The role of women peasants in the process of desertification in Western Sudan

Women peasants in the Sudan are both agents of and sufferers from the process of desertification which is taking place in the arid and semi-arid zone. The researchwork done by the author on the problem of desertification in the west of the Republic of the Sudan convinced him that women there suffer much more than men do from the decrease of land productivity. Paradoxically enough, women themselves have actively taken part in desertifying their environment in their desperate attempt to keep their families living. This paper endeavours to highlight the role of peasant women in areas prone to or already stricken by desertification. Especially in the transitional phases following drought disasters and loss of live-stock the whole brunt of catering for the family falls on the shoulders of peasant women. Three main issues are being tackled: Millet production as essentially women's task, rainfall variability and its impact on women cultivators, the settlement of nomads and semi-nomads as a new burden laid on women. Finally, some suggestions are made to improve the conditions of women's work to provide nutrition for their families without doing much destruction to the fragile environment and its limited resources.     

Paleozoic glaciation in NE Africa: field and remote sensing-based evidence from the South Eastern Desert of Egypt

ABSTRACT

Exhumed Paleozoic glacial deposits and landforms of the North Gondwana are reported here for the first time from the South Eastern Desert (SED) of Egypt. Using field observations and remote sensing datasets (Advanced Land Observing Satellite [ALOS], Phased Array L-band Synthetic Aperture Radar [PALSAR] radar, multispectral Landsat TM datasets, and digital elevation models [DEMs]), we mapped the distribution of Paleozoic glacial features (i.e. deposits and landforms) in the SED. Two main glaciogenic facies were identified in three locations in the SED: (1) massive, poorly sorted, matrix supported, boulder-rich diamictites in Wadi El-Naam and Korbiai, and (2) moderately-sorted, occasionally bedded outwash deposits in Betan area. Inspection of radar, DEMs, and Landsat Operational Land Imager (OLI) images revealed previously unrecognized ENE-WSW trending glacial megalineations (MLs) over the peneplained Neoproterozoic basement rocks in the central sections of the SED, whose trends align along their projected extension with those of glacial features (tunnel valleys and striation trends) reported from Saudi Arabia. The glaciogenic features in the SED are believed to be largely eroded during the uplift associated with the Red Sea opening, except for those preserved as basal units beneath the Nubia Sandstone Formation or as remnant isolated deposits within paleo-depressions within the basement complex. The apparent spatial correlation of the SED glacial features with well-defined Late Ordovician deposits in North Africa and in Saudi Arabia, and the reported thermochronometric analyses and fossil records are consistent with a Late Ordovician age for the SED glaciogenic features and support models that call on the continuation of the Late Ordovician (Hirnantian) ice sheet from the Sahara into Arabia through the SED of Egypt.     

Late Albian–Middle Cenomanian palynofacies and palynostratigraphy, Abu Gharadig-5 well, Western Desert, Egypt

Quantitative analyses of palynomorph assemblages, particulate organic matter (kerogen), and total organic carbon (TOC) have been made on samples of the Albian–Cenomanian Kharita and Bahariya formations encountered in the Abu Gharadig-5 well, Western Desert, Egypt. Two assemblage palynozones are defined: Assemblage Zone A (Kharita Formation) of late Albian–early Cenomanian age and Assemblage Zone B (Bahariya Formation) of early–middle Cenomanian age. Palynofacies of the Kharita Formation suggest that sedimentation of these strata took place in a warm, shallow, nearshore-marine environment. The deposition of the lower Bahariya Formation took place initially in similar conditions but subsequently further offshore in somewhat deeper water of the inner shelf. The relatively high percentage of Ephedripites, Afropollis and elaterate pollen in both formations indicates an arid climate. The Kharita Formation yields kerogen types III and IV whereas the assemblages recovered from the Bahariya Formation contain types II and III. The TOC is generally between 0.42 and 0.65% in the Kharita Formation, while it ranges between 0.42 and 0.80% in samples of the Bahariya Formation. The spores and pollen grains are pale in colour; hence little source potential for hydrocarbons is indicated.     

A Semi-Evolutive Partially Local Filter for Data Assimilation

The singular evolutive extended Kalman (SEEK) filter has been proposed recently by Pham et al. (1997) for data assimilation into numerical oceanic models. This filter has been applied in different realistic ocean frameworks and has provided satisfactory results ( Pham et al., 1997; Verron et al., 1998). However, the SEEK filter remains expensive in real operational assimilation. To reduce cost and obtain a better representativity, we introduce the idea ‘local correction basis'. Such basis however cannot be made to evolve according to the model without destroying its locality property. Therefore we shall keep this basis fixed and we augment it by a few global basis vectors which evolve. The resulting semi-evolutive partially local filter is much less costly to implement than the SEEK filter and yet can yield better results. In the first application, validation twin experiments are conducted in a realistic setting of the OPA model over the tropical Pacific Ocean.     

Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt

Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.     

Two-phase Numerical Model of Powder Avalanche Theory and Application

In this paper the powder snow avalanche is considered as a two-phase flow (air and snow particles). The equations governing this flow are the fluid mechanics conservation laws. The mass and the momentum conservation are considered for each phase. The interaction between the two phases takes into account the drag force between the particle and the air. Owing to high turbulence in the powder flow, a closure model was used based on a modified k - model in order to take into account the reduction of turbulence energy by the particles. The dense avalanche is modeled using the shallow water equations. The formation and the development of the powder avalanche is modeled using a mass and momentum exchanges between the powder flow and the dense flow. The flow area is digitized horizontally and vertically using a finite elements mesh. The numerical scheme is obtained by integrating the equations on each cell. The model thus built was calibrated using laboratory measurements of density current carried out in a flume. The model was successfully applied to reproduce many avalanches observed in France. At the end of this paper, an application of this model to an engineering case study is presented. It concerns the Uzengili path where an avalanche occurred in 1993. In this paper we use the integrated dense/powder avalanche model to define the effect of a powder avalanche flow in this path. Different simulations allow display of maps of the exposed zones for different available snow depths in the starting zone. The results were mapped in terms of dynamic pressure field and recommendations are proposed to the local authorities.     

Rapid estimation of corrected cut point in hydrocyclone classification units

In dressing plants, the rapid determination of the corrected cut point in hydrocyclone classification is desirable, useful, and important. In this work, classification tests have been carried out on white sand using a 10-cm diameter hydrocyclone to examine closely the relation between the recovery to underflow and the corrected separation size, $\text{d}{}_{50}$. The study was carried out at wide ranges of: apex diameter, vortex-finder diameter, solid content of feed, and length of vortex finder.A simple, yet reliable, equation relating the solid recovery of underflow to $\text{d}{}_{50}$, is developed using all the obtained results. The predicted data show good agreement with the experimental.     

Uranium mineralized fault zone at Wadi Um Gir locality,Central Eastern Desert,Egypt

The area of Wadi Um Gir, Central Eastern Desert of Egypt, is covered by Basement rocks of Late Precambrian age namely; the postgeosynclinal (Hammamat) sediments, intruded by a bostonite dyke of the younger postorogenic volcanics. The radioactive anomaly discovered at Wadi Urn Gir is a typical vein-type hydrothermal occurrence structurally controlled by a major fault which is among the youngest faults related to the formation of the Red Sea Rift Valley during Tertiary times. The net slip of this fault is determined by the orthographic projection method to be 260 m.Hydrothermal alteration is intense along the fault zone, and is represented by successive bands mainly of hematite, kaolinitic clays, carbonates, etc.The radioactivity is normally distributed in the fresh rocks with anomalous readings connected to the altered bostonite rock in the fault zone. The abnormal high radioactivity is found to be mainly due to secondary uranium mineralization, with a uranium content of 0.065%, and in a radioactive disequilibrium with slight deficiency of daughter elements which may be due to redistribution by the effect of ground water. The uranium mineralization is usually present as fracture-fillings or forming thin fissure veinlets mostly with hematitic alteration bands along the fault zone.Genetically; repeated movement along the major fault resulted in intense fracturing of the bostonite rocks and reopening of the tectonically related fissures. The fault provided an easy channel for the passage of the contemporaneous or immediately ascending uranium-bearing solutions. Subsequently, alteration of bostonite and radioactive mineralization took place in the secondary tension fractures. The physico-chemical conditions of the altered and sheared bostonite rocks afforded the favourable conditions for the deposition of uranium minerals carried by the hydrothermal fluids along the opened fractures.

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Zusammenfassung Das Gebiet »Wadi Um Gir« in der zentralarabischen Wüste Ägyptens besteht aus Basisgesteinen von Präkambrischem Alter. Es handelt sich um die postgeosynklinale »Hammamat«-Serie, deren Sedimentabfolge von einem Bostonitgang des jüngeren postorogenen Vulkanismus durchbrochen wird.Eine Radioaktivitätsanomalie wurde in »Wadi Um Gir« festgestellt. Sie bildet ein typisch-gangartiges hydrothermales Vorkommen und ist von einem Hauptbruch der mit der Entstehung des Rotmeergrabens verbundenen jungen Brüche bestimmt. Eine Berechnung der Sprunghöhe dieser Verwerfung mit der orthographischen Projektionsmethode ergab einen Wert von 260 m.Intensive hydrothermale Umwandlung der Muttergesteine kommt entlang der Bruchzone vor. Sie besteht unter anderem aus Successiven Streifen von hämatitischem, kaolinitischem und karbonatischem Material.Die Radioaktivität, deren Verteilung in den frischen Gesteinen normal ist, zeigt Anomalien nur noch im Zusammenhang mit dem umgewandelten Bostonit der Bruchzone, wobei die abnormal hohen Radioaktivitäts-Werte mit der sekundären Uran-Mineralisation (Urangehalt 0,065%) in Einklang stehen. Es besteht jedoch durch geringe Verarmung an gewissen Tochterelementen eine Gleichgewichtsstörung. Dies könnte auf die Umverteilung durch Grundwassereinflüsse zurückgeführt werden.Genetische Überlagerungen führen zu der Annahme, daß die wiederholte Bewegung entlang der Hauptbruchzone eine intensive Fraktur der Bostonitgesteine veranlaßt hat. Dies führte zur mehrfachen Öffnung der in Zusammenhang stehenden Spalten und damit bildeten sich Bahnen für die aufsteigenden, syngenetischen, uranhaltigen Lösungen.Die Anlagerung uranhaltiger Mineralien in den sekundären Spannungsbrüchen wurde durch die physiko-chemischen Verhältnisse des umgewandelten und abgescherten Bestonits gewährleistet.

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