Northwestern Oman Research Articles

Integrated facies analysis of the Late Cretaceous Simsima Formation in northwestern Oman mountain, Jabel Al-Rawdah, Hatta area, Oman

Integrated facies analysis of the Late Cretaceous Simsima Formation in northwestern Oman mountain, Jabel Al-Rawdah, Hatta area, Oman

The skeletal remains from Umm an-Nar tomb QA 1-1: spatial distribution and anthropological analysis

Collective aboveground circular tombs of stone are one of the main categories of architectural structures from the Umm an-Nar period (2500–2000 BC) in the Oman peninsula. The tombs have been known since the late 1950s but various aspects of their functioning still await a full explanation. Most of them survived in poor condition, often empty, only a dozen or so actually yielding any human remains. Tomb QA 1-1, one of ten Umm an-Nar-type tombs at Wadi al-Fajj in northwestern Oman, has yielded a substantial assemblage of human skeletal remains (estimated MNI 25) from the two of four burial chambers excavated between 2016 and 2018. While the excavation of the tomb should be continued, a presentation of the bone assemblage recovered to date, including a distribution analysis of the remains, deposition characteristic, and preliminary osteological analysis, adds to the existing source base of Early Bronze Age populations in the ancient land of Magan.

Groundwater Modeling and Sustainability of a Transboundary Hardrock–Alluvium Aquifer in North Oman Mountains

This study aims at modeling groundwater flow using MODFLOW in a transboundary hardrock–alluvium aquifer, located in northwestern Oman. A three-dimensional stratigraphic model of the study area representing the vertical and spatial extent of four principal hydro-geologic units (specifically, the Hawasina, ophiolite, Tertiary and alluvium) was generated using data collected from hundreds drilled borehole logs. Layer elevations and materials for four layers grid cells were taken from the generated stratigraphic model in which the materials and elevations were inherited from the stratigraphic model that encompasses the cell. This process led to accurate grid so that the developed groundwater conceptual model was mapped to simulate the groundwater flow and to estimate groundwater balance components and sustainable groundwater extraction for the October 1996 to September 2013 period. Results show that the long-term lateral groundwater flux ranging from 4.23 to 11.69 Mm3/year, with an average of 5.67 Mm3/year, drains from the fractured eastern ophiolite mountains into the alluvial zone. Moreover, the long-term regional groundwater sustainable groundwater extraction is 18.09 Mm3/year for 17 years, while it is, respectively, estimated as 14.51, 16.31, and 36.00 Mm3/year for dry, normal, and wet climate periods based on standardized precipitation index (SPI) climate condition. Considering a total difference in groundwater levels between eastern and western points of the study area on the order of 228 m and a 12-year monthly calibration period (October 1996 to September 2008), a root mean squared error (RMSE) in predicted groundwater elevation of 2.71 m is considered reasonable for the study area characterized by remarkable geological and hydrogeological diversity. A quantitative assessment of the groundwater balance components and particularly sustainable groundwater extraction for the different hydrological period would help decision makers to better understand the water resources in the Al-Buraimi region. In addition, it would assist decision makers to improve existing strategies to enhance the decision making for future developments.

An efficient surrogate-based simulation-optimization method for calibrating a regional MODFLOW model

Simulation-optimization method entails a large number of model simulations, which is computationally intensive or even prohibitive if the model simulation is extremely time-consuming. Statistical models have been examined as a surrogate of the high-fidelity physical model during simulation-optimization process to tackle this problem. Among them, Multivariate Adaptive Regression Splines (MARS), a non-parametric adaptive regression method, is superior in overcoming problems of high-dimensions and discontinuities of the data. Furthermore, the stability and accuracy of MARS model can be improved by bootstrap aggregating methods, namely, bagging. In this paper, Bagging MARS (BMARS) method is integrated to a surrogate-based simulation-optimization framework to calibrate a three-dimensional MODFLOW model, which is developed to simulate the groundwater flow in an arid hardrock-alluvium region in northwestern Oman. The physical MODFLOW model is surrogated by the statistical model developed using BMARS algorithm. The surrogate model, which is fitted and validated using training dataset generated by the physical model, can approximate solutions rapidly. An efficient Sobol’ method is employed to calculate global sensitivities of head outputs to input parameters, which are used to analyze their importance for the model outputs spatiotemporally. Only sensitive parameters are included in the calibration process to further improve the computational efficiency. Normalized root mean square error (NRMSE) between measured and simulated heads at observation wells is used as the objective function to be minimized during optimization. The reasonable history match between the simulated and observed heads demonstrated feasibility of this high-efficient calibration framework.

Evidence for early irrigation at Bat (Wadi Sharsah, northwestern Oman) before the advent of farming villages

Decades of archaeological research in southeastern Arabia (Oman and the UAE) have provided a good understanding of the evolution of human societies in this arid region, with the transition from mobile pastoralism to settled agricultural villages occurring at the start of the Hafit period (ca. 3100–2700 BCE). The delayed adoption of farming, ceramics, mudbrick architecture, metallurgy, and other technologies until the start of the 3rd millennium BCE has been a particularly salient feature of this region relative to its neighbours in Mesopotamia, southern Iran, and northwestern South Asia. However, recent geoarchaeological research at the World Heritage Site of Bat, situated within the Wadi Sharsah valley in northwest Oman, has provided evidence of irrigation practices that have been dated to the early-mid 4th millennium BCE. While direct evidence of farming from this early period remains elusive, the presence of irrigated fields at this time raises new questions about the supposedly mobile pastoralist groups of the Arabian Neolithic and the beginning of farming practices in the region.

Preferential Calcite Cementation of Macropores In Microporous Limestones

Abstract A study of limestone cores from the Upper Shu’aiba Member (upper Aptian) in an oilfield in northwestern Oman shows examples of a cementation phenomenon that appears to be widespread in microporous carbonate reservoirs and fundamental for understanding their porosity evolution during burial diagenesis. The studied reservoirs have total porosity of 4 to 36%, which consists mainly of “micropores,” defined here as pores not distinctly visible in a petrographic thin section (thus generally <30 microns diameter). In these mud-rich rudstones, floatstones, packstones, wackestones, and mudstones, calcite cement preferentially filled the larger pore spaces, while micropores remain relatively open in the more porous rocks. The present wide range in total porosity results mainly from varying microporosity of mud matrix and grains. Lack of corroded pore boundaries militates against formation of micropores by late dissolution. Preferential cementation of limestone macropores can be explained by “pore-size-controlled solubility” (PCS). Interfacial energy effects increase the solubility of very small crystals relative to larger crystals, and because only tiny crystals can fit into micropores, the micropores tend to remain uncemented at the same time as larger calcite cement crystals grow within nearby macropores. A model is proposed for evolution of the pore-throat size distribution of microporous limestones during burial cementation whereby PCS results in preferential filling of larger pores as the pore-throat size maximum is shifted progressively lower. Observations from other microporous limestones indicate that the cement-pore-size relationships observed in the Oman cores may be a general characteristic that develops in association with “chalky porosity” during burial cementation.

Hydrochemical processes regulating groundwater quality in the coastal plain of Al Musanaah, Sultanate of Oman

The Al Batinah coastal aquifer is the principal source of water in northwestern Oman. The rainfall in the Jabal Al Akhdar mountain region recharges the plain with freshwater that allowed agricultural and industrial activities to develop. The over-exploitation of this aquifer since the 1970s for municipal, agricultural and industrial purposes, excessive use of fertilizers in agriculture and leakage from septic tanks led to the deterioration of groundwater quality. The objective of this study was to investigate the hydrochemical processes regulating the groundwater quality in the southwestern section of Al Batinah. From available data collected during the spring of 2010 from 58 wells located in Al Musanaah wilayat, it was determined that the groundwater salinity increased in the direction from the south to the north following the regional flow direction. In addition to salinisation, the groundwater in the upstream and intermediate regions was contaminated with nitrate, while groundwater in the downstream region was affected by fluoride. Calculations of ionic ratios and seawater fraction indicated that seawater intrusion was not dominant in the study area. The primary factors controlling the groundwater chemistry in Al Musanaah appear to be halite dissolution, reverse ion exchange with clay material and anthropogenic pollutants.

Reservoir rock typing of Upper Shu’aiba limestones, northwestern Oman

Core samples from seven wells in Lower Cretaceous limestones of the Upper Shu’aiba Member were characterized by conventional core analyses, petrography, bulk chemistry and mercury-injection capillary pressure data to define reservoir rock types (RRT). In the main oilfield studied, lithofacies are arranged in three main belts corresponding to ramp crest, upper slope and lower slope, with bioclast content and size decreasing down depositional dip. Rock typing is based on the observation of distinct, but overlapping, porosity–permeability transforms for each lithofacies, although most samples plot in or below the class 3 field of Lucia, reflecting the presence of abundant lime-mud matrix. Because of the wide range of porosity in each of the main lithofacies, an arbitrary division at 20% porosity is used in combination with lithofacies to define RRT with both three-dimensional (3D) geological significance and distinct ranges of permeability and capillary pressure characteristics. The use of total porosity as a rock-typing criterion is based on the interpretation that porosity is controlled on the reservoir scale by the depositional clay content of the local stratigraphic environment. The seaward and uppermost parts of the clinoforms a have low clay, and, thus, highest porosity. Because both lithofacies and porosity are linked to the sedimentological and stratigraphic organization of the Upper Shu’aiba clinoforms, the RRT can potentially be implemented in a reservoir model for assigning distinct ranges of petrophysical properties to the different architectural elements comprising each clinoform. Two additional grain-dominated RRT have also been defined in a single core that was available from a second oilfield.

Lithofacies, diagenesis and reservoir quality of Upper Shu’aiba reservoirs in northwestern Oman

ABSTRACTCore and log data from Lower Cretaceous limestones of the Upper Shu’aiba Member were used to characterize the distribution of lithofacies, clay and porosity within two low-angle clinoforms that form the reservoirs for an oilfield of northwestern Oman. Data from 15 vertical wells, including four with core, and four horizontal well cores were projected into a dip-oriented cross-section derived from a static reservoir model as a basis for visualizing the above variations. Each clinoform consists of a basal “argillaceous zone” and a thicker “reservoir zone” of clean limestone, together reflecting fourth-order cycles of progradation along the margin of the Bab intra-shelf basin. Lithofacies vary in a proximal direction from mudstone and wackestone (mid-ramp) to mud-dominated packstone (slope) to mud-rich floatstone, rudstone and boundstone (ramp crest) and are arranged in a pattern of decreasing water depth and increasing energy both upwards and landward within each clinoform. In contrast, the reservoir zone of a younger clinoform from a nearby oilfield consists of well-sorted grainstone and grain-dominated packstone, illustrating the wide range of depositional conditions that occurred in the ramp-crest facies belt of different units.Except within the proximal extent of the younger clinoform, where values are transitional toward reservoir zone values, the argillaceous zones have total porosity mostly &amp;lt; 10% and baseline-normalized gamma-ray (GR) activity &amp;gt; 23 API units, reflecting clay contents of around 10–18%. In contrast, most parts of the reservoir zones have GR of 15–23 API units and porosity of 10–35%. Higher clay content is suggested to be linked with lower porosity through facilitation of both mechanical and chemical compaction, the latter providing a local supply of calcite cement. XRD analyses show that the clays are kaolin, illite/smectite and illite, similar to the clays in the overlying Nahr Umr shale. Most former macropores have been filled by blocky calcite cement in the main oilfield studied, but all lithofacies have similar wide ranges of total porosity of 8% to &amp;gt; 30%.The cores were also studied for evidence of diagenesis related to the contact with the overlying Nahr Umr Formation, but profiles of stable-isotope ratios, bulk-rock strontium, petrography and porosity-permeability data show no trends indicative of upward-increasing meteoric diagenesis below this sequence boundary. Meteoric leaching could nevertheless be pervasive throughout the Upper Shu’aiba reservoirs, at least partially accounting for extensive aragonite dissolution and low Sr and δ18O values. Two of the cores show trends of upwards-increasing bulk-rock uranium, manganese and iron, possibly indicative of sea-floor authigenesis. In addition, saddle dolomite near the tops of these cores may reflect late influx of magnesium derived from clay in the Nahr Umr Formation.

The Social, Spatial, and Bioarchaeological Histories of Ancient Oman project: the mortuary landscape of Dhank

The Social, Spatial, and Bioarchaeological Histories of Ancient Oman (SoBO) project has conducted three seasons of survey and excavation in north-western Oman. Focus- ing on third-millennium BC archaeological features, this project is unique because of the combination of geospatial survey and bioarchaeological excavation of mortuary monuments in and around the town of Dhank. Here we report our initial findings, define our survey area and techniques and discuss excavated funerary structures and associated radiocarbon dates from both charcoal and human skeletal remains. This report presents preliminary results that introduce this new project on the prehistoric mortuary landscapes of Oman and highlight the techniques the SoBO team employs to examine Bronze Age communities in this rural location.

Structural and Stratigraphical Setting of the Faiyah Range, Northwestern Oman Mountain Front, United Arab Emirates

ABSTRACTThe Faiyah Range belongs to a group of regional ridges that formed by post-obduction folding of the Upper Cretaceous-Tertiary sedimentary rocks exposed along the western margin of the Northern Oman Mountains. The Faiyah Anticline, generally trends north-northeast to south-southwest with thrust faults striking parallel to the fold axis. The anticlinal hinge was later displaced by a dextral strike-slip fault, named here as the Faiyah Fault, into two segments. The northeastern segment includes Jebels Rumaylah, Faiyah and Mulayhah, and the southwestern segment includes Jebels Buhays and Aqabah. The anticline is interpreted to result from northeast-southwest compression during the Tertiary.In the Faiyah Range the neoautochthonous sedimentary rocks are the Maastrichtian Qahlah and Simsima formations, and the Eocene Dammam Formation. Stratigraphic evidence shows that the lower part of the Qahlah was deposited in a non-marine environment while the upper part was deposited during a marine transgression. The Simsima was deposited in a shallow-marine environment. These units unconformably overlap the allochthonous Semail Ophiolite. The microfaunal content of the so-called Muthaymimah Formation (?Tertiary), of earlier authors, indicates that it is of Maastrichtian age in the Faiyah Range. This sequence is also conformable to the Simsima and therefore it is considered to be the upper member of the Simsima in this area.

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: REPLY

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: REPLY

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: DISCUSSION

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: DISCUSSION

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: DISCUSSION

A discussion is presented of the Cretaceous formations involved in Fahud field. Along the Trucial Coast, as in northwestern Oman, it is not difficult to date the time of formation of the foredeep. This article provides a stratigraphic correlation chart for the Cretaceous along the Arabian side of the Arabian Gulf. The terminology presented on this correlation chart reflects oil-industry usage in the area, including correlations published by Owen and Nasr, Loutfi and Jaber, Arabian American Oil Company, Beydoun and Dunnington, and Hassan et al.

Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman

Reservoir facies in Fahud field and throughout northwestern Oman are in shallow-shelf carbonates of the middle Cretaceous Mishrif and Mauddud Formations. Interparticle porosity formed in the Mishrif as sand aprons of lithoclast and skeletal grainstones surrounding fault-block islands, and less commonly in the Mauddud as biostromes of rudist packstones. Moldic porosity after fine rudist debris is more common than interparticle porosity and occurs in thicker stratigraphic units, interpreted to have formed locally in meteoric-water lenses associated with islands, and regionally during subaerial exposure associated with sea level lows.