Research

AGE OF SAKAKA SST

Abstract

The age of the Sakaka Sandstone, which crops out mainly wihin al—Jawf area of northwestern Saudi Arabia, is a matter of dispute. The lack of distinct micro— fossils in the outcropping Sakaka Sandstone plays a major role in the difficulty of determining its age. The Sakaka Sandstone has been dated Middle Cretaceous on the basis of its stratigraphic correlation southward with the Middle Cretaceous Wasia Formation. On the other hand, a Devonian age is assigned to the formation based on the presence of fossil wood. Nevertheless, a pre- liminary pollen analysis indicates a probable Late Devonian-Early Carboniferous age.

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AGE OF SAKAKA SST

Cementation, diagenesis and paragenetic sequence in the Biyadh—Was'l' Sandstones (Lower-Middle Cretaceous) of central Saudi Arabia

Abstract

Although most of the Biyadh—Wasi' Sandstones (Lower-Middle Cretaceous) are friable and poorly cemented, few specimens reveal some cementation principally by secondary silica (or quartz), carbonate or ferruginous material. The Biyadh—Wasi' Sandstones have undergone several important diagenetic changes during their post-depositional history. The full paragenetic sequence commenced with primary partial silica cementation, which was followed by formation of iron in the remaining pore spaces. Both stages included quartz overgrowths, produced as a result of pressure solution. Later stages resulted in precipitation of Fe-rich clays and carbonate in new pore spaces created by partial replacement and corrosion of detrital quartz grains. The lack of quartz overgrowths in the later stages is believed to be due to inhibition of pressure solution. The final diagenetic stages include weathering, which has created new pore spaces, and precipitation of silica dust (probably of aeolian origin) in such pores which resulted in the formation of secondary silica overgrowths in the form of microcrystalline quartz. This process gives rise to the ‘quartzitic’ crusts typically developed on many elevated outcrops of the Biyadh and Wasi' Sandstones.

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CEMENT.DIAG.PARA.SEQU.IN B.-WASIA .SSTS

CHRONOSTRATIGRAPHY AND HYDROCARBON PROSPECTS OF THE SAKAKA FORMATION, NORTHERN ARABIA

Abstract

The age of the so-called Sakaka Sandstone exposed in the al-Jawf area. northern Saudi Arabia. has in the past been disputed. It is assigned here to the Middle - Late Devonian and Middle Cretaceous. This age has been established from correlations of surface — subsurface sections utilising palynological and Iithological data. and also from the regional geological framework. The sequence is divided into two units. The lower unit, composed of non-marine clastic sediments. is Middle-Late Devonian. The upper unit. consisting of elastic and mixedfine- elastic and calcareous shoreline-shallow marine deposits. is considered to be pan of the Middle Cretaceous Wasia Formation.

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CHRONOSTRA.HYDROC.PROS.SAKAKA

Depositional Environments of The Buwaib — Biyad — Wasia Rocks Deduced by X—Ray Diffraction Anal

Abstract

Several samples of shales and clays from both the borehole, PW3 and the outcrop of Buwaib, Biyad and Wasia, in Central Saudi Arabia were analysed to determine first, the clay and non-clay mineral composition and second to reveal their possible depositional environments. The diffracted peaks of these samples show that kaolinite is the predominant clay mineral group in the Biyad-Wasia sediments and in perfectly to very well crystallized form. Other clay minerals which followed in amount are illite, montmorillo- nite and mixed-layer clay respectively. The predominance of kaolinite in the Biyad-Wasia sediments has suggested a continental and / or non-marine type of environment for these sediments. This is also supported by the fact that this kaolinite is perfectly well crystallized. The presence of both illite and montmorillonite are possibly related to the specific physico — chemical conditions which were obtained during processes of deposition and diagenesis. Moreover, the trace amounts of montmorillonite and illite as revealed by a few Buwaib carbonate samples may point to formation in a marine environment.

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Dep.Env.BUWAIB-BIYAD-WASIA. X-ray.DIFFRA.ANALY

Environmental Interpretation of Sand Grain Surface Textures in the Biyad — Wasia Sandstone Formations in Central Saudi Arabia

Abstract

Quartz grain surface texture from the exposed and subsurface sequences of the Biyad-Wasia Sandstone Formations in Central Saudi Arabia have been studied. Their surface textures as revealed by seaming electron microscopy, include features characteristic of desert or aeolion, beach, and river (i.e. fluvial) environments as compared with recent sands. However, this writer has concluded that quartz grain surface features are not ideally reliable indicators of their ancient environments.

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ENV.INT.S.G. SUR.TEX.BIYAD.-WASIA

Fining-Upward Cycles in the Biyad—Wasi Sandstones (Lower—Middle Cretaceous) in Central Saudi Arabia

Abstract

The stratigraphic variation in grain size distributions, in the Biyad—Wasi sequences studied have probably been produced in response to two main factors. The smaller-scale, field-recognized cycles are ascribed to fluctuations in the depositing agent(s), that is, the fining-upward cycles denote stream (fluvial) deposits, while the few coarsening upwards sequences may indicate portions of a temporary lacustrine (lake) sequence developed in the interflude region of the alluvial plain and are probably not connected with any deltaic environment but may be caused by sediment winnowing and reworking. This latter postulation is supported by the small proportions of fine silt and clay indicated by the median (Md) column. The larger-scale cycles defined by the grain-size analyses probably represent longer-term fluctuations in the grade of sediment being supplied to the depositional basin, possibly in response to tectonic or diastrophic movements in the source—area.

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FINING.UPWARD.CYCLES. BIYAD-WASI.SST

FLUVIAL ENVIRONMENT OF THE SOUTHERN PART OF UAJID SANDSTONE ( CAMBRIAN—ORDOVICIAN) DEDUCEO BY TEXTURAL ANALYSIS

Abstract

A detailed investigation of the southern part of uajid sandstone ( cambrian-ordovician ) in Saudi Arabia was carried out to describe its sedimentologic texture and to determine its paleoenvironment of deposition by using the available grain size techniques of environmental analysis. The applied techniques. i.e. The vertical variation in grain-size para- meters, the grain size distribution curves, the multivariant grain size parameter plots and the linear discriminant Funct- ion tests. suggest that the studied uajid sandstone was domi- nantly deposited in a fluvial environment. Furthermore. this study demonstrates that the outcrops sampled(UaJid Sandstone) can be characterized as negatively skewed.moderately to poor- ly sorted and relatively coarse and are thus more likely to be Fluvial. rather than beach or eolian.

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FLUV.ENVIRON.OF.WAJID SST

GEOLOGICAL AND MINERALOGICAL STUDY of RIYADH PINE AGGREGATES

Abstract

A detailed geological study of Riyadh fine aggregates is made on samples collected from crushing plants located in quarrying sites around Riyadh. Results of petrographic and mineralogical analysis,using x-ray diffraction analysis,are presented in parlance of geological terminology.

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GEO.&.MIN.STUD.OF.RIYADH.FINE.AGGREG

Lithofacies and petrography of Wajid sandstone (Cambrian-Ordovician) Saudi Arabia

Abstract

Six lithofacies are recognized in the Wajid sandstone. These lithofacies are identified as: silty and argillaceous sandstones; fine- grained sandstones; coarse-grained sandstones; pebbley to very coarse-grained sandstones; conglomerates and massive sandstones. Mineralogic composition suggests that the Wajid sandstone is considered clean sands for it consists 95 % of quartz grains 5 % heavy minerals, mica, potash feldspar, clay matrix, ferruginous cement and traces of carbonate cement. Quartz grain extinction types and inclusions plus heavy mineral types and shapes suggest nearby igneous and metamorphic sources for these deposits, i.e. the adjacent Arabian Shield rocks, in addition to repeated recycling of these sediments as indicated by the appearance of a small number of rounded to very rounded grains of heavy minerals. Furthermore, perhaps most of the secondary silica present in the Wajid was developed from solution and from silica reprecipitated later during periods of aeolian reworking of these fluvial sediments. Moreover, the ferruginous material in Wajid was very likely derived either from siderite or came in solution from igneous and metamorphic provenance or generally came from both sources; The carbonate material in the sediments might either be derived from post-Wajid carbonate formations or formed from solution of carbonate shells trapped in these sediments. X-ray diffraction analysis shows that kaolinite is the only clay mineral present in the Waj id deposits. On the other hand, spectroscopic analysis reveals the presence of Si, Mg, Al and Ca elements as major constituents in the Wajid sandstone. Moreover, according to facies characteristics, the Wajid sediments were deposited under conditions of fluvial environments.

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LITHOFAC.PETR.WAJID.SST

THE ORIENTATION OF FOSSIL BIVALVES IN A PENE-LITTORAL SEQUENCE (THE RHAETIAN of SOUTH WALES)

Abstract

Primary flow—vector criteria (symmetrical ripple marks) derived from a sequence of sublit- toral to possible shoreface sediments of Late Triassic age in South Wales yield well-defined orientations which are nearly identical at a number of widely separated outcrops and attest the prevalence of northwest-southeast oscillatory flow in this region. The bivalves Modiolus hillanus (J. Sowerby) and Rhaetavicula contorta (Portlock) occur abundantly in this sequence and at a few horizons these fossils display preferred orientations which are broadly consistent with the ripple data. However the fossil orientation patterns are not, in general, directly compatible with published experimental data and it is suggested that this discrepancy results from subsequent modification of original wave-formed patterns in response to weak unidirectional (current) flow, possibly induced by tidal or longer period currents, which otherwise has left no discernible evidence in the fine-grained sediments.

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ORIENT. OF FOSSIL.BIVALVES

PALEOENVIRONMENT INTERPRETATION OF THE SAKAKA SANDSTONE AS REVEALED BY CLAY MINERAL ANALYSIS

Abstract

The results of the qualitative and quantitative determination of clay minerals in the Sakaka borehole samples are presented and their depositional environments deduced. Perfectly crystallized kaolinite is the most predominant clay mineral in the Sakaka sediments, followed in amount by poorly crystallized illite and mixed-layer clay; montmorillonite does not appear in the analyses. lt is suggested that kaolinite was formed in a fluvial environment and the small quantities of other clay minerals were formed under marine conditions, or perhaps were derived from older sedimentary rocks. The clay minerals were most probably formed either from the weathered products of the parentrrocks (Le. igneous and metamorphic rocks of the Arabian Shield) or as a result of changes in conditions of deposition. There are no indications of diagenetic effects in the Sakaka sediments.

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PALEOENV.INTER.SAKAKA.SANDST

RECOGNITION OF FLUVIAL ENVIRONMENTS IN THE BIYADH-WASIA SANDSTONES (LOWER-MIDDLE CRETACEOUS) AS REVEALED BY TEXTURAL ANALYSIS

Abstract

A detailed study of the Biyadh (upper Lower Cretaceous) and Wasia (Middel Cretaceous) Sandstones in central Saudi Arabia was undertaken to describe their sedimentologic texture and to use some of the available techniques of environmental analysis in determining their depositional environments. Bivariant plots and frequency distribution curves indicate that fluvial deposits dominate over either beach or dune deposits in the Biyadh and Wasia Sandstones.

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RECOG.FLUV.ENV.BIYAD-WASIA STS.TEXT.ANSIS

Riyadh Sands and their Effect on Concrete Performance

Abstract

A physical and geological study of Riydh sands was made on samples mlleeted from crushing plants located in quarrying sites around Riyadh. An experimental study. following ASTM Standards. of the effects of these properties on the performance of fresh and hardened concrete was also carried out. Pctrpgraphic analysis showed that the fine aggregate particles are hard and in general suhangular to subrounded and more elongated than spherical in shape. A large number‘oi samples showed a presence of very fine sand and silt in them. The aggregates basically are classified as limestone rocks of various types. A rare occurrence of dolomitic limestone was discovered in one sample. Mineralogical analysis showed a presence of trace amounts of clay minerals in some samples of which a few had montmorillonitc. Non-clay minerals present included calcite. silica. quartz. feldspar. limonile. iron oxide. hematite and gypsum in two samples in rare amount.

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RIYADH SANDS and their EFFECTS on CONCRETE PERFORMANCE

SEDIMENTARY HISTORY AND PALEOGEOGRAPHY OF LOWER AND MIDDLE JURASSIC ROCKS, CENTRAL SAUDI ARABIA

Abstract

Eight elastic and carbonate lithofacies of Lower and Middle Jurassic age (the Marrat and Dhruma Formations respectively) have been identified. These lithofacies are mainly shales, shales-and—siltstones siltstones—and-shales, sandstones, argillaceous limestones, calcarenitic limestones, calcarenites and dolomites. Intraclasts, pellets, oolites, gypsum, algae, and coral "eefs were also found to be dominant among these lithofacies. Furthermore, these beds a contained either restricted or diversified biota, with a few sedimentary structures such as lamination, cross-bedding and common bioturbation. Thus, it is presumed that theLowerand Middle Jurassic rocks in Central Saudi Arabia were deposited in very shallow (i. e. tidal flat and lagoon), shallow-neritic, and deep-marine conditions of the Tethys Sea.

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SED.HIS.PALEOG.L.M.JUR.RCKS

Sedimentation and Environmental Interpretation of Hanifa Formation (Upper Jurassic), Central Saudi Arabia

Abstract

Detailed investigation of the Hanifa rock units (Upper Jurassic) in central Saudi Arabia has indicated that this formation is generally composed of various carbonate lithofacies which are intercalated with shale units at several levels. The carbonate lithofacies include argillaceous limestones, arenaceous limestones, reefal limestone, oolitic limestone and chalky limestones. The argillaceous limestones are composed of biomicrite (microfacies 1). The arenaceous limestones consist of biopelmicrite, biorudmicrite, biosparimi- crite, biopelsparite and bio-oosparirudite (microfacies 2—6 respectively). The reefal limestone is mainly coral reef (microfacies 7). The oolitic limestones are mainly bio-oosparite (microfacies 8). The chalky limestones are silicified biomicrite and silicified biopelmicrite (microfacies 9 and 10 respectively). The proposed depositional environments of the Hanifa lithofacies started to develop during Late Oxfordian to early Kimmeridgian times, when the area of central Arabia was under relatively deep marine water which had covered an area of great extent. These rocks were developed along a shoreline of open marine platform and formed successive belts of lagoonal and tidal-flat character responsible for deposition of pelleted calcilutites, laminated cal- cilutites, gypsum and restricted fauna. The open shelf of the basin margin lays east of the lagoonal zone, accounting for the development of oolites, coral reef, calcarenites and diversified fauna in shallow shelf. The deeper shelf is responsible for deposition of calcilutites, shales and diversified fauna.

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SEDIM.ENV.HANIFA

Sedimentation and Palaeogeography of the Buwaib Formation (Lower Cretaceous) in Central Saudi Arabia

Abstract

Investigation of the Buwaib (Lower Cretaceous) Formation in central. Saudi Arabia indicates that this formation is composed generally of carbonate lithofacies. It includes arenaceous limestones (intra- biopelsparites), argillaceous limestones (intra-biopelmicrites), chalky marls (micrites), sandy marls (quartzose micrites) dolomitic limestones (dolosparites and dolomicrites) and coquinoid limestones (biomicrudites).

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SEDIM.PALAEOG.BUWAIB.FM

SEQUENTIAL DEVELOPMENT OF HANIFA FORMATION (UPPER JURASSIC) PALEOENVIRONMENTS AND PALEOGEOGRAPHY, CENTRAL SAUDI ARABIA

Abstract

The Hanifa Carbonate lithofacies (Upper Jurassic) started to develop during Early Kimmeridgian time, when an extensive area in central Arabia was covered by relatively deep marine waters. These rock units were formed along a shoreline, resulting in successive lagoonal and tidal-flat belts, the deposition of pelleted and laminated calcilutites and gypsum, and a restricted fauna. The open shelf lay east of the lagoon zone, accounting for the development of oolites, coral reef and calcarenites, and a diversified fauna on the deeper shelf.

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SEQUENT.DEV.HANIFA.FM.PALEOE.&.PALEOG

STRATIGRAPHY AND SEDIMENTARY HISTORY OF UPPER-LOWER AND MIDDLE CRETACEOUS ROCKS. CENTRAL SAUDI ARABIA

Abstract

The Biyadh Sandstone (upper Lower Cretaceous) and the Wasia Formation (Middle Cretaceous) in central Saudi Arabia generally consist of a dominant elastic facies and a subordinate carbonate facies. The elastic lithofacies are coarse-grained sandstones, fine-grained sandstones, channel-fill conglomerates, massive quartzitic sandstones, siltstones interbedded with shales, and mudstones interbedded with shales. The carbonate lithofacies are dolomitic limestones (dolosparites and dolomicrites) and oolitic limestones (oomicrites). The elastic lithofacies of both formations represent continuous sedimentation in fluvial environments, whereas the carbonate lithofacies represent sedimentation in supratidal and shallow marine water. The intervening Shu‘aiba carbonate and clastic lithofacies originated in a very shallow marine environment, coeval with deposition of the upper Biyadh clasitic lithofacies in central Arabia. During early Barremian times, the fluvial lithofacies of the Biyadh were laid down in central Arabia and can be traced over the area of southwestern Iraq and Kuwait and over the southern part of the coastal area on the Arabian Sea. During Aptian times, the Shu‘aiba carbonate and elastic lithofacies formed between the Biyadh and Wasia; they interfinger with upper parts of the Biyadh at outcrops in central Arabia. The lithofacies are also well represented in the subsurface east of central Arabia and in the Arabian Gulf region. During Cenomanian-Turonian times, the fluvial lithofacies of the Wasia formed over most of central Arabia « and extended into northwestern Arabia, where they are now found in the Al .1an and Sakaka areas. A major marine transgression occurred during Campanian-Maestrichtian times and reached its greatest extent when the Aruma Formation carbonate rocks found near AI J awf and Sakaka were deposited near the Jordanian border.

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STRA.SEDIM.HIS.U.L.M.CRETA.RKS