Geophysical signature of the vien-type uranium mineralization of Wadi Eishimbai, Southern Eastern Desert, Egypt

The application of various geophysical tools with different responses succeeded in fixing U-mineralization in Wadi Eishimbai area. The area was studied using detailed ground spectrometric, magnetic, and filtered very low-frequency electromagnetic (VLF-EM) surveys. The interpretation of the obtained spectrometric maps clearly reflects the sharp increase of equivalent uranium (eU) content. Meanwhile, K and Th contents show sharp decreases. The eU/equivalent thorium (eTh) ratio correlates positively with eU concentrations and negatively with eTh concentrations, indicating an increase in U potentiality than the surrounding granite. The N?CS shear zone displays an eU content ranging from 20 to 140?ppm. The ENE-trending lamprophyre is characterized by elongated uranium anomalies trending in the E?CW direction, with values >90?ppm. Equivalent uranium content of the brecciated granite attains values up to 700?ppm. The ground magnetic and VLF-EM surveys played important roles in providing structural information which are proven useful in geological mapping and mineral exploration for the discovery of uranium mineralization in the study area. This study follows the expected subsurface extension of the Sela shear zone under Wadi sediments. The ground total magnetic intensity map shows a relatively narrow and an elongated shape for the lamprophyre anomaly extending for about 600?m in the Wadi toward the western direction. VLF-EM contour maps of the two used frequencies (17.1 and 28.5?kHz) show excellent agreement, indicating that the shear zone is distinguished with slightly strong conductivity westwards as an extension of the main shear zone. It is elongated in an ENE?CWSW trend and extends in the western direction, referring to the existence of conductive materials. Most of the NW/SE-trending faults cause sudden changes in the magnetic and VLF-EM contour spacing over an appreciable distance, which suggests a discontinuity in depth due to their left-lateral strike-slip displacements. The interpreted faults, with an ENE?CWSW trend representing the main trend of Sela shear zone through which hydrothermal solutions flowed, cause high alteration and uranium mineralization.     

A systematic review on approaches and methods used for flood vulnerability assessment: framework for future research

Natural Hazards - Floods have always been associated with widespread devastation and destruction since the emergence of human civilization. The intensity of this disaster has been increasing due to...     

Occurrence of diagenetic pseudobreccias within the paleokarst zone of the upper Dammam Formation in Kuwait, Arabian Gulf

A paleokarstic zone capping the Middle Eocene dolomitic Dammam Formation delineates a regional disconformity with the overlying Mio-Pleistocene fluvial deposits in Kuwait. This formation outcrops in a quarry located in the southeast of Kuwait and occurs in the subsurface of Umm Ghudair water field, west Kuwait. Karstification has affected the upper member of the Dammam Formation, which is formed of extensively chertified, vuggy chalky biodolomicrite. Karstification is manifested by two phases: a dissolution phase that was responsible for the occurrence of surface and near surface karst features and a precipitation phase during which a karst carapace and dolocretic and calcitic pseudobreccias were developed. Petrographic investigations of both the biodolomicrites host rock and the karst lithotypes revealed a complex diagenetic history that encompasses the following diagenetic events, arranged in a chronological order: (a) replacive dolomitization, (b) precipitative dolomitization, (c) precipitative silica, (d) replacive silica, (e) karstification, (f) development of karst carapace [calcretization and calcitization (development of calcitic psuedobreccia)], (g) dolocretization (development of dolocretic psuedobreccia), (h) mild karstification, (i) calcite precipitation, and (j) silica precipitation. The development of the karst carapace at the unconformity surface between the Eocene Dammam Formation dolomicrites and the overlying Mio-Pleistocene Kuwait Group clastics has played a significant role in the hydrological characteristics of Kuwait usable groundwater resources. It is recommended that the occurrence of similar diagenetic processes within the Arabian carbonate shelf deposits be investigated.     

Toxicity of organophosphorus pesticide sumithion on larval stages of stinging catfish <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

Sumithion is widely used to control brittle in paddy fields and tiger bug in fish larval rearing ponds. The objective of this study was to elucidate the toxic effects of sumithion on larval stages of stinging catfish Heteropneustes fossilis. Larvae were exposed to two concentrations (150 and 250 μg/L) of sumithion with one control in three replicates of each. Larvae samples were collected at 20- and 24-h intervals followed by observation under a digital microscope. Exposures of stinging catfish larvae to sumithion produced deformities including irregular head shape, lordosis, yolk sac edema, body arcuation, tissue ulceration, etc. The mortality rates of larvae were significantly increased in response to increase in sumithion concentrations. Furthermore, around 30% of the total adult stinging catfish reared in sumithiontreated aquaculture ponds were found to be deformed permanently. These findings highlight that exposure of stinging catfish to sumithion at the critical and sensitive stages in their life cycle may significantly reduce the number of returning adults. Therefore, the use of sumithion for crop protection needs to be considered carefully and alternatives to sumithion should to be developed for controlling aquatic insects in aqua-ponds during larval rearing.     

Hook whistlers observed at low latitude ground station Varanasi

Employing the Haselgrove ray tracing equations and a diffusive equilibrium model of the ionosphere, the propagation characteristics of hook whistlers recorded at low-latitude ground station Varanasi (geomag. lat., 16°6′.N) are discussed. It is shown that the two traces of the hook whistlers are caused by the VLF waves radiated from the return stroke of a lightning discharge which after penetrating the ionosphere at two different entry points, propagated to the opposite hemisphere in the whistler mode and were received at 16 geomagnetic latitude. Further the crossing of ray paths for the same frequency leads to the explanation of the hook whistler. The lower and higher cut-off frequencies are explained in terms of their deviating away from the bunch of the recorded whistler waves and crossing of ray paths for the same frequency.     

Subsurface structural trends of the offshore Nile Delta area, Egypt: evidences from gravity and magnetic data

Subsurface structural trends and tectonics affecting the offshore Nile Delta area, Egypt, have been studied through the interpretations of gravity and magnetic data. Reduced to the pole, regional–residual separation, Tilt derivative and Euler deconvolution techniques are applied for the processing and interpretations of the magnetic and gravity data. The average depth of the sedimentary cover, estimated from the two-dimensional power spectrum technique ranges between 8 km and 13 km. The interpretation of the gravity and magnetic data indicates that the study area is affected by many subsurface structural trends. The NW–SE is the major trend related to El-Temsah and Misfaq-Bardwil trend. The NE–SW direction is the second dominant trend, related to the Rosetta trend. Other trends defined through the interpretation of gravity and magnetic data include: the N–S direction, related to the Baltim fault trend, the E–W direction, related to the Neogene hinge line and the NNE–SSW related to the Gulf of Aqaba. Accessory trends include the ENE–WSW, WNW–ESE and finally the NNW–SSW.     

Developing a long-term monitoring network under uncertain flowpaths

A long-term monitoring well network is developed using complementary and simple approaches in conjunction with a stochastic ground water flow and transport model. The development is illustrated for a case study of a U.S. nuclear testing site (Shoal) that is undergoing environmental restoration. The network design builds on three different, yet complementary, tools for locating the monitoring wells with a main objective of detection monitoring. The first tool is applied to select potential siting horizons where monitoring wells could be located. The second tool is used to place monitoring wells in locations with high success probability. The success here is defined as the detection of migrating stochastic plumes before a certain mass percentage reaches a compliance boundary. The third tool is used to analyze detection efficiency of multiple combinations of three wells. Seventy-six different three-well networks are selected from 20 candidate locations and are evaluated for detection efficiency. From the 76 networks analyzed, 28 attain detection efficiency close to or above 70%. The results of the different analyses provide multiple alternatives for the locations of the three wells, which will become part of the long-term monitoring network at Shoal. A number of combinations are equally good, and the final choice will depend on practical considerations and future agreements between model sponsor and regulators.     

Structuring factors of the spatio-temporal variability of macrozoobenthos assemblages in a southern Mediterranean lagoon: How useful for bioindication is a multi-biotic indices approach?

The authors investigated the impact of the extension of the El Kantra Channel on the composition and structure of macrobenthic assemblages in Boughrara Lagoon (Gulf of Gabes, Tunisia along with the use of 4 biotic indices (AMBI, BENTIX, M-AMBI and TUBI). Thirteen stations were sampled seasonally in 2012–2013. Forty-one species were found in 2012–2013 not recorded in 2009–2010, including 20 species of polychaetes belonging to the trophic groups of deposit-feeders and carnivores which are expected to increase in areas disturbed by organic pollution. During the survey, we recorded a high fish mortality, essentially caused by the development of harmful algal blooms (HAB) which increased organic matter deposition, thus inducing polychaete development. This seems to weaken the bio-indicating power of biotic indices used here which, paradoxically, classified all sampled stations at a high ecological status. A review of these indices and their applicability to all marine environments is recommended.     

Preservation of enzymic activity in marine plankton by low-temperature freezing

The measurement of enzymic activity in plankton communities is useful in the study of marine ecosystems. Such measurements can lead to a clearer understanding of the biological transformations in plankton communities at a particular time. However, the assays are somewhat time-consuming. To facilitate analysis of large numbers of samples, we have developed a method of quick-freezing of whole cells and of cell-free extracts of the diatom, Skeletonema costatum, followed by storage at ?60°C for up to one week. No loss in either the electron transport system (ETS) or the glutamate dehydrogenase (GDH) activity occurs. Similar conditions of storage can be used for the preservation of ETS activity in the marine copepod Calanus pacificus. Also, no measurable loss in either the GDH or the ETS activity is detectable after the quick-frozen whole cells of S. costatum have been kept frozen for over a year.     

Spatiotemporal variation and mechanisms of temperature inversion in the Bay of Bengal and the eastern equatorial Indian Ocean

In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo（2004 to 2020） and RAMA（2...