Ahmed S. Mansour

Cementation of holocene beachrock in the Aqaba and the Arabian Gulfs: Comparative study

Extensive precipitation of aragonite and high-Mg calcite (12–14% MgCO3) cements in the intertidal sediments of the Gulf of Aqaba, Egypt and the Arabian Gulf, Qatar results in the formation of dominant beachrock exposures. The 20–60 cm thick beachrocks in both areas are parallel to the shoreline and slope gently seaward. The 14 C dating values show that the cement of the Gulf of Aqaba beachrock (2470±60y) are rather older than those of the Arabian Gulf (1360±45y). Framework grains in the Gulf of Aqaba beachrock are moderate to unsorted coarse terrigenous rock fragments, which differ than the unsorted carbonate particles of the Arabian Gulf beachrock. Carbonate cements in both the Aqaba and the Arabian Gulfs display the same architecture, which comprises: 1) thin isopachous crust made up of high-Mg calcite mosaics and/or aragonite needles that surround grains and 2) intergranular cryptocrystalline high-Mg calcites, which fill the rest of the pores. Minor dolomite mosaics may associate with the intergranular cement. The co-existence of the aragonite needles, of the isopachous crust, with the micritized grains and micritic envelopes is evidence that marine phreatic processes are dominant in the intertidal zone and that lithification has started in this zone. The bi-mineralic composition of the isopachous crust in the Aquaba beachrock is attributed mainly to kinetic factors (i.e. the rate of supply of carbonate ions) and to the composition of the substrate and/or organic control in the beachrock of the Arabian Gulf. Some physico-chemical, kinetic, hydrologic and biologic factors are believed to be effective in controlling the precipitation rates of the isopachous cement. The oxygen and carbon isotopic composition of the intergranular high-Mg calcite cement of the Aqaba Gulf (+2.0 to −1.6 and +2.9 to +4.4‰ PDB respectively) is in accord with their precipitation in equilibrium with marine water. However, the relatively depleted δ18O (−0.5 to −3 ‰ PDB) and δ13C (+0.3 to 2.2 ‰ PDB) values of the intergranular high-Mg calcite cement of the beachrock of the Arabian Gulf is attributed to extraneous source of bicarbonate ions. The minor dolomite rhombs are formed directly from seawater within microenvironments created in response to the release of Mg2+ ions to the pore water following the partial dissolution of some high-Mg calcite carbonate particles.

Diagenesis of the Middle Eocene Upper Dammam Subformation, Qatar: Petrographic and isotopic evidence

The subsurface Middle Eocene Upper Dammam Subformation in Qatar displays a complex diagenetic history related to sea level variations. The studied rocks are made up of dolomitic limestones and pervasive dolomites. Two main types of dolomite are identified based on an integrated petrographic/isotopic/mineralogic study: dolomites type (I) and (II), which affect the lower (the Umm Bab member) and the upper (the Abaruq member) parts of the Upper Dammam Subformation respectively. Dolomite type (I) is pervasive and composed of relatively coarse crystals that exhibit polymodal size distribution and different shapes of crystal boundaries (non-planar, planar-s and planar-e). Meanwhile, dolomite type (II) is selective, fine-textured and made up of unimodal equant euhedral rhombs.The marine δ18O (+0.6 to +2.8‰) values of dolomite type (I) are consistent with formation during an early transgressive phase where the rising sea level possibly caused marine pore-water to push mixing and meteoric waters ahead of it. The active circulation in the marine pore-water zone led to pervasive dolomitization. The depleted δ13C (−5.9 to −8.9‰ PDB) values of dolomite type (I) indicate that dolomitization possibly occurred within the sulphate reduction zone beneath the sediment/water interface when an oxygen-minimum zone impinged the bottom surface of the carbonate platform. The presence of mimetic and non-mimetic dolomite textures is related to kinetic factors including the rate of dissolution of the CaCO3 precursor, reactant surface area and precipitation kinetics. Dolomite type (II) was formed during a subsequent highstand period during shelf progradation. The δ18O (+0.4 to +2.6‰ PDB) and δ13C (−0.9 to −4.6‰ PDB) values, the fine crystalline fabric and the planar intercrystalline boundaries argue for its early diagenetic origin within the subtidal zone above the oxygen-minimum zone.During further shelf progradation the studied rocks have been emplaced within a mixing marine-meteoric zone. During this period the dolomitization process was interrupted by a silicification phase. The precipitation of quartz and the resultant silica fabrics are controlled by variations in the PCO2 and the pH of the porewater. At the later stages of the highstand system tract, when sea level started to fall, a meteoric lens possibly developed at the shelf margin. The section was subjected to meteoric diagenesis. A late meteoric origin is suggested for calcite mosaics, that fill some secondary pores, based on their extremely depleted δ18O values (−5.7 to −11.8‰), variable δ13C values (−2.6 to −7.8‰ PDB), low-Mg composition and their equant form.

Biostratigraphy and palaeoecological interpretation of the Miocene–Pleistocene sequence at El-Dabaa, northwestern Egypt

Thirteen shallow boreholes were drilled by the Qattara Project Authority (QPA) on the top of the second limestone ridge in the El-Dabaa area, along the Mediterranean coast, northwest Egypt. Five foraminiferal biozones could be recognized in ascending stratigraphic order: the Heterostegina costata, Praeorbulina sicana, Borelis melo melo, Globigerinoides obliquus extremus zones and an un-named zone, embracing the Middle Miocene Marmarica Formation and the Pliocene–Pleistocene Alexandria Formation. The deposition of the fossiliferous carbonate rocks of the Marmarica Formation probably took place in a warm water, inner shelf environment (0–20 m palaeodepth) subjected to some current activity, and with salinity ranging from normal to slightly hypersaline (35–50‰). The sediments of the oncolitic/shelly rocks were deposited in slightly deeper water than the overlying fossiliferous rocks and in less agitated conditions, as indicated from the high percentages of rotaliids and rarity of miliolids. The foraminiferal associations in the Alexandria Formation indicate a clear, relatively agitated, near-shore marine depositional environment in a vegetated inner neritic zone (10–25 m palaeodepth) with 25°C surface water isotherms. On the other hand, the accumulation of the clayey sediments and some geosoils (basal part of the Alexandria Formation) occurred in less agitated, intertidal water conditions, as deduced from the occurrence of planktic foraminiferal species as Globigerinoides trilobus trilobus, G. trilobus immaturus, G. obliquus extremus, G. obliquus obliquus, Globorotalia inflata, and Orbulina universa.

Dolomitization of Middle Eocene carbonate rocks, Abu Roash area, Egypt

Dolomitization is the most striking diagenetic process affecting the late Middle Eocene shelly limestone beds at Abu Roash and its neighboring areas. Petrographic investigations reveal that these rocks represent shelly-wackstone to packstone microfacies, that they were deposited probably within a shallow subtidal setting. The rock matrix has been subjected to both selective and complete dolomitization and replaced by equigranular mosaics of fine-to medium-grained dolomite (crystalline planar-s dolomite texture). Meanwhile, the embedded shell fragments show high resistance to dolomitization and their original calcite composition is mostly preserved. The petrographic features of the dolomite texture suggest that these dolomites were formed under near surface and low temperature conditions.Oxygen and carbon isotopic values of the calcite framework grains (−3.8 to −2.0‰ and +1.9 to +2.5‰ PDB, respectively) reflect marine values with some degree of alteration by the effect of slightly18O-depleted diagenetic water. Meanwhile, oxygen and carbon isotopic signatures of the studied dolomites (+0.1 to +1.5‰ and +1.7 to +2.3‰ PDB, respectively) are heavier relative to those of marine limestones. The isotopic signature of dolomites combined with petrographic data is in accord with their formation from modified-marine fluids during early diagenesis.

Comparative review of carbon nanotube FETs

Carbon nanotubes (CNTs) are strong potential replacements for silicon in VLSI due to their extraordinary capabilities. We review the theory of operation of CNT-based FETs (CNFETs), the issues regarding its modern fabrication techniques, performance parameters yielded by the latest research, and finally, we present an overview of some applications employing the unique properties of these devices.

Towards physical layer security in Internet of Things based on reconfigurable multiband diversification

Numerous IoT devices in wireless network interact and cooperate with each other to achieve diverse intelligent services. Such devices use static channel for wireless transmission, making the whole network vulnerable to eavesdroppers. This raises a need for means to allow secure data transmission/reception between IoT routing nodes. The concept of antenna diversity is used to enhance secrecy capacity by expanding the channel bandwidth trying to confuse attackers. Therefore, an efficient solution is considered by using multiband signal transmitter circuit to enable frequency-manipulation between connected devices. In this paper, we conducted security evaluation based on optimal relay selection protocols to maximize the channel secrecy capacity and improve data transmission. This approach uses channel sensing metric to manipulate the transmission characteristics between legitimate users via changing the operating frequency and bandwidth. Results showed a massive improvement in physical layer security against eavesdropping attack when using reconfigurable frequency bands.

Flexible paper-based wideband antenna for compact-size IoT devices

Last decade witness massive developments for wireless communication networks based on Internet of Things (IoT) technology. These developments indeed aim to enable efficient interconnectivity between different devices with the ability to operate in license-free ISM bands. Currently, several applications are based on IoT technology such as home automation, energy harvesting … etc. To enhance and improve wireless connectivity for heterogeneous IoT devices to communicate, they need multiple antennas one for each band or a wideband antenna. The typical challenge relies on finding enough space to hold such antennas into one small device. In this paper, we propose a promising solution that relies on using a single compact-size antenna printed on flexible substrates. Moreover, such flexible antenna exposed to special treatment by multilayer and annealing to enhance antenna bandwidth. This single multilayer flexible monopole wideband printed-antenna can operate over different wireless communication bands. Additionally, this paper presents a practical experiment by integrating the fabricated flexible antenna within a Wi-Fi-operating network. Results showed the proposed antenna design is worked perfectly for IoT applications.