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Seawater intrusion (SWI) is the main threat to fresh groundwater (GW) resources in coastal regions worldwide. Early identification and delineation of such threats can help decision-makers plan for suitable management measures to protect water resources for coastal communities. This study assesses seawater intrusion (SWI) and GW salinization of the shallow and deep coastal aquifers in the Al-Qatif area, in the eastern region of Saudi Arabia. Field hydrogeological and hydrochemical investigations coupled with laboratory-based hydrochemical and isotopic analyses (18O and 2H) were used in this integrated study. Hydrochemical facies diagrams, ionic ratio diagrams, and spatial distribution maps of GW physical and chemical parameters (EC, TDS, Cl−, Br−), and seawater fraction (fsw) were generated to depict the lateral extent of SWI. Hydrochemical facies diagrams were mainly used for GW salinization source identification. The results show that the shallow GW is of brackish and saline types with EC, TDS, Cl−, Br− concentration, and an increasing fsw trend seaward, indicating more influence of SWI on shallow GW wells located close to the shoreline. On the contrary, deep GW shows low fsw and EC, TDS, Cl−, and Br−, indicating less influence of SWI on GW chemistry. Moreover, the shallow GW is enriched in 18O and 2H isotopes compared with the deep GW, which reveals mixing with recent water. In conclusion, the reduction in GW abstraction in the central part of the study area raised the average GW level by three meters. Therefore, to protect the deep GW from SWI and salinity pollution, it is recommended to implement such management practices in the entire region. In addition, continuous monitoring of deep GW is recommended to provide decision-makers with sufficient data to plan for the protection of coastal freshwater resources. [ABSTRACT FROM AUTHOR]

Shark fossil microremains belonging to the genus Lissodus are recovered for the first time from the Lower Khartam Member of the Khuff Formation in central Saudi Arabia. Previously published research assigned the Lower Khartam Member to the Upper Permian, implying that this is the oldest known record of the genus Lissodus. On the other hand, the stratigraphic occurrence of the recovered Lissodus lies slightly below the previously defined Permian/Triassic boundary in Saudi Arabia. Because Lissodus specimens are common from the Lower Triassic to the Upper Cretaceous, they may provide paleontological evidence for a revised placement of the Permian/Triassic boundary in Saudi Arabia. The Permian/Triassic boundary has been formerly placed at the contact between the Lower andUpperKhartam members of the Khuff Formation in central Saudi Arabia. Earlier studies relied on sequence stratigraphy and geochemistry as tools for identifying the Permian/Triassic boundary. This resulted in placing the boundary at different stratigraphic levels, reflecting the ongoing uncertainty about its actual position. In this study, two scenarios are discussed arguing either for a revised placement of the Permian/Triassic boundary, or a possible Late Permian origin for the genus Lissodus on the Gondwanan continent. [ABSTRACT FROM AUTHOR]

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. • The D5 and D6 units of the Dhruma Formation (Middle Jurassic), central Saudi Arabia, are characterized by 10 lithofacies. • The depositional setting is that of a shallow carbonate ramp with lagoonal and shoal sub-environments. • The 10 lithofacies are grouped into three texturally distinct lithofacies associations. • Depositional textures and diagenetic modification ultimately control reservoir quality of the Dhruma strata. • Depositional environments and reservoir quality on outcrop are closely aligned with local and regional equivalents. [ABSTRACT FROM AUTHOR]

Previous research has explored the linkage between bioturbation, porosity, and permeability in carbonate reservoir rocks. The impact of bioturbation on natural fractures in such rocks remains relatively unexplored, however, but is crucial for effective subsurface resource management. This study focuses on the relationship between bioturbation and fracture characteristics in a well-exposed outcrop, the upper Cretaceous Khanasir Member of the Aruma Formation, central Saudi Arabia. The approach includes field investigation, petrography, imaging analysis, and CT scanning to quantify the relationship between burrows and fracture characteristics at scales from thin section to outcrop scale. At the outcrop scale, the Khanasir Member comprises three distinct units based on their fracture and burrow characteristics. These units reveal two primary categories of fractures: (1) burrow-related fractures, influenced and controlled by bioturbation; and (2) non-burrow-related fractures, unaffected by bioturbation. The characteristics of fractures within these units are influenced by multiple factors including: if burrows are filled; composition of the burrow fillings; mineralogy of host rock matrix; texture of the host rock matrix; and burrow percentage. The interplay of these factors affects fracture attributes such as density, length, and spacing, all of which have a direct impact on fluid flow behavior within subsurface reservoirs. • Bioturbated strata in the Aruma Formation display extensive burrowing and fractures. • Fractures are influenced by burrow attributes, composition and diagenesis. • Two fractures categories are identified: burrow and non-burrow-related fractures. • The burrows, fractures, and the host rock matrix forms a triple-porosity system. [ABSTRACT FROM AUTHOR]

The upper Cretaceous Aruma Formation in Central Saudi Arabia exhibits Thalassinoides -bearing strata resembling a bioturbated carbonate reservoir with large burrows. These burrows possess distinct stratigraphic characteristics. Certain intervals within the formation feature open or partially filled Thalassinoides , creating three-dimensional permeability pathways, while others contain Thalassinoides filled with low-permeability sediments. This comprehensive study investigates the paleoenvironment, ichnological features, bulk permeability influence, and stratigraphic variations of these bioturbated intervals. Incorporating field observations, laboratory analyses (including petrography, geochemical assessments, petrophysical measurements, and computed tomography scanning [CT]), we present the division of the studied interval into three biogenically influenced fluid flow media (BIFM 1–3). BIFM 1 comprises solution-enlarged open Thalassinoides (average shaft diameter: 5 cm) hosted within a mud-dominated matrix. BIFM 2 consists of Thalassinoides with mud-dominated infills (average shaft diameter: 3 cm) embedded in a dolomite matrix. BIFM 3 exhibits compacted open Thalassinoides. These BIFM units demonstrate burrow percentages ranging from 10% to 45%, featuring interconnected networks. The identified units reflect diverse depositional settings, ranging from open marine to restricted lagoon, and distinct stratigraphic positions. By highlighting the sedimentological and stratigraphic controls on the petrophysical properties of carbonate strata containing Thalassinoides with large burrows, this research contributes to the prediction of super-permeability zones in analogous settings. • Bioturbated strata in the upper Cretaceous Aruma Formation resemble a carbonate reservoir with distinct large burrows. • Thalassinoides -bearing intervals exhibit both permeability pathways and low-permeability infills. • The study investigates the paleoenvironment, ichnological, and stratigraphic variations of the bioturbated intervals. • Three biogenically influenced fluid flow media (BIFM 1–3) are identified via field observations and laboratory analyses. • Sedimentological and stratigraphic controls on petrophysical properties provide insights for predicting super-K zones. [ABSTRACT FROM AUTHOR]

The Jurassic was a time for major global changes in climate, tectonics, and oceanography, reflected in the southern Neo-Tethys Ocean by a distinct transition from carbonate-poor to carbonate-dominated sedimentation. To better constrain the effect of this turning point in the Late Jurassic, key outcrops of Oxfordian deposits of the Arabian Plate were investigated through detailed sedimentologic analysis. High-resolution (centimeter-scale) description and analysis of eight outcropping sections with a cumulative thickness of 461 m through the Oxfordian Hanifa Formation along a N–S 535 km-long transect in central Saudi Arabia are used to develop a comprehensive conceptual depositional evolution through time. Nine sedimentary lithofacies are interpreted and grouped into four facies associations. These associations include: I) outer-ramp association (FA1), II) mid-ramp association (FA2), III) inner-ramp grainy-facies association (FA3), and VI) inner-ramp reefal association (FA4). The lithofacies succession distinguishes two depositional phases, a middle Oxfordian homoclinal ramp (Phase 1) that corresponds to the Hawtah Member, and a late Oxfordian reef-bearing carbonate ramp (Phase 2) that corresponds to the Ulayyah Member. After being restricted to the high latitudes in the northern Neo-Tethys during early and middle Oxfordian ages, the carbonate ramp evolution within the Hanifa Formation reflects the expansion of scleractinian coral reefs over the southern Neo-Tethys passive margin in the late Oxfordian. However, the distribution of the corals in the Arabian Plate is mainly controlled by water salinity and siliciclastic input; they are absent northward due to hypersalinity and southward due to siliciclastic input. Furthermore, the differential subsidence and the resulting uneven topography, in addition to the eustatic sea level variation during the Oxfordian age, controls the distribution of different depositional styles over the Arabian Plate (homoclinal ramp, distally-steepened ramp, rimed shelf, and intrashelf basin). • The Oxfordian eustacy and differential tectonism controlled the basin geometry and southern Neo-Tethys' depositional model. • The findings of this study are useful for correlation to other Oxfordian successions of the southern Neo-Tethys. • Middle Oxfordian homoclinal carbonate ramp has evolved to include distributed reef buildups in the late Oxfordian. • Siliciclastic facies are described for the first time in the Oxfordian Hanifa Formation outcrops. [ABSTRACT FROM AUTHOR]

The main aim of this study is to constrain the range of reservoir properties observed in various depositional environments of the fine-grained sandstones of the early Silurian middle Qusaiba Member, Qalibah Formation, northwestern Saudi Arabia. Facies analysis, micro-X-ray fluorescence (μXRF), lamina-scale permeability measurements, automated helium porosity-permeability measurement, and pore system visualization were integrated to observe variations in these various environments. Seven main facies were recognized and interpreted to be deposited in an offshore "turbiditic-influenced" to lower shoreface paleoenvironments. These facies include current rippled siltstone (F1); Contorted silty sandstone (F2); current rippled fine-grained sandstone (F3); planar-laminated fine-grained sandstone (F4); Bioturbated to current-rippled argillaceous siltstone to silty sandstone (F5); Current rippled silty sandstone (F6); bioturbated sandstone (F7) facies. These facies were clustered into several fabric classes; 1) contorted fabrics associated with load casts flame structure that is characteristic of F2: These typically revealed slightly higher porosity and permeability values than the surrounding media with a spherical and relatively low anisotropy. 2) Planar-laminated fabrics in F4 that overlain by cryptic bioturbation: It comprises of clay mineral-rich laminae with higher porosity and permeability and the quartz-rich laminae with lower porosity and permeability probably due to abundant calcite cement associated with detrital quartz. Higher anisotropy, associated with this fabric, was observed. Cryptic bitourbated interval showed relatively low permeability. 3) In F7, three types of rock fabrics were observed, (1) Vertical sand-filled Piscichnus trace fossil: The burrow fill shows significantly higher porosity and permeability values than the laminated matrix; this fabric reveals an elliptical and highly anisotropic variance map. (2) Horizontal sand-filled Thalassinoides burrow (with iron oxide cement).: The internal core of this fabric was highly porous and permeable compared to the laminated fabric. Thalassinoides fabric had the most elliptical and highest anisotropic variance map in F7. (3) Entirely laminated fabric with bed-parallel gypsum veins: The permeability of the veins was slightly higher than that of the matrix, this resulted in a less anisotropic variance map. μCT scanning was used for F5 and F6; In the F5 facies, more significant porosity associated with quartz-rich lamina than iron oxide (e.g., siderite) and gypsum-rich lamina were observed probably due to higher chlorite alignment in the iron oxide-rich lamina. We found lower porosity and permeability within the vertical mud-filled burrows (Piscichnus) than the laminated fabric; this was also observed in the 3D pore system imaged by μCT scanning. These findings could have significant implications for different fabric types in fluid flow conduits in argillaceous sandstone and siltstone systems. • Effect of small-scale fabrics on permeability was examined in fine-grained sediments. • Lamination and deformation are the main factors controlling μm to mm-scale permeability of turbiditic deposits. • Bioturbation has an impact on permeability of lower shoreface sediments. [ABSTRACT FROM AUTHOR]

Storm-wave sediments are considered a potential unconventional resource in the Middle East region, i.e., the early Silurian Qusaiba Member of the Qaliba Formation in Saudi Arabia. Extremely few studies have examined the controls of lithofacies heterogeneity on pore types, sizes, distribution, and connectivity. Therefore, this study intended to illustrate lithofacies controls on pore systems using various integrated approaches. Based on lithofacies analysis, seven lithofacies were identified and interpreted as storm-wave-dominated distal, medial, and proximal shelf deposits. The results of this study reveal two main types of pore systems: interparticle and intraparticle pores, which have been thoroughly recongized across all recognized lithofacies. Nuclear magnetic resonance (NMR) data showed positively and negatively skewed bimodal porosity distribution curves in the proximal and distal shelf lithofacies, respectively; however, the NMR data of medial shelf lithofacies were found to be normally distributed with unimodal distribution curves. Phyllosilicate minerals associated with interparticle pores (≤1 μm) were observed in the distal lithofacies; however, larger-scale interparticle pores were observed in both medial and proximal lithofacies. Such variation was also reflected in the NMR curves, resulting in negatively and positively skewed distribution curves of T2. Diagenetic facies (i.e., calcite, phosphate, pyrite, iron oxides, and clay minerals cementations) occurred during syndepositional, early, and intermediate burial stages before oil generation window. This study facilitates the understanding of the impacts of lithofacies and diagenetic facies on the pore system, and, the petrophysical characteristics of mudrocks in similar depostional settings. • Different pore types within seven lithofacies of storm-wave influenced sediments of Qusaiba were analyzed. • Integration of NMR and SEM-EDS analyses were used. • Interparticle, Intraparticle, and Fractured pore types are common whereas organic matter porosity is absent. • The pores formed and developed during syndeposition, early and intermediate burial stages. [ABSTRACT FROM AUTHOR]