Facies analysis and sequence stratigraphy of the uppermost Jurassic– Lower Cretaceous Sulaiy Formation in outcrops of central Saudi Arabia

The Upper Tithonian–Berriasian Sulaiy Formation crops out in a broad crescent-shaped belt parallel to the Arabian Shield in central Saudi Arabia (Powers et al., 1966). It consists of a massive limestone, more than 100 m thick, that marks the return to an open-marine setting following the deposition of the Late Jurassic Hith Anhydrite (hereafter Hith Formation) evaporites across the interior of the Arabian Plate (Murris, 1980; Al-Husseini, 1997; Sharland et al., 2001). The Sulaiy Formation is an important formation for several reasons as explained below.

Firstly, the Sulaiy Formation is water-bearing in the weathered subsurface zone or below the alluvium overburden. The weathered zone can apparently extend to 20–30 m below the top of the limestone. Due to the removal of anhydrite beds from the underlying Arab-Hith sequence by solution caused by meteoric water, the Sulaiy Formation is commonly fractured, brecciated, foliated and contains numerous cavities, vugs and openings. The Sulaiy limestone aquifer is mainly used in Ad Dilam. The limestone is more like a karst-type medium than a conventional porous medium because the water circulates in channels and cavities and not in the interstices of a granular medium. Although the normal water circulation relationship cannot strictly be applied in the usual way, this limestone can nevertheless be considered to approximately constitute a large-scale porous medium so that the concept of permeability can be applied if a sufficiently large aquifer volume is taken into consideration. In practice, the transmissibility and storage coefficient may be determined by pumping tests when the duration and flow are sufficient to affect a fairly large volume of the aquifer.

Secondly, together with its lateral equivalents in other countries, it is a major source rock in the eastern Arabian Plate (Ayres et al., 1982; Sharland et al., 2001). Thirdly, below the Sulaiy Formation, the upper part of the Hith Formation contains oil in the 20–30 m-thick Manifa reservoir in several fields in Saudi Arabia (Powers, 1968) and the United Arab Emirates (Grötsch et al., 2003). However, the depositional setting and sequence-stratigraphic relationship between the Manifa reservoir and the transition between the Hith evaporites and Sulaiy limestones remains unresolved at outcrop and in the subsurface (Grötsch et al., 2003; Warren, 2006; Hughes and Naji, 2009). Therefore understanding the Sulaiy Formation stratigraphy at outcrop offers important insights for characterizing the petroleum geology of the interval spanning the Jurassic/Cretaceous boundary in the Middle East.

In addition to the Manifa reservoir, Powers (1968) reported that the upper part of the Sulaiy Formation consists of an interval of porous calcarenite, about 60 m thick, at Haradh, Ma’aqala, El Haba, Hafar al-Batin and extends to the east and northeast at least as far as Manifa and Abu Sa’fah fields. In the discovery Manifa-1 Well, this interval is oil-saturated and corresponds to the Lower Ratawi reservoir.

This paper presents the first high-resolution stratigraphic study of the formation in a region near Ar Riyad, the capital of the Kingdom of Saudi Arabia. The study area is situated along the natural Cretaceous escarpment, which is interrupted by the Wadi Nisah in its center (Figures 1 and 2). The geological map of the Ar Riyad Quadrangle (Figure 2; Vaslet et al., 1991) shows the location of the 12 litho-sedimentologic sections that were logged for the study.

The paper starts by presenting the stratigraphic framework of the Sulaiy and its bounding formations, including the likely positions of the Arabian Plate maximum flooding surfaces (MFS, Sharland et al., 2001) as revised by Le Nindre et al. (2008, this paper; Figure 3). In particular this opening section discusses the transition between Sulaiy and underlying Hith Formation at Dahal Hit, the only locality where the two formations are exposed in one section (Figures 4 and 5).

Next the paper documents the 12 sections that were logged and their properties in Figures 4 to 14; these include thickness, lithology, texture (Dunham, 1962; Embry and Klovan, 1971), grain size, components, sedimentary structures, degree of bioturbation and sequences. The logged sections were digitized with the software WellCAD. The location of each section and sample points (latitude, longitude and UTM coordinates) were recorded with a hand-held GPS. Natural gamma ray was recorded at 20 cm intervals with a hand-held spectral Gamma Ray with a bismuth germanium detector. Over 300 rock samples were taken for further microfacies analysis.

Figures 15 to 28 characterize the lithofacies types (LFT) of the Sulaiy and Hith formations. They are grouped together into lithofacies associations (LFA) and placed into depositional environments. The final parts of the paper identify characteristic cycles, cycle sets and sequences, and correlate the resulting sequence-stratigraphic framework between the studied sections.

The framework that is described in this section is based on a detailed review of earlier studies by the final coauthor, Y.-M. Le Nindre, with additional contributions by G.W. Hughes and M.I. Al-Husseini (personal communications, 2014, 2015), as well as the field observations of the other authors (Figure 3).

The type sections of the Hith Anhydrite (“Hith Formation” in this paper) and the Sulaiy Formation are located at Dahal Hit (24°29’18”N, 47°00’06”E), southeast of Ar Riyad. According to Powers et al. (1966) and Powers (1968), the Hith Formation was first described in an unpublished Aramco report by R.A. Bramkamp and T.C. Barger in 1938, published by Steineke et al. (1958), and amended in an unpublished Aramco report by R.W. Powers et al. in 1964. The Hith Formation is accessible in a dissolution cavity at the foot of the Jabal Hit (Figures 1 and 2). This is the only place where the lower contact of the Sulaiy Formation with the Hith Formation can be observed (see Hith-Sulaiy Transition, below, Figures 4 and 5).

The Sulaiy Formation is named after the Wadi as Silay, a gravel-filled channel at the foot of the Hit Escarpment. Powers et al. (1966) and Powers (1968) reported that the formation was first defined in an unpublished Aramco report by R.A. Bramkamp and T.C. Barger in 1938, and its upper and lower contacts were revised in unpublished Aramco reports by C.D. Redmond (1962) and R.W. Powers (1964), respectively.

According to Powers et al. (1966) and Powers (1968), the type section of the Sulaiy Formation measured in the hill above Dahal Hit has a thickness of 170.2 m. Vaslet et al. (1991) measured a revised type section between Dahal Hit and Wadi al Haniyah with a total thickness of 115 m, as consistent with our study.

The Sulaiy Formation contains macro and microfauna, which guide its age determination, but few species were found to have chronostratigraphic significance. In Saudi Arabia, foraminifer associations (Hughes and Naji, 2009) and macrofauna, in particular gastropod Pterocera fauna, may indicate a Tithonian age in the lower part of the formation (Vaslet et al., 1991). Tithonian coccoliths, including the species Conusphaera mexicana minor, have been recovered from the lower Sulaiy Formation, and in the absence of Cretaceous species (Osman Varol, personal communication, inHughes and Naji, 2009).

A possible Berriasian age is indicated in the upper part of the formation, south of Al Kharj, where a rare nannoflora, including Watznaueria barnesae Perch Nielsen 1968 and Haqius circumradius Perch Nielsen 1968, has been discovered (Monique Bonnemaison, written communication inVaslet et al., 1991). Hughes and Naji (2009) note that the Sulaiy Formation is considered the lateral equivalent of the Cretaceous Makhul Formation in Kuwait based on coccoliths (Al-Fares et al., 1998). It is correlated to the Rayda Formation in Oman based on uppermost Tithonian ammonites and Berriasian calpionellids (Granier, 2006, 2008). These arguments suggest that the Jurassic/Cretaceous boundary in Saudi Arabia occurs within the lower part of the Sulaiy Formation.

The stratigraphic chart extending from the Arab Formation to the Biyadh Sandstone interval was proposed by Y.-M. Le Nindre (2014, this paper, Figure 3, modified after Vaslet et al., 1991; Sharland et al., 2001; Haq and Al-Qahtani, 2005). Vaslet et al. (1991) subdivided the Sulaiy Formation into two informal sedimentologic units, S1 and S2, separated by a reworked surface, which they interpreted as a sequence boundary. In the present paper we do not attempt to tie these units to our sequence-stratigraphic framework.

In Figure 3, the age of the Biyadh Sandstone is shown as Hauterivian, above the “Late Valanginian Unconformity” (Le Nindre et al., 2008, 2013). This assignment revises the Berriasian–Hauterivian stratigraphy in Saudi Arabia as shown in several publications (Sharland et al., 2001, 2004; Haq and Al-Qahtani, 2005; Droste, 2013).

The column also shows the revised positions of the Arabian Plate maximum flooding surfaces (MFS) following Le Nindre et al. (2008). The Sulaiy Formation is interpreted to contain Upper Tithonian MFS J110 (147 Ma), Lower Barriasian MFS K10 (144 Ma) and Upper Berriasian MFS K20 (141 Ma). The first two MFSs are interpreted in the present paper. Lower Valanginian MFS K30 (139 Ma) and Hauterivian MFS K40 (132 Ma) are adopted from Le Nindre et al. (2008, 2013).

The transition between the Hith and Sulaiy formations at Dahal Hit is shown in detail in Figure 5. In ascending order the transition interval above the lower laminated main anhydrite of the Hith Formation consists of Breccia 1, a thin anhydrite bed, Breccia 2, and a thicker, deformed anhydrite bed. These intervals are assigned to the Hith Formation and are followed by evenly-bedded limestone of the Sulaiy Formation (Powers et al., 1966; Powers, 1968).

Steineke et al. (1958) positioned the Hith/Sulaiy Formation boundary between the massive anhydrite below, and breccia limestone above, and interpreted the contact as an unconformity surface, only visible at this section. However, according to Powers et al. (1966) and Powers (1968), this contact is not a disconformity or unconformity in the subsurface. They consider the breccia intervals at Dahal Hit to be due to the dissolution of the intercalated anhydrites – a solution-collapse type breccia. Vaslet et al. (1991, p. 15) consider “the top of the Hith Anhydrite is truncated by the basal beds of the Sulaiy Formation”, and in the caption of their Figure 8 interpret the contact as disconformable.

• (1) lower “anhydrite” member (92 m thick);

• (2) middle “transitional” anhydrite-carbonate member (21 m thick) consisting of interbedded anhydrite and carbonate units, each approximately 3–4.5 m thick, forming two depositional cycles (1B and 1C);

• (3) upper “carbonate” member” (31 m thick). The upper carbonate consists of four depositional cycles (2A to 2D) and its upper part hosts the Manifa reservoir (Powers, 1968), or informal “Manifa member” (Wilson, 1985).

Hughes and Naji (2009) consider the Hith/Sulaiy Formation boundary to be a possible disconformity. They described the Sulaiy-Hith transition in the offshore Manifa Field, Saudi Arabia, situated approximately 500 km northeast of Ar Riyad. They subdivided the Hith Formation (144 m thick) into three informal members (Table 1):

The proposed correlation in Table 1 suggests that the subsurface Manifa member is time-correlative to the lowermost Sulaiy Formation at Dahal Hit. This correlation is further supported by the description of the Hith-Sulaiy transition at Abu Jifan Field, situated 60 km east of Ar Riyad and approximately 550 km southwest of Manifa Field. In an Abu Jifan borehole, Vaslet et al. (1991) reported that the Hith Formation is 132 m thick, and mainly composed of white to gray anhydrite, with intercalations of halite, calcarenetic limestone, and dolomitic layers (Table 2). The uppermost 20 m contain abundant oolitic and pelletoidal calcarenite layers, known as the Manifa reservoir. It is remarkable that the Hith Formation in the Manifa and Abu Jifan fields, below the Manifa member, have essentially the same thickness (112–113 m) and that it is comparable to the thickness in Dahal Hit (90.3 m).

The comparable thickness of the Hith Formation evaporites supports the interpretation that they were deposited subaqueously in a shallow hypersaline restricted basin that extended across the Arabian Plate (Azer and Peebles, 1998; Warren, 2006; Hughes and Naji, 2009). The geographic extent of this evaporitic platform continues with comparable depositional sequences and environments northwards into the Gotnia Basin in Iraq and Kuwait, and is manifested in Morocco (High Atlas Tithonian).

Sharland et al. (2001) discussed three options for the position of Upper Tithonian maximum flooding surface MFS J110 (147 Ma) in subsurface Saudi Arabia: “probably not deposited”, or “possibly within intra-Hith Formation”, or “possibly near base of Manifa reservoir”. Haq and Al-Qahtani (2005) in their Jurassic–Neogene Chart positioned MFS J110 (147 Ma) in the lower part of the Sulaiy Formation but above the Manifa reservoir. Their chart indicates that MFS J110 may occur in a potential source rock interval but they did not discuss these interpretations in their paper. Neither Sharland et al. (2001) nor Haq and Al-Qahtani (2005) indicated a position for MFS J110 in Dahal Hit.

The lateral lithological continuity and comparable thicknesses of the Hith Formation from NE Saudi Arabia to Dahal Hit suggests that the Manifa member represents the earliest transgressive deposit of the Sulaiy Formation, which may have flooded the majority of the Arabian Plate (Tables 1 and 2). We therefore suggest the Upper Tithonian MFS J110 occurs in the subsurface Manifa member and lowermost Sulaiy Formation at Dahal Hit. We interpret the contact between the Sulaiy and Hith formations at Dahal Hit as the “Sulaiy Sequence Boundary” or “Sulaiy SB”, and the evenly-bedded Sulaiy limestones to represent the start of the transgression in Dahal Hit (Figure 5). We therefore favor correlating the subsurface Manifa member to the most basal part of the Sulaiy Formation at Dahal Hit and to position MFS J110 (147 Ma) in them.

The Yamama Formation conformably overlies the Sulaiy Formation (Vaslet et al., 1991). In the 12 studied sections the upper part of the Sulaiy Formation and its upper boundary were not studied (Figures 2 and 3). In this part of the paper, the logged sections are documented graphically with a brief sedimentological description and interpretation. For sections KW (South Dahal Hit), KP and KH, the description and interpretations are shown next to Figures 6, 7 and 8, respectively.

Section DH (24°29'9.71“N, 46°59'49.47“E; UTM: X = 702381, Y = 2709500; Figures 1 and 2) has a thickness of 116.2 m and is characterized, above the Hith Formation, by a transgressive-regressive sequence, the Lower Sulaiy Sequence (Figures 4 and 5). As discussed above (see Hith-Sulaiy Transition), the Sulaiy Sequence Boundary (SB) is positioned at the base of the evenly-bedded Sulaiy Formation.

The transgressive part is dominated by bedded bioclast-rich packstones, interpreted as tempestite storm deposits and up to 2–5 dm-thick oolitic grainstones (Figure 4d). A prominent interval of biostromes can be observed approximately 8 m below the assumed maximum flooding interval (MFI) containing Lower Berriasian MFS K10 (Figure 4c). This interval occurs in all studied sections and acts as an important marker. Maximum flooding is interpreted in an interval dominated by mud- and wackestones. Bioturbation constantly increases towards the MFI associated with destratification leading to a nodular appearance. The regressive part of the sequence consists of tempestites with increasing amounts of rudstones and bioclast-rich packstones towards the top. This succession indicates an increase of water energy. The stratigraphic contact to the overlying Yamama Formation could not be found at this locality but is exposed some 20 km in the hinterland of the Dahal Hit area.

Wadi Nisah Section NG (24°13'35.70”N, 46°59'6.00”E; UTM: X = 706310, Y = 2680513; Figures 1 and 2) is located 28.76 km south of the type locality Dahal Hit and about 22 km SW of Section AH. Section NG has a thickness of 79 m and is characterized by the regressive hemi-sequence (Figure 9). Its lower part consists of bioclastic pack- and wackestones, interpreted as tempestite sheets. This lower part of the Sulaiy Formation correlates very well with the cycle sets of the other studied sections.

The upper part is completely dolomitized. Using cathodoluminescence microscopy ooid ghosts could be identified (Figure 10). The transition from limestone to dolomite shows very high gamma-ray values. The upper part of the regressive sequence shows a shallowing-upward trend, with the succession from foreshoal-associated tempestites to a more proximal shoal margin facies and finally to a shoal facies, which is dominated by oolitic grainstones with high-angle cross-bedding. The contact with the overlying Yamama Formation could not be detected in the Wadi Nisah area.

Wadi Nisah is the only section where dolomitization is observed and Sulaiy Cycle Set SCS 12 is the first of three dolomitized cycle sets. Between SCS 12 and 13 a major change in depositional environment occurs (from foreshoal to shoal) suggesting their contact may be a sequence boundary. The uppermost part of the Sulaiy Formation is not completely studied as the contact with the overlying Yamama Formation could not be detected in the Wadi Nisah area. It might be possible that the Arabian Plate Upper Berriasian MFS K20 (141 Ma) is part of the younger, incomplete Upper Sulaiy Sequence.

Khafs Daghrah Section FI (23°50'17.20”N, 47°11'51.30”E; UTM: X = 723834, Y = 2638038; Figures 1 and 2) is the southernmost section of the study area. It is located 74.5 km south of the type locality DH and 47.75 km SE of Section NG and has a thickness of 70 m (Figure 11). The lower transgressive part is mainly dominated by bioclastic wackestones and packstones. Crinoids are present in the lower part, also scattered corals can be observed 8 m below the MFI. Mud- and wackestones are dominant around the MFI and show intense bioturbation. The upper part shows an increase of high water-energy associated facies types and is interpreted as a regressive shallowing-upward trend. In the uppermost part of the section, bioturbated tempestites within a foreshoal setting turn into proximal tempestites (e.g. rudstones) and scattered corals of a shoal margin setting. The top of the section is marked by high-angle, cross-bedded oolitic-peloidal grainstones associated with a high-energy shoal environment.

North Dahal Hit Section EH (24°29'49.20”N, 46°59'27.63”E; UTM: X = 701785, Y = 2638770; Figures 1 and 2) is located 1.5 km north of the Sulaiy and Hith type locality Dahal Hit and is 16.80 m thick (Figure 12). The lower, transgressive part consists at its base of bioclastic rud- and bioclastic pack-to-grainstones. The MFI is built by wacke- and mudstones. The regressive part above the MFI shows a gradual change in lithology to pack- and grainstones. Especially within the bioclastic packstones, grading can be observed which hints to an origin as tempestite deposits within a foreshoal setting.

Sections HL 1 to HL 4 are located 13 km north of the Sulaiy and Hith type locality Dahal Hit (24°30'17.51”N, 47°02'58.21”E; Figures 1 and 2). The thicknesses and UTM coordinates of the studied sections listed in Table 3. The studied sections have lateral distances to each others of 40, 140 and 120 m (Figure 13). The close spacing between the studied sections has the overall aim to focus on the lateral extent of the shoal geobodies. Each section shows a shallowing-upward trend, which is very similar to the trend observed in Section FI where high energy associated facies types like proximal tempestites, rud- and grainstones increase upwards. The base of the shallowing-upward trend is represented by bioturbated tempestites, interpreted as foreshoal setting, followed by proximal tempestites (e.g. rudstones) and scattered corals. This succession grades into high-angle, cross-bedded oolitic-peloidal grainstones, interpreted as high-energy shoal environment.

Section SI (23°50'11.3”N, 47°12'15.0”E; UTM: X: 724552, Y: 2635036; Figure 14) is located in the hinterland, southeast of Section FI and represents parts of its vertical succession. SI has a thickness of only 2.8 m and is therefore the thinnest of all studied sections. This is caused by lower outcrop quality due to intense weathering processes; nevertheless it shows very well the transition from a foreshoal setting into high-energy shoals. The characteristic transition starts with bioclastic and bioturbated wacke- and packstones, which are interpreted as tempestite deposits within a foreshoal environment. Bioclastic rudstones with erosive bases and scattered corals follow in the vertical succession grading into high-angle cross-bedded oolitic-peloidal grainstones, interpreted as high-energy shoal environment. A characteristic step-wise weathering profile of the landscape led to the interpretation of at least three following shallowing-upward cycles.

Section KW (24°28'25.30”N, 47°00'14.00”E; UTM: X = 702970, Y = 2708580; Figures 1 and 2) is located 2.5 km south of the type locality Dahal Hit. It is 90 m thick and consists of part of the Lower Sulaiy Sequence (Figure 6). Bedded tempestites, primarily built of bioclast-rich packstones and occasional rudstones dominate the transgressive part. Similar to Section DH, biostromes occur below the MFI. The MFI shows increasing bioturbation associated with destratification. The mud- and wackestones around the MFI are less resistant to weathering, which leads to recessive units. The regressive part of the sequence is composed mainly of bioclast-rich pack- and wacke-to-packstones. Bioturbation is very intense, resulting in a nodular appearance. A 15 cm thick brachiopod-rich bed can be found 3.7 m below the top of Section KW. The contact with the overlying Yamama Formation could not be found in Section KW.

Section KP (24°24'6.40”N, 47°6'32.50”E; UTM: X = 713872, Y = 2700336; Figures 1, 2 and 7) has a thickness of 39.2 m, and represents a part of the Lower Sulaiy Sequence. The transgressive part of the sequence is formed by bioturbated bioclast-rich packstones that can be interpreted as tempestite deposits. Biostromes are present about 9 m below the MFI, which is characterized by a recessive unit formed by bioturbated mud- and wackestones. The regressive part of the sequence is formed by bioclast-rich packstones, which can be interpreted as storm bed deposits (tempestites). Towards the top of the section, bioturbation and destratification decreases.

Section AH (24°22';55.90”N, 47°7';417.90”E; UTM: X = 715184, Y = 2698187; Figures 1, 2 and 8) has a thickness of 93 m. The transgressive part of the Lower Sulaiy Sequence is mainly formed by bioclast-rich packstones, which are interpreted as tempestites. Towards the MFI a biostromal interval can be observed and destratification is caused by bioturbation. The regressive part of the sequence is dominated by bioclast-rich packstones and wacke-to-packstones, which are interpreted as bioturbated tempestites. In general, sections AH and KP show less rudstones and pack-to-grainstones or grainstones compared to sections DH and KW. It can be assumed that sections AH and KP were deposited in lower water-energy conditions in a slightly deeper water setting.

Ten lithofacies types have been identified within the Sulaiy Formation and three from the underlying Hith Formation (Figures 15 and Table 4). For each type, biofacies, ichnofacies (Seilacher, 2007) and stratofacies have been defined (Figures 16 to 28).

Lithofacies types within the Sulaiy Formation are commonly arranged in regular, cyclic patterns. A clear hierarchy of cyclicity can be observed, which is described below following the terminology of Kerans and Tinker (1997). The smallest cyclic units are usually meter-scale and are termed ″cycles″. They usually consist of a lower transgressive hemi-cycle, a maximum flooding interval, and an upper, regressive hemi-cycle. The cycles are grouped into the following ″cycle motifs″.

Description: This symmetrical cycle motif is usually 3–4 m thick (Figure 29). Offshoal and transition zone associated facies types such as laminated and bioturbated mudstones (LFT1), graded wackestones (LFT2) and bioturbated wacke-to-packstones (LFT3) dominate. The lower part of the cycle consists mainly of wackestones, which are inter-bedded with 5–10 cm-thick, graded pack- and wacke-to-packstone units. The wacke- and packstones contain shells, shell debris and gastropods and show intense bioturbation, which can lead to destratification. In some cases the burrows are filled-up with coarser material of the overlying packstones (tubular tempestites). Mudstones (LFT1) occur in the middle part of the cycle motif followed upwards by the succession of graded wackestones (LFT 2) and bioturbated wacke-to-packstones (LFT3).

Interpretation: Graded wackestones (LFT2) and bioturbated wacke-to-packstones (LFT3) mark the base of this cycle type. They can be interpreted as bioclast-rich distal tempestites, which were deposited under low-energy conditions, representing the transgressive hemi-cycle, following mudstones containing minor amounts of very fine shell debris. The mudstones were deposited under low-energy conditions and interpreted as the MFI. In the field the mudstone section can often be recognized by its lower resistance to weathering. The regressive hemi-cycle shows the same succession of facies types like the transgressive hemi-cycle but in a reversed order. The wackestones are harder and therefore more resistive to weathering processes.

Description: The offshoal to foreshoal cycle type has an average thickness of 4 m and shows a symmetrical pattern (Figure 30). The base of the cycle is dominated by packstones that contain shells and shell debris as well as peloids and show graded bedding with erosive bases (LFT6). They form amalgamated 5–10 cm thick layers. In some sections strong bioturbation can be observed which results in destratification (LFT5). These burrows are often filled-up with packstones. Wackestones with strong bioturbation follow in the vertical facies succession (LFT3). Mudstones (LFT1) with minor amounts of very fine shell debris mark the turning point of the cycle. The upper part of the cycle motif is represented through LFT3, LFT5 and LFT6. In the field, this cycle type can be easily recognized by its characteristic weathering profile where the mudstones build recessive units.

Interpretation: The basal graded packstones (LFT6) most likely represent tempestite deposits in a foreshoal environment. The packstones, together with upward-following lower-energy wackestones (LFT3) with abundant bioturbation and a decrease in grain size, are interpreted as the transgressive hemi-cycle. The MFI is assumed to be represented by bioturbated mudstones (LFT1). The regressive hemi-cycle shows the same facies stacking pattern as the transgressive hemi-cycle but in a reversed order.

Description: The transition zone to shoal margin cycle type has an average thickness of 5 m and shows an asymmetric pattern. At its base pack-to-grainstones (LFT8) with shell debris and peloids can be observed, followed by grain-, pack- and wackestones (Figure 31). Grading can be observed and the major components are shells, shell debris, bioclasts and peloids (LFT3, LFT5 and LFT6). The most open-marine part of this cycle is represented by biostromes with corals, gastropods, bivalves, echinoderm etc. Wacke- and packstones interbedded with minor 5 cm thick pack-to-grainstones layers (LFT3, LFT5 and LFT6) build the upper part of the cycle. The shoal margin associated facies is not as dominant as in the lower part of the cycle.

Interpretation: The transgressive hemi-cycle consists of basal well-sorted pack-to-grainstones (LFT8) with low-angle, cross-bedding, interpreted to be deposited in a shoal margin setting, followed by bioturbated wacke-to-packstones (LFT3), pack-to-grainstones (LFT5) and graded packstones/grainstones (LFT6), interpreted as tempestite deposits during high-energy events within a foreshoal environment. An MFI can be recognized by prominent biostromes. The regressive hemi-cycle is significantly thinner than the transgressive hemi-cycle and consists of LFT3, LFT5 and LFT6.

Description: The foreshoal to shoal cycle type is the most proximal cycle motif that could be observed within this study (Figure 32). The thickness of this asymmetric cycle type ranges between 2–3 m. The base of the cycle consists of 5–20 cm-thick, well-sorted, fine-to-medium arenite pack-to-grainstones and grainstones with well-developed erosive bases (LFT8). Shell debris, shells, small intraclasts, peloids and ooids are the major components. Low-angle, cross-bedding can be observed in the outcrop as well as in thin sections. This is followed by a rudstone (LFT7) with shells, gastropods, bioclasts, peloids and intraclasts. The upper part of the cycle is built-up by well-sorted grainstones with bed thicknesses of 10–20 cm. Some of these grainstone units are interbedded with thin mudstone units.

Interpretation: The foreshoal to shoal margin cycle motif is clearly dominated by the regressive hemi-cycle. The thin, basal pack-to-grainstones represent a shoal margin environment (LFT8). Bioclast-rich rudstones represent the MFI. These several dm-thick rudstones (LFT7) can be interpreted as proximal tempestites within a foreshoal setting. The dominating regressive hemi-cycle consists of well-sorted grainstones (LFT8).

Cycles are commonly stacked into cycle sets. In this study cycle sets are named as SCS, which stands for “Sulaiy Cycle Set” and are numbered from 1–15. Several motifs of cycle sets could be recognized as follows.

Description: The offshoal to shoal cycle set shows an asymmetric pattern with a dominating regressive hemi-cycle set. It has an average thickness of 10–12 m, and is usually built by up to 4 cycles (Figure 33). This cycle set represents the complete succession of observed facies types. Due to erosion, the offshoal to shoal cycle set is only present in the sections FI, NG and the hinterland of DH.

Interpretation: The transgressive hemi-cycle is interpreted as a sea-level rise with the MFI marked by bioturbated mudstones. The dominating regressive hemi-cycle shows a shallowing-upward trend associated with an increase of water energy, sorting and the deposition of oolitic grainstones with high-angle cross-bedding.

The offshoal to foreshoal cycle set is the most common one in the Sulaiy Formation. It can be found in both, the transgressive and regressive part of the composite sequence. There is a significant difference in the appearance and it can be subdivided into two subtypes.

Subtype 1: Within the Transgressive Part of the Composite Sequence

Description: Stacks of up to 4 cycles form the cycle set with an average thickness of 8–10 m (Figure 34). This cycle set can be observed in all studied sections of the Sulaiy Formation. Subtype 1 is present in the transgressive part of the composite sequence, which divides the Sulaiy Formation into two parts. It can be recognized by amalgamated tempestite beds. Bioturbation is present but has only a minor effect in terms of destratification. Another difference is the occurrence of thin (5–10 cm), but high water-energy event sheets (e.g. bioclast-rich rudstones or pack-to-grainstones).

Interpretation: The transgressive part of the cycle set is characterized by tempestites and can be interpreted as a sea-level rise. The occurrence of mudstones and bioturbated wackestones is interpreted as the MFI. A shallowing-upward trend can be observed in the dominating regressive part of the cycle set with a rise of water energy and increase of grain size associated with the deposition of tempestites.

Subtype 2: Within the Regressive Part of the Composite Sequence

Description: The offshoal to foreshoal cycle set that is typical for the regressive part of the composite sequence is formed by usually 3 cycles (Figure 35). Similar to Subtype 1, it is also formed by tempestites but the appearance in field sections is different. The amalgamated tempestite beds show intensive bioturbation, which partly results in destratification leading to a more nodular appearance.

Interpretation: The transgressive part of the cycle set is dominated by destratified tempestites and is interpreted as a sea-level rise. Bioturbated mudstones and bioturbated wackestones mark the MFI. A shallowing-upward trend is present in the dominating regressive part of the cycle set indicated by bioturbated tempestites with minor destratification.

Description: The shoal margin to offshoal cycle set usually consists of 2 cycles and has a typical thickness of 8 m (Figure 36). The transgressive part of the cycle set is characterized by the presence of oolitic grainstones with thin mudstone units on their tops. The regressive part of the cycle set is formed by tempestites, which are represented by oolitic pack-to-grainstones and bioclast-rich packstones and wackestones.

Interpretation: The transgressive part of the cycle set is interpreted as a sea-level rise associated with the creation of accommodation space, which results in the deposition of oolitic-peloidal grainstones. The MFI is marked by mudstones and wackestones, which can be interpreted as distal tempestites. A rise of water energy associated with increased grain size led to the deposition of more proximal tempestites during the regressive part of the cycle set.

The sequence shown in Enclosure I is a composite of sections DH and FI (after correlation). The typical oolitic-peloidal grainstones, which are characteristic for the top of the Sulaiy Formation, are not preserved at the Dahal Hit type locality. The Lower Sulaiy Sequence has a thickness of at least 135 m, composed of 12 cycle sets (SCS 1 to SCS 12). The lower sequence boundary of the Lower Sulaiy Sequence, the Sulaiy SB, is positioned at 101.0 m at the Dahal Hit type locality (Figure 4), and starts with the first evenly-bedded limestones above the breccia from the Upper Jurassic Hith Formation. The transgressive part of the Lower Sulaiy Sequence consists at its base of bedded tempestites. Towards the MFI biostromes can be observed, as well as a constant increase in bioturbation and a decline in component/grain size. The MFI is represented by intensive bioturbated mudstones. The MFI of the Lower Sulaiy Sequence contains Lower Berriasian MFS K10 at 39.8 m.

The lower part of the regressive part of the Lower Sulaiy Sequence is marked by nodular, partly destratified and bioturbated tempestites. In the upper part, the tempestites are composed of coarser material interpreted as deposition in a higher-energy, more proximal setting. Imbrication of up to 3–5 cm large clasts can be observed. The uppermost part is represented by an oolitic-peloidal shoal complex that can be observed in sections NG, FI, SI and the hinterland of DH. The shoal complex is insufficiently sampled for regional correlation and it may represent the lower part of a younger Upper Sulaiy Sequence (see below section titled “Correlation”).

The transgressive hemi-cycle is illustrated by Sulaiy Cycle Set 4 (SCS 4, Enclosure I) from sections DH, KW and AH. In Section DH, a higher amount of oolitic grainstones and little bioturbation is present. This can be related to deposition in a shallower-water environment compared to the sections KW and AH. These sections have consistently less ooids and more bioturbation, which leads to the slightly more nodular appearance of the bedding. It can be interpreted as deposition in a more distal setting compared to Section DH.

Within the MFI, Sulaiy Cycle Set 7 (SCS 7) shows an asymmetrical pattern, which is dominated by the transgressive part of the cycle set (Enclosure I). A cycle pinch-out can be observed and is highlighted in pink. The pinch out of the cycle reflects the proximal-distal trend from DH to AH, as sedimentation rates decline with increasing water depth.

Sulaiy Cycle Set 11 (SCS 11) shows an asymmetrical pattern, which is dominated by the regressive part of the cycle set (Enclosure I). SCS 11 in Section AH is thicker, which is probably related to a more distal position and therefore greater available accommodation space. SCS 11 shows a lateral facies change as biostromal boundstones occur only in sections DH and KW. These biostromes contain fossil assemblages that suggest a more proximal setting in a shallower and higher-energy environment.

Correlations based on the observed cyclicity are the key to assemble all the studied sections into a sequence-stratigraphic framework (Aigner, 1985; Aigner and Schauer, 1998; Homewood et al., 2000). Cycle-sets were chosen to correlate the studied sections (Traverse A–A', Enclosure II). The aim of 2-D correlations is to recognize the geometry and facies distribution of the original stratigraphic framework prior to compaction, dissolution or tectonic overprint (Kerans and Tinker, 1997). The maximum flooding surface has been chosen as datum.

The natural escarpment of the Sulaiy Formation is NW-orientated and represents in general the paleo-strike direction (Traverse B–B', Enclosure II). This is in accordance with the paleofacies map from Ziegler (2001). Six cycle sets (SCS 6–11) can be correlated between sections DH to FI, a distance of 75 km, showing no major facies changes and a ″layer-cake″-like appearance. The interpretation also includes the major facies types that are not exposed in all sections, like the Hith Formation anhydrites, the contact breccia from Section DH and furthermore shoal and shoal-margin facies that are only exposed in sections NG, FI, SI and HL 1 to HL 4.

As a transgression marks the beginning of the Sulaiy Formation, the flat relief of the Hith anhydrites was flooded leading to proximal tempestite deposits. Oolitic grainstones occur as well, but are not sufficiently thick to be considered as shoal or shoal-margin facies, but rather they can be interpreted as separate sheets. This succession is followed by tempestites with a decreasing grain size towards the MFI and increasing bioturbation. Below the MFI, biostromes occur in all the studied sections. The MFI is mud-dominated and appears as a recessive unit in the outcrop. The regressive part of the Sulaiy Sequence consists in large parts of bioturbated tempestites. Bioclastic rudstones and smaller biostromes indicate the transition into grain-dominated shoal margin and shoal facies.

To obtain information about geometries and facies changes it is important to create a cross-section oriented in a paleo-dip direction. A correlation between sections NG and AH would represent an orientation in the overall dip direction over a distance of 22 km. However, due to the outcrop conditions and a missing overlap no correlation between sections NG and AH could be established. As an alternative sections DH, KW and AH were chosen because they are oriented in an approximate dip direction (Traverse C–C', Enclosure II). Seven cycle sets can be correlated (SCS 4–10). No significant lateral facies changes can be observed between sections DH and KW as they are only 1.5 km apart. In comparison to Section AH, significant differences occur in SCS 4, 5 and 6. While these cycle sets contain dm-thick pack-, grain- and rudstones in sections DH and KW, Section AH is dominated by wacke- and packstones. In general, Section AH shows smaller grain sizes, no grainstones, only very few thin rudstones and few high-energy event deposits compared to sections DH and KW. This observation leads to the assumption that Section AH was deposited in a more distal environment. This interpretation indicates a facies change in the lower section (SCS 2-3). Proximal tempestites, marked in yellow, disappear towards Section AH and grade into finer wacke- and packstones. It is observed that the proportion of facies types (more distal) associated with the transition increases towards Section AH within the transgressive part of the Lower Sulaiy Sequence.

Detailed correlations of the shoal interval (SCS 13 and above) is more difficult. This is caused by observations of grainstones in this uppermost part of the Sulaiy Formation to be restricted to the sections HL, NG, FI and its vertical succession SI. Detailed facies correlations should not be based on this sparse information since the observed shoal facies might simply reflect less regional shallow-water sandy highs caused by landscape variations. Alternatively, these cycle sets may represent the lower part of the Upper Sulaiy Sequence. High-resolution correlation attempts are therefore affected by major uncertainties. The overall observation of the existence of high-energy, shallow-water facies in the uppermost Sulaiy Formation remains unaffected.

Our analysis of the outcrops of the Upper Tithonian–Lower Berriasian Sulaiy Formation in central Saudi Arabia indicated that this formation contains 10 lithofacies types (LFT). They are grouped into lithofacies associations (LFA) forming a carbonate ramp depositional system. The most abundant facies types are associated with a foreshoal setting. Three facies types that may contain reservoir properties are: (1) oolitic cross-bedded grainstones (LFT 9) with moldic and inter-particle porosity; (2) biostromal boundstones (LFT4) with moldic porosity; and (3) bioclast-rich packstones and pack-to-grainstones (LFT6) with inter-particle porosity. The facies distribution is controlled by the geometry of a shallow-marine carbonate ramp.

At Dahal Hit, we documented the transition between the Sulaiy Formation and underlying Tithonian Hith Formation. This is the only locality where the transition is exposed and we identified 3 lithofacies types in the Hith Formation. We suggest that the lowermost part of the Sulaiy Formation at Dahal Hit was deposited at the same time as the Manifa reservoir in eastern Arabia as part of a regional Late Tithonian transgression containing maximum flooding surface MFS J110 (147 Ma).

Three orders of cycle hierarchy were identified:

• Cycles: offshoal to transition zone, offshoal to foreshoal, transition zone to shoal margin and foreshoal to shoal margin ranging from 2–5 m in thickness.

• Cycle sets (Sulaiy Cycle Sets = SCS): offshoal to shoal cycle set, offshoal to foreshoal cycle set and shoal margin to offshoal cycle set ranging from 8–12 m in thickness.

• Sequences: a transgressive-regressive Lower Sulaiy Sequence containing Lower Berriasian MFS K10, and possibly the lower part of an Upper Sulaiy Sequence.

The cycles can be correlated where the studied sections are in close vicinity (< km). Cycle sets can be correlated between the studied sections at distances of several kilometers. Lateral facies changes between sections DH, KW and AH indicate a deepening trend in a dip direction towards the east. Biostromal boundstones occur in SCS 7 below the MFI (MFS K10) and are therefore a useful marker for correlation purposes. SCS 12–15 are difficult to correlate; they can only be found as a complete succession in Section NG, whereas sections FI and HL 1–4 only show partial exposures.

The authors gratefully thank GIZ International Services/Dornier Consulting in Riyad for their help and support to make the field work in Saudi Arabia possible, especially with logistics, technical equipment and their geological experience and recommendations. We also thankfully acknowledge Wintershall for their support with this study. Per Jeisecke (University of Tübingen) is thanked for thin section preparation and the whole Sedimentary Geology Research Group (University of Tübingen) for technical discussion and ideas for this paper. Access to WellCAD was kindly provided by ALT (Luxemburg). Two anonymous referees are thanked for their important comments that have significantly improved the manuscript. GeoArabia Editor, Yves-Michel Le Nindre, is thanked for contributing his vast geological knowledge, as well as that of Denis Vaslet and Patrick Andreieff, and for accepting the invitation by the other authors to be a coauthor. We also thank Wyn Hughes for helpful discussion of the Sulaiy-Hith transition. GeoArabia’s Editor-in-Chief, Moujahed Al-Husseini, and Assistant Editor, Kathy Breining, are thanked for editing and proof-reading the manuscript, and working with Production Co-manager, Arnold Egdane, who designed the paper for press. We much appreciate the huge efforts of the outstanding GeoArabia team, and in particular that of Moujahed Al-Husseini to bring this paper into its present shape.

Philipp Wolpert studied Geology at the University of Tuebingen (Germany) and at the University de los Andes (Venezuela), with focus on Sedimentology. He received his Diploma in 2010 about the Lower Cretaceous Sulaiy Formation in Saudi Arabia. After graduation he joined Fronterra Integrated Geosciences in Aberdeen, Scotland, where he worked two years intensively with borehole images and well logs on conventional and unconventional reservoir studies. In 2013 he started to work for Shell P&T in Rijswijk, the Netherlands, and now founded his own company where he works as an independent consultant. Philipp is also a member of EAGE, PESGB, AAPG and an instructor at EAGE’s geology bootcamp.

phil.wolpert@pj-geology.com

Martin Bartenbach studied Geology at the University of Karlsruhe and at the University of Tuebingen (Germany). His Diploma Thesis (2008) was about facies analysis and 3-D modeling of Upper Jurassic carbonates and its resource- and reservoir geology implications in the Blaubeuren area in SW Germany. In his PhD Thesis, in collaboration with Wintershall Holding GmbH, he developed a systematic, multi-scale workflow for carbonate reservoir characterisation based on the Lower Cretaceous Sulaiy carbonates of the Middle East. In 2013 Martin joined Statoil ASA where he is currently working as a Senior Reservoir Geologist.

mbartenb@gmail.com

Michael-Peter Suess (Peter) studied Geology at the University of Bonn and Clausthal-Zellerfeld (Germany), with focus on Applied Geophysics and Structural Geology. He received his Diploma in 1992 with a thesis about the Blue Road Geotraverse, a crustal transect in Fennscandia. After graduation Peter continued at the University of Bonn in the Sedimentology group and received his PhD on the sequence-stratigraphic development of the Ruhr Basin (Germany) in 1996. After two more years as Post-Doc in Bonn, he worked for two years as Research Fellow and Associated Researcher at the Structural Geology group at Harvard (USA). In 2000 he joined the University of Tuebingen (Germany) as Assistant Professor and received the degree of Privatdozent (PD) in 2005. Since 2006, Peter works for Wintershall, Germany’s largest E&P company in Kassel. He currently heads an applied integrated subsurface R&D team.

suess@uni-tuebingen.de;

michael-peter.suess@wintershall.com

Randolf Rausch studied Geology and Hydrogeology at the University of Stuttgart and the University of Tuebingen (Germany), where he received his PhD in 1982. After working for a consulting company he joined the Geological Survey of Baden-Württemberg, Germany, where he was involved in many consulting and research projects. From 2003 to 2004 he headed the project “Groundwater Resources Management” at the Ministry of Water & Irrigation in Jordan, commissioned by the German Federal Institute for Geosciences and Natural Resources (BGR). From 2004 to 2014 he was Technical Director for the project “Water Resources Studies” in the Kingdom of Saudi Arabia, carried out by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH for the Ministry of Water & Electricity. The project’s main focus was the investigation of the groundwater resources on the Arabian Platform.

Since 2015 Randolf is a Professor at Technische Universität Darmstadt, Germany. He has developed many computer programs related to groundwater flow and solute transport modeling, and has authored 5 books on the subject. His current field of research is the hydrogeology of arid environments. In 1990 Randolf was awarded the “German University Software-Prize” from the Federal Minister of Research for the best simulation program in the field of engineering science. He received the “Abraham-Gottlob Werner Medal” in 2009 from the German Society of Geosciences for his achievements in groundwater sciences and was awarded the “Medal of Economics” in 2013 from the state of Baden-Württemberg for outstanding achievements in the field of economy.

randolf_rausch@yahoo.de

Thomas Aigner studied Geology and Paleontology at the Universities of Stuttgart, Tuebingen/Germany and Reading/UK. For his PhD dissertation on storm depositional systems (1985) he worked at the Senckenberg-Institute of Marine Geology in Wilhelmshaven (Germany) and spent one year at the University of Miami in Florida (USA). He then became an Exploration Geologist at Shell Research in Rijswijk/Holland and Houston/Texas focussing on basin analysis and modelling (1985–1990). Since 1991 Tom has been a Professor and Head of the Sedimentary Geology Group at the University of Tuebingen. In 1996 he was a “European Distinguished Lecturer” for the AAPG. His current projects focus is on sequence stratigraphy and reservoir characterisation/modelling in outcrop and subsurface.

t.aigner@uni-tuebingen.de

Yves-Michel Le Nindre has been contributing to Middle East geology since 1979, particularly in Saudi Arabia. After his PhD in marine Biology and Sedimentology in 1971, he received his Doctorate of Sciences from the University of Paris (France) in 1987 with a dissertation on the ‘Sedimentation and geodynamics of Central Arabia from the Permian to the Cretaceous’. Yves-Michel joined the Bureau de Recherches Géologiques et Minières (BRGM) in 1973. He was involved in many research and consulting projects in France and abroad (Saudi Arabia, Oman, Kuwait, U.A.E. Jordan, Iran, Tunisia, Morocco, Bolivia, Ethiopia, India, Russia), for sedimentary basin analysis and modeling, especially in hydrogeology. As a Sedimentologist, Yves-Michel worked in France on present-day littoral integrated management. Since 2000, he has been involved in international projects for CO2 storage, working with EU state members and CSLF countries (Russia, China, Saudi Arabia) as Expert or Project Manager and directed two PhD theses. Since July 2012, Yves-Michel is retired from BRGM, notwithstanding still continuing a scientific and consulting activity in his preferred domains of expertise. He is a member of the EAGE, ASF and of the GeoArabia Editorial Board. Yves-Michel is so far author or co-author of 63 publications related to Saudi Arabia.

yc.lenindre@wanadoo.fr