Microfacies Analysis of Berriasian–Hauterivian Carbonates, Central Saudi Arabia
Published:January 01, 2000
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Hisham T. Shebl, Abdulrahman S. Alsharhan, 2000. "Microfacies Analysis of Berriasian–Hauterivian Carbonates, Central Saudi Arabia", Middle East Models of Jurassic/Cretaceous Carbonate Systems, Abdulrahman S. Alsharhan, Robert W. Scott
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The deposition of the Lower Cretaceous in Saudi Arabia is interpreted within the framework of a model of a simple eastward–dipping carbonate ramp that formed as the result of the extensive flooding of the Arabian Plate during Early Berriasian time. Carbonate deposition was only slightly interrupted by a minor marine regression after the deposition of the Yamama Formation, and it was succeeding by bioclastic limestones of the Buwaib Formation. It was later terminated by a Barremian regression during which clastic deposition dominated most of Central and Eastern Arabia.
The Early Cretaceous carbonates of the Sulaiy, Yamama, and Buwaib formations crop out in central Saudi Arabia. According to sedimentological and paleontological data these formations consist of twenty–two successive microfacies correlated with the published standard microfacies types and belts. The Sulaiy, Yamama, and Buwaib formations were deposited in open–platform and lagoonal settings interrupted by two breaks in sedimentation: (1) a pre–Buwaib disconformity, which is marked by an abrupt change from the fine–grained lime mudstones of the upper Yamama to the sandy wackestones containing cyclamminids of the basal Buwaib, and (2) the more pronounced unconformity between the Buwaib bioclastic wackestone and the overlying Biyadh Sandstone.
Despite the fact that the Berriasian–Hauterivian carbonate succession in the subsurface of both Eastern Saudi Arabia and the Arabian Gulf region contains a number of hydrocarbon reservoirs, very little has been published on that succession, particularly at the type localities in Saudi Arabia. Published information on the Lower Cretaceous outcrops of Saudi Arabia includes the works of Steineke and Bramkamp (1952), Steineke et al. (1958), Powers et al. (1966),, Powers (1968), and Moshrif (1981), who were generally concerned with the subdivision of the outcrop sequence into lithostratigraphic units. A few faunal lists were included, but the results of detailed biostratigraphical or microfacies analysis have never been published except for a description of the lithofacies of the Buwaib Formation by Moshrif (1981). This means that understanding of the stratigraphy is confused by the fact that little subsurface data have been published by the operating oil companies, and the majority of the type sections were chosen in the outcrop belts of Central Arabia, far from the oil fields of the Arabian Gulf. Previous study by Shebl and Alsharhan (1994) shows the relationship between the outcropping sequences of these rocks in Central Arabia and the subsurface sequences of the oil–producing areas in eastern Saudi Arabia. The current study was conducted in an attempt to clarify and revise the stratigraphy of the Lower Cretaceous type sections in Central Arabia by tying these to microfacies analysis of this carbonate succession. Such analysis can be used for regional correlation of the studied sections as well as for their paleoecological and paleogeographical interpretations.
The Lower Cretaceous rocks that crop out in Central Arabia occur in the interior homocline of the Arabian Shelf (Fig. 1). The type Sulaiy Formation was designated by Bramkamp and Berger (1938), cited in Powers et al., 1966 in the cliff section above the Dahl Hit escarpment to the east of Al Riyadh City (Fig. 1). Similarly the type section of the Yamama Formation was taken by Steineke et al. (1958) from a number of short exposures on Al Qusay‘a plateau to the south of the town of Al Kharj. The Buwaib type section was also measured by the same authors in Khashm Buwaib. However, in 1962 Powers and McClure (cited in Powers et al., 1966) suggested a reference section for the Buwaib Formation about 14 km northeast of Khafs Daghrah. Here the Buwaib Limestone unconformably overlies the Sulaiy Formation without the intervening Yamama Formation. This encouraged Moshrif (1981) to choose another reference section for the Buwaib Formation at Khashm Al Thamamah, where the contacts of the formation with both the underlying Yamama and the overlying Biyadh formations are obvious. This was despite the persistent nature of the pre–Buwaib disconformity and the overstepping character of the lower boundary of the Buwaib Formation (Fig. 2). Moshrif‘s proposal is accepted here, and the Khashm Al Thamamah section is treated as a reference section for the Buwaib Formation. All these type and reference sections have been visited, studied, and sampled for the present investigation (Fig. 1). For this study, samples were collected at a regular interval of 3 m within uniform lithologic uni ts, and at both lithological changes and boundaries. Sampling was carried out using a Brunton compass, an Abney level, and a measuring tape. Each sample was described in the field and its location was recorded. A summary of the location of each sampled section, its thickness, and the number of samples collected is in Figure 1.
The first synthesis of the stratigraphic terminology in Arabia was given by Steineke and Bramkamp (1952), who raised the Thamama Formation to group status and its constituent members to formation rank. Consequently the Thamama Group included (from bottom to top) the Sulaiy, Yamama, and Buwaib formations. The Thamama Group is characteristically represented by its limestones, which clearly distinguishes it from both the underlying Upper Jurassic Hith Anhydrite and the overlying Barremian and younger Biyadh Sandstone. Aramco geologists R.W. Powers and his colleagues (see Powers et al., 1966; Powers 1968) expanded the concept of the Thamama Group (Fig. 3) by including the Biyadh Sandstone and the overlying Shuaiba Limestone, wherever present.
The Lower Cretaceous succession of the Arabian Peninsula was deposited upon an eastward–dipping carbonate ramp similar to that described by Murris (1980). The Early Cretaceous ramp of Arabia is a typical homoclinal ramp. The paleoslope dipped gently and uniformly from Central Arabia (the shoreline) to the east, toward Oman (the basin) (Murris, 1980; Alsharhan and Nairn, 1986). The general paleoenvironmental interpretation and depositional setting of the Lower Cretaceous in Arabia is illustrated in Figure 4.
During the Early Berriasian the basal part of Sulaiy Formation in central Arabia was deposited under shelf conditions with restricted circulation and upon tidal flats and protected isolated lagoons. More consistently open–platform shelf–lagoon sediments of the Yamama Formation accumulated during the Berriasian to Hauterivian and were terminated by the pre–Buwaib disconfor– mity. Again, in the Hauterivian shelf–lagoon sediments resumed, accompanied by an influx of clastic sediments from the western part of Arabia resulting in deposition of the Buwaib Formation.
The Sulaiy Formation is about 165 to 180 m thick and consists of massively bedded bioclastic wackestones to packstones with interbedded thin layers of mudstones and recrystallized coquina and oolitic grainstones mostly as its base (Alsharhan and Nairn, 1997). The contact between the Upper Jurassic Hith Anhydrite and the brecciated limestone of the Sulaiy is disconformable (Steineke et al., 1958). Powers et al. (1966) considered the boundary to be conformable and the brecciation to be the result of subsurface solution collapse rather than subaerial erosion. The brecciated limestone horizon near the base of the Sulaiy Limestone was once placed by Powers (1968) within the Hith Formation. We reject this interpretation because the brecciated limestone has the same lithology and fossil content as the overlying Sulaiy Limestone. Consequently, the lower boundary of the Sulaiy Formation is drawn at the appearance of the first limestone bed overlying the evaporites of the Hith Formation. The upper boundary is placed in the section where the dense massive Limestone of the uppermost Sulaiy Formation is overlain by the detrital limestone of the Yamama Formation.
Powers (1968) listed the following fossils in the Sulaiy Formation: Bramkampella arabica Redmond, Nautiloculina sp., Pseudocyclammina sulaiyana Redmond, Trocholina spp., Everticyclammina sp., Anchispirocyclina lusitanica Egger; Nerinea sp. aff. N. blancheti Pictet and Campiche, Nerinea sp., Aetostreon latissima Lamark, Ostrea sp., Milleporidium sp., Aporrhais sp., Diceras sp., Chaetetes sp., and miscellaneous cidaroid radioles. In addition, the following forms have been recorded in the present study: Textularia sp., Trochammina sp., Palaeomiliolina sp., Berthelinella sp., and Pseudocyclammina lituus Yokoyama. On the basis of both its stratigraphic position and fossil content, the Sulaiy Formation is here considered to be of ?Tithonian–Valanginian age.
The Yamama Formation, about 25 to 45 m thick, is composed mainly of bioclastic wackestones and mudstones. Away from the type area itcontains progressively muddier sediments dominated by micritic limestones with very thin shale interbeds (Alsharhan and Nairn, 1997). In the Al Qusay’a and the Khafs Daghrah sections (Fig. 1) it consists of golden–brown, peloidal, foraminiferal wackstones commonly with thin interbeds of bioclastic wackestones and mudstones.
The Yamama Formation rests conformably on the Sulaiy Formation. Steineke et al. (1958) believed that the Yamama Formation is conformably overlain by the Buwaib Formation, where as Powers et al. (1966) and Shebl (1989)found an unconformity. This angular unconformity at the top of the Yamama is seen only locally in outcrops and in a few oilfields. This upper boundary is mostly conformable in the sub surface of eastern Arabia, except in a few oilfields (Ma’agala, Khurais, and Jawf) where an angular unconformity is observed.
Powers (1968) recorded the following fossils in the reference section of the Yamama Formation: Everticyclammina eccentrica, E. kelleri Redmond, E. hellen Redmond, Pseudocyclammina cylindrica Redmond, P. spp., Cyclammina spp., Haplophragmoides sp., and Trocholina sp. on the basis of the occurrence of the echinoid fossils, Pygurus rostratus Agassiz, Trematopygus sp. cf. T. grasi d’Orbigny, Astrocoenia? sp., Milliporidium sp. and cidaroid radioles, and foraminifers, Bigenerina sp., Globuligerina hoterivica (Subbotina), Flabellammina sp., Pseudonummoloculina sp., Nautiloculina oolithica Mohler, Trocholina elongata Leupold, and indeterminate plank tonic foraminifera.
Other macrofossils recorded include Anisocardiasp., Aporrhais sp., Corbis sp., Corbula sp., Chione sp., Cucullaea sp., Exogyra spp., Gyrodes? sp., Gryphaea balli Stefanini, Homomya sp., Lima sp., Modiolus? sp., Natica sp., Nucidana sp., Ostrea sp., Pholadomya sp., P. decussata, Pleurotomaria? sp., Siliqua sp., Tellina sp., Trigonia sp., Trochus sp., Venus sp., unidentified ammonite genus showing affinities with Hypengonoceras, and unidentified small molluscs. The Yamama Formation is considered to be of Valanginian age.
The type section of this formation consists of 11.2 m of micritic and calcareni tic limestones with intercalated sandstone and sha le beds. The Buwaib Formation is 17.7 m thick at Khafs Daghrah and consists of interbedded shales, dolomites, and calcarenitic and micritic limestones with occasional very thin beds of quartz sandstone (Powers, 1968). In contrast, the Buwaib Formation at Khashm A1 Thamamah is about 17 m thick and is composed of bioclastic wackestones interbedded with argillaceous mudstones (Shebl, 1989).
The upper contact of the Buwaib Formation is disconformable, changing from cyclamminid bioclastic wackestones of the Buwaib Formation to black–weathering, cross–bedded sandstones of the basal Biyadh Formation (Alsharhan and Nairn, 1997).
Fossils recorded in both the studied section and in the type Buwaib include/1 mmobaculites? sp., EverticyclamminagreigiHenson, Everticyclammina hensoni Redmond, orbitolinids, unidentified lituol ids, and unidentified small molluscs. On the basis of both its fossil content and stratigraphic position an upper Hauterivian to Lower Barremian age is accepted here for the Buwaib Formation, as proposed by Banner and Highton (1990). In the drilled subsurface sections it was reported to include Choffatella decipiens Schlumberger, indeterminate orbitolinids, and unidentified small molluscs in addition to the forms recorded in the surface sections. These were taken to confirm the Hauterivian age of the Buwaib Formation (Powers et al., 1966).
In outcrop, the Biyadh Formation is approximately 300–400 m thick and has an age span from Barremian to Aptian? or younger. This formation consists of dark–weathering, cross–bedded quart– zose sandstone with some interbedded variegated shale. Variations in the depositional conditions are indicated by several horizons of conglomerates. The top of the section consists of cross– bedded quartz sandstone with abundant quartz pebbles (Powers et al., 1966; Moshrif, 1980a, 1980b; Moshrif and Kelling, 1984; Alsharhan and Nairn, 1997). The bulk of the Biyadh appears to have been deposited in al lu via 1 channels (ma inly as point–bar sands) and in flood–plain settings. In the subsurface the Biyadh is bracketed between the Buwaib Formation below and the Shuaiba Formation above. The section, as much as 625 m thick, appears to be richer in shale and argillaceous mudstone than in out crop and marks a marginal–marine setting as indicated by two thin beds of orbitolinid limestone within the succession of predominantly green shale.
The Shuaiba Formation is known only from the subsurface of Saudi Arabia and is restricted to Aptian age. It consists of massive, commonly porous and vuggy dolomite with occasional limestone. Some levels containing orbitolinids have been found. The thickness ranges from 25 to 110 m.
The type sections and reference sections of the Berriasian– Hauterivian carbonate sequence in Saudi Arabia comprise twenty– two stratigraphically superposed microfacies (Fig. 5). The microfacies are described in the following sections in ascending stratigraphic order. Facies nomenclature and depositional environments follow Fliigel (1982) and Wilson (1975). The microfossil remains have been determined using the following publications: Bozorgnia and Banafti (1964), Redmond (1964), Majewske (1969), Sampo (1969), Simmons and Hart (1987), Banner and Highton (1990), and Banner and Whittaker (1991).
Microfacies of Sulaiy Formation (A)
Microfacies A-1: Textulariid Peloidal Grainstone
This microfacies consists of about 8 m of numerous peloidal grainstones with a few superficial ooids, aggregate grains, and bioclasts cemented by calcite spar (Fig. 6A). The peloids are mostly pseudopeloids and are commonly associated with very small aggregate grains. This microfacies constitutes the basal part of the typical Sulaiy Limestone in the Dahl Hith section. It directly overlies the Hith Anhydrite with an irregular contact, which was probably produced by solution collapse.
Textularia spp., Trochammina sp., miliolids, and algae.
This microfacies is correlated to the standard microfacies (SMF) type 17, which was placed in either standard facies belt 8 (restricted platform) or 7 (open–platform shelf lagoon). However, because the pseudopeloids may have been derived from occasional reworking of sediments in an extremely shallow-water setting with restricted sedimentation (Grass and Carozzi, 1967), the interpretation of a restricted platform is preferred here. The presence of aggregate gra ins supports this interpretation because these grains usually form in shallow subtidal and intertidal shallow-water settings with restricted circulation.
Microfacies A-2: Ostracod–Ooidal Grainstone
This microfacies consists of about 6m of oolitic grainstone with recrystallized radial ooids and poly-ooids, peloids, coated grains, and bioclasts (Fig. 6B).
Numerous coated ostracode carapaces, small molluscan shells, shell fragments, and foraminifera.
Ooids with radial structures are usually found in abundance in moderate- to low-energy carbonate deposits and are formed in restricted shelf lagoons with elevated salinities. This facies is correlated to the standard microfacies (SMF) type 17, which was placed in facies belt 8 (restricted platform). This interpretation is supported by the greatly reduced diversity of organisms, by the common percentage of ostracode remains, and by broken ooids.
Microfacies A-3: Ooid Sandy Peloidal Grainstone
This microfacies consists of a 1-m-thick peloidal grainstone (Fig. 6C), interrupted by a 3-m-thick horizon of silty, fecal-pellet limestone. Superficial oolites are rare, but both the quartz grains and the pellets are more abundant. The quartz grains are generally sub angular to subrounded and highly pitted.
Molluscs (mainly gastropods), algal remains, and agglutinated foraminifera.
The peloidal grainstones of this microfacies correspond to SMF type 17, which was formed in shallow shelf settings where water circulation is restricted in such places as cut-off lagoons, coastal ponds, and tidal flats. The intercalated fecal pellets are correlated with SMF type 16, which was deposited in a very warm, shallow-water setting with only moderate water circulation but with connections to the open sea.
Microfacies A-4: First Mudst one
This microfacies is composed of about 12 m of lime mudstone with rare, scattered, recrystallized shell and bone fragments.
This microfacies corresponds to standard facies belt 7 and SMF Type 17, which is placed in an open-platform shelf lagoon setting. In such lagoonal areas marine grasses can act as sediment trappers and stabilizers, slowing down water currents and stabilizing mud.
Microfacies A-5: Peloidal Grainstone
This microfacies reaches some 3 m in thickness and is composed of peloidal grainstone with abundant detrital grains.
Rare ostracodes, agglutinated for aminifera, and shell fragments.
This microfacies is correlated to SMF type 17 (Standard Facies Belt 7), which is a shelf-lagoon setting with restricted water circulation.
Microfacies A-6: Bioclastic Wackestone
This microfacies consists of a recrystallized bioclastic wackestone (Fig. 6D) about 3 m thick, associated with quartz.
Mainly composed of completely recrystallized bivalve shell fragments.
The bioclastic wackestone microfacies is correlated to SMF type 9, deposited either in standard facies belt 2 (open-sea shelf) or 7 (open-platform shelf lagoon). The latter interpretation is supported by the absence of planktonic for aminifers as well as by the great diversity of the molluscan remains.
Microfacies A-7: Second Mudstone
This microfacies is composed of some 3 m of lime mudstone stained with iron oxide and containing scattered microskeletal fragments and rare recrystallized ostracode carapaces.
The facies was deposited in bays and open lagoons in an open platform and correlated with SMF Type 17 (Standard Facies Belt 7).
Microfacies A-8: Pseudocyclammina Bioclastic Wackestone
This microfacies is composed of about 78 m of bioclastic wackestone interrupted by 3 m of pure lime mudstone, in its lower third, which grades upward into about 3 m of a recrystallized limestone.
A fauna rich in foraminifera: Nautiloculina sp. (Fig. 6E), Pseudocyclammina sulaiyana Redmond (Fig. 6F), Pseudocyclammina sp., Bramkampella? arabica Redmond, Everticyclammina spp., Textularia spp. (Fig. 6G), Guembelitria spp., other planktonic and benthonic foraminifera, and abundant brachiopods, gastropods, bivalves, algae, bryozoans, and echinoderms.
This microfacies Is correlated to SMF type 9, which is placed either in standard facies belt 2 (open shelf) or 7 (open-platform shelf lagoon). The latter interpretation is more probable because the rock has a very low planktonic/benthonic ratio and contains stenohaline forms including brachiopods and echinoderms. This microfacies consists of abundant fragments of molluscs, bryozoa, brachiopods, echinoderms, and other benthonic remains, whereas only very rare planktonic foraminifers were recorded. It can be further sub divided into five distinctive submicrofacies based on the presence of an intercalating lime mudstone bed in its lower third and a recrystallized limestone bed near the middle.
Microfacies A-9: Third Mudstones
This microfacies consists of 12-m-thick, locally iron-stained lime mudstone with rare foraminifera.
Some Cyclammina sp. and Everticyclammina sp., together with recrystallized shell fragments.
These sediments accumulated in low-energy, slightly restricted bays and open lagoons on an open platform, and are correlated with SMF Type 17 (Standard Facies Belt 7).
Microfacies A-10: Everticyclammina Bioclastic Wackestones
This microfacies is composed of some 24 m of bioclastic wackestones, with partly recrystallized molluscan and other skeletal fragments as well as abundant benthonic and rare planktonic foraminifers.
Everticyclammina spp., Anchispirocyclina lusitanica (Egger), Bramkampella arabica Redmond, Pseudocyclammina lituus Yokoyama, and planktonic foraminifers.
This microfacies correlates to SMF Type 9 and represents an open-platform shelf (standard facies belt 7), as reflected by the more abundant agglutinated benthonic foraminifera and the scarcity of planktonic forms.
Microfacies A-11: Fourth Mudstone
This microfacies consists of some 9 m of lime mudstone with rare, scattered and recrystallized microskeletal fragments.
These sediments were deposited in bays and open lagoons on an open platform and are correlated to SMF Type 17 (Standard Facies Belt 7).
Microfacies of The Yamama Formation (B)
Microfacies B–L: Ammobaculites Peloidal Bioclastic Wackestone
This microfacies is composed of about 9 m of lime mudstone to wackestone that can be divided into three zones: the lower and upper zones consist of peloidal bioclastic wackestones (Fig. 7A), and the middle zone is composed mainly of lime mudstone and wackestone.
Ammobaculites sp., Pseudocyclammina sp., (Fig. 7B), Everticyclammina hellen Redmond, and Textularia sp., together with some globotextularids and haplophragmoids.
This microfacies is correlated to SMF type 9, which is placed in either the standard facies belt 2 (open–sea shelf) or 7 (open– platform shelf lagoon). Because of the peloidal nature of the grains an origin in an open-platform shelf lagoon can be assumed. This confirms the occurrence of open-platform shelf lagoons in central Arabia during most of the Early Cretaceous deposition.
Microfacies B–2: Lower Mudstone
This microfacies is composed of about 3 m of lime mudstone with rare recrystallized shell fragments.
Bays and open lagoons on an open platform.
Microfacies B–3: Algal, Molluscan, Bioclastic Wackestone
This microfacies is composed of some 9 m of bioclastic wackestone with recrystallized algal remains, molluscan shell fragments, and together with benthonic and planktonic foraminifera (Fig. 7C).
Hensonella sp., bivalves and gastropods, Cyclammina sp., Globuligerina hoterivica (Fig. 7D).
This microfacies is correlated to SMF type 9, and standard facies belt 7, representing an open-platform shelf lagoon.
Microfacies B–4: Upper Mudstone
This microfacies is composed of 3 m of lime mudstone with very rare, recrystallized microskeletal fragments.
This microfacies represents deposition in bays and open lagoons on an open platform.
Microfacies B–5: Flabellammina, Nautilocidina Bioclastic Wackestone
This microfacies is about 18 m thick and constitutes the uppermost part of the Yamama Formation. It changes gradually upward from bioclastic wackestone at the base Into mudstones near the top. The fine–grained matrix increases upward.
Flabellamina sp., Cyclammina sp., "Nummoloculina" sp., Nautilocidina oolithicaMobler(Fig.7E), Trocholinaelongata(Leupo\d), and planktonic foraminifera, recrystallized ostracods, bryozoans, and echinoderm and molluscan fragments (Fig. 7F).
This microfacies is correlated with SMF type 9, and is interpreted to represent an open-platform shelf lagoon (standard facies belt 7).
Microfacies of The Buwaib Formation (C)
Microfacies C–L: Cyclamminid Bioclastic Wackestone
This bioclastic wackestone with a large number of foramini– fers is about 2 m in thickness and rests directly above the pre– Buwaib disconformity (Fig. 8A).
Everticyclammina greigi Henson (Fig. 8B), Everticxjclammina hensoni Redmond, E. contorta Redmond, E. spp., Ammobaculites? sp., other benthonic foraminifera remains, and recrystallized skeletal fragments.
This microfacies is correlated to SMF type 9 and was deposited in an open-platform shelf lagoon (standard facies belt 7) as reflected by the bioclastic wackestone composition of the facies and the high percentage of benthonic foraminifers.
Microfacies C–2: Sandy Cyclamminid Bioclastic Wackestone
This microfacies consists of 5 m of bioclastic wackestones with abundant, scattered quartz grains and local iron staining near the base.
Both the abundance of quartz grains and the great diversity of the benthonic foraminifera equate this microfacies to SMF type 9 and belt 7 (open-platform shelf lagoon).
Microfacies C–3: Lower Argillaceous Muds tone
This microfacies is about 2 m thick and is composed of argillaceous mudstone with very rare skeletal fragments.
This facies suggests a very shallow environment with minimal wave and current activity such as the landward flanks of bars in a lagoonal region or the lee side of barriers in a broad shallow platform.
Microfacies C–4: Lituolid Sandy Wackestone
Foraminiferal sandy wackestone with mostly subangular to subrounded quartz grains (Fig. 8E), reaching a maximum thickness of 2 m.
Lituola sp., and algal and echinodermal remains.
A high–energy, relatively shallow marine setting is suggested, probably located on the inner shelf or contemporaneous bars where most of the current activity was concentrated.
Microfacies C–5: Upper Argillaceous Mudstone
This microfacies is composed of 1 m of argillaceous mudstone (Fig. 8F) with a few scattered microskeletal fragments.
A very shallow-water environment similar to Microfacies C– 3 is suggested.
Microfacies C–6:Cyclamminid Textulariid Bioclastic Wackestone
This microfacies is composed of about 6 m of bioclastic wackestone recrystallized in the lower and upper parts and iron stained in the middle.
Foraminifera: Everticyclammina hellen Redmond, E. contorta Redmond, Cyclammina sp., Textularia spp., Flabellammina sp., and some molluscan skeletal remains.
This constitutes the uppermost part of the measured Buwaib section in the Khashm A1 Thamamah area, where it underlies the Biyadh Sandstone. It is correlated to SMF type 9, and standard facies belt 7 (open-platform shelf lagoon).
The Lower Cretaceous strata over the Arabian Peninsula were deposited on an eastward–dipping carbonate ramp characterized by open–shelf carbonate lagoons of central Arabia and by deep shelf–margin conditions in Oman.
The Berriasian–Hauterivian rocks of central Saudi Arabia represent a transgressive carbonate phase that began with the deposition of the Sulaiy Limestone during the Berriasian and ended with the deposition of the Buwaib Formation (Hauterivian), with a minor local break (pre–Buwaib discon– formity) during the Valanginian or between the Valanginian and the Hauterivian.
The Berriasian–Hauterivian section of Central Saudi Arabia contains twenty–two successive microfacies. Paleoecological interpretation of the microfacies indicates that these sediments in Central Saudi Arabia accumulated under marine shelf conditions with restricted to moderate water circulation during the Berriasian. This interpretation is indicated by the peloidal, ooidal grainstones and open–marine fossils which are locally associated with sub angular to subrounded quartz grains. Such marine shelf conditions were followed by open– platform shelf lagoons in which the bioclastic wackestones with interbeds lime mudstones accumulated.
The first author is deeply grateful to Prof. Z. R. El Naggar for his assistance duringthe field work. The authors would like to thank Prof. C. G. St. C. Kendall, Prof. J. Kuss, Dr. R. W. Jones and Dr. R. W. Scott for reading the manuscript and for offering valuable comments and suggestions which improved the paper.
Figures & Tables
Middle East Models of Jurassic/Cretaceous Carbonate Systems
This volume will interest tectonic modelers, stratigraphers, sedimentologists, and explorationists. It is the product of the international conference of “Jurassic/Cretaceous Carbonate Platform-Basin Systems, Middle East Models” that was convened in December 1997 jointly by SEPM (Society for Sedimentary Geology) and the United Arab Emirates University in Al Ain, United Arab Emirates. The twenty-three papers present new data and interpretations arranged in three sections: 1) sequence stratigraphy, cyclostratigraphy, chronostratigraphy, and tectonic influences, 2) depositional and diagenetic models of carbonate platforms, and 3) hydrocarbon habitat and exploration/development case studies. New tectonic models of the Arabian Basin, new stratigraphic and sequence stratigraphic reference sections, new geochemical and source rock data, and new reservoir data are presented. New geologic models make this set of papers relevant to geoscientists working outside of Arabia also.