Facies model of a fine‐grained,tide‐dominated delta: Lower Dir Abu Lifa Member (Eocene), Western Desert,Egypt

Existing facies models of tide‐dominated deltas largely omit fine‐grained, mud‐rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well‐preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non‐channelized tidal bars and tidal channels. Non‐channelized tidal bars comprise coarsening‐upward sandbodies, including large, downcurrent‐dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single‐storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward‐facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically‐accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along‐strike variability defines a similar large‐scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence‐set top, and flanked by stacked, non‐channelized tidal bars and smaller channelized bodies. The tide‐dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net‐progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and tidal bar accretion at the delta front. The detailed facies analysis of this fine‐grained, tide‐dominated deltaic succession expands the range of depositional models available for the evaluation of ancient tidal successions, which are currently biased towards transgressive, valley‐confined estuarine and coarser grained deltaic depositional systems.     

The use of magnetic and geo-electrical data to delineate the subsurface structures and groundwater potentiality in Southeastern Sinai, Egypt

The study area is located in the southern part of Sinai Peninsula. This study was done to delineate the subsurface structure of the basement rocks affecting the groundwater potentiality in the study area and to perform the lateral and vertical variations in the subsurface lithologic properties. To achieve these, a high-resolution total intensity magnetic map and geo-electrical survey were acquired. Two-dimensional power spectrum, analytical signal, and Euler deconvolution techniques are applied on magnetic data. The geo-electric data interpretations concluded that, the study area can be classified into five units of sediments arranged as: (1) the top surficial layer of dry sand and gravels; (2) the second layer of silty sand layer with thickness ranging from 5 to 35 m; (3) the third layer of dry sand with thickness ranging from 5 to 130 m; (4) the fourth layer composed of saturated sand which was considered as the water-bearing zone of the investigated interval, its thickness ranges between 50m and more than 200 m; (5) the fifth layer is interpreted as basement rocks. The depth to the basement surface has an average value of 156 m at the eastern side and 758 m at the western side of the study area. This area is characterized by a graben structure bounded by major faults striking in the NW–SE direction and is considered one of the most promising regions for water resources in Sinai.     

http://www.sciencedirect.com/science/article/pii/S1674987112001041

Large igneous provinces (LIPs) are considered a relevant cause for mass extinctions of marine life throughout Earth’s history. Their flood basalts and associated intrusions can cause significant release of SO₄ and CO₂ and consequently, cause major environmental disruptions. Here, we reconstruct the long-term periodic pattern of LIP emplacement and its impact on ocean chemistry and biodiversity from δ³⁴S_sulfate of the last 520 Ma under particular consideration of the preservation limits of LIP records. A combination of cross-wavelet and other time-series analysis methods has been applied to quantify a potential chain of linkage between LIP emplacement periodicity, geochemical changes and the Phanerozoic marine genera record. We suggest a mantle plume cyclicity represented by LIP volumes (V) of V = ?(350–770) × 10³ km³ sin(2πt/170 Ma) + (300–650) × 10³ km³ sin(2πt/64.5 Ma + 2.3) for t = time in Ma. A shift from the 64.5 Ma to a weaker ～28–35 Ma LIP cyclicity during the Jurassic contributes together with probably independent changes in the marine sulfur cycle to less ocean anoxia, and a general stabilization of ocean chemistry and increasing marine biodiversity throughout the last ～135 Ma. The LIP cycle pattern is coherent with marine biodiversity fluctuations corresponding to a reduction of marine biodiversity of ～120 genera/Ma at ～600 × 10³ km³ LIP eruption volume. The 62–65 Ma LIP cycle pattern as well as excursion in δ³⁴S_sulfate and marine genera reduction suggest a not-yet identified found LIP event at ～440–450 Ma.     

Geochemistry of the uranium-thurium-bearing granitic rocks and pegmatites of wadi haleifiya area, southeastern Sinai, Egypt

There are two main granitic rocks cropping out in the study area:1) the syn-orogenic granites are moderately weathered,jointed,exfoliated and characterized by low relief.These rocks are subdivided into tonalite and granodiorite.They are essentially composed of plagioclase,quartz,biotite,hornblende and potash feldspar;and 2) the post-orogenic granites,characterized by high relief terrain and represented by monzogranite,syenogranite and alkali granite.The monzogranites suffered hydrothermal alteration in particular along joints,faults,shear zones and fractures,which recorded the highest values of radioactivity,reflecting the role of post-magmatic alteration processes in the enhancement of radioactivity.The hydrothermal alteration(desilicification and hematitization) resulted in the formation of mineralized(altered) granites.The altered granites are enriched in TiO 2,Al 2 O 3,FeO T,MnO,MgO,Na 2 O,Rb,Sr,Y,Zr,Zn,Ga and Co and depleted in SiO 2,CaO,P 2 O 5,Nb,Pb,Cu,Ni and Cr relative to the fresh monzogranite.The investigated granites contain basic xenoliths as well as pockets of pegmatites.Perthites,quartz,plagioclase and sometimes biotite,represent the essential constituents.Some accessory minerals like zircon are metamicted reflecting their radiogenic nature.The alkali granites are characterized by the presence of aegirine,rebeckite and arfvedsonite.Both syn-and post-orogenic granites show some variations in their bulk chemical compositions.The older granitoids are metaluminous and exhibit characteristics of I-type granites and possess an arc tectonic environment.On the other hand,the younger granites are peraluminous and exhibit the characteristics of post-collisional granites.It is interpreted that radioactivity of the studied rocks is mainly controlled by both magmatic and post-magmatic activities.Frequently,the post-orogenic granites host zoned and unzoned pegmatite pockets.Some of these pockets anomalously attain high radioactivity.The syenogranites and the pegmatites are characterized by high contents of SiO 2 and K 2 O and low CaO and MgO.They have transitional characters from highly fractionated calc-alkaline to alkaline.The alkali granites related to A2-subtype of A-type granites.The post-orogenic granites were originated from magma of dominant crustal source materials and related to post-collisional setting under extensional environment.     

Radioelement Mapping and Environmental Monitoring of Surface Deposits using Ground Gamma Ray Spectrometry of the Area Adjacent to El‐Ramlah Village,Southwestern Sinai,Egypt

A ground‐based gamma‐ray survey has been performed in the area close to El‐Ramlah village, southwestern Sinai, Egypt, using a GS‐512 spectrometer. The main objective of this survey was to delineate radioactive anomalies within the surface of the study area and to identify the environmental effects of natural radioelements on the new inhabitants, Bedouins, who live in the recently built village in this region of the Sinai Peninsula. The results show that the maximum radioactivity of the total count component (T.C.) was about 15.7Ur at the northern part of the study area. The average radioelements concentration were 0.4% for potassium, 1.6 ppm for equivalent uranium and 4.5 ppm for equivalent thorium. To identify and map the environmental effects of the concentration of these radioelements on El‐Ramlah village, measurements of potassium (K%), equivalent uranium (eU) and equivalent thorium (eTh) were converted into an equivalent dose rate. The results illustrate that, the levels of effective dose rate of the natural radioactivity of the area of study remains in the safe range without any harm to living organisms, and it stays within the maximum permissible radiation dose rate (1.0 mSv y^?1) recommended by the International Commission of Radiological Protection.     

Geographical information system approach for environmental management in coastal area (Hardelot-Plage,France)

The use of geographic information system (GIS) minimizes the effort and improves the efficiency of numerical models. The GIS provides a platform for high capacity collection, management, manipulation, analysis, modeling and display of spatial data. The conceptual model is created using GIS objects including points, arcs and polygons so that it can accurately represent real world condition. According to the research problem, the geographical model is based on Hypergraph Based Data Structure method, and a conceptual data model has been created from which a physical data model was elaborated in ArcGIS9.3 platform. The groundwater modeling system (GMS) provides a powerful tool for hydrodynamics modeling and it is able to solve complex problems such as the groundwater flow and seawater intrusion. The sand-dune system of Hardelot-Plage (North of France) suffers from a lack of well-developed foredune. This problem is linked to the almost constant saturation of beach sand which is the potential source of dune nourishment. In the south of Hardelot, the coastline is slowly, but constantly retreating. To remedy this situation, a coupling between a GIS and GMS was adopted, in order to find the possible scenarios which could lower the piezometric surface in the concerned area and allow dune nourishment again. The GMS used supports the Modflow-2000 code. A direct approach to designing Modflow finite difference model is tedious and less intuitive, specifically for complex boundary and initial conditions. Therefore, a Modflow model can be developed either using a grid or conceptual model approach. The preparation of input data modeling is tedious and takes a long time. The model created in GMS was calibrated against the historical and observed water level data for 1995–2006. Then a hydrodispersive model (MT3d code in GMS) was launched for evaluating sea-water intrusion. The model was run to generate groundwater and salt concentration scenario during pumping tests.     

Mineralogy, geochemistry, and origin of hydrothermal manganese veins at Wadi Maliek, Southern Eastern Desert, Egypt

The present work deals with the geology, mineralogy, geochemistry, and origin of the metagabbroic-hosted manganese deposits at Wadi Maliek in the southern Eastern Desert of Egypt. The manganese veins are found in the shear zones and channel ways of the fault planes within the metagabbroic rocks pointing to those hydrothermal solutions carrying manganese and iron load penetrating along these fractures. These faults are striking N 80° E?CS 80° W with dipping 65°. These veins vary in thickness from 15?cm up to 125?cm wide; each vein may show difference in thickness from bottom to top. Microscopic examinations, X-ray diffraction, infrared spectral, differential thermal (DTA), thermogravimetric (TGA), and ESEM-EDAX analyses revealed that the manganese minerals consist mainly of pyrolusite, psilomelane, and ramsdellite. Goethite and hematite are the common iron minerals. Petrographically, the manganese deposits can be classified into three ore types based on the predominance of manganese and iron minerals: manganese, manganese?Ciron, and iron ore types. The geochemistry of Maliek deposits indicated that the total averages of some major oxides in manganese, manganese?Ciron, and iron ore types are respectively as follows: SiO₂ (15.64%, 11.52%, and 20.58%), MnO (39.9%, 17.81%, and 0.77%), FeO* (7.13%, 33.31%, and 37.08%), CaO (5.89%, 5.82%, and 5.32%), and Na₂O (1.04%, 1.61%, and 1.53%). With regard to trace elements, the Maliek manganese deposits are rich in Zn, Ba, Pb, Sr, and V. Based on the geological, mineralogical, and geochemical results, the studied manganese deposits are considered to be precipitated from hydrothermal solution.     

Numerical groundwater modelling as an effective tool for management of water resources in arid areas

Abstract

Groundwater, possibly of fossil origin, is used for water supply in some arid regions where the replenishment of groundwater by precipitation is low. Numerical modelling is a helpful tool in the assessment of groundwater resources and analysis of future exploitation scenarios. To quantify the groundwater resources of the East Owienat area in the southwest of the Western Desert, Egypt, the present study assesses the groundwater resources management of the Nubian aquifer. Groundwater withdrawals have increased in this area, resulting in a disturbance of the aquifer’s natural equilibrium, and the large-scale and ongoing depletion of this critical water reserve. Negative impacts, such as a decline in water levels and increase in salinity, have been experienced. The methodology includes application of numerical groundwater modelling in steady and transient states under different measured and abstraction scenarios. The numerical simulation model developed was applied to assess the responses of the Nubian aquifer water level under different pumping scenarios during the next 30 years. Groundwater management scenarios are evaluated to find an optimal management solution to satisfy future needs. Based on analysis of three different development schemes that were formulated to predict the future response of the aquifer under long-term water stress, a gradual increase in groundwater pumping to 150% of present levels should be adopted for protection and better management of the aquifer. Similar techniques could be used to improve groundwater management in other parts of the country, as well as other similar arid regions.

Editor D. Koutsoyiannis; Associate editor X. Chen     

Self-organizing map for the detection of seasonal variations in Sidi Chahed Dam sediments (Northern Morocco)

ABSTRACT

A database of 88 superficial sediment samples, distributed in space and time, was collected from the Sidi Chahed Dam (northeast of Meknes city, Morocco) and from four other reference stations (in the same region) located in supposedly uncontaminated environments. Analyses were focused on the physico-chemical characteristics and concentrations of heavy metals (Fe, Mn, As, Cu, Zn, Pb, Cr, Cd). The database was processed by advanced statistical analysis techniques. The method of classification by self-organizing maps (SOM) was used, permitting understanding and visualization of the spatial and temporal distribution of samples. Principal component analysis (PCA) and SOM hierarchical classification (SOM-HC) were used to validate the classification and detect seasonal variations in heavy metal concentrations. Dependencies between different metal tracers were considered and their spatio-temporal distribution is shown, together with the ranking of clusters, according to their pollution levels. Thus, autumn samples were the only ones with high concentrations of As, compared to the four reference stations. This is due to leaching of bare soil by the first stormy rains of autumn. In winter and spring samples, the concentrations of tracers Mn, Zn, Cu, Pb, Cd and Cr were relatively high compared to those of the reference stations. Summer sample concentrations were most comparable with the reference stations, probably due to the scarcity of rainfall and runoff in this season.

Editor Z.W. Kundzewicz Associate editor E. Gargouri     

Influence of geological structures on groundwater accumulation and groundwater salinity in Musandam Peninsula,UAE and Oman

The hydrological setting and groundwater quality of Musandam Peninsula was studied to investigate the influence of geological structures on the groundwater accumulation and groundwater salinity. Five sets of modified morphometric maps were used to reduce errors and carry out the geological structures. The modification was modified by applying mean filter to the Digital Elevation Model (DEM) then applying Soble filter with 10% threshold and equalization enhancement. D8 and algorithms were used to reveal the drainage basins and drainage networks of the entire area. The algorithm determines into which neighbouring pixel any water in a central pixel will flow naturally. Flow direction in a DEM is calculated for every central pixel of input blocks of a 3 × 3 window, all the time comparing the value of the central pixel in the window with the value of its eight neighbours. The spatial association between geological structures and drainage networks was studied using 2D graph and rose diagrams. Flood basin model was applied to simulate the Arabian Gulf water intrusion into the coastal aquifer. The concentrations of solutes in groundwater samples collected from Wadi Al Bih well field and well locations were correlated with the geological structure trends and intersections. The results of the study reveal that the drainage basins, drainage network and groundwater quality are structurally controlled by subsurface geological structure displacements.