SW Saudi Arabia Research Articles

DISTRIBUTION OF PETROPHYSICAL PARAMETERS IN THE CAMBRO‐ORDOVICIAN DIBSIYAH MEMBER OF THE WAJID SANDSTONE, SW SAUDI ARABIA

The Cambrian‐Ordovician Dibsiyah Member is the lowermost unit of the Wajid Sandstone, a major aquifer in SW Saudi Arabia. The Dibsiyah is present throughout most of south‐central Arabia including the Rub'Al‐Khali Basin where it is a potential exploration target and a reservoir for gas. The Member can be divided into Upper and Lower Units based on depositional facies. The Lower Unit is interpreted to have been deposited in a fluvial setting, whereas the Upper Unit, which displays abundant bioturbation, was deposited in shallow‐marine conditions.Patterns of porosity and permeability distribution in the Dibsiyah Member were analysed statistically. In general, the Member exhibits a limited range of porosity values and a wide range of permeability values. Histograms show that the porosity distribution of both Lower and Upper Units are approximately normal, and that their corresponding vertical and horizontal permeability distributions are positively skewed.The coefficient of variation for porosity in both the Lower and Upper Units is less than 0.5 indicating that the porosity range is small. However, the horizontal and vertical permeability values are more variable due to the spatial distribution of architectural elements and sedimentary structures within both units. The dissolution of unstable minerals, together with inhomogenous grain packing and poor connectivity, has resulted in a variable permeability distribution.

Field, Mineralogical and Geochemical Characteristics of As-Sarat Laterite Profiles, SW Saudi Arabia

Field, Mineralogical and Geochemical Characteristics of As-Sarat Laterite Profiles, SW Saudi Arabia

Formation and mineral chemistry of a calcic skarn from Al-Madhiq, SW Saudi Arabia

A newly identified skarn occurrence is described from the Neoproterozoic rocks of the SW Arabian shield. It is exposed to the SE, E and NE of the Al-Madhiq town. The skarn attributes correspond to those typical of the calcic skarns that host W-deposits. It is characterized as an exoskarn of the proximal type, related to a granitoid contact close to an impure quartzite bed within the regional metamorphic rocks of mixed sedimentary and volcanic derivation. The skarn is localized along a shear zone parallel to the regional faults and other major shear zones. Samples from the studied area contain characteristic skarn minerals that include both the prograde (brownish red grossular, ferrosalite, aluminian titanite-grothite, albite-oligoclase, scapolite), and retrograde (epidote, quartz, hornblende, calcite) assemblages. The pyroxenes are ferrosalites, Mn-bearing, and more like those from “oxidized” skarns; although garnets indicate it to be a “reduced” type skarn. Epidote mimicks that from typical skarns, as it bears a pistacite content of 15.9–20.7%. Grossular composition reflects a largely reduced genetic environment; as it is in solid solution with 6.5–21.6% andradite, 0–0.15% uvarovite, 0–0.47% pyrope, 4.33–18.75% almandine, and 0.4–8.58% spessartine molecules. Titanite composition varies from aluminian titanite to grothite, that may be analogous to the newly described Al-rich titanite from the low-pressure calc-silicate rocks.

Cichlid fish biodiversity in an Oligocene lake

The Baid formation (Ad Darb locality, Tihamat Asir. SW Saudi Arabia) is Oligocene in age. The sediments have been deposited in one of a series of several alkaline continental lakes that once flanked the early Red Sea Rift. So far seven specimens of cichlid fish have been discovered there. They represent at least three different species. One species from endo‐and exoskeletal characteristics can be assigned to the basal grade of cichlids, today represented mainly in Madagascar and India. The other two species seem to belong to two different clades within the African assemblage that today comprises more than 1000 species.

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Where winds blow persistently alongshore, surface waters are forced offshore and replaced by highly productive, nutrient-rich water upwelling from below. Because of this high productivity, bottom sediments beneath upwelling systems are enriched in organic matter and microfossils of planktonic organisms, the abundance of which is a signal of upwelling intensity. Changes in climate affect the intensity of upwelling and are recorded in the sediments by strong changes in indicators of upwelling activity. Thus studies of the history of upwelling from sedimentary information can give us a clearer view of local and global changes in climate through time than we might see in other areas of the ocean where the variations in oceanography induced by climate change are more subtle. The authors focus on results from deep ocean drilling expeditions, particularly those off NW and SW Africa, Peru and Saudi Arabia. These have allowed more advanced models to be developed of the temporal and spatial palaeoenvironmental patterns associated with upwelling systems since the Early Miocene. The editors hope that this book will help to identify and explain the causes and characteristics of persistent upwelling systems, how they respond to climatic forcing and the global teleconnection between them; and make this information accessible to a wide community. Upwelling Systems will appeal to marine geologists and geochemists, palaeoceanographers, palaeoclimatologists and petroleum geologists.

Bestimmung der Paläowindrichtung mittels Runzelmarken am Beispiel einer Platte aus der oligozänen Baid-Formation (SW-Saudi-Arabien)

Bestimmung der Paläowindrichtung mittels Runzelmarken am Beispiel einer Platte aus der oligozänen Baid-Formation (SW-Saudi-Arabien)

Hydrogeochemical study of the drinking water from the Khaybar village, SW Saudi Arabia

This paper presents the results of chemical analysis of four drinking waters from the Khaybar village, SW Saudi Arabia. Four main water‐wells in the Khaybar village were investigated. The Khaybar ground water is clear without odour but its taste differs according to the amount of total dissolved solids (T.D.S.). The pH values of such water are slightly alkaline. T.D.S. of the Khaybar water is higher than the Saudi highest desired level, but it is generally within the Saudi maximum permissible level. Good drinking quality water can be found in Al Mazaab and Al Tilah water‐wells in the Khaybar village. The other two water‐wells can be used for irrigation purposes only. The geological features of the Khaybar area suggest a meteoric origin for the Khaybar ground water which has been stored in the fractured metamorphic and igneous rocks and in alluvial deposits.

The Jabal Tirf Layered Gabbro and Associated Rocks of the Tihama Asir Complex, Sw Saudi Arabia

Initiation of sea floor spreading in the Red Sea 4-5 m.y. ago was preceded by an early Tertiary period of continental extension accompanied by intrusive and extrusive magmatic activity. During the Miocene, tholeiitic basaltic magma was intruded along faults and fractures in rifted continental crust to form extensive dike swarms and layered gabbroic plutons along with associated silicic intrusive bodies. These intrusions, best exposed sporadically in a 4-6 km wide zone at the edge of the Red Sea coastal plain in southwest Saudi Arabia, are known collectively as the Tihama Asir complex. One of these intrusions, a layered gabbro at Jabal Tirf near Jizan, consists of clinopyroxene gabbro and clinopyroxene olivine gabbro, plus minor troctolite and anorthosite, displaying cumulate textures. Microprobe analyses performed on a sequence of samples, from the bottom to the top of the intrusion, reveal no systematic variation in mineral chemistry with stratigraphic height in the intrusion. Mineral compositions in the Jabal Tirf layered gabbro are similar to the Skaergaard Lower Zone a (LZa), but the intrusion shows no iron-enrichment trend like the Skaergaard. The mineral chemistry of the Jabal Tirf layered gabbro suggests crystallization at approximately 1 kb, liquidus temperature about 1200°C, solidus temperature about 950°C, and low magma water content. The layered gabbro formed by multiple influxes of already differentiated tholeiitic magma from a single source, possibly a lower crustal magma chamber. Associated diabase dikes formed from the same parental magma as the gabbro. Cogenetic silicic intrusives may result from differentiation of basaltic magma and partial melting of lower continental crust.

Climatic constraints and potential corn production in Saudi Arabia ?A study in agroclimate

A parametric crop yield model “YIELD”, which was developed by Prof. W. Terjung and his team at UCLA, was applied to calculate yield and water consumption for corn in Saudi Arabia. The model employs climatic and environmental data in order to simulate yield for several crops in different places all over the world. A network of 22 stations provided climatic data averaged over a period of 17 years (1967–1983). The nonclimatic data was derived from the FAO soil map of the world and the writer's personal experience. The main objectives of this paper are: [1] to determine suitable places and times for planting corn, under rainfed and irrigated conditions in Saudi Arabia; [2] to contrast irrigation water for corn in each province; and [3] to assess the potential yield for corn in the country in a year. This study concluded that highest yields of corn under fully-irrigated conditions (primary growing season) occurred in the mountainous region in SW Saudi Arabia (about 12,000 kg/ha, and more than 18,000 in Nimas) while lowest yields occurred in Tabuk and Al-Khawsh (about 4,000 kg/ha). Yields in most of the other stations were (5,000–8,000 kg/ha). Under rainfed conditions crop failed in all regions except in the SW region in which yields range between 2,000 kg/ha in Al-Khawsh and — 6,000 kg/ha as in Nimas. According to the findings of this study, the most suitable months for corn sowing in Saudi Arabia are December and January.