Deep-seated Structures Research Articles

Evidence of basement controlled faulting of cretaceous strata in the Middle Benue Trough, Nigeria from lineament analysis of gravity data

The Bouguer anomaly map of part of the Middle Benue Trough, Nigeria, was used to investigate the genetic relationship between the basement and intra-sedimentary structures in the study area. This was with a view to establishing the evidence of possible basement controlled faulting of the Cretaceous strata. Regional-residual separation of the anomalies was carried out to produce the gravity maps associated with crustal masses at deep and intermediate depth layers. The derived maps were further processed to produce Horizontal Gradient Magnitude (HGM) maps that were used to infer deep seated structures and structures existing at intermediate depth layer of the study area. HGM maxima of the anomaly at various altitudes of upward continuation were used to highlight the locations and dip directions of subsurface structures as controlled from deep to shallow zones. The results of this study showed that the structures at different depth layers dominantly trend in the same direction (N-S, NNE-SSW and NE-SW) and that the deep seated faults reflect structurally in the overlying sedimentary column. It was therefore concluded that basement faulting might have influenced the structures in the overlying sedimentary rocks.Keywords: Cretaceous Sediments, Lineaments, Azimuth-frequency, Fault Propagation

Aeromagnetic signature analysis of Gasus area and its surrounding, central eastern desert, Egypt

This study presents analysis and interpretation of aeromagnetic data to construct subsurface structure maps and determine the depths to magnetic basement. Subsequent analysis steps are applied to the total magnetic intensity (TMI) data. These steps include Reduction to the Pole (RTP) map that was derived from the TMI map then subjected to spectral frequency analysis to isolate RTP map into high and low frequencies and determine pseudo-depth for each map from power spectrum in which there were two main average levels (interfaces) at depth 1.3 and 0.7 km for the deep-seated and near-surface magnetic structures, respectively. 3D Euler deconvolution technique is applied to calculate the depth to the magnetic contacts; the results show clustering of solutions, the shallow solutions are related to the outcrops less than 80 m from flight level, and the solutions which are related to sedimentary cover locations (Um al-Huweitat, Wasif, and Mohamed Rabah basins) are ranged between 200 and to more than 1100 m. Moreover, anomaly enhancement techniques such as tilt derivative (TD), horizontal tilt derivative (TDX), and source edge detect (SED) are applied to enhance shallow features, and determining structure element boundary for both shallow- and deep-seated anomalies and revealing possible faults such as 2D forward modeling are applied to selected profiles to adjust the interpreted structures and map the boundaries and basement relief of the three basins (Mohammed Rabah, Wasif, and Um al-Huweitat). The analysis shows that the study area is affected with network of dip–slip faults due to high shearing and compression stress which formed grabens and horsts at different depth levels in the study area. The trends of predominant faults related to deep-seated structures are NW–SE with depths ranged between 1 and 1.4 km and in regard to the shallow-seated structure, the predominant fault trends are NW–SE, NNW–SSE, and NNE–SSW with depths ranged between 0.3 and 0.8 km.

Simultaneous inversion application for characterizing Hamra Quartzite tight sand reservoir: a case study from Hassi Messaoud (Algeria)

Channel sand acts as a stratigraphic trap for hydrocarbon accumulation in many parts of the world. Delineation of this type of reservoir is crucial as channel sand may be scarce, and inaccurate location of the drilling wells could lose a huge currency. The Hassi Messaoud (HMD) field was subjected to multiphase tectonic events, where deep-seated structures were rejuvenated leading to intensive fault complexity. The main effective tectonic events upon the studied area are the Hercynian compression and deep erosion till the Ordovician Hamra Quartzite (HQZ) oil reservoir, followed by active Triassic rifting and filling the deeply eroded areas or the graben areas by eruptive volcanic rocks at Triassic time. Hercynian erosion and volcanic rocks distribution introduce a big uncertainty to the reservoir structural model. Amplitude versus offset (AVO) method is used as a helpful tool to differentiate channel sand from surrounding formations. Several attributes (P-impedance, S-impedance, longitudinal velocity Vp, shear velocity Vs and density ρ) are estimated from pre-stack seismic inversion. They have different sensitivity to the reservoir properties. Derived attributes such as Lame parameters, incompressibility × density (λρ) and rigidity × density (μρ) can provide key lithology and fluid indicators (Goodway et al. 1997, Goodway CSEG Rec 26(6):39-60 2001). Petrophysically relating AVO attributes both to λρ and μρ and to each other in Lambda–Mu–Rho (LMR) cross-plot space can be a good tool for AVO interpretation (Rutherford and Williams Geophysics 54:680–688 1989 and Castagna and Swan Lead Edge 16(4):337–342 1997). After proper data conditioning, simultaneous inversion of pre-stack angle gathers is performed to get acoustic wave impedance (P-impedance), elastic wave impedances (S-impedance) and density ρ, then to calculate λρ and μρ volumes. In the studied area, λρ and μρ are used as a very important key to separate reservoir sands. The λρ and μρ curves are generated at each well location. Cross plots showed a fair separation of sand in the formation, i.e. higher μρ and lower λρ can detect sand. The output λρ and μρ volumes after simultaneous inversion follow the distribution of the sand which is consistent with the wells penetrating the target reservoir. This finding on the extension of the sand reservoir in terms of λρ and μρ. 3D cross-plot zonations are used for lithology discrimination. In this study, well logs were used to constrain lithology and to control the zonation filters by reducing the limits ambiguity. Other types of advanced attributes are calculated and tested. The obtained (μρ–λρ) volume acts as a good indicator for the sand distribution. It was finally used as sand presence index in the area. Also μρ has shown a good linear relationship with porosity. To note that the porosity volume is created based on the linear relationship with μρ. A product of derived porosity and the sand presence index (μρ–λρ) provides a good tool for reservoir characterization and lead to reservoir management, future planning of the field, and setting location for new wells.

On the role of incompetent strata in the structural evolution of the Zagros Fold-Thrust Belt, Dezful Embayment, Iran

The Dezful Embayment is the most important fertile oil province of the Zagros Fold-Thrust Belt. It includes several incompetent strata as basal and intermediate décollement levels that play a significant role on the structural styles and hydrocarbon preservation. Based on the interpretation of seismic profiles, the influence of the Gachsaran Formation and the evaporitic Kalhur Member of the Asmari Formation on the geometry of deformation was investigated in different parts of the Dezful Embayment. Obtained results revealed that the thickness of the incompetent strata plays a crucial role in the formation and geometry of different types of fold structures (e.g. rounded, box, chevron, detachment fold) in the Dezful Embayment. There is a sharp difference between the geometry of surface and deep-seated structures due to the existence of thick intermediate décollements (e.g. Gachsaran and Kalhur) in the Dezful Embayment. Therefore, fault geometry and fold styles in upper and lower parts of these décollements are totally different. In addition, these incompetent strata act as a barrier level against the propagation of deep-seated faults into the overlying layers. Therefore, it seems that most of the faults exposed on the surface have originated from the upper décollement levels in the study area.

New plays on the Greater East Shetland Platform (UKCS Quadrants 3, 8-9, 14-16) – part 2: newly reported Permo-Triassic intra-platform basins and their influence on the Devonian-Paleogene prospectivity of the area

Despite significant discoveries within Palaeogene-age reservoirs (e.g., Mariner) the East Shetland Platform (ESP) is underexplored, with only ten wells per 1000 km2. Mesozoic units are thin or absent whilst Paleozoic reflectors resemble acoustic basement on legacy seismic. Recent 3D dual-sensor broadband surveys (GeoStreamer) covering 17,200 km2 over parts of Quadrants 3, 8-9, 14-16 have allowed for clearer imaging. Here, this dataset is interpreted, leading to new insights into this large frontier region. The ESP petroleum system comprises multiple proven reservoir and source intervals, with viable play fairways. Up to four regional unconformities are interpreted, merging into fewer erosional surfaces on persistent highs. Elsewhere on the ESP, predominantly subsiding Permo-Triassic depocentres contain a nearly continuous Paleozoic-Mesozoic succession. The most prominent of these, to the south and south-west of the Beryl Embayment, is here referred to as the ‘Crawford-Skipper Basin’. Existing hydrocarbon discoveries on the ESP are in the vicinities (<7 km) of intra-platform Permo-Triassic basin margins. Exploration close to such basins is inherently less risky due to possible positive influences of deep-seated structures on the petroleum system. These include: (1) formation of Meso-Cenozoic closures; (2) Devonian source maturity and presence of simple fault-related migration pathways; (3) viability of sub-Cretaceous reservoir-trap-seal configurations.

New plays on the Greater East Shetland Platform (UKCS Quadrants 3, 8-9, 14-16) – part 1: Regional setting and a working petroleum system

Despite significant discoveries within Palaeogene-age reservoirs (e.g., Mariner) the East Shetland Platform (ESP) is underexplored, with only ten wells per 1000 km2. Mesozoic units are thin or absent whilst Paleozoic reflectors resemble acoustic basement on legacy seismic. Recent 3D dual-sensor broadband surveys (GeoStreamer) covering 17,200 km2 over parts of Quadrants 3, 8-9, 14-16 have allowed for clearer imaging. Here, this dataset is interpreted, leading to new insights into this large frontier region. The ESP petroleum system comprises multiple proven reservoir and source intervals, with viable play fairways. Up to four regional unconformities are interpreted, merging into fewer erosional surfaces on persistent highs. Elsewhere on the ESP, predominantly subsiding Permo-Triassic depocentres contain a nearly continuous Paleozoic-Mesozoic succession. The most prominent of these, to the south and south-west of the Beryl Embayment, is here referred to as the ‘Crawford-Skipper Basin’. Existing hydrocarbon discoveries on the ESP are in the vicinities (<7 km) of intra-platform Permo-Triassic basin margins. Exploration close to such basins is inherently less risky due to possible positive influences of deep-seated structures on the petroleum system. These include: (1) formation of Meso-Cenozoic closures; (2) Devonian source maturity and presence of simple fault-related migration pathways; (3) viability of sub-Cretaceous reservoir-trap-seal configurations.

The influence of the Great Falls Tectonic Zone on the thrust sheet geometry of the southern Sawtooth Range, Montana, USA

AbstractThe reactivation potential of pre-existing deep-seated structures influences deformation structures produced in subsequent compression. This contribution investigates thrust geometries produced in surface thrust sheets of the Sawtooth Range, Montana, USA, deforming over a previously faulted sedimentary section. Surface thrust fault patterns were picked using existing maps and remote sensing. Thrust location and regional transport direction was also verified in the field. These observations were used to design a series of analogue models, involving deformation of a brittle cover sequence over a lower section with varying numbers of vertical faults. A final model tested the effect of decoupling the upper cover and lower section with a ductile detachment, in a scenario closer to that of the Sawtooth Range. Results demonstrate that complexity in surface thrust sheets can be related to heterogeneity within the lower sedimentary section, even when there is a detachment between this section and the rest of the cover. This complexity is best observed in the map view, as the models do not show the deep-seated faults propagating into the cover. These results were then used to predict specific locations of discrete basement fault strands in the study area, associated with what is generally mapped as the Scapegoat-Bannatyne Trend. The deep-seated faults are more likely to be reactivated as strike-slip features in nature, given the small obliquity between the ENE-directed compression direction and the NE-oriented basement faults. More generally, these results can be used to govern evaluation of thrust belts deforming over faulted basement, and to predict the locations of specific fault strands in a region where this information is unknown.

Regional crustal-scale structures as conduits for deep geothermal upflow

Geothermal fluids produced from two of the largest production geothermal fields in the Great Basin have helium isotope ratios that are anomalously high relative to basin-wide trends. These data indicate that the geothermal systems, Dixie Valley, Nevada and McGinness Hills, Nevada have an anomalously high fraction of mantle derived fluid. These connections to deeply derived fluid and heat may supplement crustal heat production and be responsible, in part, for the anomalously high production capacity, relative to other Great Basin geothermal fields, that Dixie Valley and McGinness Hills support. Deep-seated crustal structures across the Great Basin and around the world are known to be associated with structural reactivation, can have relatively high permeability, and can act as fluid flow conduits. These deep seated structures across the Great Basin control upflow of deeply derived heat and fluids into the shallow geothermal systems at Dixie Valley and McGinness Hills, contributing to their productivity.

Integration of geophysical and geological data for delimitation of mineralized zones in Um Naggat area, Central Eastern Desert, Egypt

An integrated approach for geophysical, geological and mineralogical data was followed for Um Naggat area, Central Eastern Desert, Egypt, in order to delineate its mineralized zones. The albitized granites are well-defined on the Th- and U-channel images, by their anomalous shapes, reaching 150ppm and 90ppm respectively, beside low K content.Interpretations of the aeromagnetic maps delineated four regional structural trends oriented due NNW, NW, ENE and E–W directions. They are identified as strike-slip faults, which coincide well with field observations, where NW-trending faults cut and displace right laterally ENE-trending older ones. The interaction between these two strike-slip fault systems confining the albite granite is easily identified on the regional data presenting longer wavelength anomalies, implying deep-seated structures. They could represent potential pathways for migration of enriched mineralized fluids. Geochemically, albite granites of peraluminous characteristics that had suffered extensive post-magmatic metasomatic reworking, resulted into development of (Zr, Hf, Nb, Ta, U, Th, Sn) and albite-enriched and greisenized granite body of about 600m thick, and more than 3km in strike length. The albite granite is characterized by sharp increase in average rare metal content: Zr (830ppm), Hf (51ppm), Nb (340ppm), Ta (44ppm), and U (90ppm). Thorite, uranothorite, uraninite and zircon are the main uranium-bearing minerals of magmatic origin within the enclosing granite. However, with respect to Zr, Nb, and Ta, the albitized granite can be categorized as rare metal granite. The integration of airborne geophysical (magnetic and γ-ray spectrometric), geological, geochemical and mineralogical data succeeded in assigning the albite granite of Um Naggat pluton as a mineralized zone. This zone is characterized by its high thorium and uranium of hydrothermal origin as indicated by its low Th/U ratio, with rare metals mineralization controlled by two main structural trends in the NW- and ENE-directions.

Sea level change. Inherited landscapes and sea level change.

Enabled by recently gained understanding of deep-seated and surficial Earth processes, a convergence of views between geophysics and sedimentary geology has been quietly taking place over the past several decades. Surface topography resulting from lithospheric memory, retained at various temporal and spatial scales, has become the connective link between these two methodologically diverse geoscience disciplines. Ideas leading to the hypothesis of plate tectonics originated largely with an oceanic focus, where dynamic and mostly horizontal movements of the crust could be envisioned. But when these notions were applied to the landscapes of the supposedly rigid plate interiors, there was less success in explaining the observed anomalies in terrestrial topography. Solid-Earth geophysics has now reached a developmental stage where vertical movements can be measured and modeled at meaningful scales and the deep-seated structures can be imaged with increasing resolution. Concurrently, there have been advances in quantifying mechanical properties of the lithosphere (the solid outer skin of Earth, usually defined to include both the crust and the solid but elastic upper mantle above the asthenosphere). The lithosphere acts as the intermediary that transfers the effects of mantle dynamics to the surface. These developments have allowed us to better understand the previously puzzling topographic features of plate interiors and continental margins. On the sedimentary geology side, new quantitative modeling techniques and holistic approaches to integrating source-to-sink sedimentary systems have led to clearer understanding of basin evolution and sediment budgets that allow the reconstruction of missing sedimentary records and past geological landscapes.

The first data on the geology of Jeannette Island (De Long Archipelago, New Siberian Islands)

This paper presents the first actual information on the geology of Jeannette Island, one of the islands of the De Long archipelago located in the East Siberian Sea. We show that Jeannette Island has a volcano-sedimentary section dominated by volcaniclastic turbidites. The sequence identified on the southwestern coast of the island has a submonoclinal plunge complicated by secondary deformation structures, which indicate a general E-W direction of tectonic transport (in present-day coordinates). The sequence is intensely cut by multiple thin (up to a few meters) gabbro-dolerite dikes that are deformed conformably with the host rocks. The general geological framework of the island bears a close resemblance to that of nearby Henrietta Island located some 70 km to the east, which consists of a volcano-sedimentary cover of Early Paleozoic age. No organic remains have been found in the studied section of Jeannette Island. The preliminary results of isotope geochronological and paleomagnetic studies confirm the Late Precambrian-Early Paleozoic age assigned to the entire rock complex of Jeannette Island. The measured paleomagnetic directions are generally consistent with the directions of Lower Paleozoic rocks of Bennett Island (De Long archipelago) and Kotelny Island (Anzhu archipelago), which confirms our earlier conclusion that the New Siberian Islands shared a common tectonic history and that this structural element of the Arctic shelf appears to have been a terrane during the Early Paleozoic. This new information can help elucidate the possible relations between the marginal-continental, shelf, island and deep-seated structures of the Eastern Arctic.

Application of Geochemical Data as Evidence of Water-Rock Interaction in the Sarvak Formation, Izeh Zone, Zagros, Iran

The Sarvak formation from the Bangestan group is an important petroleum reservoir in Iran that we studied geochemically in 5 outcrop sections in the Izeh zone. Our results show that characteristics of the Sarvak Formation changed in the Izeh zone. High Sr/Mn ratios and Sr content with heaviest oxygen isotopes of the Sarvak Formation carbonates indicate lower dissolution processes, extensive rock-water interaction (WRI), and a closed diagenetic system. O and C isotope variations suggest marine phreatic diagenesis in the north flank of the Mish, Bangestan, and Mangasht anticlines, and meteoric diagenesis in the south flank of the Mish and Payun anticlines. Observed geochemical variations in the Izeh zone can be related to reactivation of deep-seated structures and faults that caused variation in thickness, facies, and diagenesis.

3D crustal structure and its tectonic implication for nile delta and greater cairo regions, egypt, from geophysical data

In the present study the crustal structures of Nile Delta, including Greater Cairo province, and its surroundings, were evaluated using 3D forward gravity and magnetic modeling. The interpretation is also based on the seismic reflection results, well logs data and previous density models. The present results allow to improve the understanding of both the crustal thicknesses and density distributions between the sedimentary cover and the upper mantle in the study area.The high Bouguer anomalies near the Mediterranean coast are mainly caused by deep-seated structures. The crust beneath the Mediterranean coastal region is typically continental, with a thickness of 24 km beneath Rositta and Damitta branches, which increases toward the south. The Greater Cairo province has been modeled with maximum crustal thickness of ca. 34 km. The negative gravity anomalies with minimum values are due to the effect of sedimentary cover and/or basement relief geometry.The main results of this work suggest that the study area...

Tectono-stratigraphic and kinematic evolution of the southern Apennines/Calabria–Peloritani Terrane system (Italy)

Temporal controls such as sedimentation ages, in foredeep and wedge-top basins, combined with information about stratigraphic and metamorphic evolution, ages and characterization of magmatic rocks, deep structures, burial and exhumation histories, allowed us to obtain kinematic estimations of the southern Apennines/Calabria–Peloritani Terrane system evolution from the Late Oligocene to Recent. Calculated thrust front velocities suggest to subdivide the orogenic evolution in main five kinematic stages characterized by different velocity trends. Nine kinematic complexes (from A to I), i.e. sets of tectonic units deformed in the same time range, are determined according to foredeep ages. These complexes, bounded by main regional thrust faults, encompass one or more tectonic sub-units and successions of different paleoenvironment domains. Paleogeographic evolution model indicates, according to available paleomagnetic data, a counterclockwise rotation, with a mean angle of 60°, for the Apennine Platform carbonates, whereas a mean angle of 20° for the eastern sector of the Apennine Platform and western side of Apulian Platform. Shortening estimations for the Apennine successions show values ranging between 55% and 88% and a linear best fit indicating an increase from 60% (NW sector) to ca. 90% (SE sector). Such high values are consistent with a deformation dominated by a thin-skinned tectonics, on the contrary, the low value of 28% calculated for Mt. Alpi suggests an exhumation ruled by high-angle deep-seated structures characterized by limited displacements. Tectonic vergences, referred to Middle–Late Miocene, Late Miocene and Pliocene–Middle Pleistocene, when restored, indicate an average eastward tectonic transport. Finally, tectonic evolution is summarized in eleven schematic cross sections and corresponding paleogeographic maps.

Challenges to the implementation of fiscal sustainability measures

Purpose: Fiscal sustainability is high on the global political agenda. Yet, implementing the needed performance-orientation throughout public-sector organizations remains problematic. Such implementation seems to run counter to deep-seated social structures. In this paper the aim is to shed light via key change agents' views on these social structures at the management level during the implementation of a performance-based budgeting scheme. Design/methodology/approach: The authors analyzed documentary data and conducted in-depth, semi-structured interviews with key change agents operative within central government ministries in The Netherlands. The data were analyzed using a structurational approach to identify the enablers and barriers to performance-based budgeting implementation. Findings: In total, 29 social enablers and barriers to performance-based budgeting implementation were derived. These were categorized into: Context, Autonomy, Traditional beliefs, Influence on results, and Top management support. Based on these categories five propositions were developed on how social structures enable and constrain performance-based budgeting implementation among public managers. Research limitations/implications: The study was executed in one country in a specific period in time. Although the problems with performance-based budgeting exist over the globe, research is needed to study whether similar social structures enable and impede implementation. Social implications: Policy makers and change agents aiming to improve fiscal sustainability by budgeting reform need to consider the found social structures. Where possible they could strengthen enablers and design specific comprehensive measures to tackle the barriers identified. Originality/value: This paper provides insight and develops knowledge on the social structures that enable and constrain performance-based budgeting, which in turn improves fiscal sustainability.

Integrated potential field study on the subsurface structural characterization of the area North Bahariya Oasis, Western Desert, Egypt

The present study aims mainly to delineate and outline the regional subsurface structural and tectonic framework of the buried basement rocks of Abu El Gharadig Basin, Northern Western Desert, Egypt. The potential field data (Bouguer gravity and total intensity aeromagnetic maps) carried out in the Abu El Gharadig Basin had been analyzed together with other geophysical and geological studies. The execution of this study is initiated by transformation of the total intensity aeromagnetic data to the reduced to pole (RTP) magnetic map. This is followed by applying several transformation techniques and various filtering processes through qualitative and quantitative analyses on both of the gravity and magnetic data. These techniques include the qualitative interpretation of gravity, total intensity magnetic and RTP magnetic maps. Regional–residual separation is carried out using the power spectrum. Also, the analytic signal and second vertical derivative techniques are applied to delineate the hidden anomalies. Aeromagnetic anomalies in the area reflect significant features on the basement tectonics, on the deep-seated structures and on the shallow-seated ones. Major faults and intrusions in the area are indicated to be mainly along the NE–SW, NW–SE, ENE–WSW and E–W directions. The Bouguer gravity map indicates major basement fracturing, as well as variations in the sedimentary basins and ridges and subsequent tectonic disturbances. The most obvious anomalous trends on the gravity map, based on their frequencies and amplitudes, are along the NE–SW, ENE–WSW, E–W and NW–SE trends. The main of Abu EL Gharadig Basin depositional center does not show sharp variations, because of the homogeneity of the marine rocks and the great basement depths.

Spectre of the Past, Vision of the Future – Ritual, Reflexivity and the Hope for Renewal in Yann Arthus-Bertrand’s Climate Change Communication Film "Home"

Spectre of the Past, Vision of the Future – Ritual, Reflexivity and the Hope for Renewal in Yann Arthus-Bertrand’s Climate Change Communication Film "Home"

Formation of spray cone of free jet during ejection of convoluted flow to the atmosphere

In modern world water-power, one of the predominant tendencies is to construct hydroprojects with high dams, which is associated with the necessity of solving a series of engineering and natural problems to ensure the safety of the water-development works. The building of reliable deepseated high-head water-passing structures can be classified as such a problem. Use of spiral spillways, equipped with helical gates is an effective means of its solution [1]. Helical gates (Fig. 1) in which smooth regulation of the flow being passed from zero to maximum is accomplished by rotating guide vanes, similar to the deflector of a reactive hydraulic turbine, have essentially no limit with respect to head. Beyond the spiral gate, the convoluted (circulating longitudinal) flow, which possesses, in addition to axial velocities u x directed along the conduit, azimuthal velocities u x , which are directed around its circumference and create a transverse circulation in the flow, proceeds into cylindrical discharge conduit (with a diameter 2R ). As a domestic development at the outset of the 1970s [2, 3], the vortical gates immediately gained the acceptance of specialists as one of the most reliable deep-seated high-head regulating gates. In addition, this design is considered excessively complex, and, consequently, expensive. In our opinion, the high cost of the equipment here is completely justified for purposes of reliability. If we are speaking of high heads, a small concession to quality may be transformed into not-so-small consequences. And experience indicates, the tendency to reduce the cost of the structures is accompanied by losses in their reliability, resulting in failures. The subject has acquired particular urgency in light of the return to the Rogun’ project, where construction of vortical spillways is specified. The reliability of the vortical gate lies within the principle of flow regulation by this device, which is achieved not only by throttling the water-passing opening, but also by varying the transverse circulation of the flow. By converting a significant or basic part of the mechanical energy of the flow into the energy of circulation movement and excess centrifugal pressure, they can then be extinguished over the length of the discharge conduit, or the flow can be atomized on ejection to the atmosphere. Offering little hydraulic resistance, the vortical gate accordingly exerts a minor influence on the flow, directing it easily past the rotating blades of the guide, and, in turn, experiencing a small reversing effect from the flow. Moreover, the rotating blades interacting with the flow are external to the periphery of the convoluted current that they are forming — in the zone where the high excess pressure of the centrifugal-force field suppresses

Ultrasound in Acute and Chronic Pain Medicine

Ultrasound is becoming popular in anaesthetic practice because of numerous advantages. Its introduction in pain medicine is recent and its use is growing. It allows the identification of soft tissues, vessels and nerves, without the risk of radiation. The additional advantages in pain medicine are avoidance of repeated radiations and ease of use in outpatient clinics, thus saving time and decreasing work load on interventional theatres. Ultrasound has multiple applications in pain medicine. It finds use in providing acute pain relief in the form of peripheral nerve blocks. In chronic pain, possible applications include blocks of cervical and lumbar facet joints, stellate ganglion block, intercostal nerve blocks, blocks of painful stump neuromas, caudal epidural injections and injections of trigger or tender points. The nerves can be visualised directly, thus helping in destructive processes like cryoanalgesia, radiofrequency lesioning and chemical neurolysis. The disadvantages are loss of resolution for deep-seated structures and lack of controlled trials. The article presents a review of ultrasound usage in acute and chronic pain interventional procedures.

Structural control of El Sela granites and associated uranium deposits, Southern Eastern Desert, Egypt

The El Sela area is a part of the basement complex of the Eastern Desert of Egypt and the Pan-African Shield. The area comprises outcrops of dismembered ophiolites thrust over arc volcano-sedimentary sequence and intruded by different syn- to post-tectonic granitoids. Structural analysis of the area enabled the separation and definition of four structural episodes: (E1) folding–thrusting episode associated with the cratonization of the arc/inter-arc rock association and the intrusion of the syntectonic (Older) granites. (E2) Upright folding episode associated with the compression and shortening to the ENE–WSW direction which is different from the NNW–SSE shortening direction during E1; at the end of E2, late tectonic granites were intruded. (E3) Post-tectonic granitic intrusion episode: two mica granite and granitic dikes were intruded during this episode. (E4) Fracturing, faulting, and post-granitic dike extrusion episodes caused different faults that took place after cratonization until the present. There are three generations of folds during ductile deformation (E1 and E2). The F2 folds are nearly coaxial (along ENE–WSW trend) with the F1 folds. The F3 folding is displayed by folds generally trending NNW–SSE. Therefore, the ENE–WSW and NNW–SSE trends can considered as preexisting discontinuities and mechanical anisotropy of the crust in the following structure episodes. Brittle deformation (E3 and E4) reveals the importance of those trends which control the multi-injections and many alteration features in the study area. During reactivation, a simple shear parallel to the inherited ductile fabrics was responsible for the development of mineralized structures along the ENE–WSW and NNW–SSE trends. So they can be considered as paleochannel trends for deep-seated structures and can act as a good trap for uranium and/or other mineral resources. Most of the uranium anomalies are delineated along ENE–WSW and NNW–SSE shear zones where quartz-bearing veins bounded the lamprophyre dike and microgranites and dissected them in relation to the successive fracturation and brecciation corresponding to the repeated rejuvenation of the structures. Therefore, the structural controls of the uranium mineralizations in the El Sela area appear to be related to the interaction between inherited ductile fabrics and overprinting brittle structures.