Biofacies and palaeoenvironments of the Jurassic Shaqra Group of Saudi Arabia

Sequence stratigraphy and facies analysis of the NE Gondwana Middle Jurassic inner-platform mixed carbonate-siliciclastic succession, Saudi Arabia

Article

Full-text available

May 2022

The sequence stratigraphy of the Dhruma Formation and Tuwaiq Mountain Limestone (Bajocian to middle Callovian) is based on shallow cores and outcrop measured sections along a 600-km–long N-S transect west and south of Riyadh. Correlations were extended westward in the subsurface using gamma-ray wireline logs (500 km). For the first time, the study integrates sequence stratigraphic framework with detailed semiquantitative micropaleontological analysis that allows reappraisal of stratigraphic interpretation of main biofacies associations. The outcrops provide a continuous stratigraphic record of the Middle Jurassic transgression of a large (>1000 km) epeiric tropical platform from continental braided fluvial deposits to tidal or wave-dominated mixed carbonate-siliciclastic lagoonal deposits. These formed aggraded flat-topped platform wedges and thicken northward due to evident syndepositional differential subsidence. The carbonate platforms are mud-dominated and evolved from restricted carbonate platforms that contained microbes and low-faunal diversity (early Bajocian to early Bathonian) to normal-marine carbonate platforms hosting coral/stromatoporoid-rich strata and high-faunal diversity adjacent to a deeper intrashelf basin (middle Callovian). The succession consists of two 2nd-order sequences, Dhruma and Tuwaiq sequences, separated by an unconformity (middle Bathonian hiatus). Several composite and high-frequency sequences that have a subordinate maximum flooding surface (MFS) in the lower Bathonian (zigzag Zone) and a main MFS in the middle Callovian coronatum Zone. The depositional sequences are considered to be of eustatic origin as they match well with Tethyan sea-level cycles. The carbonates developed well during late transgressive and highstand systems tract (TST and HST) of the composite sequences controlled by back stepping of the siliciclastic sources.

Spatial patterns variations of a burrowed carbonate stratum (ramp carbonates), Upper Jurassic Hanifa Formation, Central Saudi Arabia

Article

Apr 2022
SEDIMENT GEOL

Strata deposited in middle carbonate ramps are often highly burrowed. Such strata are easy to recognize in the stratigraphic record and have been recorded from numerous stratigraphic sections worldwide. However, the spatial patterns of these strata are poorly known, despite being intervals of flow zones in many hydrocarbon reservoirs and water aquifers. In this study, we trace one stratum (in the upper Hanifa Formation, central Saudi Arabia) that was deposited in the middle carbonate ramp of the Late Jurassic for ~21 km, cored it in three localities, and investigated its spatial stratigraphic, sedimentological and ichnological patterns by field investigation and laboratory analysis (petrographic analysis and computer tomography (CT) scanning). The results of the field investigation show that the stratum has a similar spatial stratigraphic pattern over the study area (sharp contacts with the underlying and overlying strata), suggesting one depositional cycle product. Nevertheless, the laboratory analysis revealed that the stratum varies spatially and distinctly in rock composition, burrow percentage (BP), and burrowing style, suggesting various controls on its rock texture. The bottom interval of the stratum comprises wackestone and packstone rock texture which are interpreted as a product of bio-retexturing that took place at the time of the initial flooding stage of the deposition cycle. In the middle (5% to 10% BP) and upper intervals (20% to 40% BP), the stratum has mudstone and wackestone host rock matrix penetrated by a Thalassinoides burrow network (pipe framework) with passive infills (grain-dominated carbonates). The stratum exhibits both vertical and lateral variations in burrow percentage and burrowing styles, which are interpreted to be controlled by variations in bathymetry due to sea-level change and seafloor topography. Such variations influenced the rock texture of the studied stratum and would eventually control the spatial patterns of its petrophysical properties. The results provide insights into the nature and controls on the spatial patterns of burrowed strata of a middle ramp carbonate, patterns that can be similar to many hydrocarbon reservoirs and can be used to predict the distribution of petrophysical properties.

Predicting marine organic-rich deposits using forward stratigraphic modelling: The Jurassic Najmah source rock – Case study

Article

Mar 2022
MAR PETROL GEOL

Predicting the distribution and heterogeneity of marine Mesozoic organic-rich rocks is a challenging task that requires multi-disciplinary data integration supported by innovative numerical modelling. This study aims at investigating the factors controlling marine organic matter production, accumulation, and preservation along the eastern Arabian intrashelf basins. Such types of basins exhibit an enhanced lateral and vertical facies variability caused by the interplay between shallow and deeper water sedimentation. The work focuses on characterizing the Mid-Upper Jurassic Najmah Formation that presents source rock, reservoir, as well as seal characteristics along Kuwait. It comprises high maturity levels (>0.6% Ro) and TOC values ranging between 2-30%. Forward stratigraphic modelling that includes organic matter production, transport, and preservation (i.e., degradation and dilution) was utilized. Models corresponding to two end-member basin types (restricted and fully open marine) have been simulated to mimic the organic matter deposition within a 3rd-order sequence stratigraphic framework. Simulation outputs provide a qualitative and quantitative assessment of organic matter characteristics (TOC, HI, and OI) at the time of deposition. Results show that (1) a combined variable eustatic sea level change and tectonic subsidence are the main driving mechanisms for sediment accommodation during the Mid-Upper Jurassic time, (2) strong anoxic conditions in the restricted basin simulations promote the preservation of organic-rich deposits in the distal northern sectors while (3) the influence of open marine bottom current oxygenation is not expected to impact the relatively shallower conditions affecting the intrashelf basin (<200m depth), (4) organic matter dilution can be observed along the southernmost sectors of Kuwait due to high sedimentation rates related to the development of gravity driven deposits. Sensitivity analysis on input parameters (i.e., primary productivity vs water depth) supports the partially restricted basin conditions with occasional connection to the open ocean during eustatic sea level rise. This study contributes to the improvement of basin models in conventional as well as unconventional petroleum system exploration.

3D forward stratigraphic modelling of the Lower Jurassic carbonate systems of Kuwait

Article

Jan 2021
MAR PETROL GEOL

This paper describes the architectural and texture/facies evolution of a complex carbonate system through the construction of a regional scale 3D stratigraphic forward model (252 × 152 km², 4 km × 4 km grid size) encompassing onshore and offshore Kuwait. The model mimics the development of a Jurassic carbonate ramp system at a 2nd to 3rd sequence stratigraphic order (1–80 Myr duration; Schlager, 2010) by simulating sedimentary processes and ecological parameters such as carbonate production versus depth, time, wave energy, as well as erosional and gravitational transport. Multi-scale 1D, 2D, and 3D geological and geophysical constraints have been used to calibrate the Lower Jurassic Marrat stratigraphic model, which resulted in the identification of (1) a dominantly transgressive lower unit composed of onlapping packages of mudstone to wackestone textures, with anhydritic intercalations; (2) a dominantly regressive middle unit composed of prograding inner ramp shoal and lagoonal facies with wackestone to grainstone textures, and finally (3) a transgressive onlapping upper unit composed of mudstones to wackestones textures in a mid-ramp system. The identification of potential reservoir facies like oncolitic shoals located onshore Kuwait, as well as possible porous reworked material transported away from the shoal loci in a relatively deeper mid ramp settings provides a better insight on further model improvement needed to de-risk stratigraphic trapping mechanisms. The identification of porous features in 3D provides crucial insights on the influence of ecological constraints on the complex Jurassic carbonate ramp systems of Arabia.

Sedimentology and Reservoir Characteristics of Middle Jurassic Dhruma Formation, Outcrop Approach, Central Saudi Arabia

Thesis

May 2017

Ibrahim M. Yousif

The study aims to characterize the lithofacies, paleoenvironment, high-resolution stratigraphic architecture and reservoir characteristics of Dhruma Formation in outcrops in central Saudi Arabia.

Depositional architecture and sequence stratigraphy of the Upper Jurassic Hanifa Formation, central Saudi Arabia

Article

Feb 2018

To document the depositional architecture and sequence stratigraphy of the Upper Jurassic Hanifa Formation in central Saudi Arabia, three composite sections were examined, measured and thin section analysed at Al-Abakkayn, Sadous and Maashabah mountains. Fourteen microfacies types were identified, from wackestones to boundstones and which permits the recognition of five lithofacies associations in a carbonate platform. Lithofacies associations range from low energy, sponges, foraminifers and bioclastic burrowed offshoal deposits to moderate lithoclstic, peloidal and bioclastic foreshoal deposits in the lower part of the Hanifa while the upper part is dominated by corals, ooidal and peloidal high energy shoal deposits to moderate to low energy peloidal, stromatoporoids and other bioclastics back shoal deposits. The studied Hanifa Formation exhibits an obvious cyclicity, distinguishing from vertical variations in lithofacies types. These microfacies types are arranged in two third order sequences, the first sequence is equivalent to the lower part of the Hanifa Formation (Hawtah member) while the second one is equivalent to the upper part (Ulayyah member). Within these two sequences, there are three to six fourth-order high frequency sequences respectively in the studied sections.

Facies analysis and depositional environments of the Upper Jurassic Jubaila Formation, Central Saudi Arabia

Article

Jun 2015

This article deals with the Upper Jurassic carbonates of the Jubaila Formation, exposed throughout the Tuwaiq Mountains, Central Saudi Arabia and discusses the succession of palaeoenvironments resulting from detailed field and lab work. Based on microfacies analysis and sedimentological data, twelve facies are identified within the Upper Jurassic carbonates at Wadi Hanifa, Central Saudi Arabia. These facies are attributed to six main facies belts. Within these facies and facies belts, four distinct biofacies assemblages are recognized. Deposition took place on an extendable ramp, which probably dipped gently eastwards to the sea. A depositional model relates the identified facies and biofacies to a downdip depositional profile of an inner, middle and outer carbonate ramp. The burrowed lime mudstone and bioclastic wackestone-floatstone of facies belt 1 accumulated in a distal middle ramp to outer ramp. The mollusk-coated grains-intraclast rudstone of facies belt 2 were deposited in the distal middle ramp. The branched stromatoporoids Cladocoropsis were deposited in the proximal middle ramp of facies belt 3. The facies of the open lagoon (facies belt 5) and the tidal-flat (facies belt 6) were deposited in the inner ramp behind the ramp crest/shoal facies belt 4. The Early Kimmeridgian Jubaila Formation has been deposited as transgressive and highstand deposits of a third-order depositional sequence, which are mainly controlled by eustatic sea-level changes. During the transgression, an aggradational trend developed , with the construction of a deep subtidal facies of small-scale stacked cycles of mudstones with frequent mottled firm ground and hard ground, storm beds and tempestites. The regressive part has a characteristic progradational trend, with shallow-water carbonate platform deposits arranged into meter-scale coarsening-upward cycles ranged from dolomitic mudstone and wackestone to stromato-poroid packstone and rudstone into bioclastic intraclastic peloidal packstone and grainstone.

Sequence stratigraphy of the late middle Jurassic open shelf platform of the Tuwaiq Mountain Limestone Formation, central Saudi Arabia

Article

Feb 2016

Sequence stratigraphy of the late middle Jurassic open shelf platform of the Tuwaiq Mountain Limestone Formation, central Saudi Arabia

Article

Feb 2016

Depositional architecture and sequence stratigraphy of the Upper Jurassic Hanifa Formation, central Saudi Arabia

Article

Feb 2020

To document the depositional architecture and sequence stratigraphy of the Upper Jurassic Hanifa Formation in central Saudi Arabia, three composite sections were examined, measured and thin section analysed at Al-Abakkayn, Sadous and Maashabah mountains. Fourteen microfacies types were identified, from wackestones to boundstones and which permits the recognition of five lithofacies associations in a carbonate platform. Lithofacies associations range from low energy, sponges, foraminifers and bioclastic burrowed offshoal deposits to moderate lithoclstic, peloidal and bioclastic foreshoal deposits in the lower part of the Hanifa while the upper part is dominated by corals, ooidal and peloidal high energy shoal deposits to moderate to low energy peloidal, stromatoporoids and other bioclastics back shoal deposits. The studied Hanifa Formation exhibits an obvious cyclicity, distinguishing from vertical variations in lithofacies types. These microfacies types are arranged in two third order sequences, the first sequence is equivalent to the lower part of the Hanifa Formation (Hawtah member) while the second one is equivalent to the upper part (Ulayyah member). Within these two sequences, there are three to six fourth-order high frequency sequences respectively in the studied sections.

Sequence stratigraphy of the late middle Jurassic open shelf platform of the Tuwaiq Mountain Limestone Formation, central Saudi Arabia

Article

Feb 2020

Middle Jurassic (Callovian) strata of Tuwaiq Mountain Limestone Formation, central Saudi Arabia are composed of thin- to thick-bedded, grainy and muddy limestones and dolostones with various skeletal and nonskeletal components. Facies analysis documents low- to high-energy environments, including lagoon, back reef, reef framework, fore-reef and intra-shelf basin lithofacies associations. Because of the narrow lateral distribution of facies and the presence of distinctive fossils, the depositional system likely represents an open marine shelf. Two third-order depositional sequences can be distinguished in the stratigraphic measured section. Transgressive sequences show deepening-upward trends, in which shallow water (lagoonal and back reef) facies are overlain by deeper-water (fore-reef and intra-shelf basin) facies. Regressive sequences show shallowing-upward trends in which deep-water facies are overlain by shallow-water facies. Most sequence boundaries in the study area are of the nonerosional (SB2) type. Correlation of depositional sequences in the studied section reveals that relatively shallow marine conditions predominated in the area.

Facies development and paleoenvironment of the Hajajah Limestone Member, Aruma Formation, central Saudi Arabia

Article

Oct 2016

The Campanian Hajajah Limestone Member of the Aruma Formation was formed during two regressive episodes. Each of them formed of three depositional facies, from base to top: 1) intra-shelf basin facies, made up of fossiliferous green shale and mudstone with ostracods and badly preserved foraminifers. 2) fore-reef facies, consists of hard, massive, marly coralline limestone. The upper part is rich with low divers, badly to moderate preserved, solitary and colonial corals, and, 3) back reef and near-shore facies, consists of fossiliferous sandy dolomitized, bioturbated limestone with abundant reworked corals, bi-valves, gastropods, and aggregate grains. On the basis of field observations, micro-and macrofossils and microfacies analysis, the Hajajah Limestone Member was deposited in distal marine settings below storm wave base in a low-energy environment changed upward to fore-reef framework in an open marine environment with moderate to high energy conditions and terminated with shallow marine facies with accumulation of skeletal grains by storms during regression.

Facies analysis and depositional environments of the Upper Jurassic Jubaila Formation, Central Saudi Arabia

Article

Full-text available

Jun 2015

This article deals with the Upper Jurassic carbonates of the Jubaila Formation, exposed throughout the Tuwaiq Mountains, Central Saudi Arabia and discusses the succession of palaeoenvironments resulting from detailed field and lab work. Based on microfacies analysis and sedimentological data, twelve facies are identified within the Upper Jurassic carbonates at Wadi Hanifa, Central Saudi Arabia. These facies are attributed to six main facies belts. Within these facies and facies belts, four distinct biofacies assemblages are recognized. Deposition took place on an extendable ramp, which probably dipped gently eastwards to the sea. A depositional model relates the identified facies and biofacies to a downdip depositional profile of an inner, middle and outer carbonate ramp. The burrowed lime mudstone and bioclastic wackestone-floatstone of facies belt 1 accumulated in a distal middle ramp to outer ramp. The mollusk-coated grains-intraclast rudstone of facies belt 2 were deposited in the distal middle ramp. The branched stromatoporoids Cladocoropsis were deposited in the proximal middle ramp of facies belt 3. The facies of the open lagoon (facies belt 5) and the tidal-flat (facies belt 6) were deposited in the inner ramp behind the ramp crest/shoal facies belt 4. The Early Kimmeridgian Jubaila Formation has been deposited as transgressive and highstand deposits of a third-order depositional sequence, which are mainly controlled by eustatic sea-level changes. During the transgression, an aggradational trend developed , with the construction of a deep subtidal facies of small-scale stacked cycles of mudstones with frequent mottled firm ground and hard ground, storm beds and tempestites. The regressive part has a characteristic progradational trend, with shallow-water carbonate platform deposits arranged into meter-scale coarsening-upward cycles ranged from dolomitic mudstone and wackestone to stromato-poroid packstone and rudstone into bioclastic intraclastic peloidal packstone and grainstone.

Al-Mojel, A. (2010). High-Resolution Sequence Stratigraphy of the Middle Jurasic Lower Fadhili Reservoir in Khurais

Thesis

May 2010

Abdullah S. Al-Mojel

The Middle Jurassic Lower Fadhili Carbonate Member of the Dhruma Formation in Khurais Field is composed of two composite sequences which in ascending stratigraphic order are: Lower Fadhili composite sequence 1 (LFC1); and Lower Fadhili composite sequence 2 (LFC2). Each composite sequence is composed of four high-frequency sequences (HFS). This study is based on detailed sedimentological descriptions of nine cored wells, a total of 370.9 meters (1,217 feet). The sequences of the Lower Fadhili reservoir are made up of five facies. The facies (in order from proximal to distal) are: skeletal coated-grain grainstone upper shoreface, peloid coated-grain grainstone and packstone lower shoreface, Thaumatoporella wackestone inner lagoon, stromatoporoid wackestone/packstone outer lagoon, and Pfenderina trochoidea wackestone/mudstone transgressive lagoon. There are two more facies have been recognized from Lower Fadhili cores and are not genetically related to the Lower Fadhili reservoir facies and sequences. These facies are: argillaceous mudstone and calcareous shale marginal marine and cemented ooid coated-grain intraclast grainstone beach facies. The base sequence boundary of the Lower Fadhili reservoir, the base of LFC1, overlies a subaerial exposure (karst) surface on top of the ooid coated-grain intraclast grainstone beach facies that contains meteoric calcite cement, which is evidence for an exposure surface and a potential unconformity. The top sequence boundary of the Lower Fadhili reservoir (top of LFC2) is marked by a major subaerial exposure surface (karst), filled from the above by the green calcareous shale facies (reservoir seal). Fining-upward small-scale cycles of the first composite sequence (LFC1) of the Lower Fadhili reservoir onlapped onto the unconformity. These cycles are dominated by Pfenderina trochoidea wackestone facies and stromatoporoid packstone/wackestone facies. The maximum flooding surface (MFS) can be traced across the fields and it coincides with a thin layer of Pfenderina trochoidea wackestone facies. In the highstand systems tract (HST), the abundance of Pfenderina trochoidea decreases upwards and the abundance of sponge spicules and Thaumatoporella increases upwards. The second composite sequence (LFC2) highstand was dominated by fining-upward cycles of stromatoporoid packstone/wackestone facies, shallow marine lagoonal wackestone and shoreface coated-grain grainstone. Thaumatoporella and Cladocoropsis are abundant in the lagoonal wackestones. Toward the top of the HST of the second composite sequence (LFC2), the abundance of Thaumatoporella increases and the abundance of stromatoporoid decreases upward. Bedding in the HFS thinned upward and was capped by a subaerial exposure (karst) surface at a sequence boundary. The Lower Fadhili was deposited in a shallow marine, tropical intra-shelf basin. The Lower Fadhili carbonate reservoir is overlain and underlain by green marls (reservoir seal). The dominant porosity type of the Lower Fadhili reservoir facies is microporosity, except that the coated-grain grainstone and packstone facies has an interparticle porosity. The peloid coated-grain grainstone and packstone facies has the best reservoir quality because the interparticle porosity is well connected. The use of high-resolution sequence stratigraphy of the Lower Fadhili reservoir has been beneficial to reservoir characterization and geological modeling.

First Bathonian (Middle Jurassic) nautiloid Paracenoceras Spath from Ethiopia

Article

Aug 2018
J AFR EARTH SCI

Sreepat Jain

The earliest find of a Bathonian nautiloid Paracenoceras aff. prohexagonum Spath from the Lower Limestone Member (former Gohatsion Formation) exposed at Mugher (Blue Nile Basin, Ethiopia) is reported. Due to lack of index forms for the entire pre–Late Jurassic duration in Ethiopia, the age estimate of the nautiloid is done on the basis of palaeobiogeography where the oldest P. prohexagonum Spath record comes from definite Saudi Arabian Early Bathonian strata and the youngest from the Middle–Late Bathonian of the Kachchh basin (Western India). Ethiopia being an intermediate region, hence, a Late Bathonian age is safe to assume. However, the key for a more well–constrained age for the Ethiopian strata may actually lie in the re–assessment of the ammonite records from the neighboring Somalia, another intermediate region and a step closer to the otherwise well–constrained records from the Kachchh basin (India). Additionally, this contribution also provides a brief stratigraphic update of the Lower Limestone Member (of the Antalo Limestone Supersequence) exposed at Gohatsion and the corresponding nautiloid–bearing section at Mugher (∼20 km southwest of Gohatsion) within the Blue Nile basin. Based on field and sedimentological observations, sequence stratigraphy, and previously published data on faunal content, the prevailing paleoenvironment and relative sea level curve for the Lower Limestone Member is also inferred. Palaeobiogeography is briefly outlined to explain the age and occurrence of the reported nautiloid.

Bulbobaculites attashensis sp. nov., a new agglutinated foraminifera from the Middle Jurassic D7 Attash Member of the Dhruma Formation, Central Saudi Arabia

Article

Full-text available

Feb 2025
ANN SOC GEOL POL

The new species Bulbobaculites attashensis sp. nov. is described from the rhythmite limestone and marl sediments of the D7 Attash Member of the Middle Jurassic (lower Callovian) Dhruma Formation in Central Saudi Arabia. This species is characterized by its coarsely agglutinated wall, streptospiral initial coiling, and a distinct bulbous initial coil. The occurrence of this species in limestone-marl rhythmite deposits suggests its adaptation to fluctuating environmental conditions, including changes in water depth, salinity, and nutrient flux, associated with rhythmic sedimentation.

Bulbobaculites attashensis sp. nov., a new agglutinated foraminifera from the Middle Jurassic D7 Attash Member of the Dhruma Formation, Central Saudi Arabia

Article

Jan 2024
ANN SOC GEOL POL

The new species Bulbobaculites attashensis sp. nov. is described from the rhythmite limestone and marl sediments of the D7 Attash Member of the Middle Jurassic (lower Callovian) Dhruma Formation in Central Saudi Arabia. This species is characterized by its coarsely agglutinated wall, streptospiral initial coiling, and a distinct bulbous initial coil. The occurrence of this species in limestone-marl rhythmite deposits suggests its adaptation to fluctuating environmental conditions, including changes in water depth, salinity, and nutrient flux, associated with rhythmic sedimentation.

Transition from coral to stromatoporoid patch reefs in Middle Jurassic equatorial warm waters

Article

Feb 2023

Sedimentologic and diagenetic controls on petrophysical properties in the Middle Dhruma Formation (Jurassic), Saudi Arabia

Article

Sep 2022
MAR PETROL GEOL

Carbonate outcrops of the Jurassic Middle Dhruma Formation (D5 and D6 units), located southwest of Riyadh, Saudi Arabia, were investigated to characterize controls on potential reservoir quality. Porosity and permeability of the outcrop lithologies are dependent upon sedimentary facies and post-depositional modification. Both field and laboratory data were integrated to identify lithofacies types and depositional environments. Standard petrography and scanning electron microscopy were used to identify and characterize diagenetic features. Integration of sedimentologic descriptions and petrographic data yielded identification of ten lithofacies between the D5 and D6 units. Based on lithologic affinities, the ten lithofacies were grouped into three related lithofacies associations. The depositional setting included a shallow restricted lagoon, back shoal, and shoal complex environments, with a majority occupying shallow-lagoon environments in the inner shelf of a carbonate ramp. Depositional texture imparted a strong, first-order control on porosity-permeability trends. This observation led to a texture-based classification for petrophysical comparisons: grainy texture (grainstones), mixed texture (packstones and rudstones), and micritic texture (wackestones and mudstones). Overall, samples with similar porosity values in the grainy textures have higher permeability than the mixed and micritic texture rocks. Diagenesis, namely micritization and cementation, also controlled reservoir quality in outcrops and subsurface units of the Dhruma Formation. A comparison between the D5 and D6 outcrops in Saudi Arabia and other equivalent outcrops and reservoirs in the region revealed a similarity in their depositional environments, bulk density, and porosity. The findings of this study can be beneficial for comparison and proper reservoir characterization and formation evaluation of local and regional reservoirs and their future exploration plans.

Diagenetic controls on porosity evolution and reservoir quality of an outcrop analogue of the Jurassic carbonate reservoirs in the Arabian Plate: An example from the Middle Jurassic Tuwaiq Mountain Formation, Central Saudi Arabia

Article

Oct 2021
J PETROL SCI ENG

The Middle Jurassic Tuwaiq Mountain Formation (TMF; formed of three members, from bottom to top T1, T2, and T3) represents one of the primary conventional and unconventional reservoirs to be assessed in Saudi Arabia. It is considered as a tight carbonate reservoir in the Jafurah Basin and conventional reservoir in the Ghawar Mega-field. Here, we investigate the depositional, diagenetic, and stratigraphic impact on reservoir quality and porosity evolution of the TMF through an integrated petrographical, geochemical and petrophysical analyses on outcrop samples. The TMF has a complex-diagenetic-history including micritization, dissolution, recrystallization and neomorphism, meteoric-cementation, evaporite-precipitation, dolomitization, silicification, dolomite-dissolution and calcitization. Dolomitization occurred via a hypersaline-fluid mechanism, based on texture, association with evaporites, and Sr concentration. X-ray diffraction results support chert-replacing-evaporite as the mechanism of the two chert beds in the T3 due to the presence of anhydrite relics in their samples. This replacement formed the necessary Ca²⁺ rich fluid for dolomite dissolution and calcitization. Therefore, Dolomite calcitization occurs locally and is stratigraphically controlled based on its position relative to chert beds in T3. T3 and upper part of T2 contain calcitized dolomites, while lower part of T2 and T1 contain only dissolved dolomite. As the fluid went deeper in the TMF, it became weaker. Therefore, the fluid was too weak to develop dolomite-calcitization process and instead of that it only affected T1 and lower part of T2 by dolomite dissolution. Overall, dolomite-dissolution and dolomite-calcitization didn't have a high impact on porosity evolution from T1 to T2 and T3 as the TMF isn't a highly dolomitized formation. The distribution of ø, K, and reservoir-quality-index (RQI) of the TMF are stratigraphically controlled. The TMF represents a regressive system tract of 3rd order depositional sequence, which is composed of seven 4th order cycles (i.e. deep lagoon cycles (DLC) and shallow lagoon cycles (SLC)). RQI, Ø, and K plots showed great fitting with the 4th order depositional-cycles as DLC had very-poor reservoir-properties (average ø = 7.7%, average K = 0.17 mD, average RQI = 0.03), while SLC had fair reservoir-properties (average ø = 15.4%, average K = 2.64 mD, average RQI = 0.11). Reservoir-quality contrast is controlled by two-factors: (1) the reduced mud-content and increased grain-content in SLC compared with DLC are governed by the increase in the depositional-energy which increased the primary-interparticle-porosity, (2) the higher primary-interparticle-porosity in SLCs compared with DLCs preferentially facilitated more infiltration of undersaturated-meteoric-fluids, resulting in enhanced grain dissolution. This is reflected on the higher proportion of moldic and vuggy porosity in SLCs compared with DLCs. The accurate assessment of the TMF micro-scale attributes and controls on an outcrop analogue in a close proximity to the subsurface intervals can provide important input for appraisal and enhanced oil recovery performance.

Orbital calibration of the Late Jurassic Hanifa, Jubaila and Arab Formations, Saudi Arabia

Experiment Findings

Full-text available

Jun 2021

In Saudi Arabia, the Pre-Hanifa Unconformity separates the Middle Jurassic Tuwaiq Mountain Limestone and the Upper Jurassic Hanifa Formation; it corresponds to a major hiatus (> 2.0 myr at outcrop) and a glacio-eustatic lowstand (Dromart et al., 2003). The Middle/Upper Jurassic (Callovian/ Oxfordian Stage) Boundary is estimated at 161.5±1.0 Ma in GTS 2020, and correlates to the post-glacial sea-level rise predicted at 161.966 Ma by the deterministic Orbital Scale of glacio-eustasy (Matthews and Al-Husseini, 2010). In this study the stage boundary is anchored at 161.966 Ma and the high-frequency sequences (HFS) in the Upper Jurassic Hanifa and Jubaila Formations, and Arab D Reservoir (Al-Mojel, 2017) are interpreted and dated as c. 0.405-myr stratons in the Orbital Scale. The age calibrations also include the Arab D Anhydrite, and Arab C, B and A Members. The correlations of HFS to stratons are consistent with the limited biostratigraphic control. Numerical ages are estimated for key glacio-eustatic events that are observed in the sequence architecture of these formations (unconformities, sequence boundaries and maximum flooding surfaces).

Stress in the tropics? Impact of a latitudinal seawater δ18O gradient on Middle Jurassic temperature reconstructions at low latitudes

Article

Aug 2020
GEOLOGY

Previous stable oxygen isotope records of calcitic fossils (δ18Oshell) from Europe have been interpreted to reflect strong climatic perturbations throughout the Jurassic, but it is unknown whether they reflect global trends because data from other regions are sparse. Here, we use bivalve and brachiopod shells from western Asia and northern Africa to examine seawater temperatures at low latitudes as well as latitudinal temperature gradients in the Middle Jurassic. Our results include the first absolute temperature estimates for most of the study areas and this time interval. Furthermore, we acknowledge a latitudinal gradient in δ18O values of seawater (δ18Osea) that leads to more realistic temperature reconstructions of tropical water temperatures, which were underestimated by earlier methods. Following this approach, δ18Oshell values translate into average equatorial water temperatures during the Middle Jurassic several degrees higher than today (as high as 34–35 °C). Such high temperatures cause environmental stress, probably explaining previously documented low diversities of low-latitudinal ecosystems (e.g., coral reefs) during this time interval. A comparison with literature data raises doubts over whether previously published European temperature curves are truly representative of global patterns. Instead, they might reflect the complex paleogeography of European basins influenced by regional and/or short-term changes in δ18Osea values.

Microfacies and diagenesis of the reefal limestone, Callovian Tuwaiq Mountain Limestone Formation, central Saudi Arabia

Article

Dec 2015

In order to document the microfacies and diagenesis of the reefal limestone in the uppermost part of the Callovian Tuwaiq Mountain Limestone Formation at Khashm Al-Qaddiyah area, central Saudi Arabia, scleractinian corals and rock samples were collected and thin sections were prepared. Coral framestone, coral floatstone, pelloidal packstone, bioclastic packstone, bioclastic wacke/packstone, algal wackestone and bioclastic foraminiferal wacke/packstone were the recorded microfacies types. Cementation, recrystallization, silicification and dolomitization are the main diagenetic alterations affected the aragonitic skeletons of scleractinian corals. All coral skeletons were recrystallized, while some ones were dolomitized and silicified. Microfacies types, as well as the fossil content of sclearctinian corals, bivalves, gastropods, brachiopods and foraminifera indicated a deposition in environments ranging from shelf lagoon with open circulation in quiet water below wave base to shallow reef flank and organic build up for the uppermost reefal part of the Tuwaiq Formation in the study area.

Microfacies, biofacies, and depositional environments of the Bajocian–Bathonian Middle Dhruma carbonates, central Saudi Arabia

Article

Full-text available

Oct 2019

Three cliff-forming outcrops of the Dhruma Formation representing the carbonate platform in the Hafirat Nisha district west of Riyadh, Saudi Arabia, were investigated to identify and understand the microfacies variability in a carbonate ramp setting. An integrated approach including detailed field investigations, petrographic, biofacies, and micropaleontological analyses was used to construct a model of the depositional environments of the investigated outcrop sections. The depositional model indicates that the identified lithofacies were predominantly deposited in outer ramp, middle ramp, inner ramp, and lagoonal settings. The presence of the benthic foraminifera Redmondoides lugeoni and Nautiloculina oolithica and the trace fossil Thalassinoides indicates deposition in shallow-water environments and the prevalence of warm climatic conditions during the Middle Jurassic. The occurrences of calcareous and agglutinated benthic foraminiferal species Pseudomarssonella maxima, Siphovalvulina variabilis, Timidonella sarda, N. oolithica, R. lugeoni, Praekurnubia crusei, Paleopfenderina salernitana, Haurania deserta, Siphovalvulina spp., Lenticulina sp., Textulariopsis sp., and Amijella amiji imply that our studied sections are situated within the Dm-2 to Dm-5 biozones (Bajocian to early Bathonian). This is also supported by the calcareous nannofossil assemblages that show a Bajocian to early Bathonian age. The depositional sequences indicate a shift in the depositional environment from low-energy lagoonal with intermittent shoal complexes in the D2 and D3 Units to predominantly shoal complex and open-marine settings in the D4 Unit, suggesting a seaward shift towards the top of the D4 Unit. The interpreted depositional settings are similar to those previously documented in the subsurface equivalent, Faridah reservoir. This indicates that the investigated D2–D4 Units outcrops are excellent analogues of the subsurface reservoir.

3D Microporosity Characterizations in the Heterogeneous Middle Jurassic Tuwaiq Mountain Formation: Insights into an Unconventional Sweet Spot

Article

Full-text available

Aug 2024

Carbonate microporosity can vary significantly across depositional lithofacies and cycles, owing primarily to the high degree of heterogeneity in their pore sizes, pore throat radius, geometry, and connectivity. This is further compounded by the complex diagenetic alterations during various stages of burial. In addition, the presence of micropores, which are abundant in carbonate rocks, but not visible using conventional techniques, is challenging to characterize. To address this issue, our study focused on the Middle Jurassic Tuwaiq Mountain Formation (TMF) due to its importance as an analogue to subsurface conventional and unconventional reservoirs. Here, we utilized eight samples and performed pore network modeling to quantify microporosity distribution and connectivity from high-resolution microcomputed tomography images of different microfacies (MF) in the TMF from both mud- and grain-dominated facies. These results were then validated with petrographic, SEM images, and porosity–permeability measurements. Our study revealed that, in the high-energy, grain-supported microfacies of the shallow lagoon depositional cycle, micropores dominated by interparticle and microvug types were abundant and well-connected, with mean pore and throat sizes of 7 and 4 μm. Conversely, micropores within the low-energy mud-dominated microfacies of the deep lagoon depositional cycle dominated by intraparticle and intercrystalline types were isolated and rarely connected, even at the microscale (1–4 μm in diameter, with an average of 2 μm). This result suggests that pore connectivity at the microscale is not always related to matrix porosity, and the pore connectivity is present in submicron scale, which goes against common concepts in unconventional carbonate reservoirs. Furthermore, our observations indicate that primary depositional processes play a major role in controlling the distribution and connectivity of the Tuwaiq Mountain Formation’s microporosity, while diagenetic processes only have minor controls. Our study emphasizes the importance of characterizing microporosity and its connectivity in heterogeneous carbonate rocks, which may reduce the uncertainty in exploring the properties of complex carbonate reservoirs worldwide.

Assessment of potentially toxic elements and health risks of agricultural soil in Southwest Riyadh, Saudi Arabia

Article

Full-text available

Apr 2024

The rise of emerging pollutants in the environment as a result of economic growth poses a worldwide challenge for the management of environmental and human health. The objective of this study was to assess the presence of potentially toxic elements (PTEs) in the agricultural soil of southwest Riyadh, Saudi Arabia, and to evaluate the potential health risks associated with these elements. Soil samples were collected from 31 farms, and the concentrations of As, Pb, Cu, Ni, Zn, and Fe were analyzed using inductively coupled plasma-atomic emission spectrometry. Various contamination and health risk indices, along with multivariate analyses, were employed in the evaluation. The mean concentrations of PTEs (mg/kg) followed the order: Fe (15,556) > Zn (53.36) > Ni (21.78) > Cu (11.92) > Pb (10.42) > As (2.64). The average PTE concentrations were found to be lower than background levels and the world-soil average. Contamination indices indicated that the studied soil was moderately enriched and contaminated for As, slightly enriched for Zn and Ni, and not enriched for Cu and Pb. This suggests that the PTEs in the soil do not pose a significant threat, although some individual samples exhibited significant enrichment for Zn and Pb. Multivariate analyses suggested a geogenic source for the PTEs, with some contribution from anthropogenic factors for As, Zn, and Pb. The average hazard index values ranged from 0.000293 (Zn) to 0.030561 (Fe) for adults and from 0.002726541 (Zn) to 0.284670158 (Fe) for children, indicating no significant non-carcinogenic risk to the population in the study area. Additionally, the Lifetime Cancer Risk values for adults and children ranged from 6.94 × 10⁻⁶ to 6.46 × 10⁻⁵ for As and from 7.13 × 10⁻⁸ to 6.65 × 10⁻⁷ for Pb, suggesting acceptable or tolerable carcinogenic risk and no significant health hazards.

Facies associations and stratigraphic sequence of the Dhruma Formation (Middle Jurassic) at its type locality, Khashm adh Dhibi, Saudi Arabia

Article

Full-text available

Feb 2024

The lithofacies, microfacies, and depositional environments of the Dhruma Formation were studied at the type locality at Khashm adh Dhibi to better understand the sedimentology and depositional history on the Arabian Platform. Twelve lithofacies were identified that can be grouped into four lithofacies associations corresponding to depositional paleoenvironments ranging from peritidal to open marine. The vertical distribution of the lithofacies and their corresponding depositional settings allow for the division of the Dhruma Formation into six 3rd-order sequences (DS1–DS6), each bounded by sharp vertical facies changes, and/or hiatuses. Abrupt negative shifts in both δ¹³Ccarb and δ¹⁸Ocarb values coincide closely with the placement of sequence boundaries on the Arabian Platform. This suggests that the carbonates in these zones underwent meteoric diagenesis during episodes of subaerial exposure. Comparison of the sequence stratigraphy interpreted from the vertical distribution of facies with published eustatic sea-level curves improves our understanding of the eustatic sea-level variation and/or local tectonics in forming both local hiatuses and regional unconformities.

Sedimentology and carbon isotope stratigraphy from the Late Jurassic – Early Cretaceous of the Arabian plate: The Weissert event and the VOICE in the Tethys Realm?

Article

Dec 2023
MAR PETROL GEOL

Unlike the Tethys Realm, the carbon isotope record from the Boreal Realm exhibits a prominent negative excursion before the Jurassic-Cretaceous boundary referred to as the Volgian Isotopic Carbon Excursion (VOICE). The VOICE has been ascribed to restricted-circulation conditions in northern high latitude basins, which decoupled these basins from the global carbon pool. Similar isotopic signal has been identified in the southern hemisphere where it has been attributed to humid conditions and influx of organic matter. The restricted circulation hypothesis is tested here by examining the depositional record of the Tethyan Late Jurassic–Early Cretaceous succession from central Saudi Arabia. A multi-disciplinary approach, involving sedimentology, sequence stratigraphy, biostratigraphy, and geochemistry, was adopted for studying a composite section covering the Hith, Sulaiy, Yamama, and Buwaib formations. The succession is characterized by restricted salina and sabkha depositional settings at the base that transition upward into an open-marine depositional system. This trend records a long-term sea-level rise during the Early Cretaceous. The carbon isotope record for this succession illustrates two prominent positive excursions of 5.2‰ and 2.6‰ amplitudes at the base and top of the succession, respectively. The larger positive excursion coincides with the restricted-environment facies and shows similarities, in terms of magnitude and trend, to the recovery phase of the VOICE. The upper positive excursion is manifested after a steady drop in the carbon isotope values, and it corresponds to the globally recognized Weissert event. The results indicate that restricted circulation in the Arabian shelf interior during the Late Jurassic duplicated the VOICE signal. The recognition of the Weissert event signal, on the contrary, denotes restored circulation of the shelf interior with the Tethys. The novelty of this study is demonstrated by the findings that the VOICE might indeed be a global signal and restricted circulation driven by eustasy is the main controlling factor for the VOICE signal.

Geoheritage and Geotourism Potential of Tuwaiq Mountain, Saudi Arabia

Article

Full-text available

Jun 2023

Exploring new geosites and geoheritage opens opportunities for geotourism. One of the geomorphic features in central Saudi Arabia is the Tuwaiq Mountain, extending from the southern margin of the Nafud Sand Sea to the northwest margin of Rub' al Khali sand sea. Appraisal study in the Tuwaiq Mountain reveals the various geological and geomorphological features like Escarpment, mesa, butte, pinnacle, wadi network, and fossil. The majestic view of the Escarpment comprises the clif, talus, and a birds-eye view of the wadi (fuvial valley), one of the prime viewpoints. Initially, cuesta was formed due to the tectonic movement associated with the opening of the Red Sea. Tectonic landforms like faults are continuously eroded and form the scarp. Gulley network indicates the dominance of a fuvial environment that later transformed into an aeolian environment. Therefore, the landforms’ evolution and geomorphic processes in diferent geological periods enhance this place’s geoheritage value. The Jurassic fossils remain in this area and are a unique geological attraction. Numerous dried-up gully networks are another viewpoint of the Tuwaiq Mountain, which is essential for biodiversity. Each potential tourist attraction is described in the context of protection, policy development, and enhanced additional attractions for geotourism development.

Microfacies architecture and depositional history of the Upper Jurassic (kimmeridgian) Jubaila Formation in central Saudi Arabia

Article

Full-text available

Nov 2020
J AFR EARTH SCI

The Upper Jurassic Jubaila Formation in central Saudi Arabia exhibits laterally coeval environments from the southwest to the northeast. These coeval environments involve inner, mid-, and outer ramps. The inner ramp occurs at the Al Haddar section in the extreme southwest and consists of mixed clastic-carbonate facies and are represented by intercalations of ferruginous calcareous quartz arenite, ferruginous sublitharenite, and burrowed dolomicrite. In the mid-ramp setting, there were changes from lateral facies in the Riyadh and the Wadi Huraymila areas to carbonates characterized by sandy lime-mudstones, dolosparie, peloidal olitic packstones, and coralline bioclastic wackestones to packstones. These are intercalated with sandy lime-mudstones that might be deposited in highly agitated environments. The outer-ramp setting occurred in the farther northeast Al Uyaynah area. It is characterized by reduced thickness and is composed of lime-mudstones, dolomitic marls, and pelletal bioclastic wackestones with thin beds of dolomitic marls. The lateral and vertical microfacies distribution in the Jubaila Formation are arranged vertically into four 3rd-order cycles that are correlate laterally overall the studied area, which are overprinted by oscillations in eustatic sea-level during the deposition of Jubaila Formation.

High-resolution sedimentology and sequence stratigraphy of the Oxfordian-Kimmeridgian, Hanifa, Jubaila and Arab outcrops along Jabal Tuwaiq, Central Saudi Arabia

Article

Mar 2020
J AFR EARTH SCI

The sequence stratigraphy of the Late Jurassic (Oxfordian to Kimmeridgian) of the central Arabia is based on outcrop measured sections. The sequence stratigraphic framework is extended eastward across the Arabian Basin through surface-to-subsurface gamma-ray correlations (550 km long to the east). It provides an insight into the development of an intrashelf basin in a large epeiric tropical platform. The outcrop depositional environments range from semi-arid shoreline to carbonate inner-lagoon and back-barrier lagoon. These formed an aggraded flat-topped platform with evident syndepositional differential subsidence. The Upper Jurassic successions are composed of several transgressive third-order sequences interrupted by short emersion sequence boundaries. The Hanifa Platform evolved from proximal argillaceous-limestone with low-faunal diversity to open-marine carbonate platforms with reef bearing and high-faunal diversity adjacent to a deep intrashelf basin in the subsurface. The Hanifa maximum flooding surfaces (MFS's) are placed in terrigenous-free open-marine carbonate sediments. The Jubaila-Arab-D is a conformable succession marked at the base by storm-influenced inner-platform grainstones with quartz sandstone, and proximal barren lime-mudstone. The Jubaila-Arab-D MFS is placed higher in the Arab-D reservoir in a backstepping of back-barrier high-energy reef facies. During sea-level highstand, the reef facies are gently prograding toward the Rimthan Arch leaving behind a restricted lagoon deposits consists of sabkhah/salina anhydride. These composite sequences are probably controlled by climatic driven eustasy, coupled with local tectonic disruption, as they have some similarity with other Tethyan sequence stratigraphy. For the first time, this outcrop study reveals a detailed and complete stratigraphic framework that subdivided the Upper Jurassic prolific petroleum systems into genetically related sequences that are not always obvious from subsurface data. The study allows the assessment of the Upper Jurassic tectono-stratigraphic events of the central Arabian Platform.

High-frequency cycles and sequence stratigraphy of the lower Jurassic Marrat Formation, central Saudi Arabia

Article

Feb 2018

Well-exposed stratigraphic sections of the Toarcian siliciclastic/carbonate deposits of the Marrat Formation exposed at the Khashm adh Dhibi area (southwest of Riyadh city, Saudi Arabia) were studied for their facies associations and controls on sequence development. Seven facies associations from tide-dominated deltaic to inner carbonate ramp were recognized. Inferences based on facies relationships, characteristics of the sequence boundary and other characteristics suggest deposition of the Marrat Formation during three 3rd order sequences. These can be further classified into seventeen 4th order shallowing-upward small-cycle sets. Correlation of the recorded sequences boundaries within the Arabian/African Plates, Europe, and global schemes, reflect a strong eustatic control during the early Jurassic age with recognizable tectonic signature of the Gondwanland rift effects that caused a long period of regional uplift and non-deposition across the Triassic/Jurassic and early/ middle Jurassic unconformities.

Paleoecology of Benthic Foraminifera in Coral Reefs Recorded in the Jurassic Tuwaiq Mountain Formation of the Khashm Al-Qaddiyah Area, Central Saudi Arabia

Article

Apr 2015

Thirty three benthic foraminiferal species belong to 23 genera and 16 families have been recorded from the coral reefs of the Callovian Tuwaiq Formation, Khashm Al-Qaddiyah area, Central Saudi Arabia. Three species: Astacolus qaddiyahensis, Nodosaria riyadhensis, Siderolites jurassica are believed to be new. Nearly all identified foraminifera are of Atlantic-Miditeranean affinity. The fo-raminiferal assemblage recorded in the present work is mixed of open marine, moderately deep marine conditions associations and shallow to deep lagoon. The reefal part of upper Twiaq Formation may have been deposited in shallow water of lower to middle shelf depth (20-50 m) as indicated by abundant corals and benthic foraminifera. The coral fauna and bearing benthic foraminifera indicated moderate water energy.

Diagenetic Alterations of the Upper Jurassic Scleractinian Corals, Hanifa Formation, Jabal Al-Abakkayn, Central Saudi Arabia

Article

Mar 2016

During diagenetic stages, the aragonitic skeletons and the inter/intra-corallite cement of the upper Jurassic corals of Hanifa Formation either dissolved or subjected to diagenetic alterations including cementation, micritization, recrystallization, silicification, dolomitization and dedolomitization. The proposed sequence of diagenetic stages is as follows: early marine diagenesis, early meteoric and mixing zone diagenesis, late meteoric diagenesis, and shallow burial diagenesis. Each stage is characterized by certain diagenetic processes. The source of sulfate solutions for dedolomitization in the studied corals is the dissolved anhydrite deposits of the Arab-Hith Formations, sometime before their erosion. A possible source of silica, needed for the formation of chert and chalcedony, is the sponge spicules dispersed in many carbonates of the Hanifa Formation.

Marine benthic invertebrates of the upper Jurassic Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia

Article

Mar 2014

26 species belong to 24 genera and 16 families have been described and illustrated from the Callovian Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia. 10 of the identified species belong to scleractinian corals, 7 to brachiopods, 4 to bivalves, 4 to gastropods and one to cephalopods. Actinastraea pseudominima, Thamnasteria nicoleti, Enallocoenia crassoramosa, Collignonastraea cf. grossou-vrei, Burmirhynchia jirbaensis, Pholadomya (Bucardiomya) somaliensis, Pseudomelania (Rhabdoconcha) raabi and Nautilus giganteus are believed to be recorded for the first time from the Jurassic rocks of central Arabia. The identified species have close affinity to Tethyan faunas known from parts in Asia, Africa and Europe. They indicated shoaling of the sea floor persisted throughout the deposition of the Tuwaiq Mountain Limestone, in water depth ranging from 20 to 30 m. The low diversity of invertebrates in the studied section may attribute to paleoenvironmental conditions prevailed during the Callovian age as high rate of sedimentation.

Marine benthic invertebrates of the upper Jurassic Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia

Article

Feb 2014

26 species belong to 24 genera and 16 families have been described and illustrated from the Callovian Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia. 10 of the identified species belong to scleractinian corals, 7 to brachiopods, 4 to bivalves, 4 to gastropods and one to cephalopods. Actinastraea pseudominima, Thamnasteria nicoleti, Enallocoenia crassoramosa, Collignonastraea cf. grossouvrei, Burmirhynchia jirbaensis, Pholadomya (Bucardiomya) somaliensis, Pseudomelania (Rhabdoconcha) raabi and Nautilus giganteus are believed to be recorded for the first time from the Jurassic rocks of central Arabia. The identified species have close affinity to Tethyan faunas known from parts in Asia, Africa and Europe. They indicated shoaling of the sea floor persisted throughout the deposition of the Tuwaiq Mountain Limestone, in water depth ranging from 20 to 30 m. The low diversity of invertebrates in the studied section may attribute to paleoenvironmental conditions prevailed during the Callovian age as high rate of sedimentation.

High-frequency cycles and sequence stratigraphy of the lower Jurassic Marrat Formation, central Saudi Arabia

Article

Feb 2018

Well-exposed stratigraphic sections of the Toarcian siliciclastic/carbonate deposits of the Marrat Formation exposed at the Khashm adh Dhibi area (southwest of Riyadh city, Saudi Arabia) were studied for their facies associations and controls on sequence development. Seven facies associations from tide-dominated deltaic to inner carbonate ramp were recognized. Inferences based on facies relationships, characteristics of the sequence boundary and other characteristics suggest deposition of the Marrat Formation during three 3rd order sequences. These can be further classified into seventeen 4th order shallowing-upward small-cycle sets. Correlation of the recorded sequences boundaries within the Arabian/African Plates, Europe, and global schemes, reflect a strong eustatic control during the early Jurassic age with recognizable tectonic signature of the Gondwanland rift effects that caused a long period of regional uplift and non-deposition across the Triassic/Jurassic and early/ middle Jurassic unconformities.

Diagenetic Alterations of the Upper Jurassic Scleractinian Corals, Hanifa Formation, Jabal Al-Abakkayn, Central Saudi Arabia

Article

Mar 2016

During diagenetic stages, the aragonitic skeletons and the inter/intra-corallite cement of the upper Jurassic corals of Hanifa Formation either dissolved or subjected to diagenetic alterations including cementation, micritization, recrystallization, silicification, dolomitization and dedolomitization. The proposed sequence of diagenetic stages is as follows: early marine diagenesis, early meteoric and mixing zone diagenesis, late meteoric diagenesis, and shallow burial diagenesis. Each stage is characterized by certain diagenetic processes. The source of sulfate solutions for dedolomitization in the studied corals is the dissolved anhydrite deposits of the Arab-Hith Formations, sometime before their erosion. A possible source of silica, needed for the formation of chert and chalcedony, is the sponge spicules dispersed in many carbonates of the Hanifa Formation.

Paleoecology of Benthic Foraminifera in Coral Reefs Recorded in the Jurassic Tuwaiq Mountain Formation of the Khashm Al-Qaddiyah Area, Central Saudi Arabia

Article

Apr 2015

Thirty three benthic foraminiferal species belong to 23 genera and 16 families have been recorded from the coral reefs of the Callovian Tuwaiq Formation, Khashm Al-Qaddiyah area, Central Saudi Arabia. Three species: Astacolus qaddiyahensis, Nodosaria riyadhensis, Siderolites jurassica are believed to be new. Nearly all identified foraminifera are of Atlantic-Miditeranean affinity. The fo-raminiferal assemblage recorded in the present work is mixed of open marine, moderately deep marine conditions associations and shallow to deep lagoon. The reefal part of upper Twiaq Formation may have been deposited in shallow water of lower to middle shelf depth (20-50 m) as indicated by abundant corals and benthic foraminifera. The coral fauna and bearing benthic foraminifera indicated moderate water energy.

Marine benthic invertebrates of the upper Jurassic Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia

Article

Full-text available

Feb 2014

26 species belong to 24 genera and 16 families have been described and illustrated from the Callovian Tuwaiq Mountain Limestone, Khashm Al-Qaddiyah, central Saudi Arabia. 10 of the identified species belong to scleractinian corals, 7 to brachiopods, 4 to bivalves, 4 to gastropods and one to cephalopods. Actinastraea pseudominima, Thamnasteria nicoleti, Enallocoenia crassoramosa, Collignonastraea cf. grossou-vrei, Burmirhynchia jirbaensis, Pholadomya (Bucardiomya) somaliensis, Pseudomelania (Rhabdoconcha) raabi and Nautilus giganteus are believed to be recorded for the first time from the Jurassic rocks of central Arabia. The identified species have close affinity to Tethyan faunas known from parts in Asia, Africa and Europe. They indicated shoaling of the sea floor persisted throughout the deposition of the Tuwaiq Mountain Limestone, in water depth ranging from 20 to 30 m. The low diversity of invertebrates in the studied section may attribute to paleoenvironmental conditions prevailed during the Callovian age as high rate of sedimentation.

Control of Pore Types and Fracture Intensity on the P-Wave Velocity of Carbonate Rocks

Conference Paper

Mar 2019

The study objective is to determine the major factors controlling on acoustic and geomechanical properties of carbonate rocks of Jurassic D5 Member of Dhruma Formation. The study integrates petrophysical, petrographic, and geomechanical analysis to characterize different lithofacies, diagenetic properties, shear and compressional wave velocity, rock strength, dynamic elastic moduli, porosity and permeability of carbonate rocks. A total of sixty samples were collected, petrographic thin sections and Scanning Electron Microscopic images were prepared, small cubes and core plugs were prepared for porosity and permeability measurements as well as wave velocities and point load index tests. Porosity and permeability exhibited moderate to poor correlations. P-wave and S-wave velocities are moderately correlated with porosity. However, they showed better correlation with permeability. Poor to moderate direct correlation between dynamic elastic moduli (Poisson ratio and Young modulus) and porosity were found. The lithofacies with large fracture intensity are related to small P-wave velocity values. Four classes were found based on pore type and diagenetic classifications control on acoustic properties: Class 1 is characterized by moldic and intraparticle pore types with limited microporosity, Class 2 is characterized by intensive micro-fracturing, class 3 is intensively cemented, and Class 4 is characterized by microporosity. Micro-fractures pore type samples show the best wave velocity versus porosity correlation followed by densely cemented microporosity and finally moldic and intraparticle show the weakest correlation. Vertical semi-variograms were measured for P and S-wave velocity as well as porosity. A spherical model was found for P and S-wave velocities with zero nugget values and sill values equal to 3 meters. Hole effect reflecting the control of cyclicity was found. Porosity semi-variogram shows exponential modeling with zero nugget value and sill value equal to three meters. This difference in semivariogram between velocity and porosity supports weak and moderate correlations between them.

Control of Pore Types and Fracture Intensity on the P-Wave Velocity of Carbonate Rocks

Conference Paper

Mar 2019

New evidence of Regressing and Transgressing Jurassic Siliciclastic Coastlines within the Dhruma Formation in Northern Central Arabia, Saudi Arabia

Article

Nov 2018
SEDIMENT GEOL

The Middle Jurassic Dhruma carbonates have long been identified as a major hydrocarbon reservoir with massive proven reserves in Saudi Arabia and other Arabian Gulf countries. Regional studies indicate that these hydrocarbon-rich carbonates are replaced laterally by siliciclastic deposits in northern and southern central Arabia. However, none of those studies have clarified how these siliciclastic deposits were formed or how they can be correlated with their carbonate counterparts. Recently drilled shallow stratigraphic wells near the outcrops of the Dhruma Formation (approximately 250 km NW of Riyadh) provide an opportunity to analyze these siliciclastic sediments. Around 1500 m of cores from six shallow stratigraphic wells are described and interpreted, providing an understanding of the transgressive and regressive Middle Jurassic siliciclastic Dhruma shorelines. An unusual aspect of the Dhruma shorelines was the long-lived transgressions (greater than half the thickness of the succession) that initially created embayed estuarine coastlines. Rivers coming into the estuaries were backfilled and strongly impacted by tidal currents entering the embayments from the sea. Fluvio-tidal and tidal sandbars filled 11 m deep inner estuarine channels and were eventually overridden by muddy central basin deposits and then by the remnants of coastal barriers with tidal inlets. Higher frequency transgressions during the middle part of the Dhruma interval left an unusual record of stacked shelf ridges, until widespread shelf carbonates developed when the clastic supply system had back-stepped far landward. In the upper third of the Dhruma Formation, the clastic supply system was re-established, with river- and tide-influenced deltas regressing across the preexisting shelf area. Five thick transgressive-regressive sequences, in addition to a series of low-supply, high-frequency mid-Bajocian transgressive events, provide the details of the evolution of this early Middle Jurassic coastline in central Arabia. Given a likely total time span of 5–7 Ma (early Aalenian to Bathonian), the Dhruma siliciclastic sequences have a duration of ~1 Ma and an average thickness of 30–80 m. The existing Middle Jurassic paleogeography map in central Saudi Arabia has been enhanced, and a correlation has been made with the Dhruma reservoir-equivalent outcrops in southern central Arabia.

Factors influencing acoustic properties of carbonate rocks: Examples from middle Jurassic carbonates, Central Saudi Arabia

Article

Oct 2018
J Afr Earth Sci

The study aims to identify lithofacies, diagenetic properties, porosity and permeability, compressional and shear wave velocity, rock strength and dynamic elastic moduli of carbonate rocks. All these aspects are used together to delineate the major factors that influences acoustic and geomechanical properties of carbonate rocks of Jurassic Dhruma Formation. A total of sixty carbonate rock samples were collected, petrographic thin sections and SEM images were prepared, core plugs and small cubes were prepared for porosity, permeability, acoustic wave velocities and point load tests, Powder samples were prepared to understand the mineralogical control on these properties. Nine lithofacies were found and minor lithofacies controls on acoustic and geomechanical properties were figured out. Porosity and permeability showed poor to moderate correlations. P-wave and Swave velocities are poorly correlated with porosity and better correlated with permeability (compared with porosity). Poor correlation between Poisson's ratio and porosity and moderate correlation between dynamic Young's modulus and porosity were found. Two failure patterns of induced fractures were found when applying point load: regular discrete (straight) pattern related to samples of higher strength index and Young's modulus, irregular patterns were found in low strength index and Young's modulus, these induced fractures are compared with natural fractures that are observed in the outcrop. Four petrographic classes were found based on pore type and diagenetic classifications control on acoustic properties: Class 1 is characterized by moldic and intraparticle pore types with limited microporosity. It shows the weakest correlation; Class 2 is characterized by intensive micro-fracturing. This class shows the best wave velocity versus porosity correlation, class 3 is intensively cemented, and Class 4 is characterized by microporosity. Vertical semi-variograms were measured for P and Swave velocity as well as porosity. A spherical model was found for P and S-wave velocities with zero nugget and range values equal to 3 m. Hole effect reflecting the control of cyclicity was found. Porosity semi-variogram shows exponential modeling with zero nugget and range value equal to 3 m. This difference in semivariogram between velocity and porosity supports weak and moderate correlations between them.

High-frequency cycles and sequence stratigraphy of the lower Jurassic Marrat Formation, central Saudi Arabia

Article

Aug 2018
MAR PETROL GEOL

Novel Insights to Unconventional Carbonate Mudstones with Quantitative Nanoporosity Characterization and Modeling of Tuwaiq Mountain Formation

Article

Oct 2024

Characteristics and evolution of pore types in marine carbonate mudrocks, selective early to late Jurassic succession, central Saudi Arabia

Article

Aug 2021
J AFR EARTH SCI

This study's main goal was to recognize pore types, sizes, and abundance within three carbonate mudrocks units (parts of Upper Marrat, Tuwaiq Mountain Limestone, and Hanifa formations) located in Central Saudi Arabia. The methods used for this study were petrographic thin section analysis, helium porosity measurements, and X-ray diffraction. Backscattered scanning electron microscopy with energy dispersive scanning, micro-computed tomographic scanning, Total Organic Carbon “TOC” analysis, nuclear magnetic resonance, N2 adsorption analyses were used for qualitative and quantitative pore type characterization. Three carbonate mudrocks lithofacies were specified in Hanifa Formation Hawtah Member: LFH1, LFH2, and LFH3. Two lithofacies were defined in the Tuwaiq Mountain Limestone mudstone: LFT1 and LFT2. Two mudstone lithofacies were identified in the Upper Marrat Formation: LFM1 and LFM2. Intra-skeletal, intraparticle, and secondary OM-hosted pores are found in the Hanifa mudstone lithofacies. Intra-skeletal, small scale interparticle (pyrite framboids), and OM-hosted pores were predominant in Tuwaiq Mountain Limestone mudstone lithofacies. Small scale interparticle pores (euhedral calcite) and secondary OM-hosted pores were found in both mudstone lithofacies of the Upper Marrat Formation. All pore types were linked to corresponding diagenetic processes and burial events. NMR-relaxation time curves and pore size distribution curves revealed that LFH1 and LFH3 lithofacies has higher pore abundance than in the LFH2 lithofacies. LFT1 and LFT2 lithofacies have similar bimodal relaxation time distribution with slightly higher abundance observed in the LFT1 lithofacies. LFM1 and LFM2 lithofacies have similar bimodal relaxation time distribution with slightly higher abundance observed in the LFM1 lithofacies. These results can be used as input parameters to generate fluid flow simulation to determine these carbonate-rich mudrock reservoirs' potentiality.

Chapter 3 Lithostratigraphy and depositional characteristics, age dating and sequence stratigraphy

Article

Nov 2020

A. O. Wilson

This chapter reviews the lithostratigraphy, biostratigraphy, age dating and sequence stratigraphy of the Arabian Intrashelf Basin to document the basic data used in the interpretations in this Memoir. The factors important to understanding these topics are discussed, including the typical facies, general depositional models, the effects of dolomitization, well log characteristics and the problems with obtaining precise age dates. Comments are included to show the interpretations preferred in this Memoir.

Mapping and assessing limestone as a raw material for the cement industry using satellite data: a case study of areas between Riyadh and Al Kharj, Saudi Arabia

Article

Sep 2020

Satellite remote sensing is a popular method utilized in mineral and natural resource exploration, particularly to reduce reconnaissance and exploration costs. Its use is widely popular for geological mapping of arid regions. The primary objective of this paper is to illustrate how remote sensing satellite data could be used for mapping and assessing potential limestone raw material for the cement industry in Saudi Arabia. Limestone rocks are identified and mapped using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) indices, band combinations, band ratio combination, and relative absorption-band depth (RBD). Band combination of ASTER-thermal infrared (TIR) data 14:12:10, 8:6:1, and QI:CI:MI in R:G:B is also used for mapping limestone rocks with high efficiency as well as differentiating between sandstone and limestone rocks in the study area. Two band ratios 6/8 and 9/8 and RBD of (band 7+band 9)/band 8 are used for detecting limestone rocks as bright pixels. The carbonate index of ASTER-TIR data are subsequently used for mapping limestone areas and categorize them into classes for the purpose of using them as a raw material in the cement industry. Study findings show that high and very high classes of CI are concentrated in the southern and central parts of the study area such as Khashm Mazalij, Jabal Hit, and Jabal Hafafah and correlate with cement limestone and high-Ca limestone sites in the study area. Other very high limestone classes are found distributed in the northwestern part of Banban. Sulaiy Formation, in Khashm Mazalij area, also constitutes the best promising potential for high-purity limestone. It is hoped that the findings of the study provide ample evidence for the usefulness of the reconnaissance tool in assessing the limestone as raw materials, which is a vital process for the cement industry decision-makers in planning and managing natural resources in Saudi Arabia.

Characterization and Modeling of the Geo-Body Geometries and the Reservoir Properties: An Outcrop Analog Study of Jurassic Carbonate Reservoirs in Central Saudi Arabia

Conference Paper

Mar 2019

Well exposed Jurassic outcrops belt in central Saudi Arabia provides good outcrop analogs which can be utilized to capture the high resolution facies types and architecture that might help to fill the inter-wells gap in the subsurface. This study is focused on the characterization and modeling the facies types, body geometries deposited in geomorphic elements of carbonate ramp system and the distribution of the reservoir properties on it. Three-dimensional models for the different facies-body geometries were conducted to provide accurate stochastic representation. This study was conducted at a selected Jurassic outcrop reservoir analog that exposed around Riyadh area. The Mesozoic carbonate strata of central Saudi Arabia are interpreted to have been deposited in ramp systems and exposed in hundreds of kilometers in the strike and dip direction of palaeoshoreline. The study integrates detailed sedimentological and stratigraphic analysis from outcrop strata to capture facies-body geometries and their petrophysical properties on the ramp system. Nine lithofacies were interpreted from the stratigraphic sections. Spatially, the porosity and permeability show different ranges of heterogeneity from micro to meso and macro scales. Laterally, the reservoir properties show steady variations in contrast with the abrupt change vertically. This variation seems to be related to the sedimentary structure, grain size, and degree of cementation. Different pore types were recognized in the studied intervals, which include fracture, intraparticle, moldic and intercrystalline porosities. Several 3D facies models were constructed using sedimentological and stratigraphic data that collected from the field. These models express the complex and heterogeneous relationship between facies-body geometries in the outcrop precisely. Integration of these data to subsurface equivalent reservoirs will provide qualitative and quantitative information useful for understanding and predicting reservoir quality and architecture in carbonate ramps.

Biofacies and palaeoenvironments of the Jurassic Shaqra Group of Saudi Arabia

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