The influence of transgression and regression on the spatial and temporal distribution of diagenetic kaolin in the Upper Ordovician glaciogenic sandstones within a sequence stratigraphic framework, Murzuq Basin, SW Libya

Linking diagenesis to depositional facies and sequence stratigraphy can provide a better understanding of some of the parameters that control the spatial and temporal distribution of diagenetic alterations and of their impact on reservoir quality. A study of the paralic, glaciogenic sandstones of the Melaz Shuqran and Mamunyiat formations (Late Ordovician) of the Murzuq Basin, SW Libya, reveals that the distribution of diagenetic kaolin can be constrained within depositional facies and sequence stratigraphy. Eogenetic kaolinite was formed by the dissolution of unstable detrital grains as a result of influx of meteoric waters into: (i) glacial, fluvial incised-valley lowstand systems tract (LST), glacial, tide-dominated estuarine transgressive systems tract (TST) during formation of overlying sequence boundary, (ii) paraglacial, tide-dominated deltaìc highstand systems tract (HST), paraglacial, foreshore to shoreface HST during progradation and basinward shift of the shoreline and/or formation of overlying sequence boundary, (iii) postglacial, Gilbert-type deltaic LST sandstones during relative sea level fall. On the other hand, formation of kaolinite immediately below maximum flooding surfaces is attributed to dissolution of unstable detrital grains by organic acids that were presumably derived from thermal alterations of organic matter, possibly during mesodiagenesis. The transformation of eogenetic kaolinite into dickite during mesodiagenesis is probably a consequence of low α_K⁺ / α_H⁺ ratio in the pore waters due to the scarcity of detrital K-feldspars.     

Assessment of hazardous mine waste transport in west central Sinai,using remote sensing and GIS approaches: a case study of Um Bogma area,Egypt

Um Bogma area is the most famous mineralized locality in Sinai, Egypt. It is characterized by the presence of manganese, iron, and copper deposits. Apart from the mill tailings and spoil heaps, the results indicated the decrease of soil contamination downstream. As a result of random manganese mining activity in Um Bogma area, many hazardous elements such as iron, copper, manganese, lead, and zinc as well as many others associating heavy metals such as arsenic, selenium, and sulfur are dispersed in the environment. This study assesses and monitors the environmental impacts of such mining activities in the west central Sinai, using multitemporal spectral remote-sensing sensors (MSS 1972, TM 1986, and ETM+7 2000). The results have shown the very high potential of temporal imagery in mining-related contamination either directly through mineral and rock mapping of the mining waste and residues and related contaminated areas.     

Diversity and distribution of gelatinous zooplankton in the Southwestern Mediterranean Sea

Gelatinous zooplankton species composition, distribution and abundance were investigated in the bay and the lagoon of Bizerte (North Tunisian coast) from January 2004 to December 2005. In total, 48 species were identified in the study area: 24 medusae, 11 siphonophores, four appendicularians, six chaetognaths, two pteropods and one doliolid. The hydromedusa Eutima mira was recorded for the first time in the Western Mediterranean Sea. The diversity in the Bay of Bizerte was greater than the diversity in the Bizerte lagoon. There was a loss of species diversity. Siphonophores were the most sensitive group to anthropogenic discharge. Only two species of siphonophores were recorded in the lagoon. Four species of gelatinous zooplankton, Muggiaea kochi, Lensia conoidea, Oikopleura longicauda and Podocorynoides minima were the most frequent species in the lagoon and may benefit from eutrophication. Appendicularians were numerically the most dominant group in the bay and the lagoon of Bizerte. Mesozooplankton density declined significantly in autumn and winter of 2004 and 2005 in relation to the dense aggregations of the scyphomedusae Pelagia noctiluca. Statistical analysis divided the study area into three zones: lagoon zone, bay zone and channel zone.     

Q-values for P and S Waves in Southern Sinai and Gulf of Suez Region,Egypt

Geotectonics - The quality agents for P- and S-waves (Qp and Qs) were estimated for earthquakes that recorded by nine seismic stations (DHA, NUB, TR1, TR2, KAT, SH2, GRB, HRG and SFG) from the...     

Geochemistry of an Alaskan-type mafic-ultramafic complex in Eastern Desert,Egypt:New insights and constraints on the Neoproterozoic island arc magmatism

Mikbi intrusion(MI) is a part of the Neoproterozoic Nubian Shield located along the NE-SW trending major fracture zones prevailing southern Eastern Desert of Egypt. In this study, we present for the first time detailed mineralogical and bulk-rock geochemical data to infer some constraints on the parental magma genesis and to understand the tectonic processes contributed to MI formation. Lithologically, it is composed of fresh peridotite, clinopyroxenite, hornblendite, anorthosite, gabbronorite, pyroxene amphibole gabbro, amphibole gabbro and diorite. All rocks have low Th/La ratios(mostly <0.2) and lack positive Zr and Th anomalies excluding significant crustal contamination. They show very low concentrations of Nb, Ta, Zr and Hf together with sub-chondritic ratios of Nb/Ta(2-15) and Zr/Hf(19-35),suggesting that their mantle source was depleted by earlier melting extraction event. The oxygen fugacity(logfO_2) estimated from diorite biotite is around the nickel-nickel oxide buffer(NNO) indicating crystallization from a relatively oxidized magma. Amphiboles in the studied mafic-ultramafic rocks indicate relative oxygen fugacity(i.e. ΔNNO; nickel-nickel oxide) of 0.28-3 and were in equilibrium mostly with 3.77-8.24 wt.% H_2 O_melt(i.e. water content in the melt), consistent with the typical values of subduction-related magmas. Moreover, pressure estimates(0.53-6.79 kbar) indicate polybaric crystallization and suggest that the magma chamber(s) was located at relatively shallow crustal levels. The enrichment in LILE(e.g., Cs, Ba, K and Sr) and the depletion in HFSE(e.g., Th and Nb) relative to primitive mantle are consistent with island arc signature. The olivine, pyroxene and amphibole compositions also reflect arc affinity. These inferences suggest that their primary magma was derived from partial melting of a mantle source that formerly metasomatized in a subduction zone setting. Clinopyroxene and bulkrock data are consistent with orogenic tholeiitic affinity. Consequently, the mineral and bulk-rock chemistry strongly indicate crystallization from hydrous tholeiitic magma. Moreover, their trace element patterns are subparallel indicating that the various rock types possibly result from differentiation of the same primary magma. These petrological, mineralogical and geochemical characteristics show that the MI is a typical Alaskan-type complex.     

Seismic microzonation of Marsa Alam, Egypt using inversion HVSR of microtremor observations

An attempt was made to estimate seismic microzonation in Marsa Alam city, Egypt based on the analysis of seismic microtremor observations. Observations were carried out at 140 sites in the study region. Analysis and processing of microtremor were divided into two steps; the first one is to measure the horizontal-to-vertical spectral ratios (HVSR) for each site and picked predominant frequency and its amplitude for each site. The second step is to measure the average shear wave velocity in the upper 30 m (Vs30) of subsoil using inversion of HVSR technique. The results show well matching of theoretical HVSR and observed HVSR for body waves in all sites. The Vs30 parameter was used to classify subsoil into classes of soil properties converted to the slandered European soil code (Eurocode-8 (2002)) as follows; Vs < 180(class D), 180 ≤ Vs < 360 (class C), 360 ≤ Vs < 800 (class B) and Vs ≥ 800 m/s (class A). Our study exhibits that most of Marsa Alam city were covered by B and C classes with small portions of class D close to the shoreline and class A at the northeastern part of the region. The developed classification soil map of the study area was correlated with the distribution of the predominant frequency in view of the surface geology and given a good matching. The results of this study will be useful for planning the Marsa Alam region to be the future tourist dream for Egypt. The method used in assessment of seismic microzonation in Marsa Alam city could be the fast and inexpensive technique to measure the Vs30 based on the HVSR of microtremor and would be applied in many other areas in Egypt.     

Physico‐Chemical and Bacterial Characteristics of Water Quality in Three Villages West of Lake Nasser,Egypt

The present study aims to investigate physico‐chemical and bacterial characteristics of Nasser Lake water and houses drinking water, as well as fish cultures and its wastewater, in three villages west of Lake Nasser, Egypt. Fifteen representative water samples (Nasser Lake, different drinking water, fish cultures, and wastewater sources) were collected from three villages (Garf Hussein, Bashaier, and Kalabsha) in the west of Lake Nasser. Physico‐chemical, total viable counts, and bacterial qualification of water were achieved. The obtained results indicated that the produced water, supposed to be for domestic use in the three villages, contained all the tested organisms. The investigated water samples of the lake and drinking water in the selected three villages are supposed to be chemically safe according to World Health Organization and to Egyptian standards for drinking water. Water pollution index (WPI) was used in this study and the result concluded that for irrigation canals from the lake to the agriculture site, fish cultures (both concrete and earth pond systems), and drainage canal of fish ponds need to be treated before it is discharged to the lake. It is better to reuse it after treatment for agricultural purposes or recycled it to the fish cultures.     

A Coastal Aquifer Study Using Magnetotelluric and Gravity Methods in Abo Zenema, Egypt

Magnetotelluric (MT) soundings and gravity methods were employed to study the deep freshwater aquifer in the area north of Abo Zenema city on the eastern side of the Gulf of Suez, Egypt. Seven MT sites and 48 gravity stations were surveyed along northeast–southwest profiles as close as possible to a line perpendicular to the coast of the Gulf of Suez. The MT survey was conducted using high and low frequencies to investigate shallow and deep areas, respectively. One-dimensional inversion was conducted using a heuristic inversion scheme of the Bostick algorithm. The MT data were also inverted with a 2-D smooth model inversion routine using the nonlinear conjugate gradient method to infer variation in vertical and lateral resistivity inside the Earth. A 100-Ohm-m homogeneous half-space initial model was used to invert the TE mode data only. Then, the inverted model obtained from the TE mode data was used as an initial model for inversion of the TM mode data. The inverted model thus obtained from the TM mode data inversion was used as an initial model for the inversion of the joint TE and TM responses. Two-dimensional (2-D) forward modeling of the gravity data was conducted using the 2-D polygon method of Talwani’s algorithm for an arbitrarily shaped body and was based on the subsurface information from the MT survey and the available information about the geological structure of the study area. This method enabled us to obtain the basement structure of the coastal aquifer in the study area. The results from the analysis and the interpretation of MT and gravity data were used to detect and delineate the groundwater coastal aquifer in the study area.     

Delineation of Near-Surface Structure in the Southern Part of 15th of May City, Cairo, Egypt Using Geological, Geophysical and Geotechnical Techniques

The integration of geological, geophysical, and geotechnical interpretation at the southern part of 15th of May City, have been used to evaluate the subsurface stratigraphy, especially the clay layer which may cause serious danger to construction. Those techniques have been used to delineate the subsurface structures as normal faults, which play a critical role on the stability of buildings. Geological setting of the area has been evaluated through the construction of a geological map from different geological sections and samples obtained from more than 30 observation points. Geophysical tools such as vertical electrical soundings (12 VESs), 2-D dipole–dipole array (7 sections), P-wave shallow seismic refraction (31 profiles) and multiple channel analysis of surface waves (31 MASW profiles) have been carried out to image the subsurface situation. Geotechnical evaluation using 26 boreholes, samples, laboratory tests and geotechnical parameters has been done at the area of interest. The geological setting demonstrates that the city had been constructed on the second and third members of Qurn Formation (Upper Eocene) composed of argillaceous limestone, marl and shale. Two normal faults are passing through the area were observed. The resistivity (VES and dipole–dipole) and seismic (P-waves and MASW) results reflect the presence of the two normal faults cross the study area, affecting the obtained section of marl, clayey marl and limestone layers. The geotechnical information indicate the presence of the normal faults and the existence of clay layer with swelling ability reaching 140%, which may cause cracks in the upper layers and/or subsidence.     

Upscaling of CO2 vertical migration through a periodic layered porous medium: The capillary-free and capillary-dominant cases

We present an upscaled model for the vertical migration of a CO₂ plume through a vertical column filled with a periodic layered porous medium. This model may describe the vertical migration of a CO₂ plume in a perfectly layered horizontal aquifer. Capillarity and buoyancy are taken into account and semi-explicit upscaled flux functions are proposed in the two following cases: (i) capillarity is the main driving force and (ii) buoyancy is the only driving force. In both cases, we show that the upscaled buoyant flux is a bell-shaped function of the saturation, as in the case of a homogeneous porous medium. In the capillary-dominant case, we show that the upscaled buoyant flux is the harmonic mean of the buoyant fluxes in each layer. The upscaled saturation is governed by the continuity of the capillary pressure at the interface between layers. In the capillary-free case, the upscaled buoyant flux and upscaled saturation are determined by the flux continuity condition at the interface. As the flux is not continuous over the entire range of saturation, the upscaled saturation is only defined where continuity is verified, i.e. in two saturation domains. As a consequence, the upscaled buoyant flux is described by a piecewise continuous function. Two analytical approximations of this flux are proposed and this capillary-free upscaled model is validated for two cases of heterogeneity. Upscaled and cell averaged saturations are in good agreement. Furthermore, the proposed analytical upscaled fluxes provide satisfactory approximations as long as the saturation set at the inlet of the column is in a range where analytical and numerical upscaled fluxes are close.