Sequence Stratigraphy and Rudist Facies Development of the Upper Barremian-Lower Cenomanian Platform, Northern Sinai, Egypt

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1 Vol. 92 No. 1 pp Feb Sequence Stratigraphy and Rudist Facies Development of the Upper Barremian-Lower Cenomanian Platform, Northern Sinai, Egypt Yasser SALAMA 1, 2, *, Michael GRAMMER 2, Shaban SABER 1, Soheir EL-SHAZLY 1 and Gouda ABDEL-GAWAD 1 1 Beni-Suef University, Faculty of Sciences, Geology Department, Egypt. 2 Boone Pickens School of Geology, Oklahoma State University, Stillwater, Oklahoma, United States. Abstract: The Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian-middle Albian) and the Halal (middle Albian-lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian-lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium-scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist-dominated ramp. Key word: Cretaceous, sequence stratigraphy, rudists, Sinai, Egypt 1 Introduction Barremian-Cenomanian shallow water carbonate successions are exposed in the Maghara and Risan Aneiza areas (Fig. 1) in northern Sinai (Bachmann et al., 2010). The age of the basal contact of the marine Cretaceous deposits with the underlying fluvial sandstone of the lower Cretaceous Malha Formation is time-transgressive from north to south Egypt (Table 1). This contact is considered to be upper Barremian or upper Aptian in northern Sinai (El-Araby, 1999; Bachmann et al., 2003; Abu-Zied, 2008), and upper Albian in northeastern Sinai (Lüning et al., 1998; El Qot, 2006; Ayoub-Hannaa et al., 2013). Several authors have placed the Albian-Cenomanian boundary in the south between the fluvial sandstone of the Malha Formation and the overlying marine deposits (Farag and Shata, 1954; Kora and Genedi, 1995; Issawi et al., 1999). Moreover, other publications projected this boundary into the Cenomanian in central Sinai and the northern Eastern Desert (Awad and Fawzy, 1956; Kuss, 1992; Kassab and Zakhera, 1999; Abdel-Gawad et al., 2007; El Qot, 2010; Gertsch et al., 2010; Nagm et al., 2010). During late Barremian late early Aptian time, the facies development on the Levant Platform (Northern Sinai and Northern Israel) was influenced by extensional movements along the Late Jurassic NW-dipping extensional normal faults related to the early stage of Syrian Arc rifting (Bachmann et al., 2010). This tectonic activity terminated during the early late Aptian, the former fault-controlled sub-basins becoming inactive and being converted to shallow ramp architecture. Since the studies of Douvillé (1916) and Moon and Sadek (1921), additional studies were carried out on the stratigraphy and paleontology of the exposed Lower Cretaceous rocks of northern Sinai (Farag, 1947; Said and Barakat, 1957; Bartov et al., 1980; Philip et al., 1988; Hegab et al., 1989; Kuss, 1992; Abdallah et al., 1996; Bachmann and Kuss, 1998; Aly and Abdel-Gawad, 2001; Bachmann et al., 2003; Aly et al., * Corresponding author. yasser.salama@science.bsu.edu.eg, yasserf@okstate.edu 2018 Geological Society of China

2 Feb Vol. 92 No Fig. 1. Simplified geological map of north Sinai (modified from Geological survey of Egypt (1992) mm ( DPI)). 2005; Abu-Zied, 2007, 2008). However, there have been few attempts to interpret the Lower-Middle Cretaceous strata in terms of sequence stratigraphy in northern Sinai. The aim of this work is to introduce a detailed sequence stratigraphic framework of the mixed clastic-carbonate ramp from the Barremian-Cenomanian successions in northern Sinai. In addition, a further objective of this paper is to provide more information on the distribution of

3 288 Vol. 92 No. 1 Feb Table 1 Correlation of the rock units from Sinai and Eastern Desert Chronostratigra Sinai phy Ora shales Abu Qada Abu Qada Fm. Unit B Fm. U Galala Fm. Cenomani Halal Fm. Galala Fm. an Raha Fm. M Hazera L Fm. Halal Fm. Abu Qada Fm. Raha Fm. Halal Fm. Halal Fm Eastern desert Galala Fm. Maghra El Hadida Fm. Galala Fm. Malha Fm. Malha Fm. Albian Aptian U M L U L Hatira Fm. Risan Aneiza Fm. Malha Fm. Malha Fm. Unit A Malha Fm. Risan Aneiza Fm. Risan Aneiza Fm. Malha Fm. U Barremian L reference Malha Fm. Bartov Hassan et al et al., 1992 Kora and Genedi, 1995 Issawi Bachmann et al., 1999et al., 2003 El Qot Malha Fm. Abu-Zied, 2008 Gertsch et al., 2010 G Raghawi This work G Yelleg This work Abdel- Nagm Gawad et al., 2010 et al., 2007 the rudists and their associated fauna in the context of a sequence stratigraphic framework. 2 Materials and Methods Two complete sections were selected that span the upper Barremian-Cenomanian interval in northern Sinai. The studied sections at Gabal Raghawi and Gabal Yelleg are exposed on elongated anticlinal structures that are located in the Syrian Arc Fold Belt (Fig. 1). The two sections were measured in the field, including a description of lithology, sedimentary patterns and fossil content. Sedimentological features and macrofossil content have been fully documented in the field. Sampling for microfacies analysis has been conducted systematically at least 1 sample per 2 m or less. The macrofossils, especially the rudists and ammonites, have been collected bed-by-bed from the studied sections and are identified to provide more biostratigraphic information. Two hundred and fifty thin sections were used to describe the various microfacies for paleoenvironmental interpretations of the studied sections. Discontinuity surfaces are integrated with the lateral facies distributions and the vertical facies successions in order to interpret the sequence stratigraphy. 3 Stratigraphy Two rock units are described from base to top: the upper Barremian-middle Albian Risan Aneiza Formation and the middle Albian-Cenomanian Halal Formation (Figs. 2 4). 3.1 Risan Aneiza Formation (upper Barremian-middle Albian) This formation is about 230 m thick (Fig. 2) and is characterized by sandstone, shale, and ferruginous oolitic limestone intercalated with fossiliferous marl and limestone (Fig. 4a). The rudist Horiopleura sp. is recorded for the first time from the base of this rock unit (Fig. 4b). The lower part spans the upper Barremian through lower Aptian, based on ammonites (Deshayesites deshayesi) and benthic foraminifers (Palorbitolina lenticularis, Praereticulinella cuvillieri, Pseudocyclammina lituus, and Istriloculina eliptica). The middle part of this rock unit is characterized by the first appearance of radiolitid rudists, Eoradiolites plicatus, in association with codicean algae (Lithocodium aggregatum, Bacinella irregularis), and the benthic foraminifers (Palorbitolina lenticularis, Everticyclammina sp., Orbitolina (Mesorbitolina) parva, and Orbitolina (Mesorbitolina) texana). Ammonites are abundant and are represented by Acanthohoplites nolani, Knemiceras gracile and Knemiceras syriacum. The upper part of this formation is mainly thick-bedded, crossbedded sandy limestone with thin shale and marl intercalations. Iron-ooids, quartz and coralline red algae (Sporolithon sp.) are more abundant. This part is topped by the red dolomitized Actaeonella bed, which is rich in Actaeonella delgadoi. The top of this Actaeonella bed represents the contact between the Risan Aneiza Formation and the overlying Halal Formation (Fig. 4c).

4 Feb Vol. 92 No Fig. 2. Stratigraphic section showing lithology, facies, rudist levels and associated fauna, depositional environments, and depositional sequences at the Lower Cretaceous Risan Aneiza Formation in Gabal Raghawi, north Sinai.

5 290 Vol. 92 No. 1 Feb Halal Formation (middle Albian Cenomanian age) The Halal Formation is used here to describe the middle Albian to Cenomanian strata. The Albian rocks of the Halal Formation comprise 187 m and 125 m at Gabal Raghawi and Gabal Yelleg, respectively (Fig. 4d). This rock unit overlies the Risan Aneiza Formation at Gabal Raghawi and it overlies the fluvial Malha Formation at Gabal Yelleg (Fig. 3). At Gabal Raghawi, Albian strata of the Halal Formation are made up of rudist-bearing limestone intercalated with dolomitic limestone, marl and dolostone intercalations (Fig. 3). The rudist species are Archaeoradiolites sp., Neocaprina raghawiensis, Neocaprina sp., Sellaea sp., Eoradiolites liratus, Eoradiolites plicatus, Agriopleura cf. marticenisis, and Ichthyosarcolites sp. (Figs. 4e to g). The Cenomanian deposits at Gabal Raghawi measured about 45 m thick and consist of recrystallized rudistbearing limestone with subordinate intercalations of marl that comprise the lower part of the Halal Formation (Fig. 3). These deposits contain Eoradiolites liratus and Orbitolina (Conicorbitolina) conica. However, the remaining strata of the Halal Formation do not occur at Gabal Raghawi but are exposed in nearby sections at Gabal El Mistan and Um Asagil in the Maghara area (Fig. 1). Although a complete Cenomanian succession is recorded at Gabal Yelleg, this study has focused on the lower part of the Cenomanian succession that composed of sandstone and marl rich in oysters (Fig. 3). 4 Rudist Distributions Rudists are abundant in the upper Barremian-lower Cenomanian deposits of northern Sinai in numerous levels associated with diverse fossil groups. At the Gabal Raghawi section, nine rudist levels are recorded in the upper Barremian through lower Cenomanian (Figs. 2 3), two of which are in the upper Barremian-lower Albian. The lowermost rudist level (GR I) is about 9 m above the base of the Risan Aneiza Formation and is characterized by rare Horiopleura sp. and Toucasia carinata, which are associated with Palorbitolina lenticularis. Level GR II at Gabal Raghawi hosts the first appearance of radiolitid rudists about m above the base of the Risan Aneiza Formation. Eoradiolites plicatus is associated with Lithocodium aggregatum, Bacinella irregularis, and the benthic foraminifers Palorbitolina lenticularis and Orbitolina (Mesorbitolina) parva. The majority of the rudists at Gabal Raghawi are in the middle-upper Albian deposits. Six rudist levels are welldeveloped, and most of them are dominated by caprinids. Level GR III is at m above the base of the Risan Aneiza Formation and it is composed mainly of Eoradiolites plicatus, Neocaprina raghawiensis, Neocaprina sp., and Sellaea sp. together with Orbitolina (Mesorbitolina) texana, Orbitolina (Mesorbitolina) subconcava and Solenopora sp. The requieniid Toucasia sp. is present in GR IV level at m above the base of the Risan Aneiza Formation. Neocaprina raghawiensis, Neocaprina sp., Sellaea sp. Archaeoradiolites sp. and Eoradiolites liratus are abundant in the thick limestone beds of level GR V at m above the base of the Risan Aneiza Formation. Furthermore, Eoradiolites liratus occurs in two limestone beds at GR VI level at m above the base of the Risan Aneiza Formation. In addition, Mathesia darderi, Agriopleura cf. marticensis and Ichthyosarcolites sp. are in life position in the marly limestone of level GR VII about 369 m above the base. Ichthyosarcolites sp. is also found in the uppermost level GR VIII at m of the Albian deposits. The uppermost part of the Gabal Raghawi succession is characterized by dolomitic and massive limestone with abundant Eoradiolites liratus, which represents the lower Cenomanian rudist level GR IX at m above the base of the Risan Aneiza Formation. At Gabal Yelleg in northern Sinai, two rudist levels (GY I-II) are recorded from the Albian-lower Cenomanian succession. The first level GY I is m above the base and it is represented by three rudist-bearing limestone beds and only Eoradiolites liratus occurs in them. Level GY II consists of bioclastic limestone with Ichthyosarcolites sp. and Mathesia darderi and it is recorded about m above the base. 5 Facies and Depositional Environments Twelve microfacies have been defined by petrographic analysis: 11 carbonates and one siliciclastic. The carbonate microfacies are further divided into 19 submicrofacies based upon variations in the relative amounts of different skeletal and non-skeletal components (Table 2). Based upon the observed microfacies, the stratigraphic section was likely deposited on a low-angle carbonate ramp (Fig. 5). The microfacies have been deposited in nearshore to deeper open-marine environments (Fig. 5). These facies and their depositional environments are summarized in Table 2 and Figs. 2 3, 5, 6 9. In general, rudists inhabited shallow marine water with favorable conditions of food supply, low energy level, light and circulation (Aly et al., 2005). However, the variations in textures and the associated biota suggest that water energy; paleo-topography and sea level fluctuations

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7 292 Vol. 92 No. 1 Feb Fig. 4. (a), The lower part of the Lower Cretaceous Risan Aneiza Formation, Gabal Raghawi. (b), Horiopleura sp.; anteriorposterior longitudinal section in upright position, Late Barremian-Early Aptian, Risan Aneiza Formation at Gabal Raghawi, north Sinai (Sample no. 6). (c), The contact between the Risan Aneiza Formation and Halal Formation occurs at dolomitized Actaeonella bed represented the sequence boundary 6. (d), Field photo for the Albian-Cenomanian Halal Formation at Gabal Yelleg. (e), Bedding plane view of Neocaprina sp. and Neocaprina raghawiensis in the rudist level V at Gabal Raghawi section, north Sinai; (pen scale 12 cm). (f), Rudist-bearing limestone with random sections in Eoradiolites liratus shells of the rudist level VI at Gabal Raghawi section, north Sinai (pen scale 15 cm). (g), Bedding plane view of Agriopleura cf. marticensis. Late Albian, Halal Formation, Gabal Raghawi, north Sinai (Pen scale is 12 cm).

8 Feb Vol. 92 No Table 2 Summary of microfacies and depositional environments for the Upper Barremian-Lower Cenomanian deposits at Gabal Yelleg and Gabal Raghawi, north Sinai. Microfacies types Submicrofacies types Common components and diagnostic features Depositional environments MFT 1 Dolostone (Fig. 6a) No marine biota. High occurrence of dolomites and Fluvial and peritidal facies ferruginous crust. MFT 2 Ferruginous dolomitic quartz arenite (Fig. 6b) Thin laminated, cross-bedded, wave ripple, herringbone cross-lamination, fossiliferous. Fluvial and Siliciclastic shoreface MFT 3 Iron-ooids packstone/grainstone MFT 4 Benthic foraminifers wackestone/packstone MFT 5 Bioclastic peloidal packstone/ MFT 6 Bioclastic intraclastic packstone/grainstone MFT 7 Bioclastic packstone/grainstone MFT 8 Bioclastic Oolitic grainstone (Fig. 7f) MFT 9 Bioclastic rudstone MFT 10 Rudists bafflestone/floatstone (Fig. 8d) MFT 11 Orbitolina packstone SFT 3a Bioclastic oolitic iron-ooids packstone/grainstone (Fig. 6c) SFT 3b Cyanobacterium iron-ooids aggregates packstone (Fig. 6d) SFT 4a Miliolids wackestone (Fig. 6e) SFT 4b Bioclastic benthicforaminifers wackestone/packstone (Fig. 6f) SFT 6a Ooids bioclastic intraclastic packstone /grainstone (Fig.7a) SFT 6b Iron-ooids bioclastic intraclastic packstone/grainstone (Fig. 7b) SFT 7a Dolomitic quartz bioclastic grainstone (Fig. 7c) SFT 7b Bioclastic red algae grainstone (Fig. 7d) SFT 7c Oolitic peloidal Orbitolina packstone (Fig. 7e) SFT 9a Rudist rudstone SFT 9b Calcareous algae-benthic foraminifera-oyster rudstone (Fig. 8a) SFT 9c Bioclastic dasycladaceanudoteacean algae Rudstone (Fig. 8b) SFT 9d Dolomitic gastropods rudstone (Fig. 8c) SFT 11a Lithocodium aggregatum- Orbitolina packstone SFT 11b Gymnocodiaceanudoteacean algae-orbitolina packstone SFT 11c Glauconitic dolomitic Orbitolina packstone (Fig. 8e) MFT 12 Planktic foraminifers SFT 12a Planktic foraminifersbioclastic-udoteacean algae bioclastic mudstone-packstone packstone/wackestone SFT 12b Planktic foraminifers- Orbitolina mudstone/wackestone (Fig. 8f) SFT 12c Planktic foraminifers mudstone/wackestone (Fig. 8g) Dominant iron-ooids, aggregates, carbonate ooids, peloids, bioclasts, cross-bedded. Dominant iron-ooid aggregates, cyanobacterium, solenoporacean red algae. Dominant miliolids and ostracodes Dominant benthic foraminifers, bivalve, echinoids, dasyclad and udoteacean algae. Microencrusters and bioturbation are common. Dominant peloids and bioclasts. Echinoids, bivalve, gastropods, benthic- and planktic foraminifers, bryozoa and calcareous algae are common. Ooids, intraclasts, quartz and glauconite are also present. Dominant intraclasts and bioclasts (rudist, gastropods, echinoids, calcareous algae and benthic foraminifers). Frequent ooids and peloids. Rare quartz and glauconites, cross-bedded Dominant intraclasts, bioclasts and iron-ooids. Bioclasts are benthic foraminifers, echinoids, bivalves, bryozoa, serpulids and calcareous algae. Rare quartz and glauconite. Siliciclastic shoreface Protected lagoon Protected lagoon Open lagoon Open lagoon, high energy shoal and fore-slope to deep open marine. high energy subtidal shoal and back-shoal high energy subtidal shoal and back-shoal Dominant quartz, oysters, gastropods, echinoids, udoteacean high energy subtidal shoal and red algae. Rare intraclastics and glauconites. Dominant solenoporoid red algae. Oyster, agglutinated foraminifers, dasyclad and udoteacean algae are also present. high energy subtidal shoal Cross-bedded. Dominant orbitolinid foraminifers, ooids and peloids. Open lagoon and shallow Echinoids, gastropods, benthic foraminifers and calcareous subtidal back-shoal algae are present. Dominant ooids. Oyster fragments, gastropods, echinoids, high energy subtidal shoal benthic foraminifers, calcareous algae, quartz and glauconites are also present. Dominant rudist fragments Dominant oysters, echinoids, calcareous algae, bryozoans, benthic- and agglutinated foraminifers. Rare glauconite and quartz. Dominant dasyclad and udoteacean algae. Echinoids, bivalves, red algae, benthic- and agglutinated foraminifers are present. Dominant gastropods. Quartz, Glauconite and peloids are also present Dominant in-situ rudists high energy subtidal shoal Rudist biostrome Dominant orbitolinids, lituolinid foraminifers, Lithocodium and Bacinella. Echinoids, udoteacean algae, peloids and Rudist biostrome intraclasts. Dominant orbitolinids, gymnocodicean and udoteacean algae. Echinoids, bivalves, gastropods, red algae, bryozoans, benthic- and planktic foraminifers are present. Dominant orbitolinids, echinoids and glauconite. Peloids, iron-ooids and intraclasts are rare. Dominant udoteacean algae, echinoids and planktic foraminifers. molluscs, red algae, bryozoa, benthic foraminifers and oncoids are present. Dominant orbitolinids and planktic foraminifers. Echinoids, bivalves, ostracodes, biserial foraminifers and calcispheres are present. Dominant planktic foraminifers, calcispheres and echinoids. Fore-slope to deep open marine Deep open marine were controlling factors for the gradient change observed in the rudist facies (Moro et al., 2016; Du et al., 2015). In the study area, the rudist facies can be subdivided into four rudist subfacies, which are defined by bafflestone, rudstone and floatstone textures (Figs. 2 3). The first subfacies is a requieniid- polyconitid rudist bafflestone/packstone that is dominated with in-situ Toucasia sp. and Horiopleura sp., with borings commonly

9 294 Vol. 92 No. 1 Feb Fig. 5. Schematic diagram showing a general depositional setting on a low angle ramp mm. distributed on the valves (Fig. 9a). The space between the rudist shells, the borings and the shell cavity are filled with peloids and ooids. The borings are syndepositional and likely preceded the transport of skeletal and nonskeletal components by waves to the rudist biostromes (Fig. 9a). These biostromes were deposited during the high energy episode of sea level regression (Fig. 9a). The second characteristic rudist subfacies are radiolitid bafflestone/floatstones dominated by in-situ rudists with open fabrics. The micro-encrusters such as microbial and algal-encrustations are widespread (Fig. 9b). Large oncoids with rudist fragment nuclei and Bacinella- Lithocodium laminations are also widespread (Fig 9b). The association of the rudists and micro-encrusters is interpreted as small biostromes deposited in very shallow, well-oxygenated environments (Pittet et al., 2002). Moreover, the open fabrics between rudists indicate isolated biostromes in restricted environments for this facies (Sanders, 1996). The third subfacies is Toucasia bafflestone, which is dominated by complete valves of requieniid rudists (Toucasia sp.). The inner aragonitic layer of the rudist shell is replaced by blocky calcite, and the outer foliated layer is calcite (Fig. 9c). The matrix is mainly lime mudstone with abundant benthic foraminifers, rudist fragments and rare dasyclad algae (Fig. 9c). This facies is dominated by low energy micrite and benthic foraminifers. We interpret it as an isolated biostrome developed in the back-reef environment. The fourth rudist subfacies is a radiolitid-caprinid bafflestone that consists of in-situ whole caprinids (Neocaprina sp.) and radiolitid rudists (Eoradiolites plicatus and Eoradiolites liratus). Micrite, micritic peloids and bioclastic fragments fill the rudist shell cavities (Fig. 9d). The rectangular cellular structures of the rudists are well-preserved in the outer layer, whereas the inner layer is recrystallized into sparry calcite. The micritic agglutinate orbitolinids and peloids are locally abundant (Fig. 9d). The high degree of fragmentation of the rudist shells supports the interpretation that this facies was close to the rudist biostrome crest. 6 Sequence Stratigraphy The aim of this part is to construct high-resolution sequence stratigraphic frameworks of the studied sections. The systems tracts recognized in the study area are lowstand systems tract (LST), transgressive systems tract (TST) and highstand systems tract (HST). The principles of sequences in this study follow the concepts that were proposed by Strasser et al. (1999). The different scale sequences may have resulted from fluctuating eustatic sea levels and local tectonics. The discontinuity surfaces (hardground and exposure surfaces) that were recorded during the field work (i.e. paleosol, ferruginous hard crusts), combined with the vertical facies evolution and diagenetic features, are criteria to recognize the sequence boundaries (SB). The facies beneath the discontinuity surfaces has been selectively dissolved due to meteoric diagenesis. Moreover, the major facies shifts from shallower to deeper or from continental siliciclastic to marine carbonate facies

10 Feb Vol. 92 No Fig. 6. Photomicrographs of facies types at the Lower Cretaceous rocks of Gabal Raghawi. (a), Dolostone (MFT 1), fine to medium, idiotopic with cloudy cores and clear rims dolomite rhombs. Scale bar = 500 µm, (sample no. 47). (b), Ferruginous dolomitic quartz arenite (MFT 2) with sand-sized quartz grains and iron-ooids. Scale bar = 500 µm, (sample no. 51). (c), Bioclastic oolitic iron-ooids packstone/grainstone (SFT 3a) with iron-ooids, aggregates, small bivalve fragments and echinoids. Scale bar = 500 µm, (sample no. 52). (d), Cyanobacterium iron-ooids aggregates packstone (SFT 3b) with biogenic encrustation of the iron-ooid aggregates by cyanobacterium Girvanella problematica. Scale bar = 500 µm, (sample no. 13). (e), miliolids wackestone (SFT 4a) with miliolids in muddy substrate. Scale bar = 500 µm, (sample no. 89). (f), Bioclastic benthic foraminifers wackestone/packstone (SFT 4b) with dasyclad green algae Montiella elitzae, benthic foraminifers and serpulids encrusting on bivalve fragment. Scale bar = 1 mm (sample no. 43). indicate sequence boundaries. 6.1 Risan Aneiza Formation sequences (late Barremian -middle Albian age) In the Lower Cretaceous Risan Aneiza Formation at Gabal Raghawi, six sequence boundaries (SB1-SB6) and five third order sequences are recognized (Fig. 2) Sequence 1 (late Barremian-early Aptian age) This sequence is in the lower part of the Risan Aneiza Formation at Gabal Raghawi. It represents the late Barremian to early Aptian transgression relative to the underlying non-marine sandstone of the Malha Formation with subaerial exposure features at the contact. Two medium-scale sequences are superimposed on the large-

11 296 Vol. 92 No. 1 Feb Fig. 7. Photomicrographs at Gabal Raghawi section. (a), Ooids bioclastic intraclastic packstone/grainstone (SFT 6a) with intraclastics and rudist fragment. Scale bar = 500 µm, (sample no. 37). (b), Iron-ooids bioclastic intraclastic packstone (SFT 6b) with red algae, echinoids, intraclastics and iron-ooids; the dolomitization affected the cement as well as the grain margins. Scale bar = 500 µm, (sample no. 33). (c), Dolomitic quartz bioclastic grainstone (SFT 7a) with red algae, bivalves, gastropods, intraclasts, quartz, oncoids and micritized peloids. The cement is highly dolomitized. Scale bar = 1 mm, (sample no. 57). (d), Bioclastic red algae grainstone (SFT 7b) with red algae and bivalves. The cement is drusy calcite and dolomites. Scale bar = 500 µm, (sample no. 56). (e), Oolitic peloidal Orbitolina packstone (SFT 7c) with large orbitolinid foraminifers, micritized bioclasts and peloids. Scale bar = 1 mm, (sample no. 5). (f) Bioclastic oolitic grainstone (MFT 8) with concentric ooids, echinoids and gastropods. Scale bar = 500 µm, (sample no. 35). scale sequence 1 (Fig. 2). SB1: The basal sequence boundary (SB1) is the unconformity between the Malha and Risan Aneiza formations. This unconformity is characterized by the change from fluvial sandstone to marine facies with the presence of a paleosol horizon containing plant remains and iron oxides. TST: After a period of subaerial exposure, the gradual rise of relative sea level is reflected by deposits of inner ramp facies. The TST is about 9 m thick, consisting of a retrogradational facies belt. It is composed of bioclastic benthic foraminiferal wackestone/packstone (SFT 4b), iron-ooid bioclastic intraclastic packstone/grainstone (SFT 6b), shale, and mudstone/wackestone facies (Fig. 2) with open marine fauna (coral, echinoids, benthic and planktic foraminifers).

12 Feb Vol. 92 No Fig. 8. (a), Calcareous algae-benthic foraminifera-oyster rudstone (SFT 9b) with udoteacean algae Arabicodium sp. and oyster bivalves. Scale bar = 500 µm, (sample no. 76). (b), Bioclastic dasycladacean-udoteacean algae rudstone (SFT 9c) with udoteacean algae Boueina sp. and dasycladacean green algae Montiella elitzae, bivalves, echinoids, benthic foraminifers, intraclasts and peloids. Scale bar = 1 mm, (sample no. 41). (c), Dolomitic gastropods rudstone (SFT 9d) with dissolved gastropod Actaeonella fragments. The moulds are filled by dolomite crystals and blocky calcite cements. Scale bar = 500 µm, (Sample no. 62). (d), Rudist bafflestone/floatstone (MFT 10) with cross sections in Eoradiolites shells and they are geopetally filled with micrites and peloids. Scale bar = 2.5 mm, (sample no. 19). (e), Glauconitic dolomitic Orbitolina wackestone/ packstone (SFT 11c) with orbitolinid tests. The glauconites selectively filled the intraparticale pores within the orbitolinid tests. Scale bar = 1 mm, (sample no. 16). (f), Planktic foraminifers-orbitolina mudstone/wackestone (SFT 12b) with Orbitolina (Conicorbitolina) conica, echinoids and planktic foraminifers in micritic matrix. Scale bar = 500 µm, (sample no. 96). (g), Planktic foraminifers mudstone/wackestone (SFT 12c) with abundant planktic foraminifers, echinoids and thin bivalve fragments. Scale bar = 500 µm, (sample no. 58).

13 298 Vol. 92 No. 1 Feb MFS: This surface is placed at the top of deep openmarine mudstone/wackestone facies (SFT 12b) containing outer ramp biota (e.g. orbitolinid and planktic foraminifers). HST: The HST of this sequence is composed of the high energy inner ramp facies of packstone/grainstone (SFT 6a and SFT 7c) and rudist bafflestone/floatstone (MFT 10) with rudists, orbitolinids, ooids, and peloids. The rudist facies of this sequence is developed during the early phase of the HST of the large-scale sequence 1 (Fig. 2). At the late HST phase, the grainy deposits indicate an increase in current energy and the loss of accommodation during the seaward shift of the shoreline and subsequent subaerial exposure of the platform Sequence 2 (early-late Aptian age) This sequence is composed of two medium-scale sequences. It comprises mainly siliciclastics at the base and is carbonate-rich in the upper part, dominated by orbitolinid and benthic foraminifers, and iron ooids. SB2: It corresponds to the exposure surface that developed during sea level fall. This surface is a thin and ferruginous paleosol crust. The upper boundary of the lower medium-scale sequence corresponds to the maximum flooding surface of the large-scale sequence 2. LST: The lowstand systems tract is marked by a significant influx of siliciclastics that consist of sandstone and sandy shale intercalations deposited in a peritidal clastic setting. TST: The transgressive deposits are marked by inner to outer ramp deposits of shale, marl and limestone containing ammonites, orbitolinid and planktic foraminifers. The gradual increase in accommodation rate during TST is represented by a gradual thickening upward trend in the depositional cycles (Fig. 2). These deposits reflect the drowning of the platform during the early Aptian as a result of a longer term relative sea level rise. The gradual rise of relative sea level allows the deposition of shallow-water deposits rich in iron ooids, quartz, cyanobacterium and red algae, and outer ramp deposits rich in planktic foraminifers and ammonites of early TST (SFTs 3b and 11c and MFT 5). The early TST deposits are separated from the late TST deposits by a transgressive surface that is marked by the occurrence of iron ooids, iron ooid aggregates, lithoclastics and cyanobacterium (sample no. 13, SFT 3b, Figs. 2 and 6d). During the late TST, the acceleration in the rate of relative sea level rise causes a gradual decrease in the iron ooids and the deposition of the retrogradational component rich in planktic, orbitolinid foraminifers and glauconite (SFTs 11c and 12b) of mid- to outer ramp environments (Figs. 2 and 8e). MFS: The change from TST to HST is represented by the transition from retrogradational to progradational sedimentation patterns. The maximum flooding surface in the large-scale sequence is best placed at the top of the mid- to outer ramp facies of the maximum flooding interval (SFTs 11c and 12 b). These facies are characterized by an abundance of Thalassinoides, planktic and orbitolinid foraminifers, glauconite and high iron impregnation at the MFS (Fig. 2). HST: This systems tract is composed of a shallowing upward (prograding) parasequence set that formed due to normal regression during a sea level highstand (Fig. 2). The HST is characterized by the evolution from orbitolinid -dominated facies to high energy shallow subtidal facies. Facies dominated by microencrusters (Lithocodium- Bacinella), benthic foraminifers and rudists (MFTs 5, 10 and SFT 11a) were deposited in the early HST (Figs. 2 and 10a). The fall in relative sea level causes the deposition of late HST deposits with shoal facies prograding basinward. These deposits consist of crossbedded, bioclastic packstone and ooid grainstone (SFT 6b and MFT 8), which are characterized by the domination of the meteoric diagenetic features (dissolution and blocky calcite cement), dolomitization and silicification Sequence 3 (late Aptian age) This sequence took place in the high energy shallow subtidal region of the inner ramp that intercalated with mid- to outer ramp environments (Fig. 2). SB3: This sequence boundary is characterized by extensive meteoric diagenesis, dolomitization, dedolomitization, iron oxide mineralization and silicification. Two medium-scale sequences are superimposed on sequence 3 (Fig. 2). The development of these sequences is controlled by higher frequency sea level fluctuations. The top boundary of the lower medium-scale sequence is characterized by a hardground with Thalassinoides and ferruginous cement at the top of ferruginous bed 25 (SFT 6b). This boundary represents the transition from the early HST to late HST deposits of the large-scale sequence 3 (Fig. 2). TST: The transgressive systems tract is recognized by mid- to outer ramp orbitolinid-bearing limestone (SFT 11c) and marl (Figs. 2 and 10a). MFS: The maximum flooding interval is characterized by burrowing, and the domination of glauconite, phosphate and iron-oxides in an Orbitolina wackestone facies (SFT 11c). HST: A falling sea level results in a basinward progradation of the high energy facies. Thus, the HST is characterized by the domination of the high energy

14 Feb Vol. 92 No Fig. 9. Photomicrographs for rudist subfacies at Gabal Raghawi. (a), requieniid Polyconitid rudist bafflestone/packstone, note the borings (bo) in the rudist Toucasia shell that are geopetally filled with micritized peloids, ooids and micrite cement, orbitolinid foraminifers (or) and the ooids (o) are highly micritized. Scale bar = 500 µm (sample no. 6). (b), radiolitid bafflestone/floatstones with microencruster laminations formed by Bacinella-Lithocodium association (black arrows) around the rudist fragments (white arrows). Scale bar = 2.5 mm (sample no. 19). (c), Toucasia bafflestone with Toucasia shell; the outer layer (red arrows) is calcitic with preserved wall structure. The inner layer was originally aragonitic, while it was dissolved and replaced by blocky calcite (black arrows). Miliolids (white arrows) are also common in this subfacies. Scale bar = 1 mm (sample no. 70). (d), radiolitid - caprinid bafflestone with transverse sections in Eoradiolites rudist shells and the well-known rectangular structures of the outer layer (black arrows). Note the shell cavities filled with rudist fragments (white arrows) and peloids. Scale bar = 2.5 mm (sample no. 88). packstone, grainstone and rudstone facies, which contain skeletal fragments, iron and carbonate ooids (MFT 5 and SFTs 6b, and 9c, Fig. 2). The early HST deposits are separated from the late HST by a hardground surface at bed 25 (Thalassinoides bed). The early HST deposits are mainly bioclastic peloidal packstone/grainstone (MFT 5) and iron ooid bioclastic intraclastic packstone/grainstone (SFT 6b) intercalated with shale (Figs. 2 and 10a). These deposits are rich in benthic foraminifers at beds and ooids in bed 25 that indicate the change from the moderate-energy of midramp to a high energy shoal facies. Late HST is mostly represented by inner to mid- ramp deposits prograding over the early HST deposits. Petrographic descriptions for this systems tract show that it comprises two shallowing upward parasequences (Fig. 2). The lower parasequence is thick and composed of midramp marl facies with orbitolinid foraminifers changing upward into the inner ramp high energy shoal facies of bioclastic peloidal packstone (MFT 5) and algal rudstone (SFT 9c). The upper parasequence is thinner and started with marl, which shallows upward into a high energy shoal grainstone that is rich in iron ooids, intraclastics and bioclastics (MFT 5 and SFT 6b) Sequence 4 (late Aptian-early Albian age) This sequence is composed mainly of high energy subtidal shoal grainstone and rudstone intercalated with marl and shale of mid- and outer ramp settings (Fig. 2). SB4: It is identified by its exposure surface, which is indicated by extensive boring, dolomitization, iron oxide cement and dissolution in bed 33 (SFT 6b). Sequence 4 is made up of three medium-scale sequences. The first and the second medium-scale sequences form the TST and the third medium-scale sequence represents the HST of sequence 4. LST: It is represented by a high energy shoal facies with oolites, quartz, peloids, glauconite, gastropods, bivalves, calcareous algae and bryozoans (MFTs 5, 8). TST: This systems tract is marked by the presence of

15 300 Vol. 92 No. 1 Feb Fig. 10. Field photographs for Gabal Raghawi (a-c) and Gabal Yelleg sections (d) show the depositional sequences with different facies and system tracts. open marine inner-to-outer ramp shale and limestone intercalations with ammonites and corals. The early TST consists of one parasequence that starts with outer ramp marl and shale with ammonites and is followed by a high energy facies (SFT 6a and MFT 8). The late TST is mainly represented by shale and marl with ammonites of the outer ramp environment and with minor intercalations of peloidal and oolitic packstone to grainstone of the shallow subtidal shoal facies (MFTs 5, 8). MFS: The maximum flooding surface of sequence 4 is placed at the top of a glauconitic shale bed and limestone with ammonites bed 40 (MFT 5). HST: The highstand deposits consist of interbedded shallow to relatively deep subtidal oolitic grainstone, bioclastic rudstone, marl and shale with ammonites, gastropods, echinoids, dasycladacean and red algae. This systems tract includes one medium-scale sequence. During the early HST, the rate of relative sea level rise was in balance with the rate of sedimentation, resulting in aggradation of two small shallowing upward parasequences (cycles) from relatively deep outer ramp shale with ammonites or mid-ramp facies to shallow subtidal high energy algae rudstone (SFT 9c and MFT 8). The late HST of sequence 4 is composed of two shallowing upward parasequences (cycles) (Fig. 2). These cycles are characterized by shallowing from mid- and outer ramp shale to oolitic grainstone of shoal environments (MFT 8), prograding seaward as the relative sea level rise decreases. The upper part of the late HST deposits is marked by very shallow protected lagoon and back-shoal facies of dolostone and packstone (MFT 1 and SFT 6b). Subfacies 6b at the top of this systems tract is characterized by the domination of the iron components and dissolution that indicate subaerial exposure Sequence 5 (early Albian-middle Albian age) Sequence 5 represents the top of the Lower Cretaceous Risan Aneiza Formation. It is characterized by a quartzdominated grainstone facies with thin beds of shale and marl, and composed of two medium-scale sequences (Fig. 2). SB5: The sequence boundary 5 of the present sequence is placed at the base of a thick sandstone bed. It is recorded as a 30 cm ferruginous thin bed with iron ooids, reworked clasts and ferruginous cement, indicating an exposure surface (SFT 6b). LST: The sandstone succession at the base of the

16 Feb Vol. 92 No sequence is rich in iron ooids and iron oxide cement, and is considered to be peritidal clastic to siliciclastic shoreface deposits. TST: These deposits are characterized by a retrogradational package of facies that begins with outer ramp facies, followed by ooid-dominated shoal facies and capped by an iron-encrusted hardground. That is followed by a shallowing upward parasequence starting with shale and followed by a high energy dolomitic red algaedominated grainstone facies (SFTs 7a b). The top of this systems tract is composed of an outer ramp facies. MFS: The maximum flooding surface is placed at the top of the deepest outer ramp shale facies. HST (Fig. 10b): The lower part is represented by aggradational stacking of shallow, inner ramp facies with abundant siliciclastic inputs in subfacies types 7a and MFT 8. It is marked by intensive dissolution, dolomitization and iron mineralization (Fig. 2). The upper part that formed during the late stage of highstand is composed of shale and marl topped with a thin gastropod rudstone bed (SFT 9d) that is exposed prior to deposition of the next sequence (Figs. 8c and 10b). 6.2 Halal Formation Sequences (middle Albian- Cenomanian age) The Halal Formation is represented by 4 depositional sequences at Gabal Raghawi that span the middle Albianearly Cenomanian. However, 2 large-scale depositional sequences form the Halal Formation (late middle Albianearly Cenomanian age) at Gabal Yelleg (Fig. 3) Sequence 6 (middle Albian age) This sequence has been preserved as limestone intercalated with shale, dolostone and marl at the base of the Halal Formation at Gabal Raghawi (Fig. 10b). The sequence represents the start of declining siliciclastic input and the domination of rudists at Gabal Raghawi. The sequence is composed of two medium-scale sequences (Fig. 3). SB6: The sequence boundary 6 is placed at the top of the reddish Actaeonella marker bed (SFT 9d). This Actaeonella bed displays the dissolution of the aragonitic gastropod shells and shows intensive dolomitization and dedolomitization (Figs. 8c and 10b). The boundary between the two medium-scale sequences of this sequence lies at the hardground in bed 67, where the facies change from grainstone (SFT 6a) to shale. TST: The transgressive systems tract of sequence 6 is composed of shale and Orbitolina-rich limestone (SFT 11c) that indicate relatively mid- to outer ramp environments. MFS: The maximum flooding surface is placed at the hardground within the Orbitolina wackestone (SFT 11c). This hardground is distinguished by burrows and intensive dolomitization. HST: Aggradational to progradational stacking patterns identify the HST in sequence 6. The early HST of the large-scale sequence 6 represents the first rudist-bearing cycle during which the platform aggraded. During the late HST, the second rudist-bearing cycle is deposited and progrades basinward (Fig. 3). The rudist-bearing cycles are identified within this systems tract and go through an ideal vertical shallowing upward from slightly low-energy and mid- ramp to high energy inner ramp facies. The first rudist-bearing cycle goes from Orbitolina wackestone (SFT 11c) to intraclastic packstone (SFT 6a) then to rudist bafflestone (MFT 10) which is capped with bioclastic intraclastic grainstone (SFT 6a) with a hardground at the top (Fig. 3). The second rudist-bearing cycle consists of marl with echinoids and gastropods in the lower part, grading up into Toucasia bafflestone (MFT 10) and rudist rudstone (SFT 9a) of very shallow inner ramp environments. The rudists include Eoradiolites plicatus and Neocaprina sp., as well as orbitolinids, benthic foraminifers and dasyclad algae, reflecting a deposition in shallow water during the HST of sequence 6.Capping grainstone and rudstone in both rudist-bearing cycles were deposited as water depth decreased due either to aggradational growth of the rudist biostrome and/or fall of sea level Sequence 7 (late middle-late Albian age) This sequence is the first one recorded in the upper Albian Halal Formation at Gabal Raghawi. It is made up of two medium-scale sequences (Fig. 3). The sequence is bounded on the base by sequence boundary 7 (SB7), which is characterized by intensive meteoric diagenesis in the form of dissolution of the aragonitic rudist shells and the deposition of blocky calcite in the rudist rudstone facies (SFT 9a). TST: This systems tract is thin and marked by shale and marl with orbitolinid foraminifers that is topped by the maximum flooding surface (Fig. 3). HST: This systems tract is composed of the early and late highstands. The early stage of HST is defined by grainstone and oyster rudstone (SFTs 7b and 9b) with abundant red and green algae followed by massive rudistbearing limestone (MFT 10) stacked in an aggrading pattern (Fig. 3). The transition from aggradational early highstand to progradational late highstand is recorded at a hardground surface at the top of a massive rudist-bearing limestone. The rudist accumulation is able to keep up with the increase of accommodation during early highstand sea level rise. The late HST is deposited during progradation

17 302 Vol. 92 No. 1 Feb and consists of marl with oysters and gastropods, shallowing up into oyster rudstone with calcareous algae, Cuneolina sp., Dicyclina sp. and echinoids forming the upper medium-scale sequence Sequence 8 (late Albian age) Sequence 8 is the thickest one in the Albian succession at Gabal Raghawi, where it is 72 m thick (Figs. 3 and 10c). This sequence consists of two medium-scale sequences. The boundaries between the medium-scale sequences are defined at a hardground that is characterized by intensive dissolution and dolomitization at bed 85. The first medium-scale sequence corresponds to outer ramp orbitolinid limestone and marl intercalations topped with shallow subtidal dolostone and rudist rudstone with extensive meteoric diagenesis. However, the second medium-scale sequence is characterized by the domination of shallower facies that consist mainly of wackestone and dolostone with miliolid foraminifers and rudist-bearing limestone at the top. At Gabal Yelleg, sequence 8 is characterized by high siliciclastic inputs with the shoal facies at the base (Figs. 3 and 10d). SB8: At Gabal Raghawi, no paleosol or iron crusts have been preserved with sequence boundary 8. However, meteoric diagenetic features in the underlying sequence at bed 76 (SFT 9b) suggest subaerial exposure. At Gabal Yelleg, this sequence boundary represents the contact between the first marine transgressions over the nonmarine sandstone of Malha Formation (Fig. 10d). TST: The base of the present sequence is marked by the change from high energetic shallow subtidal facies of the highstand deposits for the underlying sequence to the outer ramp shale overlain by inner ramp facies (SFT 6a) that represent the transgressive systems tract of sequence 8 at Gabal Raghawi (Figs. 3 and 10c). The transgressive systems tract of sequence 8 at Gabal Yelleg is represented by shale topped by bioturbated marl with open marine echinoids and bivalves (Figs. 3 and 10d). MFS: At Gabal Raghawi, the MFS is placed between a thin 1 m dolomitic packstone (SFT 6a at bed 78) containing orbitolinid foraminifers, echinoids, glauconite, phosphate and micritic intraclastics at the top and the underlying shale. However, the maximum flooding surface of sequence 8 at Gabal Yelleg is placed at the top of bioturbated marl bed 4 (Figs. 3 and 10d). HST: At Gabal Raghawi, the early HST is dominated by Orbitolina packstone facies (SFTs 11b and 11c) with echinoids, ammonites, gymnocodicean and udoteacean algae that indicate mid- to outer ramp environments. These deposits pass laterally southward into high energy oolitic and bioclastic grainstone rich in siliciclastic materials at Gabal Yelleg (Fig. 10d). The contact between the early and late HST corresponds to the boundary between the two medium-scale sequences of Gabal Raghawi and Gabal Yelleg (Fig. 3). The late HST is characterized by progradation of the platform and the deposition of restricted to open lagoon facies (MFT 1 and SFT 4a), followed by shallow subtidal rudist bafflestone (MFT 10) in both sections at Gabal Raghawi and Gabal Yelleg (Fig. 3) Sequence 9 (late Albian-early Cenomanian age) In this sequence, an abrupt sea level rise is reflected by the occurrence of deep marine marl and limestone intercalations rich in planktic foraminifers, ammonites and orbitolinid foraminifers above the shallow subtidal rudist bafflestone of the underlying sequence (Fig. 3). SB9: At Gabal Raghawi, this boundary is defined by a facies change from shallow subtidal rudist bafflestone to deep marine limestone and marl intercalations that contain ammonites, orbitolinid and planktic foraminifers (Fig. 10c). TST: The transgressive systems tract is marked by midto outer ramp facies of wackestone/packstone with orbitolinids, ammonites and planktic foraminifers (SFTs 11b, 12a and 12b) at Gabal Raghawi (Figs. 3 and 10c). The transgressive deposits at Gabal Yelleg are composed of bioturbated marl rich in echinoids and bivalves, followed by quartz bioclastic grainstone and Orbitolina packstone (SFTs 7a and 11b) with dolostone intercalations and topped by glauconitic shale, but no ammonites are recorded. MFS: The maximum flooding surface of sequence 9 is placed at the top of bed 97 of outer ramp planktic foraminifers mudstone/wackestones (SFT 12b) at Gabal Raghawi. At Gabal Yelleg it is located at the top of the most traceable open marine outer ramp facies of glauconitic shale (the top of bed 25) (Fig. 3). The maximum flooding surface in both sequences represents the sequence boundary between the two medium-scale sequences at Gabal Raghawi and Gabal Yelleg. HST: The highstand systems tract comprised the lower Cenomanian deposits of this sequence. This systems tract is represented by the upper medium-scale sequence. The early HST is characterized by an aggradational depositional pattern of low energy deep to shallow subtidal facies. This aggradational stacking pattern is represented by marl with open marine fauna, and a thin bed of oolitic grainstone followed by a thick dolostone bed that is rich in silt-sized quartz and glauconite. During the late HST, a prograding small carbonate platform of rudists was constructed basinward at Gabal Raghawi that dominated with rudist rudstone, bafflestone and marl