bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of fractures in a highly dynamic thermal, hydraulic, and mechanical system – (I) Field observations in Mesozoic Carbonates, Jabal Shams, Oman Mountains
Authors: Holland Marc , Urai Janos L. , Muchez Philippe , Willemse Emanuel J.M.
Published: October 2021

We studied an exhumed high-pressure cell in outcrops of Cretaceous carbonates on the southern flank of Jabal Shams in the Oman Mountains. This more than 2 km thick sedimentary pile contains reservoir and source rocks in northern Oman and the United Arab Emirates. It develops a complex and rapidly changing anisotropy, due to mechanical stratigraphy and several generations of pervasive regional fault and fracture sets. Calcite cement healed faults and fractures before the next sets were formed.

Burial extension within a high fluid-pressure environment led to the formation of four fracture generations by an anticlockwise rotating stress field. This was followed by bedding-parallel shear under lithostatic fluid-pressure conditions at a minimum temperature of 134–221°C deduced from primary and pseudosecondary fluid inclusions in quartz. The high pressure cell was drained along dilatant normal faults that were also repeatedly cemented and reactivated.

The rapidly changing mechanical anisotropy, in combination with a chemically reactive system formed a complex feedback system in which the mechanical strength, strain and the permeability underwent major changes in this coupled thermal, hydraulic, and mechanical (THM) system.
Diagenetic and epigenetic alteration of Cretaceous to Paleogene organic-rich sedimentary successions in northwestern Jordan, typical of the western margin of the Arabian Plate
Authors: Dill Harald G. , Kus Jolanta , Abed Abdulkader M. , Sachsenhofer Reinhard F. , Khair Hani Abul
Published: October 2021

Four reference sections through the calcareous-siliciclastic rocks of the Lower Cretaceous Kurnub Group and the Amman and Muwaqqar formations of the Upper Cretaceous to Paleogene Belqa Group in Jordan document the various processes of accumulation and alteration of organic matter (OM). Sections at Jerash, Sultani, Wadi Isal, and in the Kharazeh area were investigated by means of sedimentary petrography/mineralogy, organic petrography, and organic chemistry, and correlated with equivalent deposits in Syria and Egypt. The impacts of oxidation potential (Eh), acidity/basicity (pH) and temperature variations during the post-depositional alteration of these organic concentrations were assessed using x-y plots. Syngenetic Aptian-Albian coaly and organic-rich amber beds near Jerash developed in a tide-dominated delta under marginally alkaline conditions and were altered under slightly acidic conditions at temperatures of less than 100°C. Environmental analysis focused on Maastrichtian-Paleocene (?), oil shales in the Sultani area that were deposited in a small restricted basin on the continental shelf of the Neo-Tethys Ocean. Abnormally high contents of vanadium (V), phosphorus (P), zinc (Zn), and uranium (U) gave rise to yellow uranium ore minerals, phosphates and zinc sulfides and so bridge the gap between OM concentrations and those of uranium. The western part of the Arabian Peninsula is known for its uraniferous phosphorites and U-bearing calcretes. Reducing conditions during deposition of syngenetic OM in the oil shales may have shifted, in places, toward more oxidizing conditions in the course of post-depositional alteration at temperatures well below 200°C. Epigenetic fault-related concentration of OM was responsible for the Wadi Isal Aptian-Albian tar sand deposit and the oil seepage system in calcareous wall rocks of the Kharazeh Fault. The alteration of the tar sands (fluvial sandstones) is designated a high-sulfidation type (introduced aluminum sulfate minerals), whereas the oil seepage in Campanian shallow-marine carbonates is a low-sulfidation type (removal of aluminum sulfate minerals). Both alteration patterns may have implications for structure-bound base- and precious-metal deposits whose emplacement involves hydrocarbons as a carrier of metals in the mineralizing fluids. The Jordanian oil shales, tar sands, and uranium mineralization are possible sources of energy. Recent economic deals on the recovery and use of oil shales and uranium in Jordan are reviewed.
Subsidence history, gravity anomalies and flexure of the United Arab Emirates (UAE) foreland basin
Authors: Ali Mohammed Y. , Watts A. B.
Published: October 2021

Seismic reflection profile, gravity anomaly, and exploratory well data have been used to determine the structure and evolution of the United Arab Emirates (UAE) foreland basin. The basin is of tectonic significance because it formed by ophiolite obduction in the northern Oman Mountains and flexural loading of an underlying Tethyan rifted margin. Existing stratigraphic data shows that this margin is characterised by an early syn-rift sequence of mainly Triassic age that is overlain by a post-rift sequence of Lower Jurassic to Upper Cretaceous age. Backstripping of the well data provides new constraints on the age of rifting, the amount of crustal and mantle extension, and the flexural effects of ophiolite load emplacement. The tectonic subsidence and uplift history at the wells can be generally explained by either a uniform extension model with an initial age of rifting of 210 Ma and a stretching factor, β, of 2.5 or a depth-dependant extension model with crustal extension factor of, γ, 1.3 and a mantle extension factor, β, of 2.5. While both models account for the general exponential decrease that is observed in the tectonic subsidence and uplift between 210 Ma and 95 Ma, we prefer the depth-dependant model because the depth-to-Moho that is implied better accounts for the increase that is observed in the regional Bouguer gravity anomaly between the UAE foreland and the Oman coastline. However, there are discrepancies, which we attribute to uncertainties in palaeobathymetry, sea level, and stratigraphic ages. Irrespective, the backstrip curves suggest that there was a significant thinning of the continental crust prior to ophiolite emplacement. The timing of emplacement cannot be constrained precisely, but the backstrip curves suggest that ophiolite loading and foreland basin flexure was initiated during the Late Cretaceous. The basin shape can be explained by a simple model in which both surface (i.e. topographic) and subsurface (i.e. ophiolitic) loads were emplaced on a lithosphere with an effective elastic thickness, Te´ of c. 20–25 km. This Te is similar to what we would expect for loading of extended continental lithosphere 80 My after a rifting event. It predicts a c. 4 km flexural depression and a few hundred metres flanking bulge that is presently located beneath the Abu Dhabi region. The bulge is obscured, however, by at least 2 km of sediment, possibly because of an increase in accommodation space due to dynamic effects associated with the subduction of the Arabian Plate beneath the Eurasian Plate.
Ichnology as a tool in carbonate reservoir characterization: A case study from the Permian – Triassic Khuff Formation in the Middle East
Authors: Knaust Dirk
Published: October 2021

In the Upper Permian to Lower Triassic Khuff Formation in the Arabian Gulf, a vast shallow-marine carbonate platform developed broad facies belts with little significant changes in the lithofacies. However, trace fossil assemblages and ichnofabrics, in combination with sedimentological observations, serve in subdividing this platform and in distinguishing sub-environments. From proximal to distal, these are sabkha and salina, tidal flat, restricted lagoon, open lagoon, platform margin, shoreface/inner ramp, slope/outer ramp and basin/deeper intra-shelf. In this way, changes in relative sea level can be better reconstructed and guide the sequence stratigraphic interpretation. Meter-scale shallowing-upward cycles dominate the succession and, in addition to conventional methods, bioturbation, trace fossil assemblages and tiering patterns aid in interpreting subtidal, lower and upper intertidal and supratidal portions of these peritidal cycles. Bioturbation (and cryptobioturbation) have an impact on the primary reservoir quality before diagenetic processes overprint the deposits. For instance, deposit-feeders (such as vermiform organisms) introduce a certain amount of mud and decrease porosity and permeability considerably, whereas others like the Zoophycos-producers fill their dwellings with ooid grains and turn a mudstone from a barrier to a flow unit. This novel study demonstrates the value of ichnological information in carbonate reservoir characterization and the significance of trace fossil analysis in facies interpretation, reservoir zonation and the impact of bioturbation on the reservoir quality.
Biogenic silica microfossils in sediments of the Permian – Carboniferous Unayzah Formation, Saudi Arabia
Authors: Garming Johanna F.L. , Franks Stephen G. , Cremer Holger , Abbink Oscar A.
Published: October 2021

Biogenic silica particles (BSPs) have been discovered in sediments of the Permian – Carboniferous Unayzah Formation of Saudi Arabia. The BSPs are extracted from sediments that are generally barren of macro- or microfossils. BSPs have been found in the Basal Khuff Clastics (BKC), and the Unayzah A, B, and C members, that were sampled in six different wells over a large geographic area. More than 3,500 BSPs have been identified in 83 samples examined and have been classified into 14 different BSP morphotypes. Furthermore, three outcrop samples of the Permian – Carboniferous Al Khlata and Gharif formations of Oman were analysed. Herein seven BSP morphotypes were identified. For comparison of the Paleozoic BSPs with modern analogues, recent plant material from the Rub’ Al Khali Desert was studied. The presence of BSPs in Paleozoic deposits and their morphological difference is encouraging. Variations in morphotype abundance and occurrence may ultimately provide a means of subdividing and correlating the Unayzah Formation. Research presently underway is testing the distribution of morphotypes in terms of stratigraphic position, depositional facies, and paleoclimatic setting.
Orbital-forcing glacio-eustasy: A sequence-stratigraphic time scale
Authors: Matthews Robley K. , Al-Husseini Moujahed I.
Published: October 2021

This essay provides further explanation of the mathematical details of orbital forcing and glacio-eustatic modeling (Parametric Forward Modeling, PFM) aspects and applications. A slight tune-up of the Earth’s eccentricity calculations (LA04 of Lasker et al., 2004) produces a near-perfect repeat of 14.58 million-year period and allows PFM to predict the glacio-eustatic component of sea-level fluctuation throughout the Phanerozoic. Generalities of an exploratory grid search of the parameter space of the model are reviewed and repetitive peak sea levels and low sea levels are noted in context of the Arabian Orbital Stratigraphy (AROS) terminology and time scale. Emphasis on the straton (405,000 year “tuning fork” of stratigraphic time) will lead to improvements in sequence-stratigraphic methods and results.
Late Albian, Cenomanian and Turonian Natih Supersequence of Oman: Type section for Orbiton 7 (103.6–89.0 Ma)
Authors: Al-Husseini Moujahed I.
Published: October 2021

The Upper Albian, Cenomanian and Turonian Natih Formation in Oman was interpreted by previous authors in terms of the regional Natih I to V depositional sequences comprising 34 higher-order subsequences (referred to as the Adopted Interpretation in this paper). It mainly consists of limestones, and is separated from the underlying Albian shales of the Nahr Umr Formation by the Natih Sequence Boundary. The interpreted position of the Cenomanian Stage within the formation differs substantially depending on carbon-isotope and/or biostratigraphic data (ammonite, microfaunal and nannofossil). The top of the Natih Formation is a regional subaerial exposure surface (incised by channels with depths reaching 150–200 m) that was transgressed by Lower Coniacian marine shales (Muti Formation at outcrop, and Shargi Member of the Fiqa Formation in subsurface; Fiqa Transgression above the Fiqa Sequence Boundary). Over paleohighs the lower part of the Fiqa, Natih and older formations are eroded by the Campanian angular Intra-Fiqa Unconformity that is attributed to far-field compressional tectonism along the margins of the Arabian Plate.

The paper tunes the 34 Natih subsequences (each named a Straton) at 405 Ky/cycle: the period of the long-eccentricity signal of the Earth’s orbit. They are dated using a time scale that is based on an orbital-forcing model of glacioeustasy, which consists of ca. 14.58 My (36 stratons) repeating, orbital cycles named orbitons. Orbitons are predicted to be separated by major glacio-eustatic lowstands (regional sequence boundary), with Orbiton 1 spanning ca. 16.1 to 1.5 Ma. The Natih Formation completely falls within Orbiton 7 (ca. 103.6–89.0 Ma) in the Late Albian – Turonian time interval of the Geological Time Scale of the International Commission on Stratigraphy (GTS). The Formation consists of only 34 subsequences (compared to the 36 predicted for a complete orbiton). This implies two stratons are represented by a hiatus (ca. 810 Ky) between ca. 89.8–89.0 Ma near the end of Orbiton 7 and the Turonian/Coniacian boundary (88.6 Ma in GTS). The hiatus corresponds to a Late Turonian – ?earliest Coniacian biostratigraphic break at the Sub-Fiqa Unconformity and is correlated to a model-predicted major polar glaciation and sea-level lowstand. The hiatus is unrelated to the structural deformation in Interior Oman (First Alpine Event), which started some 10 My later in Campanian time. Orbiton 7 (ca. 103.6–89.0 Ma) correlates by architecture (sequence boundaries and maximum flooding surfaces) and age to the global Late Albian – Turonian UZA 2 Supersequence inclusive of the shortlived 100+ m sea-level drop in latest Turonian (ca. 102.5–88.6 Ma in empirical time scale). The Formation is proposed as the Natih Supersequence and the type section of Orbiton 7.
Seal turns into reservoir: Sudair equivalents in outcrops, Al Jabal al-Akhdar, Sultanate of Oman
Authors: Pöppelreiter Michael C. , Schneider Christoph J. , Obermaier Michael , Forke Holger C. , Koehrer Bastian , Aigner Thomas
Published: October 2021

The Lower Triassic Sudair Formation represents the deposits of an epeiric carbonate-evaporite-siliciclastic platform. It is widely known as top seal for the underlying Khuff reservoir in some of the largest hydrocarbon accumulations in the world (e.g. the North Dome and the Ghawar field). Towards the seaward edge of the platform however, in northeast Oman for example, the sealing anhydrites and shales pinch out. Dolomite layers turn increasingly grainy, forming up to 8 m-thick individual grainstone bodies. Thus, on a regional scale, a top seal turns laterally into a potential reservoir. This paper outlines facies, depositional environment and stratigraphic architecture of the Middle Mahil Member, the outcrop equivalent of the Sudair Formation in northeast Oman.

The Middle Mahil, some 260 m thick, is made up of just a few facies types: argillaceous, muddy, microbially-laminated, graded, and cross-bedded dolomites. These represent tidal flat, backshoal and shoal environments. Facies are arranged in regular sequences; the smallest units being 2–5 m thick cycles. A clear hierarchical organization of sequences is apparent with bundling of 4–8 cycles into cycle sets, and 2–3 cycle sets forming depositional sequences. The lower third of the Middle Mahil is dominated by rather muddy textures, the middle part is grain-dominated and the upper part again is muddier with a higher percentage of microbial laminites. The maximum grainstone thickness is observed in the middle of the Middle Mahil, at the interpreted zone of maximum flooding.

Overall the Middle Mahil shows “layer-cake” type architecture over distances of 4–8 km. Grainstone layers are laterally continuous at this scale. Pinching and swelling geometries of grainstones are widespread. Grainstones gradually increase in thickness towards the northeast, the direction of the seaward platform edge. Mapping of Middle Mahil grainstones suggest excellent reservoir potential in such platform margin settings. The observations from Oman provide a calibration point to explorationists targeting the Lower Triassic carbonate sequence in the Middle East.
Heavy mineral stratigraphy of Palaeozoic and Mesozoic sandstones of southwestern Sinai, Egypt: A reassessment
Authors: Knox Robert W.O’B. , Soliman Mamdouh F. , Essa Mahmoud A.
Published: October 2021

Improved methods of analysis and quantification of heavy mineral assemblages in Cambrian to Early Cretaceous sandstones of southwest Sinai have revealed successive changes in provenance that reflect both rejuvenation of the Arabian Shield and changes in the topographic configuration of the source area. Three mineral units have been identified in the Cambrian succession, at least three in the Carboniferous and three in the Cretaceous. It is predicted that the genetic units defined by these successive changes in mineralogy will be of regional extent and thus assist in elucidating the history of uplift of the Arabian-Nubian Shield and provide a better means of correlating sandstone units into adjacent areas. Variation in the abundance of apatite in the Cambrian succession is independent of provenance signature and is interpreted as reflecting alternating dry and humid climatic conditions.
Stratigraphic Note: Update on the palynology of the Akbarah and Kuhlan formations, northwest Yemen
Authors: Stephenson Mike H. , Kader Al-Mashaikie Sa’ad Zeki A.
Published: October 2021

Following a preliminary palynological report of two samples from the lower part of the Kuhlan Formation (Unit A) near Kuhlan village, northwest Yemen (Stephenson and Al-Mashaikie, 2010), a further seven samples from Unit A, and an additional 22 samples from the underlying Akbarah Formation in the same locality are reported. The seven new samples from the Kuhlan Formation support the 2165A to 2141A Biozone age originally suggested by Stephenson and Al-Mashaikie (2010), and the new Akbarah Formation samples suggest an age not markedly different since Anapiculatisporites concinnus and Spelaeotriletes triangulus are also present in the Akbarah Formation (e.g. samples AK-11 and AK-12). This correlation confirms that the lower Kuhlan Formation and the Akbarah Formation, are likely to be late Carboniferous in age and equivalent to the lower parts of the Al Khlata Formation of Oman.
Guadalupian (Permian) brachiopods from the Ruteh Limestone, North Iran
Authors: Crippa Gaia , Angiolini Lucia
Published: October 2021

Thirty-three brachiopod species from the Guadalupian Ruteh Limestone of North Iran are here systematically described and illustrated. Brachiopods have been collected bed-by-bed along five stratigraphic sections and in one fossiliferous locality in the region between Dorud and Shirinibad in the Alborz Mountains. Four new species and one new genus are erected in the present paper: Haydenella eminens n. sp. Perigeyerella rutehiana n. sp., Martinia bassa n. sp. and Bisolcatelasma iraniana n. gen. n. sp.

Quantitative biostratigraphic analysis of the brachiopod data based on the Unitary Association method (Guex, 1991) has lead to the construction of a local sequence of three discrete biozones: the Squamularia sp. B-M. bassa Biozone at the base of the formation, the H. kiangsiensis-N. (N.) asseretoi Biozone in its middle part and the R. exile-R. gemmellaroi Biozone at its top. The latter however has been recognized only in the Shirinabad section.

As already envisaged for the Carboniferous and Lower Permian brachiopod faunas from North Iran, the Guadalupian fauna is comprised mostly of cosmopolitan taxa, confirming the role of the Iranian microplate as a staging-post for most of the late Palaeozoic. When compared to the younger Lopingian faunas collected in the same regions of North Iran, the Ruteh brachiopods appear significantly different, indicating a marked biotic change in the brachiopod communities across the end-Guadalupian biotic crisis.
Late Oligocene–Early Miocene Nukhul Sequence, Gulf of Suez and Red Sea
Authors: Al-Husseini Moujahed I.
Published: October 2021

Egypt’s Late Oligocene–Early Miocene Nukhul Formation was deposited during the earliest geological evolution of the Gulf of Suez and Red Sea Rift System. In this paper the formation is cast as a depositional sequence based on published sections, and correlated across the Gulf of Suez and northern Red Sea. The resulting correlations indicate that deposition was initiated in local grabens by the oldest continental clastics of the lower member of the Nukhul Formation, the Shoab Ali Member. The member overlies the Suez Rift Unconformity, a term proposed for the entire Red Sea. Although this member can attain a thickness of ca. 1,000 ft (305 m) locally in grabens, it is generally absent over horsts. Sedimentary facies of the member are interpreted as indicating an initial alluvial-fluvial setting that evolved to an estuarine and coastal setting.

The upper part of the Nukhul Formation records a regional shallow-marine transgression, which can be subdivided into three correlative Upper Nukhul members. These sediments are absent over the highest paleo-horsts, but reach up to 900 ft (275 m) in thickness in grabens. In the southern Gulf of Suez the Ghara Member represents the Upper Nukhul members. In places it consists of four cycles, each of which starts with an anhydrite bed and is overlain by deposits of mixed lithology (sandstone, marl, and limestone). The four cycles are interpreted as transgressive-regressive subsequences that can be correlated across ca. 60 km in the Gulf of Suez. The Ghara Member correlates to Saudi Arabia’s Yanbu Formation, which consists of massive salt in wells drilled on the Red Sea coastal plains. The Yanbu Salt is dated by strontium-isotope analysis at ca. 23.1–21.6 Ma (earliest Aquitanian).

The Nukhul Formation is capped by the Sub-Rudeis Unconformity or correlative Rudeis Sequence Boundary, and overlain by the Rudeis Formation. The Nukhul Formation is here proposed as the Nukhul Sequence and defined in the Wadi Dib-1 Well, wherein it consists of Nukhul subsequences 1 to 10 (in descending order, ranging in thickness between 33–84 m). The lower six Nukhul subsequences 10 to 5 are characterized by shale-to-sandstone cycles of the Shoab Ali Member, and the upper four are represented by the cycles of the Ghara Member. The 10 subsequences are interpreted as tracking the 405,000 year eccentricity signal of the Earth’s orbit and to span ca. 4.0 million years between ca. 25.0 and 21.0 Ma.
Geochemistry, and carbon, oxygen and strontium isotope composition of brachiopods from the Khuff Formation of Oman and Saudi Arabia
Authors: Stephenson Michael H. , Angiolini Lucia , Leng Melanie J. , Darbyshire D.P. Fiona
Published: October 2021

Brachiopods are abundant in the Oman Khuff Formation and similar brachiopod faunas are present at a few horizons in the same formation in Central Saudi Arabia. Following extensive systematic and biostratigraphic studies of these faunas, specimens from the base of the Midhnab Member of the Khuff Formation of Saudi Arabia (Buraydah Quadrangle), and from Member 3 of the Khuff Formation of the Huqf outcrop of Oman were assessed for isotope geochemistry (Sr, O and C). Dating using 87Sr/86Sr alone is not conclusive. Five pristine Oman brachiopods from biostratigraphically well-constrained lower Wordian horizons record a range of 87Sr/86Sr values that form a separate cluster offset from the current Sr isotope seawater curve, which defines the Early Permian and earliest Mid-Permian. The 87Sr/86Sr of the pristine Saudi Arabian brachiopod sits in an area which corresponds to a wide scatter of 87Sr/86Sr in the seawater curve data. However, the Saudi Arabian data does indicate that the Midhnab Member is likely younger than Member 3 of the Khuff Formation of the Huqf outcrop.

The well-preserved brachiopod carbonate allows deductions to be made about the palaeotemperature of the Oman Khuff Formation Member 3 seawater using its oxygen isotope composition (δ18O). Assuming δ18O of seawater < –0.5‰, then palaeotemperature derived from brachiopods in the Oman horizons would be +25°C, +22°C and +17°C respectively. This is consistent with the trend of shallowing within Member 3, suggested by facies.
Sedimentological characterization of the mid-Cretaceous Mishrif reservoir in southern Mesopotamian Basin, Iraq
Authors: Mahdi Thamer A. , Aqrawi Adnan A.M. , Horbury Andrew D. , Sherwani Govand H.
Published: October 2021

The CenomanianÐEarly Turonian reservoirs of the Mishrif Formation of the Mesopotamian Basin hold more than one-third of the proven Iraqi oil reserves. Difficulty in predicting the presence of these mostly rudistic reservoir units is mainly due to the complex paleogeography of the Mishrif depositional basin, which has not been helped by numerous previous studies using differing facies schemes over local areas. Here we present a regional microfacies-based study that incorporates earlier data into a comprehensive facies model. This shows that extensive accumulation of rudist banks usually occurred along an exterior shelf margin of the basin along an axis that runs from Hamrin to Badra and southeast of that, with additional interior rudist margins around an intra-shelf basin to the southwest. Regional tectonism defined the accommodation sites during the platform development.

Facies analysis allowed the recognition of 21 microfacies types and their transgressive-regressive cyclic stacking pattern. Sequence-stratigraphic analysis led to the recognition of three complete third-order sequences within the studied Mishrif succession. Eustatic sea-level changes were the primary control on this sequence development but local tectonics was important at the Cenomanian/Turonian boundary. Rudist biostromes are stacked as thicker shallowing-up cycles composed of several smaller-scale cycles. In places, smaller cycles are clearly shingled (stacked laterally). Iraq’s Mishrif sequences are thus analogous to coeval systems across the Arabian Plate in Oman, United Arab Emirates, offshore Saudi Arabia and Kuwait, southwest Iran and the Levant.

Analysis of poroperm trends shows porosity increasing beneath sequence boundaries due to karstification and meteoric dissolution. The presence of interconnected vugs in grain-dominated fabric make the rudist biostromes the best reservoir units. Dissolution of aragonitic components of rudist shells was the most important diagenetic process that enhanced reservoir characteristics. The presence of rudist-bearing facies with their diagenetic overprint within regressive cycles is considered the primary factor in effective porosity development and distribution. As a result, because of depositional heterogeneities (facies type distribution and their 3-D geometries) and the influence of sequence boundaries on reservoir quality, each field shows unique geometrical combinations of pay zones, barriers and seals.
The eastern Mediterranean phosphorite giants: An interplay between tectonics and upwelling
Authors: Abed Abdulkader M.
Published: October 2021

About 20 billion tonnes of world-class, high-grade phosphorite resources occur in a small area of the eastern Mediterranean region, including Jordan, northern Negev (Palestine), northwestern Saudi Arabia, western Iraq, and southeastern Syria. Major deposits were formed during Campanian to Eocene times and contribute significantly to the economic development of these countries, particularly Jordan and Syria. The phosphorite deposits consist mainly of reworked granular material. The phosphate particles are peloids, such as pellets, intraclasts, nodules, coated grains and coprolites, and vertebrate fragments (bone and teeth). The phosphorite sequences are associated with extensive bedded chert, porcelanite, and organic-rich marls. The main phosphate mineral is francolite, a carbonate-rich variety of fluorapatite that has a relatively enhanced uranium content as a result of substitution for calcium in its crystal structure.

Two factors are deemed responsible for the deposition of the phosphorites and their associated chert, porcelanite, and marl within this relatively restricted area. The first was a compressional event associated with the initial collision of the oceanic forefront of the Afro-Arabian Plate with the subduction trench of Eurasia that began in Turonian times and continued into the Eocene. This event resulted in gentle folding that produced the Syrian Arc, the Ha’il, Rutba, and Sirhan paleohighs and the Ga’ara Dome, which were loci for the deposition of phosphorites. The second factor was the obstruction and consequent upwelling of oceanic currents by these tectonic highs, enhanced by winds blowing from east to west along the southern platform margin of the Neo-Tethys Ocean. The intense upwelling was associated with the Tethyan Circumglobal Current that flowed along the Afro-Arabian platform on the southern margin of the Neo-Tethys Ocean. In contrast, relatively minor phosphorite deposition took place to the north in southern Europe.

The upwelling spread cold, nutrient-rich oceanic water from the deep Neo-Tethys Ocean to the surface, thereby enhancing bioproductivity to produce organic-rich sediments. The subsequent authigenesis of phosphorites, their diagenesis and the reworking and winnowing of the phosphorite-rich sediments, concentrated the materials into economic deposits. Phosphorite deposition ended in the Late Eocene following the final collision of the Afro-Arabian Plate with Eurasia. The sub-aerial exposure of this formerly productive shallow-marine platform was the result of the separation of the Arabian Plate from the African Plate during the mid-Miocene.
High-resolution anatomy of a grainstone package in Khuff Sequence KS4, Oman Mountains, Sultanate of Oman
Authors: Maria-Louise Haase Marlene , Aigner Thomas
Published: October 2021

This study is part of a large-scale outcrop analog study on Middle Permian to Lower Triassic Khuff-equivalent strata in the Oman Mountains, Al Jabal al-Akhdar, Sultanate of Oman. The Khuff outcrop equivalent can be divided into six sequences (Khuff sequences KS6 to KS1, from base to top). The main focus of this study is the description of the internal anatomy of the shoal grainstone bodies in the lower part of Sequence KS4 (“lower KS4”). High-resolution sedimentological logging of three outcrop sections in wadis Sahtan, Bani Awf and Mistal yielded eight lithofacies types that were grouped into five facies associations. Lower KS4 strata were mainly deposited within a “shoal complex” of an epeiric carbonate ramp, resulting in a thick pile of up to 70 m of grainstones that, on first sight, appear relatively homogeneous. However, detailed facies and microfacies analysis revealed their heterogeneous architecture on various scales: (1) Minor changes in depositional environments directly affected the type of carbonate grains (ooids versus peloids/cortoids versus bioclasts), leading potentially to highly variable pore systems (moldic versus interparticle versus intraparticle). (2) Vertically, detailed sequence-stratigraphic analysis revealed a higher-order of cyclicity (“mini-cycles”) on a decimeter- to meter-scale. Four mini-cycle types were recognized. (3) Laterally, facies changes, the amalgamation of grainstone beds and mini-cycle pinch-outs were observed in 2-D correlations on a scale of a few kilometers. These different types of heterogeneities may contribute to varying production rates commonly observed in the subsurface KS4 reservoir.
Evolution, paleoecology and sequence architecture of an Eocene carbonate ramp, southeast Zagros Basin, Iran
Authors: Zohdi Afshin , Mousavi-Harami Reza , Ali Moallemi Seyed , Mahboubi Asadollah , Immenhauser Adrian
Published: October 2021

We document and discuss the results of detailed fieldwork, facies analysis and the subsequent integration of paleoecological evidence from the Middle Eocene carbonate ramp succession in the southeast Zagros Basin (Jahrum Formation). A combination of a sea-level fall and tectonic and diapiric basement uplift favored the initiation of the Jahrum carbonate platform. The lower portions are affected by pervasive, probably early diagenetic dolomitization, whilst the upper Jahrum consists mainly of limestone. Here, the focus is on the limestone portions of the Jahrum Formation. Based on the abundance, diversity and rapid evolutionary turnover of the alveolinids and nummulitids, the limestone intervals of the Jahrum Formation are interpreted for the upper Middle Eocene (Bartonian). The Jahrum Formation is capped by a major unconformity and overlain by the Lower Oligocene mixed clastic/carbonate Razak Formation.

Based on data from field sections, eight facies associations and a series of sub-types have been established, which correspond to inner-, middle-and outer-ramp depositional environments. In their overall context, these data show a southward-dipping inner-ramp-to-basin transect. Towards the Coastal Fars (e.g. Hulur-01 Well) the Jahrum grades laterally into deep-marine Pabdeh foredeep shale units. Based on facies analysis and paleoecological evidence from larger benthic foraminifera, a major transgressive-regressive pattern is recognized in all outcrop sections of the Jahrum. The lowermost stratigraphic units of the formation are here interpreted as a distally steepened ramp. Evidence comes from abundant allochthonous shallow-water facies in the distal, deeper-ramp setting. Shallow-water carbonate clasts were exported towards the basin, a feature that is probably linked to relative sea-level fall control. Furthermore, local to regional basement instabilities by salt diapir-related basement reorganization was arguably of significance. Upsection, evidence is found that the ramp system evolved from a distally steepened to a homoclinal geometry with an overall very gentle slope geometry during the Late Bartonian.

The data shown here are significant for those concerned with the Paleogene evolution of the southeast Zagros Basin and provide a well-exposed case example of a Middle Eocene carbonate ramp factory.
A refined foraminiferal biostratigraphy for the Late Campanian–Early Maastrichtian succession of northeast Iraq
Authors: Jaff Rawand B.N. , Williams Mark , Wilkinson Ian P. , Lawa Fadhil , Lee Sarah , Zalasiewicz Jan
Published: October 2021

Species of the benthonic foraminiferal genus Bolivinoides provide a refined biostratigraphic biozonation for the Late Campanian to Early Maastrichtian (Late Cretaceous) Shiranish Formation in NE Iraq. Three biozones and two subzones are identified: the Bolivinoides decoratus Biozone (Late Campanian) subdivided into a lower B. decoratus Subzone and upper B. laevigatus Subzone; the B. miliaris Biozone (Earliest Maastrichtian); and the B. draco Biozone (late Early Maastrichtian). These zones can be related to the biostratigraphical interval of the Globotruncana aegyptiaca (Late Campanian), Gansserina gansseri (latest Campanian–Early Maastrichtian) and Contusotruncana contusa (late Early Maastrichtian) planktonic foraminiferal biozones. Combined, the benthonic and planktonic foraminiferal biostratigraphy enables the informal recognition of lower and upper intervals within both the Globotruncana aegyptiaca and Gansserina gansseri biozones that may be important for more refined inter-regional correlation in the Middle East and North Africa. The new Bolivinoides biozonation precisely locates the Campanian–Maastrichtian boundary in NE Iraq. The foraminiferal assemblages also constrain the timing of a shallowing marine trend in the Shiranish Formation beginning from the latest Campanian that is consistent with shallowing facies noted globally at this time.
Modeling of the Dammam outcrop fractures: Case study for fracture development in salt-cored structures
Authors: Al-Fahmi Mohammed , Michele L. Cooke , Cole John C.
Published: October 2021

The exposed Cenozoic carbonates of the Dammam Dome are studied to: (1) characterize fractures and associated structures; (2) interpret the fracture mechanism; and (3) gain insights into fracture development within dome-like structures in the subsurface of the Arabian Gulf region. The fieldwork is integrated with structural analysis of the near-surface horizons mapped from interpretations of 3-D reflection seismic and borehole logs. Fractures are mapped from the outcrops of the middle limestone unit of the Eocene Rus Formation. The outcrops are concentrated in the central, northern and western areas of the Dammam Dome. The fractures are interpreted as opening-mode, bed-bounded joints that form orthogonal sets in most areas. The primary (older) joint set (J1) developed in long lineaments, some of which can be traced for over 300 m across entire exposures. The J1 set is found to be broadly consistent in its trend over the dome, indicating that formation of J1 fractures was systematic and not influenced by local structural anomalies (including karst collapse) formed during the Miocene to Recent. The trend of the J1 set does not correlate with the NE-SW compressional orientation of regional stresses associated with the Zagros Orogeny. Field data interpretation, allied with analysis of dome’s growth and curvature, suggest that the overall joint pattern reflects the growth of the strata as a dome. In addition, the joint density is controlled by structural position on the dome and mechanical stratigraphy. The study results provide a first-order conceptual fracture model for the subsurface reservoirs to guide future development.
Proposed correlation of Oman’s Abu Mahara Supergroup and Saudi Arabia’s Jibalah Group
Authors: Al-Husseini Moujahed I.
Published: October 2021

The Ediacaran–Cambrian Middle East Geologic Time Scale is extensively revised in the 2014 version (Enclosure). It suggests the top of the Abu Mahara Group glacial diamictites in Oman represent the termination of the late Cryogenian Marinoan Glaciation at 635 Ma. The overlying Ediacaran Nafun Group of Oman is shown between 635 and 547 Ma based on geochronologic data, and divided into: (1) the Lower Nafun Supersequence (635–582 Ma) consisting of the Hadash Formation (cap carbonate), the Masirah Bay Formation (clastics) and the Khufai Formation (carbonates); and (2) the Upper Nafun Supersequence (582–547 Ma) consisting of the Shuram Formation (clastics and carbonates) and the Buah Formation (carbonates). The Nafun Group lies below the Ediacaran– lower Cambrian Ara Group (evaporites and carbonates), which contains the Ediacaran/Cambrian Boundary currently dated at 541 Ma.

The Sub-Shuram Unconformity, which corresponds to the global Shuram δ13C Negative Excursion, separates the Nafun supersequences. Its age was estimated by assuming the thicknesses of the Nafun formations are proportional to time in the Masirah-1 Well, where the Nafun Group attains its greatest-known thickness of 2,308 m in Oman. This assumption coincidently estimated the unconformity at 582 Ma, the same age as the Ediacaran Gaskiers (Varanger or Varingian) Glaciation. The new calibration was used to correlate the Nafun formations to the rock-time units of the Jibalah Group in several isolated basins along the Najd Fault System in the Arabian Shield, using recently published geochronologic data and δ13C measurements, as follows.

The younger part of the Lower Nafun Supersequence (635–582 Ma) is here correlated to the Lower Jibalah Supersequence (605 ± 5 to 582 Ma), represented by the Umm al-Aisah Formation in the Jifn Basin, located along the Halaban-Zarghat Fault Zone of the Najd Fault System. The Umm al-Aisah Formation consists of volcanics and clastics that give way to the Umm al-Aisah Limestone. The Upper Nafun Supersequence (582–547 Ma) is here correlated to the Upper Jibalah Supersequence, which unconformably overlies the Umm al-Aisah Limestone, with its basal unit being the Gaskiers-coeval Jifn Polymictic Conglomerate (≥ 200 m thick). In the Bir Sija Basin, located along the Rika Fault Zone of the Najd Fault System, the likely Gaskiers-coeval polymictic conglomerate (150 m thick) is overlain by a 20 m-thick limestone unit, the Bir Sija Limestone, possibly a cap carbonate. The Upper Jibalah Supersequence continues with clastics overlain by the Muraykhah Formation (carbonates) or mixed clastics-carbonates of its equivalent formations. In several outcrops the Upper Jibalah Supersequence is overlain by the lower Cambrian Siq Sandstone Formation (≤ 525 ± 5 Ma) implying the Sub-Siq Unconformity represents a hiatus between 547 and 525 ± 5 Ma. The Jifn Formation in the Jifn Basin, however, may represent continuous deposition between 582 Ma and 525 ± 5 Ma.
Multi-level stratigraphic heterogeneities in a Triassic shoal grainstone, Oman Mountains, Sultanate of Oman: Layer-cake or shingles?
Authors: Obermaier Michael , Ritzmann Nicklas , Aigner Thomas
Published: October 2021

A fundamental question in the correlation of 1-D sedimentologic data is whether to use a layer-cake or shingled correlation approach. The resulting reservoir geometry has important implications for the characterization of reservoir heterogeneities and fluid flow. On the Saiq Plateau in Oman, epeiric carbonate ramp deposits of the Triassic Sudair Formation are well exposed and can be investigated in detail over several kilometers. There, reservoir heterogeneities on different scales have been documented by creating various outcrop wall panels and 2-D correlations. Multi-level architectural elements with different depositional geometries were discovered, which were linked to a sequence-stratigraphic hierarchy consisting of three levels. Level 1: A “layer-cake”-type stratigraphic architecture with minor thickness variations over several kilometers becomes apparent when correlating fourth-order cycle set boundaries. Level 2: The correlation of fifth-order cycle boundaries reflects horizontally continuous geometries, within which, however, internal grainstone layers were discovered to be arranged in a shingled fashion. Muddy layers in between these shingles illustrate sixth-order mini-cycle boundaries. Level 3: Within sixth-order mini-cycles another scale of a shingle-like architecture can be observed. Amalgamated cm-thick grainstone units form thin wedges with subtle but clearly inclined dipping geometry.

Fourth-order cycle sets and fifth-order cycles can be traced over several kilometers, and therefore assumed to be related to allocyclic stratigraphic processes. The internal shingle geometries within fifth-order cycles are traceable over 100s of meters and presumably reflect an autocyclic lateral migration of a shoal complex. Cm-thick shingling grainstone wedges within sixth-order mini-cycles are interpreted as storm-related spill deposits. Their event-driven character is reflected by frequent amalgamation and reworking of the preceding deposits.

The results of this study of epeiric carbonate ramp deposits suggest that a “layer-cake” correlation approach is appropriate when correlating 10s of m-thick grainstone units over a distance of several kilometers. However in the documented example, these thick grainstone units consist internally of small-scale architectural elements, which show inclined geometries and require a shingled correlation approach. These small-scale heterogeneities within an overall “layer-cake” architecture might have an impact on fluid flow in similar subsurface reservoirs and should be taken into account for detailed reservoir correlations and static reservoir models.
Facies, sequence stratigraphy, reservoir and seal potential of the Mafraq Formation, Sultanate of Oman: An integrated outcrop analogue study
Authors: Bendias Daniel , Aigner Thomas
Published: October 2021

The mixed carbonate-siliciclastic Lower to Middle Jurassic Mafraq Formation unconformably overlies the Triassic Mahil Formation in outcrops of the Oman Mountains (pre-Mafraq Unconformity, known as pre-Marrat unconformity in other regions of Arabia). Together with the overlying Dhruma Formation, it is part of the Sahtan Group. This study provides: (1) a detailed facies analysis based on sedimentological logging of 12 outcrops. Twenty-four facies types were established and grouped into five facies associations, which can also be recognized in subsurface core intervals; (2) a detailed sequence-stratigraphic framework of the Mafraq Formation. Facies stacking and log patterns reveal cycle hierarchies on four scales from m-scale cycles, to several m-thick cycle sets, to tens of m-thick, high-frequency sequences, to 100 m-thick composite sequences; and (3) a documentation of potential reservoir and seal units. The study follows an approach from 1-D (outcrop sections) to 2-D (correlations and potential reservoir dimensions). The Mafraq outcrop type section, located in Wadi Sahtan is documented in an integrated way (facies, litho-, bio-, chemo- and sequence stratigraphy), together with additional outcrops of the Mafraq Formation throughout North Oman.

2-D correlation of the Mafraq Formation throughout North Oman is essentially based on cycle sets and provides key information about the lateral paleogeographic development of the formation. A general proximal-distal trend, from south to north, has been proposed by Ziegler (2001); outcrop data from the Oman Mountains confirms this trend and adds an EW-deepening component. The mixed carbonate-clastic Lower Mafraq Member (Sequence) with a coastal/estuarine to shallow-marine environment forms onlaps onto the pre-Mafraq Unconformity below, and thins out completely after some 10s of kilometers towards the southeast. The Upper Mafraq Member (Sequence) seems to be continuous over 10s of kilometers with less thickness decrease. Instead, a transition from a more distal carbonate shoal - backshoal environment in the northwest to a proximal clastic coastal/estuarine/terrestrial environment in the southeast can be observed. On a 100s km-scale significant thinning and a change towards terrestrial clastic facies can be observed southeast of the Oman Mountains area. Combined results from lateral/vertical logging, paleoenvironmental interpretations and correlation provided 3-D information about the dimensions of potential reservoir and seal units.

Several potential reservoir/seal intervals and their dimensions in dip direction could be identified: (1) Lower Mafraq Sequence: various types of sandbodies, most of them with a lateral extent ca. 5 km, sealed by shales. (2) Upper Mafraq Sequence, northwestern part: oolitic grainstones, laterally correlative over 10–20 km, sealed by shales. (3) Upper Mafraq Sequence, southeastern part: channelized sandstones units, lateral extent up to km, sealed by shales.