unconformities, or substantial time breaks in the rock record, are defined using the criteria of Bates and Jackson (1980), especially in the use of nonconformity, or angular unconformity, and disconformity, or parallel unconformity. Where regional evidence such as seismic, outcrop or stratigraphic relations, has been used to establish an unconformity, then this term has been used without further qualification in well sections where the geometric relationships are often difficult to prove.

SAUDI ARABIAN RED SEA LITHOSTRATIGRAPHY: SUMMARY

Obsolete Rock Units

Al Bad formation

Baid formation

Khuraybah formation

Raghama formation

Shumaysi formation (possibly Shumaysi member, further study required)

Shumaysi series (possibly Shumaysi member, further study required)

Umm Himar formation (possibly Umm Himar member, further study required)

PROTEROZOIC BASEMENT

The Proterozoic Basement consists of ultramafic, metavolcanic, and metasedimentary rocks and granitic plutons which have been intruded by basalt, rhyolite, and dolerite dikes (Figure 4). The Proterozoic Basement has been dated at about 600–700 million years before present (Ma) (Gardner et al., 1996), and is considered to have been formed along an accreting Proterozoic volcanic arc. Exploration drilling shows that the Proterozoic Basement rocks are often fractured and leached. The granitic character of the Proterozoic Basement indicates a continental rift origin for the proto-Red Sea rather than spreading and generation of oceanic crust (Bosworth, 1993; Sultan et al., 1993).

SUQAH GROUP

The Suqah Group consists of the Adaffa, Usfan, and Matiyah Formations, or all the pre-rift Upper Cretaceous to Oligocene successions exposed or drilled in the Saudi Arabian Red Sea area (Figure 5).

Name: R.S. Johnson, D. Rodgers and G.R. Savage (1995, Saudi Aramco Report) named the Suqah Group after Wadi as Suqah near Jiddah (Figure 1d).

Regional Equivalents: The pre-rift stratigraphy of the northern Red Sea coast is similar to that of the southern Gulf of Suez (Bosworth et al., 1998), which consists of the Naquus and Malha Formations and the Cretaceous to Eocene Raha, Wata, Matulla, Brown Limestone, Sudr, Esna and Thebes Formations. There is, however, no record of Oligocene sediments in the Gulf of Suez. The Suqah Group is equivalent to the Tawilah Group of west Yemen (Al-Subbary et al., 1998).

Type Section: The Suqah Group is defined in the Saudi Aramco onshore well Jiddah-1 (JIDH-1: 22°10′06.4″N, 39°12′39.1″E) between 1,918–3,662 ft (1,744 ft, 531.7 m thick), Saudi Arabian Red Sea (Figures 1d and 5).

Adaffa Formation, Suqah Group

This oldest sedimentary sequence (Adaffa Formation) is exposed in the Midyan area (Figure 1a) and has a late Cretaceous age based on macrofossils.

Name:Clark (1986) named his Adaffa formation after Al Adaffa Village in Wadi ash-Sharmah in the Aynunah area of southeast Midyan (Figure 1a). Much of the succession that Clark originally assigned to the Adaffa formation (including the fossiliferous calcarenite) has been reassigned to the Miocene Maqna Group. Therefore, the Adaffa Formation, as described below, corresponds to the lower part of Clark’s formation. Also, Hughes and Filatoff (1995) assigned the sequence to the ‘Unnamed Clastic Unit’.

Type Section: The Adaffa Formation is defined in the Aynunah Graben (Figures 1a and 6) in southeast Midyan (28°05′45″N, 35°16′03.4″E) (Clark, 1986).

Reference Section: Probable Adaffa Formation is represented in the Saudi Aramco onshore well Jiddah-1 (JIDH-1) between 3,662–4,208 ft, Saudi Arabian Red Sea (Figures 1d and 5).

Thickness: Clark estimated the Adaffa formation to be possibly 200 m (656 ft) thick. In Jiddah-1, the Adaffa Formation is 546 ft (166.5 m) thick.

Regional Equivalent: The Adaffa siliciclastics are the equivalent of various carbonate units in the Gulf of Suez such as the Duwi (Lower Campanian) and Sudr (Upper Campanian-Maastrichtian) Formations. The Adaffa Formation is also considered to be equivalent to the Lower Tawilah Group in west Yemen (Al-Subbary et al., 1998).

Lithology: The Adaffa section is made up of a thin basal conglomerate (Figure 7) overlain by approximately 300 ft (91.5 m) of yellow to reddish-brown, cross-bedded sandstones (Figure 8) and gray-green shale (Figure 9). The conglomerate (Figure 10) contains granite cobbles and pebbles, phosphatic nodules, dinosaur (Figure 11) and turtle bones, and petrified wood fragments. The sandstone is a well-sorted quartz arenite that, when exposed, weathers into low-lying hills formed almost exclusively of disaggregated sands (Figure 12) (A.M. Afifi, T.C. Connally, M. Senalp and G.W. Hughes, 1993, Saudi Aramco Report; Milner et al., 1993).

Distribution: The distribution of the Adaffa Formation is not known in detail, but it is present in outcrop in Midyan and at depth in the Jiddah area. Similar rocks crop out in the Wadi Azlam Basin on the Red Sea coast between Duba and Al Wajh (Figure 1).

Contact Relationships:Clark (1986) stated that the siliciclastics in the lower part of his Adaffa formation had a faulted contact with the Proterozoic Basement. Although the upper contact was not clearly defined, Clark suggested that it is conformably overlain by the Oligocene Sharik formation. In the present study, neither the lower nor upper Adaffa contacts were visible due to sand and gravel covering much of the low-relief exposures. Preservation of the Adaffa Formation in the southeast corner of the basin may result from its location in an area of postdepositional faulting and graben development (G.S. Ferguson, Saudi Aramco unpublished seismic interpretation). There is no evidence in Midyan for the Usfan and Shumaysi formations that have been described only from the Jiddah region (Karpoff, 1956; Al Shanti, 1966; Abou Ouf and Gheith, 1998). In Jiddah-1 well (Figures 1d and 6), the Adaffa Formation lies nonconformably upon the Proterozoic Basement and is unconformably overlain by the Usfan Formation.

Age:Clark (1986) cited microfossil evidence of Andrieff (Le Nindre et al., 1981; Redmond and Teixido, 1980) to support a late Cretaceous to Eocene age. In addition, in the Aynunah region, a thin bed of limonitic sandstones at the top of the sandstone succession contains bones of a sauropod (titanosaurid) dinosaur and turtle plates (Ref: 28°05′45″N, 35°16′03.4″E) (Milner et al., 1993). The coexistence of Albian-Maastrichtian dinosaur bones and Cretaceous to Holocene turtle plates provides an Albian to Maastrichtian age for the Adaffa Formation. A similar assemblage of dinosaur and turtle remains, together with crocodiles, lungfishes and theropods, has been found in Sudan and given a late Cretaceous age (Buffetaut et al., 1990). A late Cretaceous microflora has been found in similar rocks approximately 290 km to the south at Wadi Azlam (Clark, 1986; Giot et al., 1980).

Paleoenvironment: A.M. Afifi, T.C. Connally, M. Senalp and G.W. Hughes (1993, Saudi Aramco Report) have suggested a fluvial depositional environment for the Adaffa Formation. In Sudan, the fossil assemblages similar to those of the Adaffa Formation have been interpreted as indicative of a lacustrine and braided-stream environment (Buffetaut et al., 1990). The significance of the phosphatic nodules is unclear, but their presence within conglomerates suggests high energy derivation from a possible bone bed source.

Usfan Formation, Suqah Group

The name Usfan Formation was originally used by Karpoff (1957) to define surface exposures first noted in the Jiddah area of Saudi Arabia. In this study, the Usfan Formation is considered a possible lateral facies equivalent of the Shumaysi formation (see below) because the latter formation has not been recognized in recent subsurface work.

Name: The Usfan Formation was first named by Karpoff (1957) as the Usfan series after the Usfan Village.

Type Section: A locality situated 2.5 km north of Usfan Village (21°57’N, 39°21’E). Brown et al. (1963) renamed the “series” as the Usfan Formation.

Reference Section: Saudi Aramco onshore well Jiddah-1 (JIDH-1) between 2,458–3,662 ft, Saudi Arabian Red Sea (Figures 1d and 6).

Thickness: In Jiddah-1, the Usfan is 1,204 ft (367 m) thick; and Vail et al. (1983) (in Moore and Al-Rehaili, 1989) state that it is 215 m (705 ft) thick.

Regional Equivalent: The siliciclastic Usfan Formation is considered to be equivalent of the Sudr (Upper Campanian-Maastrichtian carbonates), Dakhla (Maastrichtian-Lower Paleocene claystones, marls and carbonates), Esna (Upper Paleocene shales) and Thebes (Lower Eocene carbonates) Formations of the Gulf of Suez. It is also probably equivalent to the Medjzir Formation of the Upper Tawilah Group of west Yemen (Al-Subbary et al., 1998), the Mukawwar Formation of Sudan (Whitman, 1971), and the Umm Himar Formation inland western Saudi Arabia (Whybrow and Madden, 1995).

The Shumaysi formation (Shumaysi series of Karpoff, 1957), previously considered to be stratigraphically younger than the Usfan Formation (Karpoff, 1957; Al-Shanti, 1966; Moltzer and Binda, 1984; Ramsey, 1986; Abou Ouf and Gheith, 1998) is considered to be a facies equivalent of the Usfan Formation (Spencer, 1987; G.S. Ferguson, 1993a, b, Saudi Aramco Reports). Recent work by Abou Ouf and Gheith (1998), however, supports a separation of the formations based on their different age assignments (see below). The Usfan Formation is confined to the Suqah trough and the Shumaysi formation crops out both in the Suqah trough and Wadi Shumaysi. Although certain similarities between the Usfan and Shumaysi rocks are noted in their work, they recognize that the top of the Usfan Formation contains marine phosphorite and limestone and crops out only northeast of Jiddah, whereas the Shumaysi formation contains oolitic ironstones, freshwater limestones, and cherts, and crops out to the east of Jiddah. It seems likely that the rich vertebrate bone-bearing limestones described from the Umm Himar region of western Saudi Arabia (Whybrow and Madden, 1995), and dated as Paleocene, may represent a facies variation of the Usfan Formation.

We have not seen sufficient sections of this age in the subsurface to confidently differentiate between the Usfan and Shumaysi rocks. The descriptions and stratigraphic discussions of both formations by Abou Ouf and Gheith (1998, p. 138-141) are very convincing, and we tend to agree with their conclusions that “the Usfan Formation is both lithologically distinct and older (late Cretaceous to Eocene) than the Shumaysi formation (late Oligocene to early Miocene)”. While they may divide it into three units, the overall age of the Shumaysi formation in Abou Ouf and Gheith (1988, their Figure C2.4) extends from the Eocene to the middle Miocene, and is therefore considered equivalent to the syn-rift sediments reviewed in detail in this study. This very broad definition of the Shumaysi formation would not be in agreement with earlier considerations of Usfan equivalence, and we find it difficult to agree that the fundamental changes within the sediments of this age range in the Red Sea region should be contained within a single formation.

Lithology: The Usfan Formation consists of marine and littoral sediments, marly limestones (Figure 13), sandstones (Figure 14), coquinas and conglomerates; it is also fossiliferous (Figure 15) and phosphatic in places. Black shales and light-colored siltstones are found interbedded with mature sandstones (Figure 16) along with rare bioclastic limestones, coals and oolitic ironstones in the upper part (Figure 17). Poorly-sorted, locally kaolinitic, pebbly sandstones are also found interbedded with minor siltstones. Oolitic ironstones (Figure 18) are a characteristic feature of the Usfan Formation (Al Shanti, 1966; Hamilton, 1973), and are considered to form a regionally correlative stratigraphic layer near the top of the marine section (G.S. Ferguson, 1993b, Saudi Aramco Report). The color varies from beige to brown to reddish purple, and basalt is locally intruded (Figures 19 and 20). In the Jiddah-1 well (Figures 1d and 5), a 332-foot-thick (101.2 m) gabbro occurs between 3,030–3,362 ft. The Usfan Formation contains one significant limestone bed exposed as the “Great Wall’ limestone near the town of Usfan (Figures 21 to 23).

Distribution: Undefined specifically, but the Usfan Formation is present in the Jiddah region of the Saudi Arabian Red Sea (Karpoff, 1957; Al Shanti, 1966; Brown et al., 1963; Ramsay, 1986).

Contact Relationships: The Usfan Formation nonconformably overlies Proterozoic Basement at the type locality. In Jiddah-1 (Figures 1d and 5), the Usfan Formation unconformably overlies the Adaffa Formation and is unconformably overlain by the Matiyah Formation. In Wadi Ash Sham, the Usfan Formation is reported to be conformably overlain by the Shumaysi formation and also by sub-horizontal Upper Miocene to Pliocene basalts of the Hammah Formation (Abou Ouf and Gheith, 1998; Moore and Al-Rehaili, 1989).

Age: The Usfan Formation was originally dated by Karpoff (1957) as late Maastrichtian to Eocene based on molluscs and shark teeth. Brown (1970) dated a glauconitic bed beneath the “Great Wall” limestone as 43–55 Ma using K-Ar dating, although he suspected that this may be an anomalously young age due to the poor quality sample. Maastrichtian nautiloids and baluchicardid molluscs from a phosphatic bed in the lower Usfan Formation were identified by Basahel et al. (1982). Abou Ouf and Gheith (1998) state that radiometric and biostratigraphic evidence indicate that the Usfan Formation is clearly of Maastrichtian to Eocene age whereas the Shumaysi formation is late Oligocene to early Miocene in age. The Umm Himar Formation, a possible lateral equivalent, is dated as Paleocene based on the rich vertebrate fossils (Whybrow and Madden, 1995).

Saudi Aramco palynological work supports a Maastrichtian to middle Eocene age for the Usfan Formation. The spore Gabonisporis vigourouxi and dinoflagellate Dinogymnium spp. indicate a Maastrichtian age for part of the succession. The palm pollen Proxapertites spp. and the dinoflagellates Apectodinium/Wetzeliella spp., which evolved at the beginning of the late Paleocene, and palm pollen Longapertites vaneendenburgii and pollen Retidiporites magdalenensis and Saturnia enigmaticus, with extinctions at end of the Paleocene, indicate a Paleocene age for at least part of the formation. Eocene sediments are confirmed by the presence of the pollen Spirosyncolpites bruni and Retibrevitricolpites triangulatus. The absence of the upper Eocene pollen Verrucatosporites usmensis restricts the formation to an age not younger than middle Eocene. Moltzer and Binda (1984) provided palynological evidence to support an early Eocene age for rocks assigned to the Shumaysi formation. A lava flow east of Jiddah has been dated as 32 and 25 Ma based on K-Ar age determinations and provides a late Oligocene to Miocene age limit to the underlying rocks assigned to the Shumaysi formation by Brown (1970). In the Medj-zir Formation of the upper Tawilah Group of west Yemen (Al-Subbary et al., 1998), the presence of gastropod genera Tarebia and Coptostylus indicate Paleocene to Holocene and Paleocene to late Oligocene ages, respectively.

Paleoenvironment: Interpreted as shallow, nearshore marine at the base (deltaic/estuarine) grading to non-marine low-energy fluviatile at the top, with localized areas of shallow carbonate sedimentation between the estuaries and deltas. Abou Ouf and Gheith (1998) concluded a fluviatile environment for the “sands and conglomerates, capped by a transgressive-regressive unit of limestones, dolomites and gypsiferous shales”.

Palynological assemblages are generally rich and well-preserved and dominated by Palmae pollen. Dinocysts are common and kerogen typically consists of coarse well-preserved terrestrial vegetal fragments. Microfauna are generally rare, but assemblages of small agglutinated benthonic foraminifera are sporadically distributed with charophytes, thus providing evidence for brackish and freshwater environments, respectively. Fluvial, shallow marine and lacustrine depositional facies have been recognized in the Medj-zir Formation of the upper Tawilah Group of west Yemen (Al-Subbary et al., 1998).

Matiyah Formation, Suqah Group

The name Matiyah Formation is here formally proposed for a lithological unit found in the subsurface of the southern Saudi Arabian Red Sea, which is interpreted to represent the youngest pre-rift sediments.

Name: The name Matiyah Formation is derived from the equivalent Mata’ah member of the Shumaysi formation (Spencer, 1985, 1987).

Type Section and Thickness: The Matiyah Formation is defined in Saudi Aramco exploration well Jiddah-1 (JIDH-1) between 1,918–2,458 ft (540 ft, 164.6 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1d and 5).

Regional Equivalent: Although poorly age-constrained, it is possible that the Matiyah Formation may be stratigraphically equivalent, in part, to the Tayiba Formation of the Gulf of Suez (Hermina et al., 1989; Abul Nasr, 1990; McClay et al., 1998).

Lithology: The lithology of the Matiyah Formation consists of purplish, red to variegated, weathered siltstones and fine-grained sandstones that are sometimes interbedded with basalt flows (Figure 24).

Distribution: The Matiyah Formation is found in the Jiddah area.

Contact Relationships: The Matiyah Formation may represent “proto-rift” sedimentation and volcanism and is separated unconformably from both the pre-rift Usfan Formation of the Suqah Group below, and the syn-rift Tayran and Jizan Groups above. An unconformable relationship is based on the absence of Middle to Late Eocene sediments.

Age:Skipwith (1973) provided a K/Ar age of 32 Ma for a basalt that overlies the Shumaysi. The Matiyah Formation is early Oligocene (33–34 Ma) in age as determined by radiometric dating methods on basalts from Jiddah-1 well (J.D. Cocker, 1992, Saudi Aramco Report) and the presence of the following palynomorphs: Magnastriatites howardii (spore) (origin at the beginning of the Oligocene); Pediastrum delicatites (green alga) (origin during the middle Eocene) (Filatoff and Hughes, 1996).

Paleoenvironment: The depositional environment of the Matiyah Formation is interpreted as a low-energy, oxidizing, fluvio-lacustrine regime with volcanic episodes. Palynological samples are barren or yield very sparse assemblages strongly dominated by the freshwater green alga, Pediastrum delicatites, and rare spores/pollen. Organic yields are very low and typically consist of disseminated fines.

JIZAN GROUP

The Jizan Group is named after the Jizan region (Figure 1f) and consists of undifferentiated volcanics, volcaniclastics, metasediments, sediments and basalt. The Jizan Group is interpreted as representing initial syn-rift volcanism in the southern Red Sea interbedded with the earliest syn-rift sediments (Figure 3).

Name: The Jizan Group was informally named after exposures in the Jizan area by Brown and Jackson (1958), R.S. Johnson, D. Rodgers and G.R. Savage (1995, Saudi Aramco Report).

Regional Equivalents: It is possible that the Jizan Group is equivalent, at least in part, to the Abu Zenima Formation of the Gulf of Suez (Montanet et al., 1998), and also to part of the Baid formation (Schmidt and Hadley, 1984).

Type Section: The Jizan Group is defined in the Saudi Aramco onshore exploration well Ghawwas South-1 (GWWS-1: 19°21′56.5″N, 41°11′06.6″E) between 2,976–6,035 ft (Figure 25).

Reference Section: The Jizan Group is represented in the Saudi Aramco onshore exploration well Jizan North-1 (JZNR-1: 16°46′51.9″N, 36°43′52.2″E) between 9,607–10,450 ft (Figures 1f and 26).

Thickness: In the GWWS-1, the Jizan Group type section is 3,059 ft (932.6 m) thick, while it is greater than 843 ft in the reference well.

Lithology: The Jizan Group consists of undifferentiated volcanics, volcaniclastics, metasediments, sediments and basalt (Figures 27 and 28). Interbedded lava flows, sandstones, graywackes, limestones and volcanic tuffs have been assigned informally to the Baid formation by Greenwood (1975), and are here considered to probably represent a transitional facies between the Jizan Group and the Al Wajh Formation of the Tayran Group.

Distribution: Available evidence indicates that the Jizan Group is restricted to the Jizan area.

Contact Relationships: The Jizan Group is generally nonconformably overlain by the Burqan Formation and unconformably overlies Proterozoic Basement in the type section. In the Saudi Aramco Jizan South-1 (JZSO-1) well, however, the Jizan Group is nonconformably overlain by a thin shale unit that is interpreted as belonging to the Al Wajh Formation of the Tayran Group. This is the only example in which both the Jizan and Tayran Groups are in contact.

Age: Basalt flows in the Baid formation (Sebai et al., 1991) in the Qunfudah area have been dated as early Miocene, 18.4 to 21.7 Ma, but as the Miocene/Oligocene contact is about 23.8 Ma (Berggren et al., 1995), this section is considered to represent the youngest part of the Jizan Group. Basalts of the Abu Zenima Formation of Egypt have been dated at 22 Ma (Ott d’Estevou et al., 1986), and this tends to support the lithostratigraphic comparison with the Saudi Arabian Red Sea succession. The oldest syn-rift sediments found in the Red Sea inter-layered with basalts range from 27.0 to 22.0 Ma and are found at Sharm El Qibli (El-Haddad, 1984; in Al-Husseini et al., 2003) and Sharm El Bahari (Roussel et al., 1986; in Al-Husseini et al., 2003). This conforms to the age of magmatism on the western edge of the Arabian Plate which Ghazot et al. (1998; in Al-Husseini et al., 2003) maintain ranges from 26.0–20.0 Ma. The presence of freshwater fish fossils attributed to Barbus and Tilapia (Brown, 1970) has been used to suggest a Miocene age for the Baid formation (Schmidt and Hadley, 1984).

TAYRAN GROUP

The Tayran Group consists of the Al Wajh, Yanbu, and Musayr Formations (Figure 3) and is associated with the early period of Red Sea rifting. Recent studies of surface and subsurface data have clarified previously inconsistent classification schemes. In the Egyptian Red Sea, the early syn-rift sediments lie with less than 10 degrees of angular unconformity upon a pre-rift sedimentary succession that reaches 2,000 m in thickness (Montanet et al., 1998). The facies deposited during early rifting reflect the paleotopographic irregularities of the Red Sea proto-basin. We interpret contemporaneous deposition of multiple facies as follows: reef and carbonates occurring on submerged paleohighs, shale deposited in zones of slightly deeper water, sands occurring in marginal basins, and isolated evaporites deposited on the central Saudi Arabian Red Sea margin and in the north.

Name:Bokhari (1981) first assigned the name Tayran formation after Jabal Tayran, Midyan area, onshore coastal Red Sea.

Regional Equivalents: The Tayran Group is correlated to the Nukhul Formation of the Gulf of Suez and Red Sea based on lithological and paleontological similarities (Sellwood and Netherwood; 1984; Hughes et al., 1992; Hughes and Beydoun, 1992; Hughes and Filatoff; 1995; Ravnas and Steel, 1998). It is considered equivalent to the Hamamit Formation of Sudan (Schroeder et al., 1989), the Ranga Formation in the northwest Red Sea (Montanet et al., 1998, their Figure C3.2) and the Nutaysh Formation (Purser and Hotzl, 1988). The Tayran Group is equivalent to the early syn-rift tectono-sedimentary unit A of Plaziat et al. (1998).

Lithology: The Tayran Group consists of conglomerates, sandstones, shallow-marine carbonates, and in the subsurface, anhydrite. Bokhari (1981) divided his formation into three members: (1) the lower Wadi al Hamd member consisting of red siliciclastics; (2) the upper Wadi al Kils member, a shallow-marine carbonate unit; and (3) the Wadi Telah member, a laterally-equivalent, mixed siliciclastic-carbonate unit. Bokhari’s formation formed part of the Raghama group (Richter-Bernburg and Schott, 1954) that included the entire ‘Oligocene-Miocene’ succession (Skipwith, 1973; Brown et al., 1989). In the subsurface, it is made up of anhydrite and was referred to as the Sharik formation by Clark (1986). The Tayran Group, as currently defined, displays significant lateral and vertical lithological variations. The siliciclastic Al Wajh Formation makes up the entire Tayran Group at certain subsurface localities but, as exposed in Midyan, is overlain by carbonates of the Musayr Formation. In the subsurface of the Yanbu Basin and elsewhere in the Saudi Arabian Red Sea area, the Al Wajh siliciclastics are often overlain by anhydrite of the Yanbu Formation.

Distribution: In the Midyan region, the Tayran Group is exposed along the northeastern margin of the Ifal Plain and in the Jabal ar Risha area. Regionally, both the Al Wajh and Yanbu Formations are present in the Al Wajh and Yanbu Basins, and as far south as Jiddah (Figure 1). The Tayran Group has not been identified in wells drilled in the Ghawwas or Jizan Basins.

Contact Relationships: The Tayran Group is nonconformable on Proterozoic Basement rocks, both onshore and offshore; and is probably unconformably overlain by the Burqan Formation, as seen in the Midyan exposures and in the subsurface, where a distinct lithological and paleoenvironmental contrast is evident.

Age: Recent biostratigraphic studies (Hughes and Filatoff, 1995; Filatoff and Hughes, 1996) suggest an early Miocene age for most of the Tayran Group with definite evidence of an early Miocene age for the Musayr Formation. Jado et al. (1990), however, provide late Eocene macropaleontological evidence for pre-rift siliciclastics at a small exposure 10 km north of the coastal town of Maqna. If correct, this may indicate the presence of the Shumaysi formation, or time-equivalent sediments, within a succession currently attributed to the Al Wajh Formation in the Midyan region.

Paleoenvironment: The Tayran Group represents the early syn-rift stage in the evolution of the Red Sea and the progression from a siliciclastic to carbonate, and locally evaporitic, depositional regime resulting from the progressive regional increase of marine influences. The term “proto-rift” has been proposed for this early phase of rift associated sedimentation (Orszag-Sperber and Plaziat, 1990; Plaziat et al., 1990) and should be considered as an appropriate tectonic category.

Al Wajh Formation, Tayran Group

The Al Wajh Formation represents the oldest unit of the Tayran Group. It consists of red siliciclastics that are barren of fossils, although microfossils have been recovered from its subsurface equivalent. The mineralogical and lithological components of the siliciclastic rocks and their proximity to underlying and adjacent exposures of the granitic Proterozoic Basement, indicate a direct derivation from the Proterozoic Basement. Clark (1986) provisionally assigned the succession to the Sharik formation of Remond and Teixido (1980).

Name:Hughes and Filatoff (1995) published the name ‘Al Wajh Formation’ following its use by Saudi Aramco in detailed lithological and biostratigraphic studies on samples from several shallow boreholes in the Al Wajh Basin. The Al Wajh Formation was previously named the Wadi Al Hamd member of the Tayran formation by Dullo et al. (1983) and Bayer et al. (1988).

Regional Equivalents: The Al Wajh Formation section is probably equivalent to the Bathan formation described from the Jiddah region (Brown et al., 1989). When Hughes and Filatoff (1996) named the formation, the regional equivalent of the Al Wajh Formation in the Midyan region was not defined. Its similarity to the Shoab Ali Member (basal sands and sandstones) of the Nukhul Formation of the Gulf of Suez (Saoudi and Khalil, 1984) was noted. It is possible that the Miocene lacustrine sediments described by Schmidt and Hadley (1984) as the Baid formation represent a facies of the Al Wajh Formation, although the Baid contains interbedded lava flows in the Qunfudah area, and may represent a transitional facies of the Jizan Group. The Al Wajh Formation is considered equivalent to the Ranga, Abu Ghusun and Nakheil formations of the northwest Red Sea (Plaziat et al., 1998), the Hamamit Formation of Sudan (Hughes and Beydoun, 1992; Carella and Scarpa, 1962; Sestini, 1965) and to the Ghaydah Formation of the Yemeni Red Sea (Watchorn et al., 1989).

Type Section: The Al Wajh Formation is defined in the Saudi Aramco exploration well Al Wajh South-1 (AWSO-1: 25°14′23.8″N, 37°12′28.6″E) between 12,787–13,420 ft, onshore coastal Saudi Arabian Red Sea (Figures 1b and 29).

Thickness: In AWSO-1, the Al Wajh Formation has a minimum thickness of 633 ft (193 m). Dullo et al. (1983) recognized a maximum thickness of 114 m (350 ft) for what is now the Al Wajh Formation, whereas in the subsurface of the Saudi Arabian Red Sea, as much as 600 m (1,968 ft) has been measured (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). At the Ad Dubaybah locality in the Midyan area (28°27′09.9″N, 35°05′19.8″E), a total thickness of 93 ft is exposed beneath the limestone of the Musayr Formation.

Lithology: The Al Wajh Formation consists of red and gray-green mudstones (Figures 30 and 31) and poorly-sorted, often arkosic sandstones and conglomerate (Figure 32). The basal conglomeratic sandstones unconformably overlie the Proterozoic Basement (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). It contains several rock types of granitic composition, but chert pebbles (Figure 33) are only present in the subsurface equivalent sediments.

Distribution: Although widespread in the Red Sea coastal basins, the Al Wajh Formation is largely replaced by the Jizan Volcanics in the south. The Al Wajh Formation is well exposed in Midyan at several localities in the northern part of the Ifal Plain and in the Jabal as Safra region (Figure 1a). North of Al Bad’, sandstones and conglomerates are well exposed in a roadcut at 28°35′27.7″N, 35°03′07″E. At some localities (e.g. 38°32′30.8″N, 35°00′37.5″E), oyster shells are preserved within thin beds of poorly-sorted and poorly-bedded, reddish-brown sandstones. At Ad Dubaybah (28°27′09.9″N, 35°05′19.8″E), well-bedded sands with large-scale cross-bedding are exposed beneath carbonates of the Maqna Group. Cross-bedded, very friable sandstones are 18 ft thick in Wadi Waqb (28°11′19.3″N, 34°44′07.8″E) where they rest directly on Proterozoic Basement. They are overlain at this locality by oyster-bearing, blocky packstones and grainstones of the Musayr Formation. In the Al Wajh Basin, upholes U-60748 through U-60751 have recovered most of the stratigraphic section in the back-basin (Figure 34) showing that the basin fill consists of a thick sequence of alluvial plain deposits within the Al Wajh Formation.

Contact Relationships: The Al Wajh Formation is the lowermost unit of the Tayran Group and unconformably overlies Proterozoic Basement. In a complete section, it is disconformably overlain by carbonates of the Musayr Formation (Figure 35) in Wadi al Hamd (28°23′55.9″N, 34°54′4.2″E) and on the east flank of Jabal Dhaylan in the Al Wajh Basin (Figure 36). Often, however, the Al Wajh Formation represents the only section within the Tayran Group and is unconformable with the overlying Burqan Formation or even younger units (Figure 37). In the type section (Al Wajh South-1, Figures 1b and 29), the base of the Al Wajh Formation was not penetrated, but it is conformably overlain by anhydrite and anhydritic siltstones and shales of the Yanbu Formation in other areas.

Age: No palynological evidence has been obtained for the age of the Al Wajh Formation in the Midyan region. An early Miocene age (Hughes and Filatoff, 1995), however, was established in the type section based on the presence of Acanthaceae-type pollen (origin at the beginning of the Miocene), Fenestrites spinosus (originates during the early Miocene), and the absence of charred Gramineae (not recorded in lower Miocene). Echinoids recently found within the siliciclastics at Ad Dubaybah are related to those considered typical of Miocene rocks in the Gulf of Suez (D. Hamama, Cairo University, personal communication, 1998). Similar echinoids found north of Maqna in the extreme northwest of the Midyan region have been assigned a late Eocene age based on their similarity to species from the upper Shumaysi formation of the Jiddah region (Jado et al., 1990). Further sampling is necessary to prove or refute the Paleogene age because such an age would prove the existence of an additional pre-rift lithostratigraphic unit in northern Midyan.

Paleoenvironment: The environment of the Al Wajh Formation is interpreted as fluvio-lacustrine with marginal marine (possibly estuarine) pulses. A brackish to freshwater paleoenvironment in Midyan is indicated by the presence of the freshwater alga Pediastrum spp. and the benthonic foraminifera Ammonia beccarii, together with charophytes and unornamented ostracods in the subsurface. Le Nindre et al. (1986) concluded that the sediments are of fluvial to alluvial fan in origin, and R.S. Johnson, D. Rodgers and G.R. Savage (1995, Saudi Aramco Report) similarly categorized the basal conglomeratic sandstones and red mudstones. The Al Wajh Formation was deposited during the early stages of slow subsidence and shows the first effects of a gradual marine transgression similar to the Nukhul Formation in the Gulf of Suez. The presence of freshwater fish fossils (Brown, 1970) and of the lower jaw of a hippopotamus-like Masritherium provide freshwater conditions for part of the Baid formation (Schmidt and Hadley, 1984).

Yanbu Formation, Tayran Group

The Yanbu Formation is considered to represent the middle unit of the Tayran Group and consists of halite and/or anhydrite. Its localized distribution and often cryptic layering represent precipitation in hypersaline water. In at least one location (Yanbu Basin), the section has been significantly re-mobilized following deposition. The Yanbu Formation is not exposed in the Saudi Arabian Red Sea region.

Name:Hughes and Filatoff (1995) named the Yanbu Formation for a subsurface succession of evaporites in the Yanbu region of western Saudi Arabia (Figure 1c).

Regional Equivalents: The Yanbu Formation is correlated to the Ghara Member of the Nukhul Formation (Saoudi and Khalil, 1984) in the Gulf of Suez and Egyptian Red Sea; and in the subsurface in the Yemeni and Somali Gulf of Aden (Hughes and Beydoun, 1992).

Type Section and Thickness: The Yanbu Formation is defined in the Saudi Aramco exploration well Yanbu-6 (YNBU-6: 24°06′54.0″N, 38°08′59.0″E) between 2,684–3,145 ft (461 ft, 140.5 m thick), onshore coastal Saudi Arabian Red Sea (Figure 38).

Lithology: The Yanbu Formation consists of halite, anhydrite and minor shale (Figures 38 and 39).

Distribution: The Yanbu Formation is not exposed along the Red Sea coast, but halite and anhydrite have been penetrated in exploration wells in the Yanbu Basin and to the north in Midyan (Cocker and Hughes, 1993). Only one of the wells (both shallow and deep), however, drilled in the Midyan region contains anhydrite (20 ft thick) in the expected stratigraphic position (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). Later sedimentological loading has generally mobilized the evaporites resulting in an unequal and often localized distribution. Scattered exposures of anhydrite in the Midyan region, which are considered by G.S. Ferguson, M. Senalp and A.M. Afifi (1993, Saudi Aramco Report) to represent the Yanbu Formation, are probably evaporites of the Middle Miocene Maqna Group or Mansiyah Formation. They display an identical satellite image signature to those of the Maqna Group. Recent field excavations of anhydrite exposures revealed Proterozoic Basement and proved their superficial position.

Contact Relationships: In the subsurface, the Yanbu Formation consists of anhydrite and halite that conformably overlie the Al Wajh Formation siliciclastics and in places are interbedded with them. Within the YUBA-1 well, however, a thin anhydrite layer (< 10 ft) of the Yanbu Formation is interpreted as being beneath 155 ft of coarse clastics belonging to the Al Wajh Formation. In a normal sequence, the Yanbu Formation is interpreted to be unconformably overlain by the Burqan Formation, based on the dramatic paleoenvironmental contrast between the shallow, restricted Tayran Group and the deep-marine Burqan sediments. Exposures in the Midyan region also provide evidence for this unconformity.

Age: An early Miocene age is assigned to the Yanbu Formation based on its stratigraphic position in the subsurface and its palynoflora, which is similar to that of the Al Wajh Formation. Strontium isotope dating of anhydrite laminae and crystals in a thick halite sequence gave an absolute age of 22–23 Ma (Figure 40) (Cocker and Hughes, 1993).

Paleoenvironment: The deposition of the Yanbu Formation is probably due to an early restricted marine incursion related to the earliest stage of the opening of the Red Sea. Orszag-Sperber et al. (1992) suggest that the deposition of the evaporites was related to the beginning of the Red Sea rift and to the tectonic control of restricted marine conditions rather than to a fall in sea-level. The purity of the evaporites argues against a sabkha origin and they probably formed in localized hypersaline ponds in a salina setting, although sabkha evaporites may exist locally. Palynoflora from the intra-evaporitic sediments include the halophytic pollen Retiperiporites spp. but lack marine indicators; no microfauna are present.

Musayr Formation, Tayran Group

The Musayr Formation represents the youngest unit of the Tayran Group. It consists of shallow-marine carbonates that are locally developed and contain rich macrofossil and microfossil assemblages. Where the lower contact is exposed, there is a rapid transition between the Musayr Formation and the underlying red beds of the Al Wajh Formation.

Name:Clark (1986) informally named the carbonates in the Jabal Musayr region as the Musayr Formation. They had previously been considered as the Wadi Al Kils member of the Tayran formation by Dullo et al. (1983).

Regional Equivalents: The Musayr Formation is equivalent to the Gharamul Member of the Nukhul Formation in the Gulf of Suez (Saoudi and Khalil, 1983), and the informal Wadi Al Kils member of the Tayran formation (Dullo et al., 1983), and the Ubbur formation of Spencer (1987).

Type Section and Thickness: An almost complete Musayr section of well-bedded carbonate (323 ft thick) is found in Wadi Al Hamd dipping at 33° to the northeast (N35°E) (Figure 41).

Lithology: The Musayr Formation consists of a basal calcareous sandstones (Figures 42 and 43) overlain by skeletal grainstone (Figure 44) and pack/wackestone carbonates (Figure 45); rich in both macro- and micro-fauna (Figures 46 and 47).

Distribution: The Musayr Formation is restricted to the Midyan region where its distinctive carbonate succession crops out on the flanks of Jabal Musayr and where contacts with the underlying Al Wajh Formation are well exposed. The Musayr Limestone forms distinctive escarpments on the northern flank of Jabal Tayran. The carbonates are particularly well exposed and accessible in Wadi Al Hamd (28°23′55.9″N, 34°54′04.2″E) and also in Wadi Al Kils. At Wadi Al Hamd, the Musayr Formation directly overlies the Proterozoic Basement, and the transitional basal beds consist of calcareous sandstone that grade vertically into a sequence of skeletal grainstones and packstones. At this locality, the gorge wall is characterized by recessive oyster beds that alternate with more resistant massive beds (Figure 48) (R.A Kamal and G.W. Hughes, 1993a, Saudi Aramco Report). At the Jabal Musayr locality, large compound corals derived from the Musayr Formation are scattered along the foot of the mountain.

Contact Relationships: The Musayr Formation overlies the Proterozoic Basement at the south flank of Jabal Ar Risha (28°17.00’N, 34°45.21’E) and disconformably overlies the Al Wajh Formation at Wadi Al Hamd. It is unconformably overlain by the Burqan Formation, as evidenced in the wellexposed contact relationship between the two formations in the vicinity of the eastern entrance to Wadi Al Hamd. There is no evidence that the Musayr Formation overlies evaporites of the Yanbu Formation. Instead, it probably correlates to the upper portion of the Yanbu Formation.

Age: The presence of the benthonic foraminiferal genera Miogypsinoides and Miogypsina (Figures 46 and 47), including Miogypsina tani, within the carbonates indicate an early Miocene age for the Musayr Formation, equivalent to the Tertiary Upper Te Letter Stage (Adams, 1970; Boudagher-Fadel and Banner, 1999). The late Oligocene age suggested by Dullo et al. (1983) is based on larger benthonic foraminiferal specimens misidentified as Nummulites fichteli, whose illustrated thin sections (Dullo et al., 1983; his Figures 14) have been re-assigned to Operculinella venosa in this study. Oysters are a characteristic bio-component of the Musayr Formation and are well represented at the Wadi Al Hamd locality (Figure 48) and on the south flank of Jabal Ar Risha.

Paleoenvironment: The depositional environment of the basal calcareous sandstones of the Musayr Formation is intertidal. The oyster beds, corals, and miogypsinid assemblages in the overlying carbonate rocks indicate a warm, shallow marine environment, such as a shallow marine carbonate platform. In contrast to the other formations of the Tayran Group, dinoflagellate cysts are prominent in the palynoflora recovered from the Musayr Formation, and are species of Systematophora and Polysphaeridium.

BURQAN FORMATION

The Burqan Formation (Figure 3) is a thick succession of deep-marine calcareous mudstones (Figure 49) with thick sand interbeds (Figure 50). As in the case of other syn-rift rock units, the Burqan Formation is highly variable in lithology, depositional environment, and thickness, all of which can be related to its deposition over a very irregular, often heavily faulted, Miocene paleotopography. The Burqan Formation is well exposed in the Midyan region west of Jabal Rughama (Raghama) flanking the Maqna Massif and along the Gulf of Aqaba coast. Two members are recognized, the sanddominated Nutaysh Member of the Burqan Formation (Clark, 1986) and the mudstone-dominated Subayti Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). Nonmarine equivalents of the Burqan Formation may exist in the Jiddah Basin near Harrat Buraykah.

Name: The name Burqan Formation is taken from the Auxerap/Tenneco exploration wells drilled in the offshore Burqan field. The Burqan Formation was informally called the ‘Globigerina Marls’ in unpublished (non-Saudi Aramco) oil company reports. The intensive investigation by Saudi Aramco has justified clarification of the previous informal lithostratigraphic assignment.

Regional Equivalents: Based on biostratigraphic evidence, the Burqan Formation is time-equivalent to the lower part of the Rudeis Formation of the Gulf of Suez and Egyptian Red Sea (Abdine, 1979; Hughes and Beydoun, 1992; Hughes et al., 1992; Bosworth and McClay, 2001). It is also equivalent to the Maghersum Formation of Sudan (Hughes and Beydoun, 1992; Carella and Scarpa, 1962 and Sestini, 1965) and the open-marine syn-rift tectono-sedimentary unit B of Plaziat et al. (1990). It is likely that an upper Rudeis equivalent exists in the inboard portions of the Red Sea. The data available to the authors, however, are located on the more marginal parts of the Saudi Arabian Red Sea and do not yet support this conclusion.

Type Section and Thickness: The Burqan Formation is defined in the Auxerap/Tenneco exploration well Burqan-3 (BRQN-3: 34°04′04″N, 27°55′47″E) between 6,881–10,561 ft (3,680 ft, 1,122 m thick), offshore Midyan area, Saudi Arabian Red Sea (Figure 51).

Lithology: The Burqan Formation is well exposed in the Midyan region. Turbidites (see Figure 57), conglomerates, and sandstones of the Nutaysh Member characterize the basal part of the sequence, especially in the western part of Midyan. In most of the exposures to the southeast, however, the upper part of the Burqan Formation is exposed and consists of calcareous mudstones of the Subayti Member (Figures 52 and 53). Clark (1986) estimated a total thickness of 400 m (1,312 ft) for the entire Burqan Formation. The calcareous mudstones are typically soft and characterized by ramifying anhydrite veinlets. The sandstone forms thick, massive, poorly consolidated beds as much as 15 ft thick (Figure 53) and is particularly well exposed in the western area of the region in road-cuts along the ‘old Maqna road’ (from 28°20′53.8″N, 34°46′38.5″E to 28°20′04.6″N, 34°45′26.5″E).

Distribution: The Burqan Formation is well exposed north of Al Bad’ to Maqna road on the Gulf of Aqaba coast south of Maqna, and along the western and eastern boundaries of the Proterozoic Basement that forms the core of the Maqna Massif. The Burqan Formation is widely distributed along the Saudi Arabian Red Sea in the subsurface.

Contact Relationships: The deep-water turbidites of the Burqan Formation lie unconformably on the Tayran Group, as decribed earlier, and also on the Proterozoic Basement (Figure 54). At Jabal ar Risha (28°17′00″N, 34°45′21″E), sandstones of the Nutaysh Member conformably overlie oyster-bearing carbonates of the Musayr Formation. At this and other localities within the region, the Burqan Formation is unconformably overlain by anhydrite of the Kial Formation of the Maqna Group, as seen in the variable exposures in the Midyan region and also in interpretations of subsurface contacts. Such contacts are also well exposed south of the Maqna road on the western slope of Jabal Rughama (28°26′01.5″N, 34°56′45.9″E). The Burqan Formation is well-bedded (Figure 55) and dips radially away from the exposed Proterozoic Basement core of the Maqna Massif. It is apparent that during deposition of the Burqan Formation, localized Proterozoic Basement highs were exposed, and these sites of non-deposition continued until late early Miocene times when carbonates of the Wadi Waqb Member (Jabal Kibrit Formation, Maqna Group) were deposited on them. In Wadi Waqb (28°11′19″N, 34°44′07.8″E), carbonates of the Musayr Formation are overlain by 105 ft of interbedded soft marl and hard calcareous sandstone of the Subayti Member of the Burqan Formation. In the Jizan Southeast-1 well, the Burqan Formation is faulted out, while in the Nakhlah-1, it is missing due to erosion.

In the type section, the Burqan Formation rests unconformably upon the Al Wajh Formation of the Tayran Group and is unconformably overlain by the An Numan Member of the Jabal Kibrit Formation (Maqna Group). The unconformity at the top of the Burqan Formation is based on the presence of planktonic foraminifera and calcareous nannofossils of zones N6 and NN3 respectively at variable depths, including immediately below, the An Numan Member. In the Gulf of Suez, the upper Rudeis displays well represented sections of N7 and NN4 zonal equivalents below the Markha Member of the Kareem Formation. Within the Burqan section, missing microfaunal assemblages suggest the presence of at least two intraformational hiatuses.

Age: An early Miocene age (late Aquitanian to early Burdigalian) has been assigned to the Burqan Formation based on the presence of age-diagnostic planktonic foraminifera and calcareous nannofossils (Hughes et al., 1992; Hughes and Filatoff, 1995). These zones are based on the well-established extinction datums and include Planktonic Foraminifera Zone N7, Globigerina ciperoensis forma atypica; Zone N6, Globquadrina praedehiscens; Zone N5 Globigerinoides primordius, and Calcareous Nannofossil Zone NN4, Helicosphaera ampliaperta; NN3, Sphenolithus belemnos; and NN2, Triquetrorhabdulus carinatus. Although of limited age significance, numerous echinoids are present within shale exposed at 28°17′13.5″N, 34°48′11.1″E.

Paleoenvironment: The depositional environment of the Burqan Formation varied between structural elements. Cyclical flooding and differential subsidence of fault blocks were responsible for variations in both clastic supply and water depth.

The presence of certain benthonic foraminifera, including Bathysiphon taurinensis, hispid Uvigerina spp. and Nodosaria spp., and the generally high diversity planktonic and deep-marine benthonic foraminiferal assemblages, indicate a predominantly bathyal depositional environment for the mud-dominated succession of the Nutaysh Member. Well-developed trace fossils occur at the base of many of the beds, such as those at the head of the long wide wadi south of Wadi Waqb (Figure 56). Sandstones interbedded with the mudstones typically contain allochthonous penecontemporaneous shallow-marine microfossils.

Exposures of the Burqan Formation in the belt of northwestern outcrops in Midyan were interpreted as deep submarine-fan deposits (G.S. Ferguson and M. Senalp, 1993, Saudi Aramco Report) with several sediment sources. In the northwest, proximal turbidites display decreasing grain size towards the southeast where they become distal fan turbidites. In the southeastern outcrop, however, flute marks on the base of beds exposed at the head of Wadi Waqb (28°12′58.4″N, 34°44′40.6″E) indicate transport of sediment from the southeast. At this locality, the beds dip northwest (N35°W) at 32°. A 15 ft thick bed of massive sandstone is also exposed near here.

Lacustrine sediments considered to be a back-basin equivalent to the Upper Rudeis have been described from Egypt (Wescott et al., 2000), but similar sediments have not yet been recognized in the Saudi Arabian succession.

Nutaysh Member, Burqan Formation

The Nutaysh Member is sand-dominated (Figure 57) and is readily distinguished from the mudstone-dominated Subayti Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). It was originally described by Clark (1986).

Name: The name Nutaysh Member was proposed by Clark (1986), for the sanddominated unit. The member was informally called the ‘Globigerina Marls’ in unpublished (non-Saudi Aramco) oil company reports. The intensive investigation by Saudi Aramco has justified clarification of the previous informal lithostratigraphic assignment.

Regional Equivalents: Based on biostratigraphic evidence, the Nutaysh Member is time-equivalent to the sanddominated lower part of the Rudeis Formation in the Gulf of Suez and Egyptian Red Sea (Abdine, 1979; Hughes and Beydoun, 1992; Hughes et al., 1992).

Type Section and Thickness: The Nutaysh Member is defined in the Saudi Aramco exploration well Al Wajh South-1 (AWSO-1) between 9,433–12,531 ft (3,098 ft, 944.5 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1b and 58).

Lithology: The Nutaysh Member consists of coarse- and fine-grained sandstones with minor siltstone and shale (Figures 59 and 60). The section contains rare allochthonous limestone (Figure 61) and granite (Figure 62).

Distribution: The Nutaysh Member is widely distributed in the Midyan region where the thick sandstones form massive, steep cliffs in outcrop, or are present in the subsurface as thin beds that act as hydrocarbon reservoirs (Burqan field).

Contact Relationships: In the Al Wajh South-1 well, the Nutaysh Member unconformably overlies the Yanbu Formation of the Tayran Group, based on regional exposures, and is unconformably overlain by the Umm Luj Member of the Jabal Kibrit Formation (Maqna Group), based on the rapid vertical transition from deep marine to shallow marine sediments.

Subayti Member, Burqan Formation

The Subayti Member is mudstone-dominated (Figures 50 and 53) and is readily distinguished from the sandstone-dominated Nutaysh Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).

Name: The Subayti Member was named after the Subayti region of northwestern Midyan by G.S. Ferguson and M. Senalp (1993, Saudi Aramco Report).

Regional Equivalent: Based on biostratigraphic evidence, the Subayti Member is time-equivalent to the shale-dominated lower part of the Rudeis Formation in the Gulf of Suez and Egyptian Red Sea (Abdine, 1979; Hughes and Beydoun, 1992; Hughes et al., 1992).

Type Section and Thickness: The Subayti Member is defined in the Auxerap/Tenneco exploration well Burqan-3 (BRQN-3) between 6,881–10,561 ft (3,680 ft, 1,122 m thick), offshore Midyan area, Saudi Arabian Red Sea (Figure 51).

Lithology: The Subayti Member consists of calcareous shales and siltstones with minor limestone.

Distribution: The Subayti Member characterizes much of the Burqan Formation. It is found extensively in the Midyan Basin and the onshore flanks of the Gulf of Suez in Egypt. It is also present at all subsurface localities bordering the Red Sea.

Contact Relationships: In the Burqan-3 type section, the Subayti Member rests unconformably upon the Al Wajh Formation of the Tayran Group (Figure 51). It is here disconformably overlain by the An Numan Member of the Jabal Kibrit Formation (Maqna Group), based on the absence of dateable N7 sediments in the Subayti.

MAQNA GROUP

The Maqna Group consists of two evaporite-bearing formations: (1) the lower to middle Miocene Jabal Kibrit Formation; and (2) the middle Miocene Kial Formation (Figure 63) (Hughes and Filatoff, 1995; R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). In the Midyan area, the Maqna Group forms an extensive blanket of gypsum and anhydrite that covers much of the central part of the basin (Figures 64 and 65). In the subsurface, the siliciclastic Umm Luj Member underlies the carbonate Wadi Waqb Member of the Jabal Kibrit Formation, but lateral facies equivalents are considered likely with probable local interfingering between both formations.

Name: The first published use of the name Maqna Group (after the town of Maqna on the Gulf of Aqaba) was by Hughes and Filatoff (1995) following in-house usage by Saudi Aramco since 1992.

Regional Equivalents: The Maqna Group is regionally equivalent to the combined Belayim and Kareem Formations of the Gulf of Suez and other areas of the Red Sea (Hughes and Beydoun, 1992; Hughes et al., 1992) and to the Abu Imama and Khor Eit Formations, respectively, of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992; Hughes et al., 1992). The Maqna Group is equivalent to the open-marine, syn-rift tectono-sedimentary unit C of Plaziat et al. (1990).

Type Area: Although well exposed in the Midyan region, the definition of the Maqna Group has been based upon the better-understood subsurface stratigraphic relationship. The subsurface succession consists of relatively thin units of interbedded anhydrite or halite, calcareous mudstones and sandstones.

Thickness: In the subsurface, the Maqna Group varies in thickness from absent (Al Khurmah-1) or from a minimum of 165 ft (Yuba-1) to a maximum of 3,679 ft (Al Wajh-1). The maximum thickness in the Maqna Group seems to coincide with those areas in which the clastics of the Umm Luj Member (Jabal Kibrit Formation) are best developed (Al Wajh and Yanbu Basins).

Lithology: The Maqna Group consists of exposed deep-marine carbonates, shallow-marine carbonates, and anhydrite. In the subsurface, it consists of deep-marine mudstones and generally finegrained sandstones and anhydrite. At Jabal Rughama in the Midyan region, anhydrite is interbedded with soft, calcareous mudstones that overlie Burqan mudstones (Figure 66). The thickness of the interbedded mudstones varies along the length of the exposure, most probably due to slumping of the anhydrite cap. A.A. Al-Laboun (Saudi Aramco, oral communication, 1998) has confirmed that some of the repeated mudstone-anhydrite sections are the result of a series of gravity slides of the poorly consolidated mudstones. There are, however, undisturbed alternations between siliciclastics and interbedded anhydrite within the Kial Formation.

Distribution: The Maqna Group is exposed along the eastern and western margins of the Ifal Plain in the Midyan region.

Contact Relationships: In a complete section, the Maqna Group unconformably overlies the Burqan Formation (Figure 66) and is conformable with the overlying Mansiyah Formation. Local variations exist due to local topographic irregularities, and include the Maqna Group lying unconformably upon siliciclastics of the Tayran Group (Figure 67), and as either absent or missing significant upper section, with the Mansiyah Formation lying unconformably on either Proterozoic Basement (Al Khurmah-1; Midyan Basin).

Age: The Maqna Group was dated as early to middle Miocene based on the presence of age-diagnostic planktonic foraminifera and calcareous nannofossils (Hughes and Filatoff, 1995). Samples collected from the surface and the subsurface confirm this age. The occurrence of charred Gramineae cuticle in the palynological assemblages (the richest and most diverse in the Neogene succession) has served to differentiate the Maqna Group from underlying units. This age range is consistent with the early to middle Miocene age of the Kareem Formation, and to the middle Miocene age of the Belayim Formation, in the Gulf of Suez.

Paleoenvironment: Sediments of the Maqna Group were deposited under a variety of conditions, each of which is discussed under the various formal members. Deep- and shallow-marine carbonates and siliciclastics are present, together with evaporites that are interpreted as having a submarine origin.

Jabal Kibrit Formation, Maqna Group

The Jabal Kibrit Formation is represented in outcrop within the Midyan region only by the carbonate Wadi Waqb Member (see below), but elsewhere it is sometimes replaced by the siliciclastic Umm Luj Member (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). An anhydrite unit is here termed the An Numan Member, while the uppermost clastic unit is called the Dhaylan Member (Figure 63). Equivalent Miocene carbonates of the Egyptian Red Sea, adjacent to Midyan, have received considerable attention in recent years (Aissaoui et al., 1986; James et al., 1988; Shaban et al., 1997; Youssef, 1997).

Name:Hughes and Filatoff (1995) first published the name Jabal Kibrit Formation (after Jabal Kibrit) following in-house usage by Saudi Aramco since 1992. In the present understanding of the stratigraphy of the Midyan region, the carbonates of the Khuraybah formation and the siliciclastics of the Usayliyah formation, as defined by Clark (1986) in the Aynunah area, are assigned to the Jabal Kibrit Formation. Clark’s Usayliyah formation is exposed to the west of the main outcrop of the Adaffa Formation (28°07′43″N, 35°12′01″E) and overlies the Khuraybah formation.

Regional Equivalents: The Jabal Kibrit Formation is equivalent to the Kareem Formation in the Gulf of Suez (the youngest part of the Gharandal Group) and other areas of the Red Sea (Hughes et al., 1992; Hughes and Beydoun, 1992), and also to the Khor Eit Formation of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992). The siliciclastics assigned to the Usayliyah formation by Clark (1986) are considered to be possibly equivalent to the Umm Luj Member of R.S. Johnson, D. Rodgers and G.R. Savage (1995, Saudi Aramco Report).

Type Area: The type area for Jabal Kibrit Formation is Jabal Kibrit in the central Midyan region

Reference Section and Thickness: The Jabal Kibrit Formation is represented in Saudi Aramco exploration well Midyan S-1 (MDYN-1: 28°10′34.4″N, 34°52′12.9″E) between 6,876–7,447 ft (571 ft, 174.1 m thick), onshore coastal Saudi Arabian Red Sea (Figure 68).

Lithology: The Jabal Kibrit Formation consists of calcarenites, marl, sandstones, siltstones, and shales. The calcarenites and marls in these sections could be a distal equivalent of the Wadi Waqb Member.

Distribution: The Jabal Kibrit Formation (represented by the Wadi Waqb Member) crops out in Midyan in the Wadi Waqb, Ad Dubaybah, and Al Khuraybah areas. It is widely distributed in the subsurface in Midyan and elsewhere along the Saudi Arabian Red Sea. Where missing (Al Khurmah-1), it is generally due to local uplift and erosion during the late Miocene.

Contact Relationships: In a complete section, the Jabal Kibrit Formation unconformably overlies the Burqan Formation (Figure 69) and is conformable with the overlying Kial Formation; there is no evidence that these relationships have been influenced by rheid flow in the surface, although this cannot be discounted in the subsurface.

Age: An early middle Miocene age (Langhian) was interpreted from the subsurface presence of planktonic foraminifera belonging to Zones N9 and N8 in the upper unit of shales and claystones (Hughes and Filatoff, 1995). Planktonic Foraminiferal Zone N9 (early middle Miocene) was based on the first downhole occurrence of Praeorbulina glomerosa, P. transitoria, and Globigerinoides sicanus with the presence of Orbulina suturalis and Orbulina bilobata. Zone N8 (earliest middle Miocene) was based on the first downhole occurrence of P. glomerosa curva in the absence of Orbulina species. Calcareous nannofossils Sphenolithus heteromorphus in the absence of Helicosphaera ampliaperta indicated Zone NN5 (Hughes and Filatoff, 1995). Analysis of samples collected during the recent fieldwork confirms the age.

Paleoenvironment: From subsurface evidence, the sediments of the Jabal Kibrit Formation are considered to have been deposited under deep-marine outer-neritic to possible upper-bathyal conditions as indicated by the rich and diverse assemblages of deep-marine planktonic and benthonic foraminifera (Hughes and Filatoff, 1995). Micropalaeontological evidence from the interbedded shales can offer conclusive evidence for a submarine, moderately deep environment for the evaporites. Coarse-grained facies, however, may be the products of penecontemporaneous downslope transport from a shallow-marine source (see Wadi Waqb Member). The distribution of the evaporitic An Numan Member suggests local submarine deposition within more restricted basins.

An Numan Member, Jabal Kibrit Formation, Maqna Group

The An Numan Member is characterized by a predominantly anhydritic lithology and regional subsurface presence. It is easily recognized as the first post-Burqan evaporite.

Name: The Member is named, for the first time, after the Tenneco exploration well An Numan-1 (ANMN-1), situated offshore in the northern part of the Red Sea.

Regional Equivalents: The An Numan Member is correlated to the Markha Member of the Kareem Formation in the Gulf of Suez (Saoudi and Khalil, 1983).

Type Section and Thickness: The Member is defined in the Tenneco exploration well An Numan-1 (ANMN-1: 27°04′43″N, 35°46′31″E), between 5,628–5,748 ft (120 ft, 36.6 m thick), coastal Saudi Arabian Red Sea (Figure 70).

Lithology: The Member consists of anhydrite or interbedded anhydrite and mudstones.

Distribution: The An Numan Member is found in the northern offshore (type section in ANMN-1), the Yanbu Basin (Badr-1, Yanbu-1) and the Jizan Basin (Jizan North-2 and -3, Jizan South-1). Subsurface control in the Al Wajh (Hamim-1, Al Wajh South S-1), Jiddah (Jiddah-1), and Ghawwas Basins (Ghawwas-1, Ghawwas South-1) show the An Numan Member to be absent in those regions.

Contact Relationships: In the type section, the An Numan Member unconformably overlies the Burqan Formation and is conformably overlain by the Wadi Waqb Member of the Jabal Kibrit Formation (Figure 70). The upper contact relationship is well exposed in Wadi Waqb (Figure 71).

Age: An Numan Member is early Miocene in age based on foraminiferal evidence for the early middle Miocene boundary within the calcareous mudstones of the overlying Wadi Waqb Member. The Markha Member in the Gulf of Suez is similarly of early Miocene age as it lies beneath Shagar sediments that still contain Praeorbulina species but without Orbulina species.

Paleoenvironment: The environment of deposition of the An Numan Member is interpreted as submarine hypersaline within locally restricted basins based on the regional association with deep marine benthonic and planktonic foraminiferal bearing sediments. Shallow-marine equivalent hypersaline sediments have not yet been encountered in fieldwork, and cored samples display laminations indicative of a deep restricted basin origin.

Wadi Waqb Member, Jabal Kibrit Formation, Maqna Group

The Wadi Waqb Member is a carbonate unit that is an important hydrocarbon reservoir in the Midyan region (Kamal and Hughes, 1995) and which also occurs in outcrop. The carbonates were previously included in the Al Bad’ formation by Dullo et al. (1983). Several exposures mapped by Clark (1986) as being equivalent to limestones of the Musayr Formation have now been identified as belonging to the Wadi Waqb Member. In particular, the assemblages of planktonic and benthonic foraminifera in the Musayr Formation limestones and the Wadi Waqb Member differ greatly both in terms of biostratigraphy and environmental indicators.

Name:Kamal and Hughes (1995) mapped a carbonate unit on the southwestern flanks of Jabal Kibrit, believing its outcrop to be regionally extensive, but the recent fieldwork has shown that the Wadi Waqb Member exposures are limited to the Wadi Waqb vicinity.

Regional Equivalents: Biostratigraphic evidence from G.W. Hughes and R.A. Kamal (1993b, c, Saudi Aramco Reports) confirmed that the Ad Dubaybah (Figure 72) and Al Khuraybah (Figure 73) carbonates mapped by Clark (1986) as belonging to the Musayr and Khuraybah formations, respectively, are stratigraphically equivalent to those at Jabal as Safra, and belong to the Wadi Waqb Member. In the Abu Shar platform of the Gulf of Suez, four carbonate facies that may be equivalent to the Wadi Waqb Member have been named the Kharaza, Esh el Mellaha, Bali’h and Chaotic Breccia members (Cross et al., 1989). The Wadi Waqb shallow-marine lagoonal facies closely resemble those described by James et al. (1988) from the Egyptian Red Sea. This locality was adjacent to the Ad Dhubaybah area during the time the Wadi Waqb Member was deposited.

Type Section: The best exposures of the Wadi Waqb Member (Figures 72 and 73) are in a small, unnamed wadi immediately east of Wadi Waqb (28°12′19″N, 34°45′49″E). A total thickness of 677.4 ft has been measured and, but faulting may have affected this determination.

Reference Section and Thickness: The Wadi Waqb Member is defined in the Saudi Aramco exploration well Midyan S-1 (MDYN-1: 28°10′34.4″N, 34°52′12.9″E) between 7,000–7,447 ft (447 ft, 136.3 m thick), onshore coastal Saudi Arabian Red Sea (Figure 68).

Lithology: The carbonates of the Wadi Waqb Member (Figures 74 to 80) are typically rich in corals and rhodoliths. East of the mouth of Wadi Aynunah near Al Khuraybah, the succession is 205 ft thick and consists of large compound corals and Mya-like bivalves set within mudstones, wackestones, and dolomitic limestones. The compound corals increase in number upward through the measured sections. The youngest beds of the Wadi Waqb Member contain well-developed stromatolites (for example, at 28°11′26.7″N, 34°44′37.1″E). Bedding attitudes vary, but generally strike at about N100°E with a dip of 45–50°S.

Distribution: The Wadi Waqb Member carbonates exposed at Ad Dubaybah (28°27′09.9″N, 35°05′19.8″E) and at the mouth of Wadi Aynunah near Al Khuraybah (28°04′50.2″N, 35°11′36″E), have similar assemblages of foraminifera and are considered to be equivalents of those in the Wadi Waqb region (Figures 81 to 83). The Wadi Waqb Member also forms the upper part of the two hills of Jabal as Safra north of Al Bad’ (28°31′02″N, 35°01′54.9″E). In addition to the northern subsurface penetrations, the existence of the Wadi Waqb Member has been proved in the Yanbu Basin (Yanbu-1 and 5) and the Jizan Basin (Jizan North-3). The Wadi Waqb Member has not been penetrated to date by wells drilled in the Al Wajh, Jiddah and Ghawwas Basins.

Contact Relationships: The Wadi Waqb Member carbonates are unconformable on the Proterozoic Basement in the Wadi Waqb and Khuraybah (Figure 81) localities, on sands of the Adaffa Formation immediately north of Khuraybah, and on siliciclastics of the Al Wajh Formation in the Jabal As Safra area north of Al Bad’ and at Ad Dhubaybah. In outcrop, the Wadi Waqb carbonates are everywhere directly overlain by anhydrite assigned to the Kial Formation (Figure 71). In the subsurface of the Midyan region, the Wadi Waqb carbonates unconformably overlie either basinal mudstones of the Burqan Formation (reference section in the Midyan S-1) or are nonconformable on Proterozoic Basement (Nakhlah-1). In both cases, the Wadi Waqb carbonates are unconformably overlain by basinal calcareous mudstones of the Dhaylan Member of the Jabal Kibrit Formation. While the Wadi Waqb is conformable with the underlying An Numan Member in the An Numan-1 (type section well for the An Numan Member), it is, however, unconformably overlain by the Sidr Member of the Kial Formation.

Age: The presence of the benthonic foraminifera Borelis melo alone (Dullo et al., 1983) indicates a Miocene age (Jones et al., 2002) for the Wadi Waqb Member (Figure 82). Well-preserved specimens of B. melo were found in carbonates collected from the small valley east of Wadi Waqb in recent fieldwork (G.W. Hughes, in preparation). Carbonates at Ad Dubaybah and Khuraybah also contain B. melo (R.A. Kamal and G.W. Hughes, 1993c; G.W. Hughes and R.A. Kamal, 1993c; Saudi Aramco Reports). The matrix of the deep-marine carbonates at Wadi Waqb contains planktonic foraminifera (Figure 83) assigned to Praeorbulina spp. and therefore is of late early Miocene to early middle Miocene age (Zones N7-N9).

Paleoenvironment: The Wadi Waqb Member in the subsurface in Midyan field and at the Wadi Waqb outcrops consists of a deep-marine, planktonic foraminiferal-bearing wackestone matrix containing transported allochthonous bioclasts derived from a shallow-marine carbonate setting (Figures 84 and 85) (Kamal and Hughes, 1995, Saudi Aramco Report). Possible sources for the shallow-marine components are considered to be similar to the shallow-marine, coral- and rhodolith-dominated carbonates that are now exposed along the eastern margin of the Ifal Plain at Ad Dubaybah and Khuraybah (R.A. Kamal and G.W. Hughes, 1993a; G.W. Hughes and R.A. Kamal, 1993b, c; Saudi Aramco Reports). At Ad Dubaybah, the carbonates rest directly upon moderately well-bedded sandstones that resemble distal facies of the Al Wajh Formation. The sandstones may represent, however, a proximal shallow to marginal marine facies of the Jabal Kibrit Formation because the granitic Proterozoic Basement lies a short distance to the east. The carbonates in the Khuraybah-Aynunah region rest directly upon Proterozoic Basement rocks and contain large corals in growth positions.

Dhaylan Member, Jabal Kibrit Formation, Maqna Group

The Dhaylan Member is characterized by very fine- to coarse-grained siliciclastic sediments that is predominately calcareous. Thin carbonate beds may sometimes be present.

Name: The Dhaylan Member is named, for the first time, after the Saudi Aramco exploration well Dhaylan-1, onshore coastal plain of the Red Sea.

Regional Equivalents: The Dhaylan Member is correlated to the Shukheir Member of the Kareem Formation in the Gulf of Suez (Saoudi and Khalil, 1983).

Type Section: The Dhaylan Member is defined in the Saudi Aramco exploration well Dhaylan-1 (DYLN-1: 25°30′37.2″N, 37°02′54.6″E) between 10,703–12,857 ft, onshore coastal Saudi Arabian Red Sea (Figure 86).

Reference Section: The Dhaylan Member, in the reference section in Midyan S-1 (between 6,876–7,000 ft, onshore Midyan area, Saudi Arabian Red Sea), consists of shale and fine-grained sandstone and is thinner than in the type section (Figures 86 and 87).

Thickness: In Dhaylan-1, the Dhaylan Member has a minimum thickness of 2,154 ft (656.7 m). In Midyan S-1 it has a thickness of 124 ft (37.8 m).

Lithology: The Dhaylan Member lithology is predominately calcareous mudstones and siltstones with subordinate very fine- to fine-grained calcite cemented quartz sandstones.

Distribution: The Dhaylan Member is found only in the subsurface. Drilling, to date, has confirmed the presence of the Dhaylan Member in Midyan (reference section in the Midyan-1, Burqan-1), Al Wajh (type section in the Dhaylan-1, Hamim-1), Yanbu (Yanbu-1) and Jizan Basins (Jizan North-2 and -3). Subsurface penetrations in the Jiddah (Jiddah-1) and Ghawwas Basins (Ghawwas-1, Ghawwas South-1) indicate the Dhaylan Member to be locally absent.

Contact Relationships: In the type section, the base of the Dhaylan Member is not seen. In the Badr-1 and Mansiyah-1 wells, the Dhaylan Member is conformable with the underlying An Numan Member but unconformable with the overlying Mansiyah Formation. In a complete section, the Dhaylan Member is conformably overlain by the Rayaman Member of the Kial Formation.

Age: The Dhaylan Member is early to middle Miocene in age based on the foraminiferal evidence.

Paleoenvironment: The depositional environment of the Dhaylan Member is deep marine based on the regional association with deep-marine, outer neritic to upper bathyal benthonic and planktonic foraminiferal-bearing sediments.

Umm Luj Member, Jabal Kibrit Formation, Maqna Group

The Umm Luj Member is characterized by a predominantly coarse-grained siliciclastic lithology. It has a sporadic distribution and variably replaces the Wadi Waqb Member as a lateral facies equivalent.

Name: The Umm Luj Member is named, for the first time, after the Saudi Aramco exploration well Umm Luj-1, onshore coastal plain of the Red Sea.

Regional Equivalents: The Umm Luj Member is correlated to the Shagar Member of the Kareem Formation in the Gulf of Suez (Saoudi and Khalil, 1984).

Type Section: The Umm Luj Member is defined in Saudi Aramco exploration well Al Wajh South-1 (AWSO-1) between 6,336–9,443 ft, onshore coastal Saudi Arabian Red Sea; it displays both the lower and upper contacts of the Member (Figures 1b and 88).

Reference Section: The reference section of the Umm Luj Member in Auxerap/Tenneco exploration well Burqan-3 (BRQN-3) between 6,528–6,711 ft, offshore Midyan area, Saudi Arabian Red Sea, displays a thinner, fine-grained shale and mudstone equivalent of the Member (Figure 89).

Thickness: The Umm Luj Member in UMLJ-1 has a minimum thickness of 2,116 ft (645.1 m); in Al Wajh South-1: 3,107 ft (947.3 m); and in Burqan-3: 183 ft (55.8 m).

Lithology: The Umm Luj Member lithology is coarse-and fine-grained arkosic sandstones (Figure 90) and laterally equivalent non-calcareous siltstones and mudstones.

Distribution: Drilling has shown the Umm Luj Member to be present only in the subsurface of the Al Wajh Basin. No other onshore or offshore wells have recovered equivalent section.

Contact Relationships: In the type section, the base of the Umm Luj Member is not seen. The Umm Luj Member is conformably overlain by the Rayaman Member of the Kial Formation. In Al Wajh South-1 reference section, the Umm Luj Member unconformably overlies the Burqan Formation, (see the biostratigraphic discussion above as evidence for this interpretation), and is conformably overlain by the Rayaman Member of the Kial Formation.

Age: The Umm Luj Member is early to middle Miocene in age. The early Miocene age for the lower part is based on the presence of Praeorbulina glomerosa subspecies in the absence of Orbulina species. The evolution event of Orbulina suturalis and O. universa occurs within the member and determines a middle Miocene age for the upper part.

Paleoenvironment: The depositional environment of the Umm Luj Member is deep marine, based on the regional association with deep-marine, outer-shelf to upper-bathyal benthonic and planktonic-bearing sediments.

Kial Formation, Maqna Group

The Kial Formation can be considered as representing a continuation of the depositional environments of the Jabal Kibrit Formation as it consists primarily of interbedded siliciclastic and evaporite members (Figure 65) with localized carbonate equivalents. Two hypersaline events alternate with normal salinity events. In a very few marginal locations, the members of the Kial Formation may be difficult to identify with certainty mainly due to the presence of condensed sequences. The Kial Formation is well represented throughout the Saudi Arabian subsurface as well as within the Red Sea region.

Name: R.A. Kamal named the Kial Formation after Kial Village adjacent to the Midyan field (Figure 1a) where the section is well-developed. The name was first published by Hughes and Filatoff (1995). The Kial Formation consists in the subsurface of five formal members (from bottom to top): (1) Rayaman; (2) Yuba; (3) Nakhlah; (4) Sidr; and (5) Sabya. It is not easy to distinguish the members in the surface sections in Midyan; some members pinch out along strike and it is difficult to distinguish them from each other and from the overlying Mansiyah Formation. A carbonate facies equivalent of the Sidr Member is also recognized for the first time and is formally called the Sabya Member.

Regional Equivalents: The Kial Formation is stratigraphically equivalent to the Belayim Formation of the Gulf of Suez and Red Sea as both are of planktonic foraminiferal zone N9 (upper) and of calcareous nannofossil zone NN5 (Hughes et al., 1992; Hughes and Beydoun, 1992), and to the Abu Imama Formation of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992).

Type Section and Thickness: The Kial Formation is defined in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 6,561–6,876 ft (315 ft, 96 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1a and 91).

Distribution: The Kial Formation is widely distributed along the Saudi Arabian Red Sea, but is best exposed along the escarpment on the western flank of Jabal Rughama in Midyan. At a locality south of the road to Maqna (28°26′01.5″N, 34”56′45.9″E), the Burqan Formation is overlain by at least four well-defined ‘benches’ of anhydrite belonging to the Kial Formation. Resistant anhydrite forms the tops of the benches, whereas the underlying soft, friable calcareous mudstone beds are recessive. The thickness of the anhydrite beds is apparently uniform, but that of the mudstones varies. Interbedded siliciclastics and anhydrite are also confirmed as present in the Jabal Kibrit and Jabal Musayr areas.

In the subsurface of the Yanbu Basin, all the Kial Members are seen in three wells (Yanbu-1, 4 and 6; Figure 1c), but are absent in the remaining five wells either through non-deposition or erosion. The presence of the Kial Formation in the Ghawwas Basin is questionable; it is interpreted as present in the offshore even though it was not penetrated in the Ghawwas-1 (which blew out immediately upon drilling the first siliciclastic section below the Mansiyah Formation), and as absent in Saudi Aramco’s onshore Ghawwas South-1. Further south, local presence of the Kial Formation is proven at least in the Jizan North-1 and -2 wells. The Kial Formation may be locally missing on structures, however, due to late Miocene uplift, lowstand and erosion.

Lithology: The Kial Formation consists of a variety of lithological types that include thick interbeds of calcareous siltstones and mudstones, anhydrite and carbonate.

Contact Relationships: The contacts of the Kial Formation are generally conformable on the underlying Jabal Kibrit Formation, although unconformable relationships do exist, as in An Numan-1, where the Sidr Member unconformably overlies the Jabal Kibrit Formation. The Kial Formation is elsewhere noted to be unconformable on the Burqan Formation. In a complete section, the Kial Formation is conformably overlain by the Mansiyah Formation. Probably due to intense structural uplift and erosion, the Kial Formation is absent, however, in several locations, with the Mansiyah Formation lying unconformably on either Proterozoic Basement (areas of the Midyan Basin; Al Khurmah-1) or the Jabal Kibrit Formation (areas of the Jizan Basin; Jizan South-1). These conformable and unconformable relations are indicated by missing sections in the studied wells.

Age: The Kial Formation is early middle Miocene (Langhian) in age based on planktonic foraminifera and calcareous nannofossils in calcareous mudstones in the subsurface. Orbulina suturalis, Praeorbulina glomerosa circularis and P. glomerosa glomerosa (Hughes and Filatoff, 1995) belong to Planktonic Foraminifera Zone N9, and the calcareous nannofossil Sphenolithus heteromorphus (but without Helicosphaera ampliaperta) is indicative of Zone NN5. These marker species are also well known in the Belayim Formation, where further evidence is provided by the presence of Borelis melo curdica.

Paleoenvironment: The depositional environment of the Kial Formation is moderately deep marine, with shallow carbonate platform facies locally developed. The interbedded relationship of evaporites with planktonic foraminifera-bearing mudstones in the subsurface suggests deposition in a deep, episodically hypersaline, submarine environment.

Rayaman Member, Kial Formation, Maqna Group

The Rayaman Member is the basal evaporitic member of the Kial Formation and is well-developed across the region and within the Red Sea generally. The Rayaman Member represents a hypersaline phase that succeeded the normal salinity conditions of the upper Jabal Kibrit Formation.

Name: The Rayaman Member is named after the Tenneco exploration well Rayaman-1, drilled offshore in the Midyan area, where it is well developed. The term was first used by Saudi Aramco (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).

Regional Equivalents: The Rayaman Member is equivalent to the Baba Member of the Belayim Formation in the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Rayaman Member is defined in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 6,802–6876 ft (74 ft, 22.6 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1a and 91).

Lithology: The Rayaman Member consists of evaporites (anhydrite with local halite).

Contact Relationships: The Rayaman Member conformably overlies the Jabal Kibrit Formation and is overlain conformably by the Yuba Member of the Kial Formation.

Distribution: The Rayaman Member is widely distributed in the subsurface of the northern Red Sea with ten wells, drilling thicknesses ranging from 37 ft (Nakhlah-1) to 214 ft (Midyan-2). While variable thickness of the Rayaman Member over a short distance seems to be normal (Burqan-2: 63 ft; Burqan-3: 125 ft), locally the section can be absent due to erosion (Al Khurmah-1 and An Numan-1) or thin due to faulting (Sidr-1). In the Al Wajh Basin, subsurface control shows the Rayaman Member significantly thickens from east (Al Wajh South-1: 263 ft; Umm Luj-1: 155 ft) to west (Dhaylan-1: 1,125 ft). While the Rayaman Member is present in several of the onshore Yanbu wells, it is absent in the Badr-1 well, immediately offshore of Yanbu, probably due to erosion. Presence of the Rayaman Member has not yet been proven in the Jiddah or Ghawwas basins, but variable thicknesses ranging from absent (Jizan South-1) to 114 ft (Jizan North 2) are seen in the Jizan area.

Age: The Rayaman Member is early middle Miocene (Langhian) in age (see above).

Paleoenvironment: The depositional environment of the Rayaman Member is shallow to generally moderately deep-marine, hypersaline, based on its stratigraphic position above and below normal salinity deep marine sediments of the upper Jabal Kibrit Formation and of the Yanbu member of the Kial Formation, respectively.

Yuba Member, Kial Formation, Maqna Group

The Yuba Member consists of a widely distributed, fine-grained siliciclastics that were deposited during a return to normal salinity conditions following the Rayaman hypersaline event.

Name: The Yuba Member is named after the Auxerap/Tenneco exploration well, Yuba-1, drilled offshore in the Midyan area, where the Member is well developed. The term was first used by Saudi Aramco (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).

Regional Equivalents: The Yuba Member is equivalent to the Sidri Member of the Belayim Formation of the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Yuba Member is defined in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 6,779–6,802ft (23ft, 7 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1a and 91). The Yuba Member is generally a very thin unit when compared to other members of the Kial Formation.

Lithology: The Yuba Member consists of calcareous mudstones with minor carbonate and sandstone.

Distribution: The Yuba Member is widely distributed throughout the Red Sea as a thin veneer in the subsurface. Ten Midyan Basin wells document Yuba Member thicknesses ranging from 7–50 ft (2.1–15.2 m), while it is absent due to erosion in several of the offshore structures (Al Khurmah-1, An Numan-1 and Yuba-1). Wells in the Al Wajh, Yanbu and Jizan basins encountered the Yuba Member with thicknesses generally ranging from 20 ft up to 70 ft (6.1–21. 3 m). The thickest interval encountered to date (455 ft, 138.7 m), however, was drilled in Dhaylan-1 well on the extreme western edge of the Al Wajh Basin. Existence of the Yuba Member has not yet been proved in the subsurface of either the Jiddah or Ghawwas Basins.

Contact Relationships: The Yuba Member conformably overlies the Rayaman Member, and is overlain conformably by the Nakhlah Member of the Kial Formation.

Age: The Yuba Member is early middle Miocene (Langhian) in age (see p.109).

Paleoenvironment: The depositional environment of the Yuba Member is moderately deep marine, based on the presence of planktonic foraminifera.

Nakhlah Member, Kial Formation, Maqna Group

The Nakhlah Member represents a post-Yuba return to hypersalinity and the precipitation of regionally extensive deposits of anhydrite with minor halite.

Name: The Nakhlah Member is named after the Saudi Aramco exploration well Nakhlah-1 (NKLH-1), drilled onshore in the Midyan area, where the Member is well developed. The term was first used by Saudi Aramco (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).

Regional Equivalents: The Nakhlah Member is equivalent to the Feiran Member of the Belayim Formation in the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Nakhlah Member is defined in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 6,645–6,779 ft (134 ft, 40.8 m thick), onshore coastal Saudi Arabian Red Sea (Figures 1a and 91).

Lithology: The Nakhlah Member consists of evaporites (anhydrite with local halite and gypsum), and thin beds of mudstones and siltstones (Figures 92 and 93).

Distribution: Subsurface control shows the Nakhlah Member to be generally widely developed along the margins of the Red Sea with average thicknesses varying from 65 ft (Yanbu-1) up to just in excess of 150 ft (Rayaman-1). Only two depocenters with sections in excess of 200 ft (60.9 m) of Nakhlah Member are known: (1) eastern Al Wajh (Dhaylan-1: 582 ft, 177.4 m; Hamim-1: 365 ft, 111.6 m); and (2) Jizan (Jizan Southeast-1: 227 ft, 69.2 m; Jizan North-2: 337 ft, 102.7 m). Existence of the Nakhlah Member in the subsurface has not yet been shown in either the Jiddah or Ghawwas basins. The Nakhlah Member may locally thin due to faulting (Nakhlah-1), and be absent on offshore structures, due to severe erosion (An Numan-1, Al Khurmah-1 and Badr-1).

Contact Relationships: The Nakhlah Member conformably overlies the Yuba Member of the Kial Formation and is conformably overlain by the Sidr Member of the Kial Formation.

Age: The Nakhlah Member is early middle Miocene (Langhian) in age (see p. 109).

Paleoenvironment: The depositional environment of the Nakhlah Member is moderately deep marine and hypersaline, based on its stratigraphic position above and below moderately deep-marine, planktonic foraminiferal-bearing sediments of the Yanbu and Sidr Members, respectively.

Sidr Member, Kial Formation, Maqna Group

The Sidr Member represents a further return to normal salinity conditions prior to the establishment of a longer period of hypersalinity that produced the overlying Mansiyah evaporites. The term was first used by Saudi Aramco (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report).

Name: The Sidr Member is named after the Saudi Aramco exploration well Sidr-1, drilled onshore in the Midyan area, where it is well developed.

Regional Equivalents: The Sidr Member is equivalent to the clastic facies of the Hammam Faraun of the Belayim Formation in the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Sidr Member is defined in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 6,561–6,645 ft (84 ft, 25.6 m), onshore coastal Saudi Arabian Red Sea (Figures 1a and 91).

Lithology: The Sidr Member consists of siliciclastics and minor anhydrite (see An Numan-1) carbonates, sandstones (rarely arkosic; Figure 94), and calcareous mudstones. In the southern part of the Saudi Arabian Red Sea, this member consists of interbedded conglomeratic sandstones and conglomerates. A carbonate facies equivalent is here termed the Sabya Member.

Distribution: Subsurface evidence suggests that the Sidr Member is widely distributed throughout the margins of the Red Sea, except in the Jiddah and Ghawwas basins. Existing well control indicates that, except for more local depocenters, the Sidr Member generally does not exceed 85 ft in thickness, with the exceptions in the north being the Sidr-1 and Midyan-2 wells (both 245 ft). In the Al Wajh Basin, however, well control indicates a shift in deposition as equivalent section in the Hamim-1 (Sidr Member, 510 ft) exceeds that found in the Dhaylan-1 well (423 ft). In the Jizan Basin, the Jizan North-2 well drilled 260 ft of Sidr Member. Interpretation of the Jizan North-1, however, is complicated by the local presence of a Sabya facies that is developed within the Sidr Member.

Contact Relationships: The Sidr Member conformably overlies the Nakhlah Member of the Kial Formation and is overlain conformably by the Mansiyah Formation.

Age: The Sidr Member is early middle Miocene (Langhian) in age (see p. 109).

Paleoenvironment: The depositional environment of the Sidr Member is moderately deep marine, based on the presence of a predominantly plantonic foraminiferal assemblage. The scarcity of benthonic foraminifera in this member and the Yuba Member indicates adverse bottom-water conditions that may have been hypersaline.

Sabya Member, Kial Formation, Maqna Group

The Sabya Member is a locally developed carbonate that completely or partly replaces the Sidr siliciclastics within the region. It was deposited under normal salinity conditions within areas where siliciclastic sedimentation was minimal.

Name: The Sabya Member is named after Sabiyah Village, north of the Jizan-1 well locality, where this Member is well developed.

Regional Equivalents: The Sabya Member is considered as equivalent to the carbonate facies of the Hammam Faraun Member of the Belayim Formation of the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Sabya Member is defined in Saudi Aramco exploration well Jizan North-1 (JZNR-1) between 8,640–8,800 ft (160 ft, 48.8 m thick), onshore coastal Saudi Arabian Red Sea (Figure 95).

Lithology: The Sabya Member consists of bioclastic carbonates, interbedded with conglomeratic sands and conglomerates, and thin calcareous shales.

Distribution: The Sabya Member has been seen only in the subsurface with deposition limited to the Yanbu Basin (Yanbu-6) and the Jizan Basin (Jizan North-1 and Jizan Southeast-1).

Contact Relationships: In the type section, the Sabya Member lies within the Sidr Member and is therefore a facies variation.

Age: The Sabya Member is early middle Miocene (Langhian) in age (see p. 109).

Paleoenvironment: The depositional environment of the Sabya Member is considered to have been shallow-marine, based on the absence of planktonic foraminifera encountered in cuttings samples analysis.

MANSIYAH FORMATION

The Red Sea middle Miocene massive salt succession in the subsurface of Saudi Arabia is characterized by a thick deposit of gypsum, anhydrite, and halite named the Mansiyah Formation.

Name: The Mansiyah Formation is named after the Mansiyah-1 (MNSY-1) exploration well north of Jizan. The Mansiyah Formation in the Midyan area has, at various times, been considered as part of the middle Raghama formation of Skipwith (1973), the upper part of the Al Bad formation (Dullo et al., 1983), part of the Bad’ formation of the Raghama group of Clark (1986), the Raghama formation of Brown et al. (1989), and within the Bad formation of Jado et al. (1990).

Regional Equivalents: The Mansiyah Formation is equivalent and lithologically comparable to the South Gharib Formation in the Gulf of Suez and other areas of the Red Sea (Hughes et al., 1992; Hughes and Beydoun, 1992) and to the lower part of the Dungunab Formation of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992). The Mansiyah Formation is also equivalent to the open-marine syn-rift tectono-sedimentary unit B of Plaziat et al. (1990).

Type Section: The Mansiyah Formation is defined in the Auxerap exploration well Mansiyah-1 (MNSY-1: 17°12′00.2″N, 42°22′10.4″E) between 7,500–11,371 ft, onshore coastal Saudi Arabian Red Sea, 40 km north of Jizan (Figure 96).

Reference Section: The Mansiyah Formation is represented in Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 5,804 and 6,561 ft, onshore coastal Saudi Arabian Red Sea (Figure 97).

Thickness: In the type section, the Mansiyah Formation is 3,871 ft (1,180.2 m) thick, and in the reference section 757 ft (230.8 m) thick.

Lithology: The Mansiyah Formation consists of massive halite, gypsum, and anhydrite, with thin interbeds of calcareous shales and mudstones, and subordinate sandstones and siltstones (Figure 98). In the Mansiyah-1 type section, the Mansiyah Formation consists almost entirely of halite, except for a thin bed of dolomite towards the upper part of the section. In the Midyan-1 reference section, the Mansiyah Formation has a varied lithology and consists of interbedded anhydrite, halite, shale and silt.

Distribution: The eastern dip-slope of Jabal Rughama in the Midyan region is characterized by a blanket of white anhydrite that may be part of the Mansiyah Formation, but could also represent part of the Kial Formation. A similar extensive exposure of anhydrite blankets the western and southern flanks of Jabal Mundassah. The Mansiyah Formation is well represented in the subsurface, but it is difficult to distinguish in outcrop from the underlying Kial Formation.

Contact Relationships: In the type section, the Mansiyah Formation overlies the Jabal Kibrit Formation with possible conformity, but this has not been proved and a disconformable relationship is suggested; while at other locations, it lies nonconformably upon Proterozoic Basement (areas of the Midyan Basin; Al Khurmah-1). In the reference section, however, the Mansiyah Formation conformably overlies the Kial Formation. In the field sections, the Mansiyah Formation overlies the Kial Formation with apparent conformity, although some faulted unconformable contact relationships are present in areas adjacent to halokinetic glide planes. The Mansiyah Formation is overlain with probable conformity by the Ghawwas Formation.

Age: The Mansiyah Formation has been interpreted as middle Miocene based on its stratigraphic position (in the absence of age-diagnostic biostratigraphic evidence) above the biostratigraphically constrained basal middle Miocene Kial Formation and beneath the middle to upper Miocene Ghawwas Formation. In the Gulf of Suez, marine diatoms indicate the presence of middle Miocene sediments within the lower part of the overlying Zeit Formation (Osman Varol, oral communication). Palynological age criteria in the inter-evaporitic siliciclastics are as for the Jabal Kibrit Formation but supplemented by the presence of the dinoflagellate cyst species Systematophora ancyrya/placacantha (extinction at top middle Miocene); and Pentadinium laticinctum (extinction near top middle Miocene) (Hughes and Filatoff, 1995).

Paleoenvironment: The depositional environment of the Mansiyah Formation was moderately deep restricted marine, and conditions of extreme hypersalinity led to the precipitation of evaporites. This paleoenvironmental interpretation is based on examination of cored samples and the presence of normal marine dinoflagellates of which the named genera are known to occupy outer shelf and inner to outer shelf respectively (Stover et al., 1996; Merrell Miller, oral communication, 2004). A marine environment is indicated by the presence of dinoflagellate cysts in inter-evaporitic shales; anoxic conditions are suggested by an abundance of pyrite-impregnated amorphous kerogen (Hughes and Filatoff, 1995). The hypersaline episode was probably regional in extent and, based on the traditional silled deep-basin model, resulted from the isolation of the Red Sea from the Gulf of Aden and the Mediterranean (Hughes and Beydoun, 1992; Crossley et al., 1992; Al-Husseini et al., 2003).

GHAWWAS FORMATION

The Ghawwas Formation is a thick succession of interbedded fine- to coarse-grained siliciclastics and thin beds of anhydrite which has been intensively studied by Saudi Aramco.

Name:Hughes and Filatoff (1995) named the Ghawwas Formation. In Midyan, it was previously included within the middle Raghama formation (Skipwith, 1973), the upper part of the Al Bad formation (Dullo et al., 1983), the Bad formation of the Raghama group (Clark, 1986), the Raghama formation (Brown et al., 1989), and the Bad formation (Jado et al., 1990). The present name Ghawwas Formation is based on the succession present in the Ghawwas-1 (GHWS-1) exploration well. Unfortunately, this well does not have a full suite of logs, so an additional reference well has been defined.

Regional Equivalents: The Ghawwas Formation is equivalent to the Zeit Formation in the Gulf of Suez and other areas of the Red Sea (Hughes et al., 1992; Hughes and Beydoun, 1992), and to the upper part of the Dungunab Formation of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992). The Ghawwas Formation is also equivalent to the open-marine, syn-rift tectono-sedimentary unit C of Plaziat et al. (1990).

Type Section: The Ghawwas Formation is defined in Arabian Sun exploration well Ghawwas-1 (GHWS-1: 19°49′21.18″N, 40°23′02.88″E) between 3,359–7,299 ft, offshore coastal Saudi Arabian Red Sea (Figures 1g and 99).

Reference Section: The Ghawwas Formation is represented in the Saudi Aramco exploration well Midyan S-1 (MDYN-1) between 1,424–5,804 ft, onshore coastal Saudi Arabian Red Sea (Figures 1a and 100).

Thickness: The thickness of the Ghawwas Formation is 3,940 ft (1,201.2 m) in the type section, and 4,380 ft (1,335.4 m) in the reference section.

Lithology: The Ghawwas Formation consists of conglomerates, sandstones, minor claystones, carbonates, and local evaporites.

Distribution: The Ghawwas Formation is distributed widely along the Saudi Arabian Red Sea in both the surface and subsurface.

Contact Relationships: The Ghawwas Formation overlies the Mansiyah Formation with probable conformity, and is unconformably overlain by the Pliocene-Pleistocene Lisan Group (R.S. Johnson, D. Rodgers and G.R. Savage, 1995, Saudi Aramco Report). The top of the Ghawwas Formation is difficult to pick with certainty from electric logs, with Ghawwas section sometimes grading into the Ifal Formation of the overlying Lisan Group.

Age: The Ghawwas Formation is middle to late Miocene in age based on diatom evidence within the region together with the stratigraphic position of the formation above rocks regionally dated as middle Miocene (Hughes et al., 1992; Hughes and Filatoff, 1995). In the Gulf of Suez, the middle to late Miocene boundary is placed within the lower part of the Zeit Formation based on diatom evidence (Osman Varol, oral communication; Tawfik and Krebs, 1994). A Late Neogene age is suggested by the relatively common occurrences of Plumbaginaceae-, Papilionaceae- and Nyctaginaceae-type pollen.

Paleoenvironment: Regional studies indicate that the Ghawwas Formation was deposited under a variety of shallow-marine to restricted marginal-marine environments, perhaps with the periodic development of sabkha conditions. Marine microfauna, for example, are scarce (Hughes and Filatoff, 1995; Filatoff and Hughes, 1996), but freshwater Pediastrum spp. and Anthoceros-type spores are common.

LISAN GROUP

The Lisan Group is a fluvial succession deposited during the opening of the Gulf of Aqaba in the early Pliocene. Lisan formation is upgraded to group status in this nomenclature to acknowledge the formational status of the Ifal and Badr members.

Name: The Lisan formation (here Lisan Group) was named by Clark (1986) to replace the term ‘Ifal formation’ of Bokhari (1981). It consists of two discrete lithologies: (1) a siliciclastic succession, assigned here to the Ifal Formation; and (2) a carbonate lithology assigned here to the Badr Formation.

Regional Equivalents: The Lisan Group is equivalent to the Wardan (siliciclastic) and Shukheir (carbonate) formations of the Gulf of Suez, and the Abu Shagara Formation of Sudan (Carella and Scarpa, 1962; Sestini, 1965; Hughes and Beydoun, 1992). The Lisan Group is also equivalent to the open-marine syn-rift tectono-sedimentary unit D of Plaziat et al. (1990).

Type Section: The type section of the Lisan Group is located at the western edge of the Ifal Plain (Clark, 1986).

Reference Section: The Lisan Group is defined in the Auxerap/Tenneco exploration well Yuba-1 between 2,541–4,011 ft, onshore coastal Saudi Arabian Red Sea (Figures 1a and 101).

Thickness: As stated above, the base of the Lisan Group is difficult to pick with certainty from electric logs because the clastics of the Ghawwas Formation sometime grade into the Ifal Formation. The Lisan Group ranges in thickness from 1,470 ft (448.2 m) in the reference well to in excess of 4,500 ft (1,372 m) in wells drilled in the Al Wajh Basin.

Lithology: The Lisan Group consists of carbonates and rhythmic, alternations of poorly consolidated, fluviatile sandstones and conglomerates. Clark (1986) described thin, concentric beds of gypsum that emerge from the Ifal Plain as ridges that may represent part of the general Ghawwas-Lisan Quaternary succession. These features may be due to the deep-seated diapiric movement of evaporites. In the Midyan subsurface, the Lisan Group consists of coarse- and fine-grained siliciclastics and carbonates.

Distribution: The Lisan Group crops out on the eastern margin of Jabal Rughama underlying much of the Ifal Plain. It is distributed widely along the Saudi Arabian Red Sea in both the surface and subsurface.

Contact Relationships: The Lisan Group is unconformable on the Ghawwas Formation. Clark (1986) described an unconformity between the Lisan formation (here Lisan Group) and the Mansiyah Formation east of Jabal Rughama in the Midyan region. In the type section, the Lisan Group unconformably overlies the Ghawwas Formation. In the reference section, the Ifal Formation is unconformable with the Ghawwas, requiring the use of seismic and/or paleontology to pick the contact.

Age: A Pliocene age is interpreted from the stratigraphic position of the outcropping Lisan Group above the upper Miocene Ghawwas Formation. In the subsurface, a Pliocene to Pleistocene age is based on planktonic foraminifera and calcareous nannofossils (Hughes and Filatoff, 1995). The fossil evidence is as follows: Planktonic Zone N21 (late Pliocene) based on the first downhole occurrence of Globigerinoides extremus; Nannofossil Zone NN17 (late Pliocene) based on the first downhole occurrence of Dicoaster pentaradiatus; Nannofossil Zone ?NN16–15 (late to early Pliocene) based on the first downhole occurrence of Reticulofenestra pseudoumbilica and of Sphenolithus moriformis. While the Ifal Formation is typically nearly barren of both palynmorphs and kerogen, the Badr Formation has yielded sparse dinocyst assemblages typified by Tuberculodinium vancampoae.

Paleoenvironment: In outcrop, the Lisan Group consists mostly of fluvial and delta-plain deposits. Along the southern flank of Jabal Kibrit, gypsum beds and limestones contain echinoids and bivalves that indicate shallow marine depositional conditions. Subsurface foraminifera suggest environments that range from supratidal, intertidal, and shallow marine to upper bathyal.

Ifal Formation, Lisan Group

Name: The name of the Ifal Formation is taken from the Ifal Plain in the Midyan area. It was originally used as the Ifal formation of Bokhari (1981).

Regional Equivalents: The Ifal Formation is equivalent to the Wardan Formation of the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section and Thickness: The Ifal Formation is defined in the Auxerap/Tenneco exploration well Yuba-1 (YUBA-1: 27°46′00.39″N, 38°08′42.93″E) between 2,541–4,011 ft (1,470 ft, 448.2 m thick), offshore coastal Saudi Arabian Red Sea (Figures 1a and 101).

Lithology: The Ifal Formation refers to the siliciclastic sediments of the Lisan Group, and consists of fine- and coarse-grained sandstones and siltstones.

Distribution: The Ifal Formation is widely distributed along the margins of the Saudi Arabian Red Sea in both the surface and sub-surface.

Contact Relationships: The Ifal Formation is disconformable on the Ghawwas Formation and is disconformably overlain by carbonates of the Badr Formation. The disconformable contact at the base of the Ghawwas is considered to probably be nonconformable as it is related to the tectonic event that preceeded the opening of the Gulf of Aqaba at the Pliocene/Miocene boundary.

Age: The Ifal Formation is Pliocene in age based on correlation with the Wardan Formation in the Gulf of Suez, that is dated on planktonic foraminifera and calcareous nannofossils evidence recovered from the Wardan Formation in the Gulf of Suez (Hughes and Varol, written communication in a confidential report on a 65 well study by Robertson Research for the Egyptian General Petroleum Corporation).

Paleoenvironment: The depositional environment of the Ifal Formation is shallow to marginal marine. The shallow-marine paleoenvironmental interpretation is based on the presence of distinctive benthonic foraminifera such as Elphidium and Ammonia species. In the Gulf of Suez, the Wardan Formation contains moderately deep-marine benthonic foraminiferal assemblages (Hughes, written communication in a confidential report on a 65 well study by Robertson Research for the Egyptian General Petroleum Corporation).

Badr Formation, Lisan Group

The Badr Formation refers to the carbonate sediments of the Lisan Group.

Name: The Badr Formation is named after the subsurface carbonate section encountered in the Arabian Sun exploration well Badr-1 (BADR-1; 23°35′52.3″N, 38°26′22.7″E) between 1,075–2,556 ft, offshore coastal Saudi Arabian Red Sea. While the formation may extend from 200–2,256 ft, no samples were recovered in this well above 1,190 ft, and electric logs began at 1,075 ft.

Regional Equivalents: The Badr Formation is equivalent to the Shagara Formation of the Gulf of Suez and Red Sea (Hughes and Beydoun, 1992).

Type Section: The Badr Formation is defined in the Arabian Sun Badr-1 exploration well (BADR-1: 23°35′52.3″N, 38°26′22.7″E) between 1,075–2,556 ft, offshore coastal Saudi Arabian Red Sea (Figure 102).

Reference Section: The Badr Formation is represented in the Tenneco Rayaman-1 exploration well (RYMN-1: 27°51′35″N, 35°06′00″E) between 122–2,487 ft. This well has been selected as a reference section because the basal contact with the Ifal Formation is penetrated, and there is a more complete suite of logs available (Figure 103).

Thickness: The Badr Formation is 1,481 ft (451.5 m) at the type section, and 2,365 ft (721 m) at the reference section.

Lithology: The Badr Formation consists of bioclastic carbonates.

Distribution: While widely distributed along the Saudi margins of the Red Sea, the Badr Formation is less well developed in both the surface and the subsurface than the Ifal formation.

Contact Relationships: The Badr Formation conformably overlies the Ifal Formation of the Lisan Group at the type section.

Age: The Badr Formation is Pliocene in age, based on biostratigraphic evidence recovered from the Gulf of Suez (see discussion in Ifal, above).

Paleoenvironment: The depositional environment of the Badr Formation is shallow marine, based on shallow marine benthonic foraminiferal evidence recovered from the Gulf of Suez (see discussion in Ifal, above).

QUATERNARY SEDIMENTS

The Ifal Plain and extensive areas between the hills west of Jabal Rughama are covered with undifferentiated sands and gravels, and locally with sand dunes. Seven uplifted carbonate reef terraces are exposed along the coast south of Maqna Village and are similar to ones on the western coast of the Gulf of Aqaba and the southern shore of the Midyan region. Similar terraces have been described by Al-Rifaiy and Cherif (1988) from Al-Aqaba in Jordan where they were attributed to four major cycles of reef development caused by eustatic changes in sea level. In the Midyan region, however, eustasy is considered to have provided an additional control on the development and present distribution of the terraces. The highest terrace is 120 ft above sea level and may correspond to those in the area of Ra’s Sheikh Humaid at the southern extremity of the Midyan Peninsula.

CONCLUSIONS

This paper presents, for the first time, the lithostratigraphy of the Saudi Arabia Red Sea sedimentary succession in outcrop and subsurface in a lexicon style. The rock units are formally defined in outcrop or/and subsurface reference wells in terms of groups, formations and members. Their ages range from Late Cretaceous to Pleistocene, with the lower Miocene representing the oldest syn-rift succession. Most previously defined rock units in Saudi Arabia are related to the proposed formal rock units now adopted by the Saudi Arabian Oil Company, Saudi Aramco. The present study summarizes the work of many geoscientists starting from 1990.

Although the lithostratigraphic nomenclature used in this contribution has been applied to all Saudi Arabian Red Sea wells, there was a requirement for the units to be comprehensively defined and formalized. This lithostratigraphic scheme will permit future Red Sea exploration and development activities to adopt a consistent rock unit nomenclature in which newly drilled sections could be correctly identified and related to adjacent wells. In addition, the subsurface type and reference sections have been related to their characteristic wireline log signatures for calibration with new uncored wells and to assist seismic interpretation.

Exposures of the Saudi Arabian Red Sea succession are limited, and maximum use has been made of the well-exposed Cretaceous and Neogene sections in the Midyan region. Here, a series of locations has been identified where most of the lithostratigraphic units can be visited and examined. In this region, the Wadi Waqb Member is well exposed, and provides an excellent opportunity for this carbonate to be studied within the same region where its reservoir is located.

ACKNOWLEDGMENTS

The Saudi Arabian Ministry of Petroleum and Minerals, and Saudi Aramco are thanked for their permission to publish this contribution. This study is based on the geological and geophysical activities of Saudi Aramco geoscientists of whom there are too many to mention here. The authors worked together during the entire project and integrated the biostratigraphic and lithostratigraphic information of new wells as they were drilled and studied. The calcareous nannofossil determinations of Osman Varol, and the palynological determinations of Patrice Brenac, with palynological interpretations by John Filatoff, contributed significantly to refining the age determinations. The support by Saudi Aramco for the numerous field trips along the Red Sea coast was rewarded by the added confidence given to the subsurface sections by comparison with the biostratigraphy and lithology of the exposed successions.

The fieldwork benefited significantly from oral and written contributions by Tom Connally, Abdulkader Afifi, Rami Kamal, Muhettin Senalp, Scott Fergusson, Mahdi Abu-Ali, Abduljaleel Abu-Bshait and Ra’ed Dakhil of Saudi Aramco. Dogan Perincek and Abdulrahman Jarad from the King Fahd University of Petroleum and Minerals provided satellite image and field support during the last trip to the Midyan area. The authors would also like to thank the anonymous reviewer for the valuable comments on the ages and correlations of rock units from the Gulf of Suez to the Red Sea of Saudi Arabia. The ages of some of the Suez units remain uncertain in the literature, and these were reconciled based on the interpretations of the first author. The authors are especially grateful to John Filatoff for his careful editing of the penultimate version of the manuscript. The suggestions by Moujahed Al-Husseini, who led the initial Saudi Aramco Red Sea exploration campaign from 1989–1992, are greatly appreciated. Saudi Aramco’s Graphic Design Unit of the Cartographic Imaging Division is thanked for their preparation of the logs, especially Nasir Al Maddy, Dhafar Al Qarni and Eugene Cousart. Finally, the GeoArabia team is thanked for preparing the final design of the paper.

ABOUT THE AUTHORS

Geraint Wyn Hughes is Senior Geological Consultant and Leader of the Carbonate Systems Support Group in Saudi Aramco’s Geological Technical Services Division. He gained BSc, MSc, PhD and DSc degrees from Prifysgol Cymru (University of Wales) Aberystwyth and in 2000 he received the Saudi Aramco Exploration Professional Contribution award. His biostratigraphic experience includes 10 years with the Solomon Islands Geological Survey, and 10 years as Unit Head of the Middle East-India region for Robertson Research International. Wyn’s professional activities are focused on integrating micropalaeontology with sedimentology to enhance the sequence stratigraphic understanding of Saudi Arabian hydrocarbon reservoirs. He maintains links with academic research as an Adjunct Professor of the King Fahd University of Petroleum and Minerals, Dhahran. He is a reviewer for GeoArabia, and a member of the British Micropaleontological Society, the Dhahran Geoscience Society, the International Fossil Alga Association and the Cushman Foundation for Foraminiferal Research.

geraint.hughes@aramco.com

Robert (Bob) Johnson was a Geological Consultant with the Area Exploration Department of Saudi Aramco until his retirement in early 2004. Bob received a BA in Geology and Psychology from Hope University in 1976, and an MSc in Geology from the University of Kentucky in 1979. He worked with Amoco between 1979 and 1989 in onshore and offshore exploration in southeastern USA and Cairo, Egypt. Bob joined Saudi Aramco in 1989 and has worked at both the regional and prospect level in the Red Sea, central Arabia, and the Eastern Province. He worked on a regional Devonian study and assisted Saudi Aramco with its natural gas investment program.

johnsors0@yahoo.com