Fracture flow modelling based on satellite images of the Wajid Sandstone, Saudi Arabia

Large-scale geological features have been identified by satellite imagery and global positioning system data in the Wajid Sandstone in Saudi Arabia. The main objective is to evaluate the importance of fractures for the overall flow behaviour in this fractured rock aquifer and to estimate in-situ hydraulic apertures. Data on fractures and lineaments were available for three outcrops. By applying a “cut-out” routine on the fracture endpoint data of these fracture trace windows, three deterministic discrete fracture networks (DFN), with an area of 100 m?×?100 m, could be generated. These were used to simulate the fracture flow and to determine the hydraulic conductivity tensors. Using additional data on hydraulic pumping tests and matrix conductivities, in-situ hydraulic apertures could be determined. Average in-situ hydraulic apertures range from 1,300 to 1,700 µm. Observations from the field support these results. In addition, a hydraulic conductivity ratio between the matrix and fracture system was used to identify the contribution of the DFN to the overall fluid transport. A ratio of 10.4 was determined, which indicates that the effective flow behaviour in the Wajid Sandstone aquifer is not entirely dominated by the fracture system, though evidently strongly controlled by it.     

Holocene shorelines and tectonic movements in eastern Saudi Arabia

Although Quaternary marine terraces have been reported from eastern Saudi Arabia at heights of up to 150 m, unambiguous shoreline deposits could be identified only within 3 m of present-day High Water and close to the modern shoreline. Unaltered aragonitic mollusc shells from five such deposits yielded ¹⁴C ages of 3700–6000 yr B.P. Comparison of their elevations with those of coeval deposits on the Zagros coast of Iran demonstrates the relative stability of the Saudi shore of the Gulf during the late Holocene.     

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.     

Regional tectonic and megadepositional cycles of the Paleozoic of northwestern and central Saudi Arabia

The Paleozoic succession of the Greater Arabian basin is severely affected by series of major tectonic and climatic events which have caused major stratigraphic breaks and pronounce facies change. The major tectonic movements have resulted in dividing the succession into pronounced megatectonic and depositional cycles. In more tectonically active areas, the succession is less preserved and boundaries between the cycles are more complicated due to longer periods of erosion by later movements and/or nondeposition. Minor stratigraphic breaks within the megacycles subdivide the cycles into smaller subcycles. Following the stabilization of the Arabian–Nubian shield, the Gondwana shelf went through a gentle uplift and tilt probably related to the Assyniyc tectonic movements and thick siliciclastics of the Saq and Qasim Formations were deposited. During Late Caradocian and following the deposition of the Qasim Formation, the area went through a gentle uplift and tilt probably related to the Taconic tectonic movements. Thick succession of the Qasim and Saq Formations were eroded and deep paleovalleys incised in the two formations and underlying basement. The movements were followed by drop of sea level due to glaciation events. Glacial and periglacial deposits of the Zarqa and/or Sarah Formations filled paleovalleys and rest on older units from Ordovician to Precambrian. The third main event occurred during Late Silurian where the preexisting successions, mainly on paleohighs, were affected by tectonic movements synchronous with the Acadian tectonic phase of the Caledonian tectonic movements. The Early Devonian Tawil Formation unconformably rests on eroded Silurian and Late Ordovician deposits of the Sharawra, Qusayba (Qusaiba), and Sarah Formations in the Qusayba Depression in central Arabia. The forth main event is a regional movement contemporaneous with the Hercynian tectonic movement which has reached its maximum phase in the Late Carboniferous. Earlier successions from Carboniferous to Precambrian were affected and the Permo-Carboniferous Shajra Formation unconformably rests on all underlying Paleozoic rock units toward the central Arabia arch and other paleohighs. The Shajra rests on the Devonian Jawbah (Jubah), Jawf (Jauf) and Tawil formations, the Silurian Sharawra, Qusayba, and Uqlah formations, the Ordovician Zarqa/Sarah, and Qasim formations, the Cambro-Ordovician Saq Formation, and finally rests on Precambrian Basement complex in Central Arabia. The tectonic movements played important role in shaping the structural framework of Arabia. The Paleozoic succession included source, reservoir, and seal rocks. Oil and gas have been discovered in sandstone and limestone reservoirs in these rocks in several oilfields in the basin.     

Finite Strain Analysis of the Wadi Fatima Shear Zone in Western Arabia,Saudi Arabia

Neoproterozoic rocks, Oligocene to Neogene sediments and Tertiary Red Sea rift-related volcanics (Harrat) are three dominant major groups exposed in the Jeddah tectonic terrane in Western Arabia. The basement complex comprises amphibolites, schists, and older and younger granites unconformably overlain by a post-amalgamation volcanosedimentary sequence (Fatima Group) exhibiting post-accretionary thrusting and thrust-related structures. The older granites and/or the amphibolites and schists display mylonitization and shearing in some outcrops, and the observed kinematic indicators indicate dextral monoclinic symmetry along the impressive Wadi Fatima Shear Zone. Finite strain analysis of the mylonitized lithologies is used to interpret the deformation history of the Wadi Fatima Shear Zone. The measured finite strain data demonstrate that the amphibolites, schists, and older granites are mildly to moderately deformed, where XZ (axial ratios in XZ direction) vary from 2.76 to 4.22 and from 2.04 to 3.90 for the R_f/φ and Fry method respectively. The shortening axes (Z) have subvertical attitude and are associated with subhorizontal foliation. The data show oblate strain ellipsoids in the different rocks in the studied area and indication bulk flattening strain. We assume that the different rock types have similar deformation behavior. In the deformed granite, the strain data are identical in magnitude with those obtained in the Fatima Group volcanosedimentary sequence. Finite strain accumulated without any significant volume change contemporaneously with syn-accretionary transpressive structures. It is concluded that a simple-shear deformation with constant-volume plane strain exists, where displacement is strictly parallel to the shear plane. Furthermore, the contacts between various lithological units in the Wadi Fatima Shear Zone were formed under brittle to semi-ductile deformation conditions.     

化德群的重新厘定及其大地构造意义

区域填图研究表明，化德群上、下亚群并不是上下关系，而是层位相当的一套地层，而且商都一带的白云鄂博群也属化德群的一部分。依据详细的构造解析和地层剖面研究，重新建立了化德群的地层层序，从老到新划分为毛忽庆组、戈家营组和三夏天组。侵入化德群的杂岩体分别获得1854Ma、1808Ma和2091Ma、2154Ma锆石U-Pb年龄，表明化德群形成时代为古元古代，而不是过去所认为的中新元古代。化德群经历了两期构造变形，早期为北东东走向的复式向斜，晚期又遭受了构造叠加，形成了北北西向褶皱构造，其主期变形可能发生在2．0Ga左右，它的褶皱造山是华北克拉通在古元古代向北增生的体现，这对研究华北克拉通的增生、裂解具有重要意义。     

Fractures system within Dammam Dome and its relationship to the doming process,Eastern Saudi Arabia

Dammam Dome is an oval-shaped structure that covers an area of about 500 km² and encompasses Al Khobar, Al Dhahran and part of Ad Dammam cities, east of Saudi Arabia. The dome characterizes by the presence of well developed fractures system that exposes at its apex and extends to its peripheries. Based on their size, trend and extent, fractures within Dammam Dome are divided into three types: regional (major) fractures, local (minor) fractures and very small size-localized fractures. This study discusses the criteria used in classifying those fractures, and the relationship of the regional (major) ones to the doming process. A model for the trends pattern of fracture is suggested for those fractures, and examined with the concentric and radial fracture pattern associated normally with dome structures. The suggested model is compatible and concordant with the dome model, which proves that the major fractures in the area are related to the dome emplacement and process. Outcomes and findings of this study are crucial for understanding the behavior and distribution of fractures associated with domes. Additionally, the suggested model of fractures and their trend pattern is important model in similar setting for hydrocarbon exploration and for any urban development and major constructions within the Dome vicinities.     

Provenance, diagenesis, tectonic setting and geochemistry of Tawil Sandstone (Lower Devonian) in Central Saudi Arabia

The Tawil Sandstone (Lower Devonian) in Central Saudi Arabia overlies the Sharwara Member of the Tayyarat Formation (Silurian) and succeeded conformly by the Shaiba Member of the Jauf Formation. Petrographical data reveal that the Tawil Sandstone comprises 96% quartz, 3% feldspar, and 1% rock fragments and all samples are classified as quartz arenites. The presence of well sorted, altered to fresh feldspar, and discriminate function analysis suggests that the sediments have been subjected to substartial reworking resulting in a high level of maturity. Modal analysis data (Q–F–L) suggest a stable cratonic provenance for the sediments and accumulation in a passive margin basin is indicated (binary plot of SiO₂ vs K₂O/Na₂O). Diagenetic features include dissolution of feldspar and rock fragments, compaction, reduction of the existing pore space through rearrangements, and rotation and fragmentation of grains resulting in dissolution of quartz grains and cementation.     

Correlation of lineaments and groundwater quality in Dasht-e-Arjan Fars,SW of Iran

The NE-oriented Dasht-e-Arjan graben is located 65 km west of Shiraz and has resulted from the active Kare-e-Bas fault segmentations. This extensional graben bounded by two fault system east-Arjan and west-Arjan to the Shahneshin and Salamati anticline. In these study using Landsat 7 ETM images with resolution 2.5 m and directional filtering in the four azimuths and semi-automatic technique for linear structure in the study area. Using the obtained data from extracted lineaments, the rose diagrams of the main strike lineaments are well confirm with field measurements of faults with N56° ± 4°E direction. The structural lineaments of the study area show that the Dasht-e-Arjan area is underlain by the limestone, sandstone, and marl. LANDSAT imagery of the area has been analyzed and interpreted in order to determine the lineament and groundwater quality across the area. The fracture is structurally controlled and mostly influences both the groundwater and surface water pollution and flow directions in the Dasht-e-Arjan. Using visual interpretation, determining the lineaments on the satellite image is very difficult and subjective, and it requires an experienced interpreter. In this study, the lineament analysis is undertaken to examine the orientation of the lineament, the relationship between lineaments and tectonic features and groundwater quality. Lineament density maps show that the lineament density is high around areas. Areas having high lineament density represent areas with relatively high groundwater pollution. Field observations agreed with the results from the analysis of the imagery.     

Hydrogeology of Al-Lith Sabkha,Saudi Arabia

In Saudi Arabia, coastal sabkhas cover extensive areas along the coasts of the Red Sea and Arabian Gulf in addition to the continental sabkhas scattered in many places inland. Al-Lith sabkha is one of the typical coastal sabkhas located along the Red Sea coast. Sabkhas, in general, pose a number of geotechnical problems and need to be carefully investigated before being urbanized.A generalized geologic section in Al-Lith sabkha indicates a salty crust at the surface followed by yellowish brown silt and silty sand, olive gray silt and sandy silt and bottomed by coralline reefal limestone. Within this succession, there are several isolated lenticular bodies of sandy silt, silty sand and shelly silty sand. The clay minerals constituting the fine-grained portion of the soil are, in decreasing order, kaolinite, illite and montmorillonite in addition to minor chlorite.The depth to groundwater in 17 observation wells ranged from 0.18 to 1.81 m with a maximum fluctuation of 0.60 m between summer and winter. The permeability of the top silt layer was found to be very low with an average of 5.4×10⁻⁴ m/day. A pumping test was performed in a deep well penetrating the coralline limestone. The measured permeability is 1.1×10² m/day and the estimated storage coefficient is 4×10⁻⁵.Soil water evaporation was measured using a lysimeter constructed with undisturbed soil samples having different depths to the water level. The rate of evaporation ranges from 2.8 to 27.8 ml/day decreasing with an increase in depth to the water level.Groundwater samples were analyzed for their major anions and cations. Salt concentrations show a general increase toward the sea except for the calcium and carbonates that show a landward increase. The groundwater could be classified as a Cl+SO₄ brine. The salinity of the groundwater was determined at different depths in the pumping well and was found to be low in the top 4 m. It sharply increases until it reaches a value approximately 10 times the salinity of the top layer indicating groundwater intermixing with freshwater and salt-water intrusion. The change in the salinity during pumping was erratic but within a range of 2%.     

Effect of tectonic prominence and growth of the Arabian shield on Paleozoic sandstone successions in Saudi Arabia

Paleozoic successions in Saudi Arabia are exposed around and bordering the south, north, and northeastern edge of the Arabian shield. They are represented by the Wajid group in the south and by the Taymah, Tabuk, Qalibah, Huj, and Buraydah groups in the north and northeast. The Wajid group includes Dibsiyah, Sanamah, Khusayyan, and Juwayl formations. The Taymah group includes Siq, Amai’er, Quweira, Saq, and Qasim formations. The Tabuk group includes Zarqa, Sara, and Hawban formations. The Qalibah group includes Baq’a, Qusaiba, and Sharawra formations. The Huj group includes Tawil, Jauf, and Jubah formations. The Buraydah group includes Berwath, Unayzah, and Khuff formations. The Wajid group form one block in the south and the other groups form another block in the north, and they can be correlated. There are similarities between the northern belt which consists of the Cambro-Ordovician formations of the Tayma and Tabuk groups and the southern belt which consists of the Dibsiyah and Sanama formations of the Wajid group. Similarities include sandstone composition, sedimentary environment, paleocurrent directions, unconformities, tectonic events, and influence of Gondwana glaciations. These formations and probably some or all the rest of the Paleozoic formations used to form one block but later separated after erosion caused by gradual tectonic growth, uplift, and prominence of the Arabian shield. During early Paleozoic time, the process started by poststabilization then sedimentation and at a later stage the growth and uplift of the shield occurred gradually. Growth of shields is a fact and it is the only way to explain the exposure of the Wajid sandstone on top of the highest mountain of the shield which exceeds 3,000 m in As Sawdah in Asir area in southwestern Saudi Arabia. The sandstone sediments of these outcrops were deposited on a low lying basin before been raised to this elevation.     

碧口群火山旋回及其地质构造意义

通过详细的野外剖面观察和室内岩石地球化学研究,将碧口碧火山岩划分为3个火山旋回,每个旋回下部为基性火山岩（细碧岩及细碧质凝灰岩）,上部为酸性火山岩（石英角斑岩或石英角斑质凝灰岩）。基性火山岩富集LREE及LIL。第一旋回基性火山岩属碱性系列,第二、三旋回基性火山岩属拉斑玄武岩系列。基性火山岩浆形成于与洋岛玄武岩类似的地幔柱源,其中第三旋回基性火山岩浆晚期受岩石圈地幔混染;酸性火山岩为地壳重熔作用的产物。碧口群火山岩属大陆裂谷双峰式火山岩系,是中一新元古代扬子地块北缘大陆拉张作用的产物。这种拉张作用是秦岭造山带从震旦纪开始的大规模扩张作用的先兆。     

镁铁-超镁铁岩的分类及其构造意义

镁铁-超镁铁岩分类是镁铁-超镁铁岩研究最基本的问题之一。镁铁-超镁铁岩（不包括金伯利岩、煌斑岩和碱性超镁铁岩等）按照产出的构造背景、岩石组合、伴生矿产大体可分为5类,即：蛇绿岩、义敦型岩体、阿拉斯加型岩体、层状侵入体和橄榄岩-闪长岩型岩体。蛇绿岩代表大洋岩石圈地幔及其分异物,义敦型代表大陆岩石圈地幔及其分异物,阿拉斯加型岩体来自岛弧、活动陆缘环境或具岛弧之下地幔特征的源岩,层状侵入体来自板内伸展构造背景,橄榄岩-闪长岩型岩体的构造背景与阿拉斯加型类似,但是也有产于板内环境的。蛇绿岩是学术界最关注的问题之一,笔者认为,1972年彭罗斯会议确定的蛇绿岩的定义仍然是适用的,斯泰因曼三位一体的概念仍然是有效的,而Delik的蛇绿岩定义和分类是不可取的。笔者认为,义敦型的概念是合适的和有用的。蛇绿岩与义敦型岩体有许多相似之处,但是,它们的构造含义不同。它们之间的区别不是依靠岩石组合本身,也不依靠地球化学,而是依靠野外产出位置和伴生的围岩性质以及构造情况。不同类型的镁铁-超镁铁岩形成的构造背景不同,伴生的矿产类型不同,具有不同的大地构造意义。在野外实践和室内研究中注意它们之间的区别,无论对于理论研究还是找矿研究都是非常重要的。     

Strength and compressibility of Abqaiq marl, Saudi Arabia

The increasing number of construction projects and the lack of good quality soil for use in these projects in eastern Saudi Arabia necessitate the use of available marginal soils. Most, if not all, engineering projects use the fine-grained calcareous sediments, known locally as marl, either as a foundation material or as a fill material. The lack of published information on their engineering characteristics and behavior under ambient conditions has resulted in many construction and post-construction problems. This investigation is one of a series to evaluate the geotechnical properties of selected marl soils obtained from different areas in eastern Saudi Arabia. Marl samples, obtained from Abqaiq, were prepared in the laboratory under controlled conditions and subjected to different tests including CBR (soaked and unsoaked), triaxial compression, unconfined compression and one-dimensional compression tests. Samples were prepared at different moisture contents on both the wet and dry sides of optimum. X-ray diffraction analysis indicates that this marl contains high percentages of dolomite and calcite, in addition to other materials. The molding water content significantly affects the engineering properties of this material. Compaction on the dry side of optimum resulted in samples that have some swelling potential and highly compressible characteristics when subjected to a load after inundation.     

Structural Setting and Kinematic Analysis of the Halaban Region,Eastern Arabian Shield,Saudi Arabia

The vorticity analysis technique was applied to measure the different lithological units,such as schist,metagranite and metavolcano-sedimentary rocks,which are present in the Halaban region.This work aims to interpret the relationship between the different lithologies and the tectonic setting,in order to elucidate the nature of kinematic analysis in the Halaban region.The kinematic analyses were applied to feldspar porphyroclasts,quartz and hornblende for twentysix samples.The kinematic vorticity number (W_m) for deformed rocks in the study area ranged from～0.6 to 0.9.The direction of the long axes for finite strain data (X axes) revealed a WNW trend with shallow dipping.The direction of the short axes for finite strain data (Z axes) were represented by vertical with associated horizontal foliation.The results of the kinematic vorticity and strain analyses are characterized by simple shear with different degrees of deformation in the Halaban region.Furthermore,our finite strain data shows no significant volume change during deformation.The subhorizontal foliation was synchronized with thrusting and deformation.Furthermore,throughout the overlying nappes,the same attitudes of tectonic contacts are observable,the nappes in the orogens being formed from simple shear deformation.     

Analysis of the Achievments in Tectonic Dynamopetrologenic and Dynamo—metallogenic Simulating Experiments and Their Geological Significance

Under the action of tectonic stress ore fluids carrying ore-forming materials can migrate from a higher stress district to a lower one.This is a fact which has been widely accepted by geological cir-cles.However,can the components migrate in solid rocks under the action of stress?This problem has long attracted the attention of many geologists.The author has made a series of simulating experi-tal system.The results show that mylonite was produced as a consequence of shear flowage deformation in dolomite .The contents of the elements in porphyryclast and flowage deformation matrix were analyzed by means of electron microprobe,and the results show that Pb and Zn are obvi-ously concentrated in the shear-flowage deformation zone.Furthermore,Pb is concentrated in its cen-tre while Zn is concentrated on its margins .Newly-formed micro-grained galena can be detected locally.     

Vorticity Analysis and Deformation History of the Mizil Gneiss Dome,Eastern Arabian Shield,Saudi Arabia

The Mizil gneiss dome is an elliptical structure consisting of an amphibolite-facies volcanosedimentary mantle and a gneissic granite core. This dome is located at the northern tip of the Ar Rayn terrane only a few kilometers from the eastern edge of the Arabian shield. Previous investigations have shown the intrusive core to be an adakitic diapir with a U–Pb zircon age of 689 ± 10 Ma; this age is 50–80 Ma years older than other granites in this terrane. Vorticity analysis was carried out on samples from the intrusive core and volcanosedimentary cover; the Passchier and Rigid Grain Net (RGN) methods were used to obtain the kinematic vorticity number (W_k) and the mean kinematic vorticity number (W_m). The W_k and W_m values show a marked increase towards the south; such a pattern indicates a N-S movement of the core pluton thus creating an inclined diapir tilted to the south. Analogue experiments simulating the flow of magma diapirs rising form a subducted slab through the mantle wedge have shown that supra-subduction zone oblique diapirs are produced close to the trench and are elongated normal to the convergence direction as is the case in the Mizil pluton. This effect was found to increase with increasing slab dip due to enhanced drag along the upper surface of the subducted lithospheric plate. Spontaneous subduction which is often associated with rollback resulting in back-arc extension and steep dipping slabs is thought to have occurred in the Mozambique Ocean by 700 Ma. The Mizil pluton is coeval with the back-arc Urd ophiolite from the adjacent Dawadimi terrane, and could therefore have been produced by incipient subduction of a relatively cold slab as observed in many Pacific margin adakites. The tectonic evolution of the eastern shield, as deduced from the Mizil dome and other data from Ar Rayn and neighboring terranes, begins with the subduction of >100 My-old lithosphere beneath the Afif terrane resulting in back-arc spreading and the splitting of the Ar Rayn arc from the Afif microplate, with the concomitant production of a small volume of adakite melt. Other arc terrane(s) docked east of Ar Rayn with the westward-directed subduction still going but a lower angles and greater depth due to trench jump; this phase produced the more prevalent non-adakitic group-1 granites. A major collisional orogeny affected the entire eastern shield between 620–600 Ma and sutured the eastern shield terranes with northern Gondwana.     

月海盆地线性构造展布及其成因分析

综合多源遥感数据识别提取月球正面南北纬50°之间的线性构造,重点分析月岭和月溪的影像特征、分布规律和时空关系,结合月海沉降模型分析两者的成因机制,结合地形和重力场数据预测影响月岭类型的因素。研究表明,在质量瘤盆地,月岭和月溪存在明显的时空关系和构造成因联系,两者主要由月海沉降产生的局部应力引起,前月海时期盆地的均衡状态和月海充填的几何形状可能影响了月岭的分布类型。