Origin and Petrogenetic Implications of Spessartine Garnet in Highly-Fractionated Granite from the Central Eastern Desert of Egypt

A highly-fractionated garnet-bearing muscovite granite represents the marginal granitic facies of the Abu-Diab multiphase pluton in the Central Eastern Desert of Egypt. New electron microprobe analyses(EMPA) and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) data from garnets are reported, in order to constrain their origin and genesis. Garnet in the Abu-Diab host granite is euhedral to subhedral, generally homogeneous and, in rare cases, it shows weak zonation. The garnet contains appreciable amounts of MnO and FeO, with lesser amounts of MgO and CaO, yielding an end-member formula of Sps_(61–72)Alm_(25–35)Prp_(1–4)Adr_(0–1). Moreover, it is depleted in large ion lithophile elements(LILE) with lower values of Ba, Nb and Sr relative to the primitive mantle. Additionally, it contains high concentrations of HREE and Y and their REE pattern shows strong negative Eu anomalies. The garnet was crystallized under relatively low temperature(646°C–591°C) and pressure( 3 kbar) conditions. The textural and chemical features indicate that the garnet is magmatic in origin and is chemically similar to that from highly-fractionated A-type granite. It was probably formed at the expense of biotite in a highly-evolved MnO-rich magma and/or by hydroxyl complexing of Mn during the ascending fluid phases.     

Unusual diatoms linked to climatic events in the northeastern English Channel

The composition of the micro-phytoplankton was investigated at two fixed stations in the northeastern English Channel from November 1997 to December 2005. In late summer-autumn 2005, proliferations of the centric diatoms Proboscia indica and Rhizosolenia hebetata f. semispina were recorded for the first time in this area. The weather in 2005 was abnormal: a cold winter and early arrival of summer conditions that extended to late autumn. This resulted in an unusually long, sustained calm and warm period. We suggest that the reduction in mixing may have allowed diatoms of more-stratified waters to be competitive in the normally highly mixed northeastern English Channel in summer-autumn 2005. In 2003 and in 2005, two warm-water diatom species were recorded for the first time. A colony of Eucampia cornuta was observed after an exceptional heat wave in September of 2003, and again in September 2005. Simultaneously at both fixed stations, Chaetoceros peruvianus was recorded in the warm October of 2005. The climatic events are associated with the northward spreading of thermophilic diatoms such as E. cornuta and Ch. peruvianus in the European Atlantic waters, and the proliferation of diatoms of stratified environments such as P. indica and R. hebetata f. semispina in the usually highly turbulent waters of the northeastern English Channel.     

An overview of the Late Cretaceous-Eocene positive inversions and Oligo-Miocene subsidence events in the foreland of the Tunisian Atlas: Structural style and implications for the tectonic agenda of the Maghrebian Atlas system

Structural interpretation of surface and subsurface data in the Eastern foreland basins of Tunisia, allows us to recognize positive inversion structures, i.e. related to compressional events, expressed and recorded in the Paleogene sedimentary pile of the Atlas domain. These episodes are followed by a period of relative tectonic quiescence during Oligocene-Early Miocene with development of extensional structures with slightly tilted panels, grabens and locally the development of listric normal faults branched at depth on “décollement” levels.Comparison of the seismic interpretations and field data collected along the South Atlas Front as well as in the Atlas belt, allows us to propose a tectonic scenario at the scale of Eastern Tunisia Atlas. In particular, we emphasise the role of the so-called “Atlas event” (Middle-Late Eocene), which was initially defined in Algeria but poorly outlined in Tunisia. We will show that the tectonic agenda defined in Eastern Tunisia is consistent with the one proposed elsewhere in the Maghreb allowing us to propose a unified view of the geodynamic evolution of the whole Atlas system during this period.The negative inversion recorded during Oligocene-Early Miocene along with the occurrence of synsedimentary normal faults are related to an increase of the subsidence rate in the frame of continuous shortening coeval to basin formation in the front of the Atlas. The whole Oligo-Miocene evolution results from two different mechanisms: flexuration in the front of the Atlas and the onset of the extension of the Pantelleria-Linosa-Malta rift system of central Mediterranean, which attained a climax stage later during Pliocene-Quaternary.     

Impacts of an uncontrolled phosphogypsum dumpsite on summer distribution of phytoplankton, copepods and ciliates in relation to abiotic variables along the near-shore of the southwestern Mediterranean coast

In connection with the Taparura Project, studies of spatial distribution of the crustacean zooplankton community, nutrients, phytoplankton and ciliates were conducted in July 2007 at 45 stations spread over fifteen transects along the coast north of Sfax. The results showed that the N/P ratio was lower than the Redfield ratio, suggesting potential N limitation. Phytoplankton was characterised by the proliferation of several diatoms, while ciliates were largely dominated by spirotrichs. Copepods were the most abundant zooplankton present during the entire study period, comprising 61% of the total zooplankton community. Twelve copepod families were identified at every station, with a high percentage of Oithonidae (77% of copepods) dominated by Oithona nana. The abundance of this species was correlated with that of diatoms, Cocoolithophorideae and ciliated Colpodea, suggesting that O. nana may feed on a wide range of prey. Despite human pressure and industrial activities, the coastal waters north of Sfax showed a wide diversity of phytoplankton, ciliates and zooplankton.     

Inactivation of the gene katA or sodA affects the transient entry into the viable but non-culturable response of Staphylococcus aureus in natural seawater at low temperature

We have investigated the fate of Staphylococcus aureus by starving the cells and maintaining them in natural seawater at 22 and 4 °C. At 22 °C, cells developed a long-term survival state where about 0.037% of the initial population remained culturable over more than 7 months, whereas at 4 °C, bacteria lost culturability and transiently entered into the viable but non-culturable state (VBNC). However, after 22 days of entry into the VBNC state, the number of viable cells detected via the direct viable count method decreased significantly. We show here that mutational inactivation of catalase (KatA) or superoxide dismutase (SodA) rendered strains hypersensitive to seawater stress at 4 °C and consequently, part of the seawater lethality on S. aureus at low temperature is mediated by reactive oxygen species (ROS) during microcosm-survival process. Shifting the temperature from 4 to 22 °C of totally non-culturable wild-type cells induced a partial recovery of the population. However, deficiencies in catalase or superoxide dismutase prevent resuscitation ability.     

Calpionellid zonation of the Jurassic–Cretaceous transition in North-Atlasic Tunisia. Updated Upper Jurassic stratigraphy of the ‘Tunisian trough’ and regional correlations

The analysis of calpionellid associations from jebels Amar and Jédidi sections in North-Atlasic Tunisia provides, for the first time, a precise biozonation of the Jurassic–Cretaceous transition succession. In the light of the new data obtained and considering recently published results, the age of Upper Jurassic formations is clarified, allowing correlations with the Tunisian ‘Dorsale’ and the North–South Axis successions. Within the Maghrebides' range, sections from the external zones correlated to the Tunisian successions are quite distinctive from their equivalent in the internal zones. Both have evolved in different palaeogeographic domains related to the early structuration of the northwestern and southwestern Tethys margins. To cite this article: M. Boughdiri et al., C. R. Geoscience 338 (2006).     

Using landforms of Saudi Arabia for scenic and recreational purposes (With special reference to the Riyadh area)

The landform of Saudi Arabia in general and the Riyadh area in particular have their own potentiality for scenic and recreational purposes. The higher lands or features which have well cemented material in some areas of Riyadh have been recommended for scenic use, while lower lands like wide natural lakes, sand dunes and others can be mostly used for recreational purposes. Such features and purposes found here may be extrapolated into other similar areas within Saudi Arabia and may be compared with other areas elsewhere in the world.     

The magnetic field in the solar atmosphere

This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.     

Considering groundwater use to improve the assessment of groundwater pumping for irrigation in North Africa

Groundwater resources in semi-arid areas and especially in the Mediterranean face a growing demand for irrigated agriculture and, to a lesser extent, for domestic uses. Consequently, groundwater reserves are affected and water-table drops are widely observed. This leads to strong constraints on groundwater access for farmers, while managers worry about the future evolution of the water resources. A common problem for building proper groundwater management plans is the difficulty in assessing individual groundwater withdrawals at regional scale. Predicting future trends of these groundwater withdrawals is even more challenging. The basic question is how to assess the water budget variables and their evolution when they are deeply linked to human activities, themselves driven by countless factors (access to natural resources, public policies, market, etc.). This study provides some possible answers by focusing on the assessment of groundwater withdrawals for irrigated agriculture at three sites in North Africa (Morocco, Tunisia and Algeria). Efforts were made to understand the different features that influence irrigation practices, and an adaptive user-oriented methodology was used to monitor groundwater withdrawals. For each site, different key factors affecting the regional groundwater abstraction and its past evolution were identified by involving farmers’ knowledge. Factors such as farmer access to land and groundwater or development of public infrastructures (electrical distribution network) are crucial to decode the results of well inventories and assess the regional groundwater abstraction and its future trend. This leads one to look with caution at the number of wells cited in the literature, which could be oversimplified.