1 (1), 1-10
Measurements of the stress orientation are directly relevant to a tectonic analysis and can be related to both visible structures and to the kinematic pattern. The most widely used method for obtaining stress orientation data is by analysing earthquake focal mechanisms using P-wave first motion analysis. Other tectoniques include the study of shear wave polarization, direct measurement by overcoring, or else indirectly by measuring borehole breakout or from a study of fault slip data. The origins of tectonic stresses are discussed and a composite stress map for Southern and East Africa is presented. Once the orientation of the neotectonic (present day) stress field has been determined it is possible to predict which pre-existing structures are favourably orientated for re-activation by strike-slip or normal motion. It is postulated that these structures would be the most favourable aquifers. A case study of the application of this technique in the Swartwater area is presented.
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1 (1), 11-20
As part of the National Water Master Plan study for Botswana the country's ground water resources were assessed. Borehole data were used and processed to determine aquifer representative values for borehole yield, success rate, aquifer thickness, ground water level and transmissivity. Aquifer basins were delineated from geological and hydrogeological maps. Extractable ground water resources were determined on a regional scale assuming a wellfield of 3 x 3 wells spaced 500 m in a regular and. Over a pumping period of 30 years a certain restricted drawdown was allowed. Recharge was calculated using different methods as a soil water balance modelling, chloride mass balance and ground water modelling. The main aquifer formations of Botswana were described and the available resources were calculated. Ground water quality data were processed to determine principal hydrochemical characteristics and to assess potability. There is sufficient ground water of good quality to meet the predicted demand to the year 2020. However, locally, overdevelopment of the ground water will be unavoidable if Botswana's economic development is to be sustained at the current pace.
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1 (1), 21-26
Rehabilitation is the process whereby a borehole is restored to its optimum production-level/condition or better. This can be achieved by either physical/mechanical, chemical or other means. However, the rehabilitation of a borehole, admits to the fact that basic house-keeping procedures have been neglected or ignored and/or that especially the subsurface component of a ground water supply system are poorly understood. The basic house-keeping procedures are appropriate and proper monitoring and maintenance. It is information from these that will indicate which method/s will produce the desired result of restoring/improving production. This paper looks at the three basic aspects for the proper management of ground water resources, viz. monitoring, maintenance and rehabilitation, as well as the hydrofracture stimulation technique and the Blended Chemical Heat Treatment (BCHT) rehabilitation technique, and highlights their value to the ground water scientist and the end user.
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1 (1), 27-35
The search for ground water in the Rural Areas and adjoining farms in the North West Cape, at the time of writing under the jurisdiction of the House of Representatives, had prior to 1989 been undertaken purely on an ad hoc basis. No integrated database existed and plans showing borehole localities were incomplete and out of date. To rectify the situation, a hydro-census was initiated in 1990, which entailed the location and sampling of all water points, dry and abandoned boreholes, using a Magellan Global Positioning System. This is currently being followed by detailed geological mapping and geophysical investigations involving resistivity and magnetic profiling, before carrying out drilling operations. Because of demographic considerations, it is not always possible to drill at the optimum site. Nevertheless a success rate of 80% has been attained since the inception of the programme in 1990 which has involved the drilling of some 80 boreholes totalling 8 408 m. A management programme, which involves the monitoring of the water supply to 26 villages on a regular basis and the supervision of six desalination stations, has been initiated. A public awareness programme which entails regular meetings with the communities and illustrated lectures to schools, involving various competitions and the distribution of a specially designed pamphlet, is under way.
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1 (1), 37-43
The philosophy of presenting South Africa's ground water situation on a national map is discussed. Borehole prospects and depth of ground water level below the surface based on a statistical analysis of some 70 000 boreholes, are to be shown on a scale of 1:2 million against a background of simplified lithostratigraphy. The map will be complemented by two smaller maps: a ground water availability and a quality map. Recharge in relative terms is to be shown against four main (saturated) hydrogeologic types: fractured rock; fractured and decomposed/disintegrated rock; karst; and strata with primary porosity. Quality will be depicted by electrical conductivity. Areas where nitrate and fluoride reach critical values are to be outlined.
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1 (1), 45-61
As part of a hydrogeological project in Botswana, BRGM has carried out a multimethod geophysical survey of a large sedimentary basin (50 x 30 Km) in the Kalahari desert. The aim of the survey was first to map the basement topography, affected by horst and graben structures, and then to accurately site the reconnaissance boreholes needed for evaluating the water resources of the basin. The regional mapping of the basement was performed using audio-magnetotellurics (AMT), gravimetry and magnetometry. AMT proved by far the most effective method (much more suitable than magnetometry, more cost-effective and quantitative than gravimetry) as a result of certain favourable conditions (good resistivity contrast between the basement and the cover rocks, regional uniformity of the sedimentary structure, and absence of disturbing "static" effects). The high productivity obtained with AMT was due mainly to the discovery of a fast quantitative interpretation procedure based on reading a single frequency (10 Hz). This procedure used an experimental correlation, established from 22 boreholes, between the depth to basement and the apparent resistivity at 10 Hz. Satisfactory theoretical justification for this correlation was obtained through 1D modeling with models that reflect the specific sedimentary organization of the basin. This correlation is thus mainly a consequence of the regional sedimentary history. 2D modeling did not provide a better explanation of the phenomenon and, moreover, it is more difficult to handle because the results depend on each particular geometry. At the end of the regional survey, 20 favourable areas covering the junctions between horsts and grabens were selected for detailed HLEM and DC profiling, the purpose of which was to precisely locate the fractured zones at the edges of deep grabens, which are ideal targets for hydrogeological exploration drilling. This approach was successful since six out of the 20 boreholes gave an air-lift yield greater than 30 m³/h.
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1 (1), 63-70
It is commonly accepted that under natural conditions and without abstraction, there exists a dynamic equilibrium between recharge and drainage in the aquifers of eastern Botswana. For the Kalahari Basin, the question as to whether there is such a dynamic equilibrium has not yet been satisfactorily resolved. Progress has been made recently with the development of lumped-parameter recharge simulation models which make explicit use of the dynamic equilibrium between recharge and drainage, using a simple linear reservoir to simulate aquifer drainage characteristics. Precipitation and evapotranspiration measurements are used as input to these models which may be calibrated with observed soil moisture and water level values. Statistical analysis of the available data, coupled with the results of such a recharge simulation model, indicates that the distribution of recharge events can be modelled by a compound Poisson process with a simple exponential event distribution. The first and second moment of natural groundwater level fluctuations can then be calculated through the theory of random differential equations, yielding expressions relating water level changes to specific yield, drainage resistance, frequency of recharge events and long-term average recharge values.
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1 (1), 71-79
Ground water for supplying the demand of Otjiwarongo town is abstracted from a marble aquifer. Expansions to the existing abstraction facilities were preceded by geohydrological investigations, facilitating characterisation and conceptualisation of this heterogeneous and fissured water table aquifer. Application of a water balance model, based on the saturated volume fluctuation (SVF) method, indicated a ground water recharge potential of three percent of average annual rainfall and an average storativity value of 2.7/10³, assuming no inflow to and outflow from the aquifer compartment. Despite aquifer heterogeneity, a satisfactory simulation of ground water levels in the oldest production area, the so-called Omatjenne Compartment, was achieved by an in tandem utilisation of the inverse model AQUA-INV and the 2-D finite element model AQUAMOD. Calibration and verification of the model did, however, indicate certain limitations to the present model's prediction capabilities, especially concerning transient recharge anomalies and prolonged recharge events associated with the dissipation of a recharge mound resulting from dam-bed infiltration from the Omatjenne Dam.
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1 (1), 81-88
The Mueda plateau in northern Mozambique is a Cretaceous sandstone erosional feature rising 200-300 m above the surrounding countryside. Its plane summit is densely wooded and is largely devoid of surface drainage. The recent sharp increase in population of the plateau has put pressure on water supplies. A pumped reticulation system deriving its water from some of the many springs which emerge at the foot of the plateau has repeatedly failed due to the erratic fuel supply. The alternative of a borehole water system is being investigated. Environmental isotope data from several springs show that the rain recharge over the plateau is very uniform, and that ground water residence times are of the order of a century. Calculated nett rain recharge to the deep ground water mound is much larger than the total flow of known spring occurrences, implying major losses due to diffuse ground water discharge. The alternative of a borehole-based water supply on the plateau itself may therefore be considered as: (1) yields will be more reliable than springflow, (2) water can be supplied where required and (3) various power sources could be employed.
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1 (1), 89-94
Ground water is a major source for the water supply in Botswana and elsewhere in Africa. The major part of all villages and all mining centres of Botswana depend on wellfields and their future relies on the availability of reliable water. Therefore good monitoring schedules are required as warning systems for the water supply and the economic development of Botswana. There are currently 27 major wellfields in Botswana. The geological set-up for these wellfields varies from place to place, but the major aquifers are weathered or fractured Basement Complex, Transvaal Dolomites, Fractured Waterberg, Karoo Sandstones and Arkoses, Kalahari Beds and Sand river beds. All wellfields are monitored by the Department of Water Affairs (DWA) and Department of Geological Surveys (DGS). Ground water level, abstraction rates and ground water quality are monitored on a regular basis. Each wellfield is equipped with a number of automatic water level recorders with charts being changed every 32 days. It is a convenient system considering the wide areal distribution of the wellfields. All recorders are installed in observation boreholes to monitor the general ground water level fluctuations in aquifers. In addition manual water levels are taken in production boreholes using standard electrical dippers. To ensure that water levels do not drop to pump intake levels without the knowledge of the operator, two measurements are taken in the production borehole each day of operation; before production starts and before it is switched off. These water levels are taken together with readings of the amount of ground water abstracted. The data collected during the monitoring of the wellfields are stored in a database developed by DWA in co-operation with DGS. Data in the database can be easily retrieved, displayed and used to evaluate the ground water situation. Periods of drought have had an effect on water level fluctuations in the wellfields with high abstraction. Basically the ground water abstraction in these wellfields exceeds the natural replenishment and the wellfields are operating under mining conditions. The most affected areas are Maun to the northwest of Botswana, Moshupa within the Gaborone area and Orapa in the central part of the country. DWA regards the water resources monitoring as an issue of extreme importance and the monitoring system is continuously upgraded including additional water level recorders, improved operational schemes and personnel training.
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1 (1), 95-99
In special conditions of arid, semi-arid and wet and dry regions, ground water is one of the most important African natural resources. In semi-humid parts of the African tropics ground water also plays an important role since many surface resources are intermittent or polluted and infected and thus local supply needs, cattle watering, irrigation and even industry depend on ground water sources. An effective ground water management becomes one of the prerequisite conditions of the sustainable development in Africa. In addition, a proper ground water management is an efficient tool in the restoration and conservation of the African environment. Effective management and development of ground water resources and restoration of the damages done to the ground water resources and aquifers elsewhere in Africa are important and challenging tasks for modern African research and technology.
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1 (1), 101-106
The population of Maputo and its suburbs mainly depend on shallow ground water for its water supply. Deep aquifers are not suitable for exploitation due to their high salinity. A sedimentary sequence hosts a shallow aquifer beneath the city; several hundreds of water wells, both for private and public use, are present. The shallow aquifer is highly heterogeneous, with transmissivities ranging from 4 m²/d to 1200 m²/d. A transmissivity map is presented and an analysis of the correlation of transmissivity (T) and specific capacity (Qs) is attempted. Ground water quality is affected both by salinity levels and nitrate concentrations. Salinity is related to past marine ingressions and to present day salt water intrusion. Nitrates appear to be related to high population density and to current sanitation practices; the NO3 map shows good correspondence of high nitrate areas with the longest and most densely inhabited districts of the city. Recharge to the shallow aquifer is predominantly local, and recharge areas generally coincide with high NO3, densely populated areas. An analysis of frequency distribution of NO3 concentrations indicates that 27.7% to 48.5% of ground water samples are above the 50 mg/l W.H.O. limit for potable water. Both local infant-feeding practices and existing literature suggest that the W.H.O. limit may be an unnecessarily strict goal in specific situations. Though no data are currently available on industrial/chemical ground water contamination, this should be considered as a potential high risk factor for both ground water quality and human health.
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1 (1), 107-111
The majority of water resources in Southern Africa are principally surface water and have resulted in larger scale development. However, water supplies of up to 5 million cubic metres per year can be adequately supplied by means of ground water. Distinction is made between primary and secondary aquifers. Analysis is made in terms of capital and operating costs of surface and ground water schemes. This paper assesses merits and relative costs of ground and surface water as a resource in southern Africa.
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1 (1), 113-118
The importance of ground water as a supply source for rural communities in South Africa, and the need for the management of the resource to ensure its sustainability in terms of both quantity and quality have been emphasized by recent droughts. Records of failed supply systems due to the malfunctioning of equipment and/or over-utilisation is considered to be attributable to a large degree to poor management. A prerequisite for the management of any system is an understanding of that system. Basement aquifers, which constitute the main aquifer in large parts of South Africa, are particularly difficult to define because of their great variability in terms of storage capacity and transmissivity. They can, however, be characterised broadly on the basis of geological environment, and recharge. Input data for the ongoing management of a rural ground water supply system must be easily obtainable at a local level and must also not require expensive or sophisticated equipment. Basic data requirements include rainfall figures, usage volumes, water level fluctuations, water quality and equipment status. This information must be fed into a central database for the district or region and must be evaluated, interpreted and acted upon by qualified people at regular intervals. The maintenance of the quality of the resource must be a responsibility at local level, particularly with regard to the uncontrolled disposal of domestic and other waste. This paper proposes a basic approach for the development of a ground water management system for rural communities. Experience gained in the rural areas of the Northern Transvaal and the Transkei are used to illustrate the feasibility of the approach.
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1 (1), 119-123
In many regions of Africa, consumers are dependent on ground water or surface-water supplemented by ground water. An important part of water supply management in such regions is assessing the reliability of the ground water resource being exploited. This paper proposes a Monte Carlo simulation method assessing the reliability given the uncertainty of the physical characteristics of an aquifer and the unpredictability of rainfall as the source of recharge.
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1 (1), 125-130
About 62 percent of the Mozambican territory is underlain by the Precambrian crystalline basement, frequently covered by a weathered overburden. Ground water forms the principal water source for the population in these areas. The national programme for rural water supply (PRONAR) has started since 1984 to execute boreholes, equipped with hand pumps, to improve the actual coverage of about 25%. Since these boreholes have relatively modest yields (Q < 1.5 m³/h), they can be supported by small local systems in the weathered overburden, provided the saturated weathered thickness is sufficient. Geoelectrical surveys (Schlumberger configuration) have proven to be a rapid and efficient tool to site boreholes. No conclusive relations between geoelectrical parameters (specific resistivity and depths) and the hydraulic potential (specific capacity and yield) were derived. Combining of the geoelectrical methods with other methods (especially geomorphological surveys through aerial photographs and field observations) contribute importantly to the effectiveness of the method. Examples in the Manica provinces show an increase of success rate from 60% to over through siting.
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1 (2/3), III-IV
The West African sub-Saharan Iullemmeden basin, covers most of the western half of the Niger Republic extending into Mali, Benin and North-west Nigeria. The relatively stable intracratonic setting of the basin is ideal for the study of eustatic changes. The near-horizontal topography of the flanks of the basin amplifies the lateral displacement of shallow marine invasion along the shore-line (Rat et al., 1991). Four new major observations are presented: (1) During the Upper Cretaceous, the Tethys already extended as far south as eastern Niger with the deposition of alternating sedimentary sequences consisting of (i) marine deposits (mainly limestones and sandy shales with Mesogean fauna) confirming warm epicontinental marine conditions, and (ii) sub-continental deposits made up of shales and sandstones, rich in fossil wood and vertebrate fossils (Dikouma et al., 1993). The following trangressions occurred: (a) The Upper Cenomanian - Lower Turonian transgression typified by Neolobites and Nigericeras (Mathey et al., 1991; Courville et al., 1991; Alzouma, 1992; Pascal et al., 1993). The theory proposed by Greigert (1966), of a regression ending up with the replacement of the marine environment by a highly salinated transitional environment with shales and primary gypsum, should be abandoned. Isotopic analysis confirm that the gypsum is secondary and resulted from the re-oxidation of sulphur originating most probably from sulphato-bacterial reduction processes within a confined environment (Mathey et al., 1991). (b) The Upper Turonian to Coniacian transgression which is still not adequately studied but is typified by the presence of the ammonite Coilopeceras inflatum of Upper Turonian and probably Coniacian age (Meister et al., 1992). (c) The Upper Maastrichtian transgression with two fluctuations typified by the presence of Libycoceras and Laffiteina. The first Maastrichtian fluctuation in southern Niger corresponds with the Farin-Doutchi Formation also known as "Mososaurus Shales" or Dukumaje Formation in NW Nigeria. The second fluctuation is related to the deposition of a lateral equivalent in NW Nigeria known as the Wurno Formation (Dikouma et al., 1993). The marine sedimentation at the beginning of the Tertiary was biochemical in character as suggested by the dominance of limestones, phosphates and palygorskites. The transgression was typified by the presence of the foraminifera Ranikothalia and Lockhartia. The deposits include the Garadoua Formation and the lateral equivalent in N-W Nigeria (Gamba Formation, Kalambaina Formation and Dange Formation). They were considered by previous authors as the first phase of the (Ct1) sedimentary cycle dated late Cenozoic. They are now considered in this volume by Alzouma and Dikouma as the end of a sedimentary cycle during the Eocene (Fig. 2). The Continental Terminal sensu stricto (Ct2 and Ct3) consists of a ferrugineous facies overlying the first level of oolites discordantly. It represents a different sedimentary cycle (Dubois and Lang, 1981; Lang et al., 1986,1990). (2) The Lower Paleocene is absent in the Iullemmeden basin as new palynologic and micropaleontologic data confirm the Upper Maastrichtian age for the Farin-Doutchi and In-Wagar Formations. A large part of the Garadoua Formation has been attributed to the Upper Paleocene by Carbonnel et al. (1990), Dikouma (1990), Dikouma et al. (1993). These confirm the existence of a break in sedimentation during the Lower Paleocene. The Lower Paleocene unconformity has also been recognised in the coastal basins of Benin-Togo (Bio Lokoto, 1991) and Côte D'Ivoire (Goua Tokpa, 1993a and b, Goua Tokpa et al., 1994). (3) The Iullemmeden basin, located within the heart of the African continent, was linked up by marine transgressions with the Tethys during Upper Cretaceous and Lower Tertiary periods. The Mesogean fauna originating from the Cenomanian-Turonian transgression include the nautilus Angulithes lapparenti and ammonites Neolobites vibrayeanus, Exogyra olisiponensis, Mecaster pseudofourneli and Heterodiadema Libycum (Neraudeau, 1991; Mathey et al., 1994; Neraudeau et al., 1994). The basin was also occasionally linked up with the South Atlantic during two well-dated periods (Greigert, 1966; Reyment, 1971, 1980; Petters, 1977; Kogbe, 1981; Dufaure et al., 1984; Bellion, 1989; Dikouma, 1990; Alzouma, 1992). (a) Paleontologic evidence based on the presence of ammonites from the Iullemmeden basin, Nigerian coastal basins and the Benue Trough (Courville et al., 1991; Courville, 1993; Meister et al.), confirm the linkage by a "seaway" during the end of the Cenomanian. The transgression attained a maximum development by the Cenomanian-Turonian passage corresponding with Horizon IV (Gadeni) and probably Horizon Va (Cauvini) of the global scale of transgressions. The Cenomanian-Turonian boundary corresponds to a sequence boundary (Pascal et al., 1993). Horizon III ("dalle à Exogyres") confirm the linkage of both seas with the higher calcareous content resulting from an increase in the volume of sea water. The higher content of Sr and Ni in Horizons III and IV suggests the opening-up of the sea-way (Pascal et al., 1991). (b) Similarity between the Iullemmeden basin, the North African basins (Mali, "Détroit Soudanais", Algerie, Tademait and Tinrhert) and the Nigerian sedimentary basins (Sokoto, Benue, Niger Delta) is confirmed by the same species of macrofossils found in all the basins. These include echinoderms (Plesiolampas, Linthia sudanensis, etc.); bivalves (Pseudomiltha chavani, Ostrea aviola, Ostrea multicostata, Pycnodonta senegalensis) and gastropods (Gisortia brevis, Heligmotenia molli, Chenopus etc...) - Dikouma, 1992. These similarities further confirm a linkage of the Tethys with the South Atlantic during the Upper Paleocene. The discovery of the Paleocene nautilus Deltoidonautilus sudanensis, Deltoidonautilus chudeaui in the basin provide additional favourable evidence (Dikouma et al., 1987). The ostracod fauna tend to be a useful evidence of a mixed fauna from both the Algerian coastal basin and the north African (Lybian) and middle-eastern basins (Carbonnel et al., 1990). (4) Cenomanian-Turonian marine fluctuations coincide with global eustatic movements which are closely related to regional climatic changes brought about by cyclic sea level changes (Mathey et al., 1991). The abundance of palygorskite during the Upper Paleocene suggests a much drier climate than during the Upper Cretaceous as the equator was slightly displaced southwards.
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1 (2/3), 131-281
The Iullemmeden basin is an intracratonic basin covering an immense area extending from the Republic of Mali in the west to the western borders of the Chad Republic (1000 x 800 Km² approximately). It is, however, relatively shallow with an Upper Cretaceous marine sequence not exceeding a hundred meters in thickness. The continental surfaces over which the transgressions occurred were relatively flat. The marine transgressions were therefore rapid as evidenced by the Cenomanian-Turonian transgression overlying the "Continental Intercalaire" (Rat, Lang, Alzouma, Dikouma et al., 1991). The facies succession confirmed a rapid progression of the sea over an alluvial plain. The slightest fluctuations of the sea level produced noticeable geographic repercussions involving important displacement of the coast-line. They also influenced the migration and re-organisation of the littoral biosedimentary systems resulting in lateral facies changes.
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1 (2/3), 283-424
The Campano-Maastrichtian transgressions arrived earlier along the coastal basins of West Africa during the Upper Campanian or Lower Maastrichtian. They were only recorded in the Iullemmeden basin during the Upper Maastrichtian. Similarly, the Paleocene transgression occurred in the coastal basins during the Danian but was recorded in the Iullemmeden basin only in the Thanetian. The Eocene was regressive in the Iullemmeden basin whereas in the coastal basin the marine transgression attained its maximum development during the same period. It is important to note that the slightest changes in sea-level resulted in very important paleogeographic modifications within the Iullemmeden basin as a result of important displacements of the shoreline and the sedimentary systems.
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1 (4), 425-447
East African Karoo rifts underwent four evolutionary stages. Each rift cycle produced characteristic sediments, i.e. postglacial, lacustrine shales, coals and associated fluvio-lacustrine sediments and synrift sequences. Rifting in intracratonic settings started either during the Permian and continued until Middle to uppermost Triassic. Prolific coal fields are located in the SW-Tanzanian Ruhuhu rift where peat swamps developed during early rift stages. During the main rift stage, deep water anoxic and turbiditic sequences prevailed, the post-rift thermal subsidence stage is characterized by several kilometre-thick fluviatile successions, correlated on a regional scale as a quasi synchronous event. A similar development is recorded from rifts outside of Tanzania (Zimbabwe, Mozambique and Malawi). Pericratonic rifts developed in coastal areas, starting after the termination of the Karoo cycle in the Lower to Middle Jurassic leading from an initial rift to a drift stage. Coals represent the major energy resources of the Karoo rifts. Organic geochemistry, coal petrography and mineralogy indicate fair source rocks for the postglacial Asselian sequence, the Lower Permian coal-bearing and the Upper Permian lacustrine sequences. Similar observations are made in time-equivalent horizons from neighbouring countries, i.e. Zimbabwe, Zambia, Malawi and Mozambique. Coals are gas prone vitrinite-inertinite-rich, high ash varieties, but occasionally, liptinites indicate a marginal potential for the generation of liquid hydrocarbons.
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1 (4), 449-453
I hereby propose an explanation of the discordance observed in the magnitudes determined in Lwiro (Eastern Zaïre) as pointed out by Ambraseys (1972) and Bäth (1975). I also propose a correction for magnitudes determined at Lwiro in order to constitute an earthquake catalogue for the Western Branch of the African Rift Valley. Moreover, an evaluation of the anelastic attenuation of Lg waves is done. A set of 117 regional earthquakes with magnitudes determined both at the Lwiro (Zaïre) and the Bulawayo (Zimbabwe) seismographic station constitutes the basic data to this paper.
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1 (4), 455-467
The Miocene to Subrecent volcanic rocks of Jordan are part of the widespread Cenozoic volcanic province within the Arabian Plate. The magmas have changed in composition with time from older hawaiites to younger and more voluminous alkali-olivine basalts and basanites, with the later showing a primitive character and containing a wide variety of crustal and mantle xenoliths. The alkali-olivine basalt was derived from a peridotitic source by a higher degree of partial melting (~12%) than basanite (~5%). The alkali olivine basalt and hawaiite have also been modified by limited open system fractionation of olivine and clinopyroxene. The volcanic activity occurred in phases corresponding in time to two stages of rifting and later sinistral displacement along the Jordan Rift. The tectonism relates to the opening of the Red Sea in the south, and the subduction of the Arabian plate to the north.
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1 (4), 469-474
A 250 Km Bouguer gravity anomaly profile (southwestern tip at 26.5°N, 55.7°E, NE tip at 27.2°N, 56.6°E) was made to evaluate the thickness and configuration of the sedimentary section (to the pre-Permian basement) at the southernmost part of the Arabian Gulf and the Strait of Hormuz. A relatively steep gravity gradient decreasing towards the Makran (Lran) at -0.2 mGal/Km may be related to the increasing thickness of the post-collisional Arabian plate sediments near the edge of the Arabian and central Iran Plates. The residual gravity anomalies pattern indicates several positive and negative anomalies. Calculations show that some of these are related to thickness variation of the saliferous section of the Mid. Upper Eocene, others related to anomalous thickening at the edge of an interpreted high angle thrust fault. Broader anomalies are found caused by lithology variation (from dolomite to limestone) of the Upper Jurassic to Lower Triassic Permian Khuff and by thickness variation of the salt members of the Infracambrian Hormuz Series. Larak and Hormuz Islands are shown occupied by piercement type salt domes arising from the Hormuz Series. The calculated gravity pattern shows shortening of the section which is in agreement with geologic theorems advocating accretionary sedimentary columns which constitute the continental margin of the Makran. Although other subsurface models are plausible (for the given gravity distribution), it is felt that the presented one is the most feasible geologically.
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1 (4), 475-494
New chemical analyses data are presented for basic lavas covering the plateaus on either sides of the Ethiopian rift. On the Southeastern plateau, the Bale basalts are 2-30 Ma old and consist of alkalic lavas that are intercalated with tholeiites in the lower part. Coeval basalts extending from Muger to the rift margin on the Western plateau are uniformly transitional in composition. Major elements melting systematics indicate that the silica-undersaturation of the alkalic magmas relative to the transitional ones is only due to their higher depth of segregation than the latter, which is estimated to be (greater than or equal to) 50 Km. Both types of basalts bear clear evidence for a decrease in the degree of partial melting with time. This was accompanied by changes in the source regions of the alkalic basalts from an early one with recycled oceanic crust and mantle-wedge type geochemical signatures and located within the lithospheric mantle, to a later deep-seated convecting mantle similar to that of the Tristan da Cunha ocean island basalts (OIBs). The transitional and tholeiitic basalts were exclusively derived from the lithospheric and Tristan OIB - type sources, respectively. These observations suggest that Tertiary magmatism in Ethiopia was triggered by the rise of a hot blob of material lacking an underlying plume and that alkalic and tholeiitic magmas were generated by melting of adiabatically upwelling mantle diapirs in areas of normal crustal thickness. It appears that transitional basalts were formed at the expense of alkalic magmas where mantle upwelling coincided with crustal extension.
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1 (4), 495-502
A detailed study of structural history of the metamorphic rocks of Haramsam area has shown that they have been subjected to folding of five generations and shearing of various types. Folds of first generation (F1) are isoclinal with well developed axial planar foliation (S1). The second generation folds range from close to isoclinal, resulting in folding of the axial planes of F1 and S1 foliation. Folds of the third generation (F3) are represented by synforms and antiforms with NS to NE striking axial planes. The fourth generation folds (F4) are open to close generally with N-S axial planes. These have been overprinted by gentle to open folds (F5) which resulted in a swing in the strike of the foliations and axial planes of the earlier folds. Ductile and brittle-ductile shearing events synchronous with F1, F2 and F4 folding, and brittle shears related with the folds of fifth generation have affected the rocks. The F1-2 folds and associated structures are interpreted to be related to accretion-subduction processes. The F3 and F4 folds are the results of E-W oriented compression and shearing respectively; and the F5 fold and associated brittle structures are formed during N-S oriented compression accompanied by uplift.
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1 (4), 503-514
The Nubian Shield is built up of metavolcanics, metasediments and plutonic rocks of oceanic lithosphere, accretionary prisms, subduction zones and evolved island arcs of Neo-Proterozoic, Pan-African age. Shear-zones are a characteristic structural feature and are developed both within and between the two major structural tiers of gneissic (tier 1) and low grade (tier 2) sequences. In places, they form linked faults and antiformal stacks, in the core of which the gneissic rocks are exposed. The largest of these antiformal structures in Egypt is the Wadi Hafafit Culmination (WHC), which is investigated here with emphasis on shear-zones and mineral deposits. After a brief general characterization of shear-zones the paper deals with the Gabal Um Siwirab Cu-Zn sulphide occurrence which is related to the shear-zone at the WHC's southern margin. Microscopic studies revealed that the primary magmatic fabric with fine-grained ore minerals is overprinted by shearing and, in turn, overprinted by coarse-grained recrystallization. Accordingly, shearing released the economic elements from the primary fabric and allowed concentration and recrystallization. A review of published data and our observations show a majority of the Pan-African mineral deposits in the WHC and environs to be either genetically related to shearing or to have acquired the present texture, economic mineral concentration and geometry during deformation. In contrast to earlier views, the low angle nature of the shear-zones at a regional scale favours the interpretation that recrystallization and remobilization occurred at relatively high crustal levels and potentially present fluids cannot be directly related to high-angle faults tapping deeper crustal or mantle sources.
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1 (4), 515-521
Many placers containing potentially useful minerals occur along the Somali coast of the Gulf of Aden, especially at the estuaries of watercourses draining areas where the crystalline basement outcrops nearby. The most abundant heavy minerals are Ti-magnetite and ilmenite, but Th-monazite (sometimes exceeding 2%), zircon and rutile are also locally plentiful. The beach sands of Batalaleh contain about 38% of heavy minerals. Ti-magnetite and ilmenite are very abundant in them and their fabrics suggest that they are mainly derived from gabbroid rocks and metabasites; zircon and rutile are moderately widespread and show more varied lithological origin. Monazite contains up to 61% of REE2O3 and up to 2.9% of Y2O3 Ce2O3 accounts for about 29%; La2O3 ranges between 14% and 19% and ThO2 between 3% and 12%. The lower La and Th contents correspond to the most significant enrichments in Nd, Sm, Gd and Y. Monazite is essentially derived from the small outcrops of eroding granitoids and pegmatites in the basin feeding the Batalaleh beach. The abundant monazite reported in the coastal sands slightly west of Berbera is due to the widespread occurrence in the adjacent western basin of both masses Pan-African granitoids and pegmatitic swarms with Nb, Ta, Be and REE minerals.
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1 (4), 523-532
Two types of phosphatic sand crusts were found in the shallow, southern part of Lake Malawi. The laminated sand crust is brown with patches of purple and green coloration, medium to coarse grained, with subrounded to angular quartz and feldspars as the major minerals while the micronodular crusts are also brown with patches of about a millimetre in diameter, blue sphaeroids covering over 70% of its upper surface. XRD results for the sand crusts show that the dominant detrital mineral is quartz, which constitutes about 48% of the crust. Feldspars are second in abundance at about 24% while the main authigenic minerals are carbonate hydroxyapatite [Ca10(PO4)3(CO3)3(OH)2] (francolite) at 12%, carbonate fluorapatite [Ca10(PO4)5CO3F.5(OH)], vivianite (Fe3(PO4)2.8H2O) and anapaite [Ca2Fe(PO4)2.4H2O]. The phosphate in the sand crusts is from fish bones. Anoxic conditions introduced by cutting off of oxygen supply to the sediments due to the "blanketing" of the sands by finer sediments and/or cementing together of the sand particles by iron oxides and clays have led to the formation of vivianite and anapaite. The crusts were formed by desiccation in a period of a lower lake level.
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1 (4), 533-545
In Northeast Tunisia, two contemporaneous types of deformation are demonstrated. The first is deformation combining strike-slip and reverse faulting in the northwestern part of the study area, the second is a combination of strike-slip and normal faulting in the southeastern part of Northern Tunisa. The orientation of principal stresses σ1 > σ2 > σ3 and the ratio R = σ2-σ3/σ1-σ3 which characterises the shape of the stress ellipsoid is calculated using microtectonic data. From the Oligocene to Messinian rocks, contemporaneous types of stress tensor can be determined, one is associated with a horizontal maximum compressive stress σ1 striking N14°E in the north, the other one is related to an extensive stress regime in the southern part Kechabta and surrounding areas: (sub-vertical σ1 and horizontal N130-140° striking σ2. The interchange between σ1 and σ2 resulted from a decrease in the value of the maximum horizontal stress (σh max) from Northwest to Southeast. Field investigations show that the compressive deformation propagated in space and time from northwest to southeast from the Late Oligocene to Villafranchan. The maximum horizontal stress has a constant NW-SE direction.
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1 (4), 547-556
Chemical, X-ray fluorescence and X-ray diffraction analyses of sixteen samples from the upper part of Eocene Gercus Formation (Zawita, Iraq) indicate that these sediments are poor in the major oxides (SiO2O2, FeO and K2 relative to average shales. This is a consequence of the fact that the rocks are carbonates, rich in clay minerals and consequently poor in quartz and clay minerals. Normative mineralogy indicates that the Gercus sedimentary rocks consist of clay minerals (45.73%), carbonates (41%), quartz (10.27%), haematite (2.5%) and heavy minerals (0.5%). The clay and clay-like minerals, in their order of abundance are palygorskite, chlorite, monmorillonite and antigorite. The Gercus sedimentary rocks are depleted in the trace elements sulphur and strontium, whereas they are enriched in chromium, nickel and cobalt. Sulphur is partitioned between a sulphide and a sulphate phase. Strontium is mostly found within carbonate and sulphate phases replacing calcium. The elements Cr, Co and Ni are almost exclusively contained within the clay minerals. In addition, a correlation has been found between the intensity of the red colour and the Fe3/FeO ratio of these sediments.
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1 (4), 557-566
A total of 1488 events reported in the Dead Sea region by the Jordan Seismological Network are used to study the earthquake recurrence of the area. The events cover the period from September 1983 to September 1986 and lie in a magnitude range between 1.4 and 5.1. The frequency-magnitude relation for the considered period has been derived in the form, log N = a - bML, where N is the cumulative number of events per year for events with magnitude (greater than or equal to) ML, A = 5.271 and b = 1.025. The b-value is considered to be representative of the region since in the process of its evaluation it was found that incorporating events of the high magnitude end of the range utilized tends to produce a more stable and constant b factor. The relation seems to fit well with the pattern of the historical earthquakes in the area. It also characterizes the region as a highly active one for the continental rift and platform-block seismotectonic zone. The geographic distribution of both historical and instrumental events show, in many cases, a relation to geologically known surface faults. Earthquakes follow NW-SE faults in the southern parts, while in the central and northern parts they are associated with the main Dead Sea rift direction and the E-W and NE-SW fault systems.
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1 (4), 567-578
The Dead Sea rift forms the NW tectonic boundary of the Arabian plate, from the northern Red Sea to SE Anatolia. The rift was considered a prime example of a transform fault, due to its association with geological indications for 105 Km of sinistral displacement. Recent investigations cast doubt on the magnitude of that lateral offset, and bring forth new evidence for extension across the rift. Noteworthy are the arcuate salt diapirs in the northern Red Sea, that show the swing of the tectonic axis from the Red Sea into the Gulf of Elat. Also important is the age determinations that date the initiation of the Red Sea and the Suez Rift in the Miocene, and the Dead Sea rift in the Plio-Pleistocene. Consequently, it is suggested that the Dead Sea rift is an excellent example of continental breakup, that seems to grow into an oblique oceanic spreading center.
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1 (4), 579-592
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community. The bibliography will, henceforth, appear in each issue of the Africa Geoscience Review.
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2 (1), 1-8
Audiomagnetotelluric (AMT) measurements in the frequency range 8-5000 Hz were carried out on profiles across two small anorthosite-bearing Abontorok and Tagueï ring complexes in central Aïr, in order to determine the electrical character of the rocks and the possible subsurface shapes of the intrusions. The AMT responses from sites ranged from isotropic to strongly anisotropic, sometimes with parallel behaviour between the measured apparent resistivity curves. Static shift effects due to local near-surface inhomogeneities are present at some of the sites. An interpretation of the data considered to be free of static distortion was obtained with one-dimensional models consisting of three or four layers. Modeling indicates a thin, moderately conductive zone at a depth of 1.3 Km under Abontorok, except near its centre where the rocks are characterized by high resistivities of the order of 20,000 Ohm.m, possibly related to a feeder pipe. No clear electrical signature was associated with the Tagueï complex, the absence of contrast with the country rocks being related to the occurrence of monzo-anorthosite and the suggested presence of granite below it. The large anisotropy observed at some sites at Abontorok may be explained by the two-dimensionality of the structure.
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2 (1), 9-23
Structural control of the dry valley systems within the Kalahari of Botswana and eastern Namibia has previously been noted in the literature but its importance has never been demonstrated. The extent of such structural control is mapped using a specially adapted technique of network orientation analysis which identifies valleys showing close alignment with geological lineaments. In many cases there appears to be structural control of valley location even in areas where bedrock is buried by thicknesses of Kalahari Group sediments. A link between valley development and geological structures is proposed for many valleys, invoking the process of deep-weathering as an erosive mechanism by the movement of groundwater along preferential subsurface flow paths. Deep weathering is proposed as an important factor in the early stages of Kalahari valley development, controlling the location of many valley systems, but only appears to operate where the sedimentary cover is less than 30 m thick.
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2 (1), 25-35
New geochemical data (major elements) on birimian volcanic rocks from Toumodi area, confirm the existence of a bimodal volcanism, without intermediate terms, which may be approaching to modern island arc. The correlations with the bordering and same age (approximately equal to 2.1 Ga) volcano-sedimentary complexes enable to propose a geodynamic evolution model for all the country.
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2 (1), 37-60
On the basis of a new geological map, the magmatic evolution of a sector of the Main Ethiopian Rift, South of Addis Abeba, has been studied. In the area, between the two villages of Dera and Nazret the volcanic rocks have been subdivided into 8 Units. From the oldest unit they are: Eastern Margin and Nazret (basaltic flows and ignimbrites associated to rhyolitic lava flows and domes), Keleta and Boku-Tede (ignimbrites and pumice falls associated with a few acid lava domes), Bofa (basaltic flows), Dera-Sodore and Gedemsa (ignimbrites, pumice falls and acid domes) and Wonji (lava flows, cinder and spatter cones). In this area, flows and tuff of basaltic and rhyolitic composition have been erupted closely spaced in time. Intermediate products are practically absent. The basaltic units are mainly transitional, whereas the acid rocks show a predominantly peralkaline character. The major and trace element variation diagrams show chemical variations within the basic and acid members that could be related to fractional crystallization processes. The REE patterns show an enrichment in LREE with a negative Eu anomaly for the acid members. These patterns seem to confirm an important role of the fractional crystallization process. However, the 87Sr/86Sr ratios (0.704-0.710) and some incompatible elements ratios (Ba/Rb and Rb/Sr) suggest that this process cannot act alone. The geochemical diversity of the basaltic and acid products can be interpreted as a result of assimilation-fractional crystallization (AFC) processes. The diversity of basalts seems to derive from a assimilation of lower crustal rocks during fractionation. The petrogenesis of acid rocks is more questionable. Rhyolites can be derived from a basaltic liquid by a moderate upper crustal assimilation rate (r = 0.1), whereas the peralkaline rocks require a very low assimilation rate (r = 0.04) and a more significant fractionation rate (75%< F< 85%).
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2 (1), 61-76
The evolution of the calco-carbonic system in the groundwaters in Côte d'Ivoire reveals that the different families of waters identified in the ISC-ISD diagram according to their relative age, are located on sensibly parallel lines. In water samples belonging to the different families, values of Ca/Mg and Ca+Mg are inversely proportional to water age: thus Ca/Mg decreases as Ca+Mg increases. Consequently, these two parameters may be used as cationic indices for age determination in groundwaters. However, only Ca+Mg values present a constant evolution in all groundwaters collected from various regions of Côte d'Ivoire. In general, variations of this parameter follow an arithmetical series particularity characteristic of groundwaters from Dabou area. On the contrary, since Ca/Mg values depend on the heterogeneity of enclosing rocks, they are more of an index of the age of waters within homogeneous rocks or within those rocks with identical weathering behaviour.
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2 (1), 77-89
The Late Oligocene(?) - Middle Miocene rift sediments in Wadi Wizr-Wadi Assal area south of Quseir could be subdivided into four lithofacies: Facies A: Dominantly alluvial, coarse clastic, fans (lower part of Ranga Formation). Facies B: Fluviatile coarse and fine siliciclastics, with marine evaporites near the top (upper part of Ranga Formation). Facies C: Open marine, mixed coralgal carbonate-siliciclastic sediments (lower part of Um Mahara Formation). Facies D: Restricted marine, algal laminated carbonate and siliciclastic sediments (upper part of Um Mahara Formation). Synsedimentary tectonics have played a great role in the distribution of these facies in the studied area. Thus by Late Oligocene (?) time, the intersection of NW and SE faults created two structural depressions trending NW and N separated by a NW trending high. Facies "A" was deposited on the lows. No sedimentation took place on the high. By Early Miocene time, Facies "B" was deposited on both the high and lows but with thicker and coarser siliciclastics in the lows. By middle Miocene time rejuvenation along NW trending faults resulting in the formation of NW fault blocks, thus giving rise to new highs and lows with NW orientation influencing the deposition of Facies "C" and "D".
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2 (1), 91-99
Sediments of the Dubaydib Formation and Tubeiliyat Member (Mudawwara Formation) of Early Ordovician age (previously known as the Sabellarifex and Conularia sandstones) in the southern desert of Jordan, comprise at least 330 m of siliciclastic sediments. These sediments were divided into three major lithofacies; hummocky cross-stratified sandstone, channelled sandstone and silty shale. The most striking sedimentary features in these sediments are the hummocky cross-stratification and the subaqueous channels, which are considered to be diagnostic of inner shelf storm deposits, and have been attributed to the action of strong storm-wave surges. The interaction of intermittent storm-wave events and fair weather conditions, associated with eustatic sea-level changes and minor transgressive-regressive phases, were responsible for the accumulation of several coarsening-upwards sequences, in an inner to mid shelf setting.
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2 (1), 101-105
The Kabba-Okene granodiorite gneiss, a widely occurring orthogneiss unit in the basement complex of Nigeria, has yielded an U-Pb zircon age of 2103±8 Ma. The age supports the claim of an Eburnean (early Proterozoic) thermotectonic event in Nigeria. More importantly also, because the gneiss contains xenolithic inclusions of the associated low grade metasedimentary schists (younger metasediments) hitherto believed to be late Proterozoic supracrustals, the age information constrains the minimum age of the metasediments to early Proterozoic. One obvious implication of this is the urgent need for a review of the existing chronology of the basement complex of Nigeria.
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2 (1), 107-119
During the late Cenozoic (Miocene, Pliocene and Quaternary) Israel was structurally located between two subsiding basins in which sediments accumulated at a considerable rate, the Jordan - Dead Sea Rift to the east and the Mediterranean to the west. Both basins had been drilled in search of natural gas or oil. Many of the penetrated sections have been subject to pollen analysis in order to obtain palynostratigraphic scheme of the region. The Quaternary sequence was subdivided by Horowitz and Horowitz (1985) into ten palynozones: QI-QII of preglacial Pleistocene age, QIII through QIX of Glacial Pleistocene age and QX representing the Holocene. In this study sedimentological methods were employed to investigate the processes of deposition that prevailed in the preglacial Pleistocene QI palynozone of boreholes Amiaz-1 (1100-1600 m) and Melekh-Sdom 1 (2410-3280 m) at the southern part of the Dead Sea. The QI palynozone envisaged in the Amiaz-1 borehole comprises varying proportions of very coarse to fine clastic beds alternating with clays, marls and subordinate amounts of salt and anhydrite. The studied interval of Melekh-Sdom 1 borehole consists alternating layers of sandstone and limey mudstone. Textural parameters derived from the sand fraction of this palynozone in the Amiaz-1 borehole imply, to some extent, conditions characterizing braided stream depositional environments but they are most similar to sands deposited by aeolian processes. The mudstone layers of this interval probably precipitated in partly confined aquatic basins under arid climate. In the Melekh-Sdom 1 borehole the lithological and textural characteristics of the investigated rock sequence imply depositional processes that commonly prevail in lake environments. The sand layers have settled from distal parts of currents originated from river mouth during relatively humid periods. The mudstone layers reflect more arid phases when ionic concentrations in the lake rose. The Dead Sea Rift at the preglacial QI palynozone time span showed only slight subsidence which made some of its parts intermediate lakes on the way of rivers from Transjordan to the Mediterranean during a rather wet, temperate climate with a somewhat drier period in its middle part.
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2 (1), 121-139
Cotonou town is located alongside the Atlantic Ocean on a margin-coastal complex composed of Quaternary formations revealing a sand gravel-stone levels and clay levels cycle in continuous layers or lens-shaped. Their morphological evolution is indicated by the presence of a table land to the north and littoral plain to the south. The hydrogeological work deals with the coastal zone and the south border of the table land. Besides the superficial aquifer, three other main aquifer horizons have been identified about 150 to 200 metres deep. Their hydrodynamic parameters are exposed and are characterized by some considerable spatial variations showing the heterogenous nature of reservoirs. Water has a favourable chemical quality for human consumption and for current agricultural and industrial uses, except those with high levels of nitrate. Nevertheless their bacteriological quality requires disinfection before consumption. Having a clear-cut idea about the geometry, the functioning and the hydrochemical quality of worked aquifers for water supply in Cotonou town, some relevant suggestions for the exploitation of existing workable resources, important though vulnerable, have been mentioned.
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2 (1), 141-149
A seismotectonic map is drawn up by using recent seismological, geological and neotectonic data. The comparison of the seismological with the neotectonic data shows a certain relationship between the seismic activity and the active faults. The focal mechanism of some earthquakes in the Rift indicates a correlation between the sub-meridian direction of the pressure axis and the main Plio-Quaternary tectonic stress owing to the Africa-Europe plates convergence.
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2 (1), 151-162
Lake Malawi occupies the southernmost part of the East African Rift system. Ferromanganese nodules and ooids occur at water depths of 80 to 160 m at the facies boundary between sands and muds. In most cases, the nodules have been found at the water/sediment interface. The nodules/micronodules range in colour from dark brown to rusty brown or yellowish. Some tend to be of metallic lustre on the outside. The size of the nodules range from about a millimetre to about a centimetre in diameter, but on average most are about 3 mm. The shapes of the nodules may be spherical, mamillated, potato-like and pea-like. Internally, the nodules may be banded therefore have a laminated cortex or homogeneous. The nodule core may be a central cellular portion with a distinct or unclear central nucleus and tends to have voids of variable sizes and shapes. The physical characteristics of the nodules suggest both stable and unstable environments of formation influenced by the nature of bottom water currents. The organic matter content and trace element composition of the nodules indicate the possible influence of bacteria in their formation.
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2 (1), 163-178
Seismic reflection and well velocity data have been used to study the structure of the FF-GG area in the central part of the Gulf of Suez. Five seismic reflectors have been identified and correlated with the prominent reflectors in the Gulf area and aged. The youngest one of them is correlated with the top Zeit Formation, while the oldest is correlated with the pre-Miocene unconformity. Five seismic units between these reflectors have been described seismically. Four structure contour maps have been produced (in T. W T.) for top Zeit, top south Gharib, top Belayim and top Kareem Formations. The study reveals that the pre-Miocene high block have been eroded forming the pre-Miocene unconformity. This unconformity is well represented to the east of the study area and stopped at the west forming an edge or escarpment. The pre-Miocene unconformity has been followed by intensive normal faulting. These faults have the Gulf of Suez trend and affected most of the Miocene. The faulting system have been crossed by a small shear component probably at the late Miocene time (or younger) mostly with a N20°E trend (Gulf of Aqaba trend). The study indicates that the faulting system of the Suez Gulf and the Red Sea rift activated during the Late Oligocene-Early Miocene was rejuvenated during the rest of the Miocene. The main structural features in the investigated area comprise (from west to east); a half graben, a relatively high or uplifted block and monocline or eastward tilting block.
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2 (1), 179-188
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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2 (1), 189-203
PANGIS network, supported by UNESCO, ACCT and bilateral French and Belgium Cooperation since 1989, is a pool of African and European documentation centers working in the field of African Geology, all using the same tools for micro-computerized information management and connected together for data supply, information exchange, training support and publishing. PANGIS is also a micro-computerized bibliographic database co-compiled by the 20 members (10 more members are expected for 1995) of the network gathering about 30,000 references (both published and unpublished documents) with analytical descriptions of documents. The material in this bibliography on African Sedimentary Basins is available in the libraries mentioned at the end of each reference or at the library of CIFEG (see address above); CIFEG being the coordinating center of PANGIS.
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2 (2), 205-213
Seismicity due to the compressional motion (0.9 cm/yr.) in North Africa has an important effect on the instability of the Pliocene-Quaternary sediments on the Algerian continental margin. The 1954 and 1980 Ech-Cheliff earthquakes induced turbidity currents that cut several submarine telephone cables at the foot of the continental slope. The bathymetry and the seismic reflection data reveals the existence of a cone-shaped sedimentary accumulation (2600 m depth). This sediment body is interpreted as formed by the high earthquake activity of the Ech-Cheliff area.
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2 (2), 215-217
In the District of Kogo in Equatorial Guinea (N1°11', E10°1'), a morphological semi-circular feature corresponding to an astrobleme can be recognized both on radar and thematic mapper imagery. It is located on the Congo Craton (Central Africa) with a diameter of 4,670 m. Since Neocomian faulting cross-cuts the circular feature, the impact of the astrobleme must be older than 145 Ma.
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2 (2), 219-225
Sm-Nd and Rb-Sr whole-rock data on gneisses from SW Nigeria are in agreement with the Late Archaean-Early Proterozoic crustal growth, with known geology and existing U-Pb and Rb-Sr ages. In contrast, similar gneisses from northern Nigeria yield consistent Archaean (TNd, TSr) model ages of 3.5 Gal, which are in agreement with U-Pb and Rb-Sr crystallisation ages from that region. The lack of Eburnean ages in northern Nigeria by the same radiochronologic methods calls into question the spatial significance of the Eburnean event and its tectonothermal importance vis-a-vis the widespread Late Proterozoic Pan-African orogeny. The U-Pb zircon ages of 2.5-2.4 Ga on grey gneisses from northern and SW Nigeria are in agreement with Sm-Nd and Rb-Sr data presented herein and suggest a distinct crustal initiation event with significant crustal growth at the Archaean-Proterozoic boundary. This event is correlated with the development of the Birrimian system on the West African craton.
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2 (2), 227-245
In the Uwaynat region, there are hundreds of volcanic plugs, dykes and lava flows, ranging in composition from carbonatites to olivine mela-nephelinites, alkali-basalts and minor phonolites and trachytes. Olivine mela-nephelinites, basanites and alkali basalts are the most abundant rock types. These rocks are from ring complexes and mafic plugs located between the Uwaynat Inlier and the Al Kufrah basin, in the Libyan desert. These volcanic rocks range from 28.2 to 26.7 Ma in age. Olivine mela-nephelinites and basanites are characterised by extremely high titania (up to 6 wt.%) and incompatible trace elements contents. Minor ferro-carbonatites are also present and they are also characterised by high content of titania and related high field strength elements and higher content in incompatible trace and rare earth elements than olivine mela-nephelinites and basanites. No large variations in the initial Sr and Nd isotope compositions are observed. This may suggest none or very little contribution of crustal rocks-magma interaction. A similar isotopic signature for the source of olivine mela-nephelinites and ferro-carbonatites is inferred. Olivine mela-nephelinites and basanites are not genetically related to each other by fractionation but they represent primitive magmas generated by different degrees of partial melting of a metasomatised upper mantle source. Incompatible trace elements in olivine mela-nephelinites may be modelled with small degrees of partial melting of such a source. Close relationships are also observed with the slightly older volcanic rocks from Gilf Gebir (SW Egypt), suggesting that Uwaynat magmatism is possibly related to a northeastward migration of the African plate above an intracontinental hot spot.
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2 (2), 247-265
During and after the very wet 1991/1992 winter experienced in Jordan, significant slope failures occurred along several sections of the new Irbid-Amman Highway in Jordan. The topography over most of the route is hilly, and significant amounts of cut and fill were used to construct the highway. Many of the failures appeared to display classic, rotational slip geometries which are typical of failures in soil and fill profiles. One such slope instability is an embankment foundation failure that lies at km 40+700 on the highway south of Jerash City. This paper deals with the overall stability of the slope at km 40+700. It presents the geological and geotechnical studies carried out at this site, identifies the causes and mechanism of instability, and presents appropriate remedial measures. Also, slope stability back analysis was carried out for the slope to assess the conditions at time of failure, and estimate most representative shear strength parameters of foundation materials. Slope stability analysis was also carried out for proposed remedies, using the computer programme STAB5M (Siegel, 1975). As Jordan is an earthquake prone area, probabilistic seismic hazard analysis was carried out for the landslide site using the computer programme FRISK (McGuire, 1978). A Peak Ground Acceleration (PGA) value of 0.2 g was estimated for design. This corresponds to a 90% probability of not occurring in a 50-year-design life of the highway. Dynamic slope stability analysis was also carried out. The study concluded that the landslide movement occurred within the foundation colluvium material. It resulted primarily from the excessive load of the embankment and excess piezometric pressures generated within the slope. Most representative shear strength parameters of colluvium materials at time of failure were found to be residual values: cohesion c' = 0 and angle of friction φ' = 20.0. The most feasible remedial measure to stabilize the area was partial removal of existing embankment, and reconstruction using imported rockfill of a split level embankment. Also, a surface and subsurface drainage system was recommended at the site.
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2 (2), 267-278
The geological surroundings of the horst of N'diass during the Campano-Maastrichtian period was a detrital platform oscillating between the upper limit of the littoral one to the down limit of the middle one, under subtropical climate. It was locally affected diverging subtidal chenals. The detrital material come from an uniform sedimentary stock which has suffered several phases of abrasion. The campano-maastrichtian sea level variation upon which depend the conditions of transportation and sedimentation determines the textural and mineralogical characteristics of sediments and their space and temporal distribution inside the platform.
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2 (2), 279-310
The micromammal fauna from the Neogene continental deposits of Aït Kandoula basin have been studied. 23 species distributed among 10 genera of rodents are found in seven fossiliferous localities. The localities extend from Middle Miocene to Late Pliocene. The Western basin has yielded a new fauna of middle Astaracian age, situated below breccia, which allows us to identify and precisely date one of the Atlas orogenic phases. The basin is subdivided into two subbasins, Oued Tabia to the West and the other to the East named "new village". The gradation occurred from W to E, the mean sedimentation rate was estimated to correspond to about 130 m/Ma. The sedimentation series in the basin is syntectonic. The periods corresponding to a lacustrine or marshy sedimentation could have corresponded to relative periods of low tectonic activity. They contrast with periods of high detritic sedimentation, which attest to an orogenic pulse. Palaeomagnetic analysis permit to give to the Oued Tabia locality an age of 10.9 Ma. The Argon/Argon dating of a volcanic ash layer from the eastern basin indicates an age of 5.9±0.5 Ma. The two western European species of micromammals discovered beneath that ash level indicate that transmediterranean terrestrial faunal exchanges occurred before the Messinian crisis and are therefore not directly related to that event.
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2 (2), 311-321
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports,, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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2 (3/4), VII-VIII
This volume on climatic changes and sedimentary records during the Quaternary in the central part of the Sahel (Niger and Chad Republics) is the product of two complementary methods of investigation. One approach is to start with the past and move towards the present as was exemplified by the IGCP-IUGS project 210 on the continental sediments in Africa (C. A. Kogbe, J. Lang, E. Klitzsch, 1983-1989) applying the principles of stratigraphy, sedimentology and geochemistry to investigate the "Continental Terminal" in Africa. - The second approach is to move from the present to the past as exemplified by the PALHYDAF - INSU project (J.Ch. Fontes and F. Gasse) which involved the study of recent geodynamics. Analysis of climatic evolution with time is based on phenomena resulting from breaks in the equilibrium of a system dominated by energy exchanges. These breaks produce effects (particularly with regards to temperature and humidity) the intensity and duration of which are important with regards to the capacity for record preservation. The analysis is made from geosystems that are best adapted to sedimentary records that reveal climatic changes once their functions are understood (research of CNRS Unite 157, J. Chaline and B. David). The approach is centered around three important questions: - which climatic phenomena were precisely recorded and what is the role of the sedimentary environment in these records? - what degree of confidence and precision should be attributed to a poorly preserved original record? - which stratigraphic events can be reconstituted from sedimentary records and subsequently, - what are the controlling roles of local and global factors on the recorded events? For recent periods, it is possible to recognise slight climatic anomalies of no stratigraphic importance; important climatic crises of global importance, and a chronologic reference (eolian sand dynamics; variation in the lake levels; palaeolandscapes etc). The classical question of autochtony and allochtony in analysis of different sedimentary facies (bauxites, carbonates, coal etc) should also be relevant to eolian sands. In order to evaluate the real importance of eolian sands at different periods of the late Quaternary with regards to the culmulative character of wind actions, it is important and relevant to initially define the inherited component from preceding times. The Kanemian (20,000-12,000 years 14C BP) will no longer appear to be a long period of aridity of more than 10,000 years but will be recognised as a succession of several periods of which some are even more humid than present times. Another important question relates to the differentiation of lacustrine and palustrine facies. The palaeolake Megachad of 6000 years ago characterising a very humid period could very well have been the juxtaposition of many palustrine and lacustrine entities. This will tend to contest the existence of large deltas and a vaste "peri-lacustrine ridge" with an altitude of 325 m. The "peri-lacustrine ridge" would have a structural, fluviatile or eolian origin and did not result from major fluctuations in the level of the lake. In other words, emphasis should be on the predominance of eolian and alluvial conditions within an unstable structural setting rather than the lacustrine deposits representing marker horizons within a stable structural setting.
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2 (3/4), 323-614
The study areas lie in the heartland of Africa, in the Republics of Niger and Chad which range approximately from 0° - 24° East and 8° - 23° North. These areas are part of two major hydrological, geomorphological and geological systems: the Chad Basin in the East (by reference to Lake Chad) and the Iullemmeden Basin in the West (by reference to the Touareg community in its centre). Instead of this latter relatively recent name (Racier, 1959), we shall refer to the "Eastern Basin of Middle Niger" (Chudeau, 1910). The Middle-Niger stretches from the outlet of the Inland Niger Delta in Mali to northern Nigeria (ORSTOM, 1970). The eastern part of this basin includes all those areas potentially drained by the Niger's left-bank tributaries in Niger. It also includes the River Sokoto of which half the catchment area is in Nigeria. At the time I first undertook this study, earlier works had reached three main conclusions: - The surface area of Lake Chad, recently some 24 000 Km² for an average depth of 4 m, had attained more than 330 000 Km² during the Holocene with depths in excess of 160 m locally: Lake Megachad. - The period from approximately 20 000 to 12 000 years 14C BP in the Sahel had been hyperarid: the Kanemian. The Sahara had spread significantly during this period and aeolian sands had been deposited as South away as the present day Sudanian zone. - Winter rains, now exceptional in the Sahel, and directly related to the advection of polar air masses, were allegedly major features at several times during the Late Quaternary. Now my early sedimentological field work in the Chari "deltas" revealed neither traces of an "inland sea" nor any record of "hyperarid periods", but fluctuations apparently comparable with those observed since the turn of the century. Nor was there any indication of advections of polar air masses. What could be more unsettling for a fledgling researcher than to quickly reach conclusions radically opposed to those of his seniors, or to have to admit his failure to understand. The organisation of this work retraces the course followed in responding to this challenge and in reviewing these issues from zero, this time with the necessary tools. An understanding of the present-day model is basic to this process. Therefore, after defining the geographical and geological framework of the study, we shall briefly introduce the concepts and facts concerning the climate and the present-day environment. The following chapters reflect this determination to take a fresh look at two major questions. Hyperaridity, deduced primarily from the occurrence of identical facies (azoic sands) and the extent of gaps in the sedimentary records, seemed to be essentially a problem of methodology and stratigraphy, viz. how can aridity be quantified and dated, how can aridity and aeolian phenomena be related? In fact, in order to judge the true significance of aeolian sands at various times in the late Quaternary, given the cumulative character of aeolian processes, we first had to specify to what extent they were the legacy of earlier periods. The question of what criteria could be used for recognising aridity was all the more prominent as in recent decades situations heretofore unobserved have occurred, ascribed to hyperaridity in keeping with the criteria used in earlier works: drying up of Lake Chad, almost complete interruption of flow of the Chari and the Niger, formation of a new erg (sand sea) near Timbuktu, etc. By contrast, the problem of the Holocene Megachad characterising a very humid period proved to be of a completely different order. Evidence of Megachad deposits and their age was not convincing. The hypothesis of neotectonic phenomena, however, seemed an interesting lead. The neotectonics hypothesis was not new in Chad, but the slow growth of the Megachad hypothesis over 150 years had gradually led to formal opposition to any suggestion of recent movement. Beyond the geological facts, the historical and conceptual aspects were surely important points to be verified. These different topics will therefore be covered on the basis of those geosystems beatable to provide sedimentary records that can account for the climatic dynamics once we have understood how they work. The presentation of analytical questions is kept to the strict minimum required for supporting the interpretations proposed. A description of the 100 sections made and the 1600 samples that, inter alia, were systematically subjected to grain size analysis would have burdened the work without adding anything. Moreover, upon analysis many sections taken from wells turned out to be composed entirely of uniform sands and so of no interest here. On the other hand, most of the 800 mineral and chemical analyses (heavy minerals, carbonate contents, X ray diffractometry, organic matter, radiocarbon, k13C and k18O) and most of the 200 palaeobiological analyses (pollen, diatoms and molluscs) are set out in the report where necessary. Some findings have been presented more exhaustively either in earlier publications (e.g. Durand, 1978 or Durand et al., 1984) or as part of a different area of research by the co-worker in charge of the analyses (Lesieur, 1982; Icole et al., 1983; Gasse, 1987b). A few dozen analyses only have not been presented. As, for instance, the pollen analyses by E. Schulz and C. Caratini, in view of the lack of significant results because of the extreme paucity of the samples. This is also the case of quartz surface textures analysed in conjunction with I. Zimmerlin and P. Hommeril, but here because the results were not relevant to the objective pursued. These sands have been subjected to alternating arid and humid conditions for sometimes more than one million years. Accordingly they are far too similar and cannot readily be interpreted in terms of palaeo-environmental and stratigraphic markers.
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2 (3/4), 615-626
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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2 (3/4), 627-639
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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3 (1), 1-16
Site-specific techniques of seismic hazard assessment suitable for large engineering projects, such as radioactive and toxic waste disposal sites, require a detailed knowledge of the geological structures that are active over the region under scrutiny. Neotectonic faults and other seismogenic structures were identified across South Africa by means of several techniques including seismic databases, Landsat, SEASAT, and GEOSAT satellite imagery, aerial photography and detailed field mapping. On-shore neotectonic activity is currently taking place in the southwestern Cape, in Namaqualand, and over a broad area extending from the Free State to the Northern Transvaal and to Natal. Neotectonic activity in southern Africa is analyzed in terms of known stress fields. NW-SE trending maximum horizontal compression directions (SHmax) developed from southern Angola to the offshore Transkei basin are defined as the Wegener stress anomaly (WSA). The interaction between the WSA and the other stress fields acting on the African plate (linked to ridge-push, and to the southern propagation of the African Rift) causes neotectonic faults and intraplate seismicity, possibly including some of the largest events experienced in the South African mines. Neotectonic activity could also constrain the long-term performance of waste disposal facilities.
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3 (1), 17-30
Following intensive regional and site investigations, the National Radioactive Waste Disposal Facility for intermediate- to low-level radioactive waste was established at Vaalputs in Bushmanland. The investigations were applied to study the rocks as a natural analogue to waste disposal. The more important radionuclides present in the waste are 60Co, 90Sr, 137Cs and 134Cs, while some 238U may also be present. The geological investigations led to the identification of an arenaceous and argillaceous surficial succession overlying a crystalline basement, comprising mainly granitic gneiss. Clay minerals derived from the hydrolysis of basement rocks constitute the major components of the surficial rocks, and are important in the concentration of certain elements through ion-exchange reactions. It is concluded that eight major processes have been operating h the geological environment at Vaalputs to give rise to the present distribution of elements. It is shown that mechanisms exist to significantly retard the mobility of elements, including the radionuclides present in the radio-active waste. The extent to which these elements are adsorbed and retarded are controlled by the physico-chemical conditions prevailing h the sedimentary environment. The approach adopted in this study may be applied to the selection of sites for other waste types. The geological integrity of the site may adequately compensate for the absence of other selection criteria.
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3 (1), 31-38
The general objective of a safety assessment is to estimate the impact of radioactive waste disposal on human and the surrounding environment The heterogeneity in the geosphere and biosphere, as well as the time scale of interest in safety assessments, introduce a lot of uncertainties into the process. One can distinguish two approaches to address uncertainties in predictive simulation: (1) deterministic simulation using sensitivity analysis, and (2) probabilistic simulation. In this paper a safety assessment methodology is proposed using probabilistic simulation. It is based on a revised decision-making model proposed by Freeze et al. (1990), taking into consideration geological, geohydrological, hydrological and repository parameters, in a Bayesian statistical framework. The application of the decision-making model in safety assessment can be described as a sequence of decisions between alternative safety assessment scenarios under conditions of uncertainty. It takes the cost and benefits of each alternative into account but give also weight to the associated risk, which are influenced by the uncertainty. Three models can be identified in the methodology: a decision model based on a risk-cost-benefit objective function, a predictive simulation model, and an uncertainty model. The iterative nature of decision analysis makes it particularly attractive for implementation into a safety assessment methodology. The proposed methodology can be divided into two stages. The first being the site characterization and problem formulation, and the second the implementation of the decision model.
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3 (1), 39-46
As specified in almost all permit conditions, some form of groundwater monitoring is required at waste disposal sites. Minimum requirements have been developed for this type of monitoring in order to ensure a co-ordinated and meaningful monitoring programme. These requirements are based on the BATNEEC principle. However, one of the real dangers of setting generalised monitoring requirements is that a "data rich - information poor" syndrome will result. Effective monitoring requires a systems approach which entails far more than merely sinking a borehole and grabbing a sample. A proper understanding of the prevailing site-specific geohydrological regime is required before valid monitoring results can be obtained. Two case studies are presented to illustrate the dangers of not adopting a systems approach and the need for a proper understanding of prevailing groundwater conditions. Both waste sites are located on primary aquifers, the dynamics of which are usually considered fairly easy to understand. In the first case, initial monitoring results showed that a garden and building rubble site had seemingly caused marked groundwater contamination to occur. More detailed investigation later showed that the contamination was in fact caused by other sources. In the second study, conflicting groundwater chemistry data was obtained from four boreholes. Full consideration of borehole position, geohydrological regime, borehole construction and sampling protocol was required to identify that a valuable aquifer, which had been developed for water-supply, was in fact in the process of being destroyed.
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3 (1), 47-52
The preservation of South Africa's groundwater resources is of critical importance if the future water demand of this country is to be satisfied. The impact that waste disposal sites have on these resources is an area of serious concern. A recently completed project, funded by the Water Research Commission, developed a systematic, physically based method to evaluate the suitability of existing or proposed sites as waste disposal facilities. The evaluation only considers geohydrological criteria Following the examination of over 29 methods used elsewhere in the world, a conceptual methodology was developed. Waste site permit application reports as well as field investigations performed at 10 waste sites throughout South Africa were used to quantify the method and ensure that it is valid, appropriate and accurate under South African conditions. The method comprises of three distinct but interrelated factors, namely the Threat Factor, the Barrier Factor and the Resource Factor. An individual score is assigned to each Factor and, by means of a nomogram, the Factor scores combined to obtain an index. The obtained index relates to the suitability of the site, based on geohydrological considerations only, for waste disposal activities.
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3 (1), 53-74
The mining sector plays a very important role in the sustenance and development of the economy of many African states. Foreign exchange earnings from export of mineral resources, increased government revenue from taxes, employment opportunities for nationals and provision of necessary infrastructures, are some of the major benefits that the mining industry has generated in the continent. Despite these benefits, serious environmental damages resulting from mining activities have been overlooked. The environmental assessment system during the mining project cycle consisting of identification, preparation, appraisal, implementation and post-evaluation phases is described in this paper in order to promote an effective environmental impact monitoring and management. Guidelines on environmental assessment during the pre-mining, operational and rehabilitation phases are outlined for small-, medium- and large-scale mining activities. The importance of adequate legislative measures to guarantee adherence to the environmental mining guidelines is emphasised and an environmental impact check-list and sensitivity index score sheet to facilitate impact assessment by supervising officials is provided. The paper concludes with annexes including internationally approved values for air and water pollutions as well as noise and vibrations recommended limits.
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3 (1), 75-82
Mining activities in Africa are closely associated with environmental degradation which should be avoided as far as possible. This objective can be attained if prior to implementation of the mining project, careful planning design and management guidelines are established. African countries must maintain a balance between the economic and environmental impacts of mining projects. Possible adverse effects of mining should be forecasted and mitigation measures established. Compensation for natural resources that will be affected by the project and rehabilitation of degraded land should be envisaged. Adequate funding should be set aside for post-mining re-habilitation process. Priority environmental issues to be considered should include, water and air pollution control, toxic and hazardous waste control, soil disposal control, tailing disposal control, deforestation, erosion, sediment control, visual impact and visible health hazards. Environmental monitoring should be facilitated by the establishment of a training programme for staff who can monitor and enforce standards and regulations effectively.
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3 (1), 83-96
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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3 (1), 97-156
PANGIS network, supported by UNESCO, ACCT and bilateral French and Belgium Cooperation is a pool of African and European documentation centers working in the field of African Geology, all using the same tool for micro-computerized information management and connected together for data supply, information exchange, training support and publishing. PANGIS is also a micro-computerized bibliographic database co-compiled by the 30 members of the network gathering about 35.000 references (both published and unpublished documents) with analytical descriptions of documents. The references listed below have been extracted from a printed bibliography published by CIFEG in 1994 called "Africa and Environment: A selective bibliography, 1990-1993" sponsored by the French Ministry of Foreign Affairs. The material in this bibliography is available in the libraries mentioned at the end of each reference or at the library of CIFEG (see address above, CIFEG being the coordinating center of PANGIS). Global changes: climatic and human influences. African regions. African countries. Water Management: Quantity, quality. Natural hazards. Surface and underground planning.
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3 (2), 157-174
Diamonds were discovered in the aeolian system of the Namib Desert on the west coast of southern Africa in 1908. The economic significance of aeolian placers was later surpassed by the discovery of onshore marine diamond deposits from 1925 onwards. The onshore diamond deposits extending both onshore and offshore over some 600 Km of coastline represent the world's greatest secondary diamond deposit. The geological history of the marine deposits on the continental shelf off southwestern Africa is complex, involving the interaction of fluvial, marine and aeolian systems. The rock record of events is incomplete due to the extensive erosion of sequences by the marine and aeolian systems. Diamonds were introduced to the continental shelf via several river systems draining the interior of southern Africa. The offshore deposits contained in composite marine lag gravels are the product of repeated reworking of material on the continental shelf during numerous regressions and transgressions which are overprinted by events during the last glacial maximum. The formation of the offshore deposits has largely been controlled by marine coastal and nearshore processes, but in Namibia aeolian processes reworked palaeoshorelines whilst they were subaerially exposed during regression(s). This enabled the high-energy, unidirectional aeolian system operating within the narrow, coastally located deflation basin to transport diamonds up the continental shelf, resulting in the formation of aeolian diamond placers. Offshore shallow-water marine mining commenced in the early 1960s. Deep-water exploration to the edge of the continental shelf {200 m below sea-level (mbsl.)} was initiated in 1971. De Beers Marine (Pty) Ltd. is currently the world's deepest-water mining operation, and produced some 400 000 carats during 1994. This is more than double the entire shallow-water production. The success of the deep-water mining operation has led to widespread deep-water exploration activity by numerous companies.
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3 (2), 175-189
The diamond production figures and geological framework of the main alluvial diamond deposits in South Africa occurring above the escarpment, are reviewed. The oldest post-Gondwana deposits are Late Cretaceous in age and have been subjected to deep chemical weathering processes. Younger deposits are of Miocene, Plio-Pleistocene and Late Pleistocene/Holocene age and can all be mineralised to some degree. The older terraces, particularly along the Vaal and Orange Rivers which are characterised by terrace-stepped development, have historically been the more economic deposits. Concentration of diamonds has occurred close to, but off, the horizontally-bedded sediments of the Karoo Supergroup and, with the exception of three isolated small deposits, most alluvial diamond deposits are found along the north-western rim of the Karoo basin. This can be explained by preferred trapsites as a result of bedrock competence and coarse matrix, the latter derived from weathering of the basal Karoo tillites and exfoliated, Ventersdorp lava bedrock. However, despite the presence of these trapsites, less than 1% of the diamonds eroded from known kimberlites during Late Mesozoic and Tertiary degradation have been captured within these alluvial systems.
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3 (2), 191-201
Group II kimberlite dyke complexes have proved to be viable diamond deposits in certain cases in South Africa. They persist to depths greater than current mining levels (-600 metres) showing no evidence of grade depletion. Typically not all the dykes in an individual swarm will be viable to mine and some may even be completely barren of any mantle minerals. Closely related dykes and different parts of the same dyke can contain widely differing samples of mantle minerals as well as different diamond grades. In the case of Helam Mine, grade variations are routinely monitored by reference to these variations. A barren dyke at Helam is completely devoid of high pressure (upper mantle) phases.
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3 (2), 203-216
Comparison of chemical compositions of chromite macrocrysts (390 grains) and chromites in mantle-derived xenoliths and xenocryst assemblages (78 samples) from diamond-bearing kimberlites in southern African kimberlites reveals that virtually all chromite macrocrysts are xenocrysts derived by disaggregation of mantle peridotites. Ti-rich chromites (up to 4.0 wt% TiO2), previously interpreted as early formed phenocrysts in Group II kimberlite magmas, are abundant as macrocrysts at Kamfersdam and Bultfontein Group I kimberlites in Kimberley, South Africa, where essentially complete compositional overlap exists between macrocrysts and chromites in garnet-bearing and garnet-free mantle assemblages. Garnet-free peridotites may be the dominant source of low-Al (< 6 wt% Al2O3) and high Al2O3 (> 15 wt% Al2O3) chromite macrocrysts. Comparison of chromite xenocryst populations with chromites included in diamonds from Finsch, Bultfontein and Roberts Victor (South Africa) and Orapa (Botswana) reveals little to no compositional overlap between included chromites and xenocrysts. The lower Cr2O3 and MgO of the xenocryst populations indicates substantial post-diamond formation chemical reequilibration in the open system of peridotite outside of the diamond armoring. Similar core to rim decreases in MgO and Cr2O3 in chromites intergrown with garnet xenocrysts is suggestive of generally operating processes producing low Cr/Mg chromites, likely cooling and/or uplift. The high Cr-Mg "diamond inclusion chromite field" may not be a realistic target in diamond exploration programs due to post-diamond reequilibration of unarmored chromites in peridotites.
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3 (2), 217-230
Located in two main areas, the alluvial diamond deposits in the Central Africa Republic (C.A.R.) are in spatial relationship with two detrital Mesozoic formations, the Carnot Formation in the west and the Mouka-Ouadda Formation in the east. These two fluvial formations act as the diamond host rocks. The origin and history of the diamonds are discussed on the basis of sedimentological data and knowledge about diamond geology in Central Africa. The primary diamond sources probably date from the Kibarian age. Located in the northern Congo and Zaire, they belong to the diamond fields of the Congo and Gabon which extend towards the San Francisco craton in Brazil.
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3 (2), 231-246
The Kéniéba diamond province in Mali was discovered only a few decades ago, although the region has been known to contain gold deposits exploited by small-scale miners since centuries. The geology consists of rocks of Palaeoproterozoic age overlain in the east by sub-horizontal sandstones of Upper Proterozoic age. The presence of diamonds in Late Quaternary palaeoplacers was revealed by local small-scale miners. A study of associated minerals and airborne magnetometric investigations, backed-up by field investigations, confirmed the presence of about 20 kimberlite bodies arranged in a step-like form with occasional scattered relic craters within the Birrimian or Upper Proterozoic. The distribution of the kimberlite bodies seem to be regionally controlled by SSW-NNE lineaments and locally controlled by a system of N105°-115°E fractures. Ilmenite and chromite are the most frequent minerals; garnet is rare, but diamond is present. This kimberlitic magmatism could also be of probable Lower Cretaceous age but the diamond characteristics suggest the contributory role of a Proterozoic kimberlitic magmatism towards the mineralisation of detritic Birrimian facies. Geomorphologic studies of the Quaternary reveal a probable extension of the palaeoplacers.
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3 (2), 247-260
This brief review of the occurrences of diamonds in the republic of Zaïre, provides basic information on the successive historical milestones marking the geological research and exploration that constitute the basis of the discovery of the major diamond fields in Zaïre. The origin of most of the deposits is associated with kimberlite satellites situated further south in the republic of Angola. The direction of transport of the depositional current is from south to north as evidenced by the decrease in size and density of the diamond grains in alluvial beds and terraces.
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3 (2), 261-272
Ghanaian diamond deposits originate from two major diamond fields: the Bonsa and the Birim fields. The Bonsa diamonds occur in Early Proterozoic Tarkwaian fluvial sediments known as the Kawere and Banket conglomerates. The Birim field is underlain by Birimian rocks which consist of nearly vertical grey, blue and black phyllites with interbedded tuffaceous greywackes and schists. There are occurrences of rocks of "ultramafic" composition (Junner et al., 1943). Superficial deposits are gravels, sands, clays, laterite and soils. The diamonds in the Bonsa have better grades (3 ct/m³, 15 stones/carat) but production in the Birim field exceeds that of the Bonsa field. The Birim field has produced over 50 million carats of diamonds from 1923 to the present. Sizes of diamonds vary from 4 mm to 0.5 mm and the average grade of the gravel ranges from 1.2 to 2.33 ct/m³. Field and analytical work has shown that what Junner et al., 1943 termed as ultramafic rocks in the Birim area are actually intensively hydrothermally altered and regionally metamorphosed kimberlitic rocks that have now become actinolite schists. The major and minor element chemistry fit well with kimberlite that is characterized by high concentrations of REE enriched in the light REE. The rock appears to be a composite of kimberlite and country rock as do other kimberlite intrusions. The name metakimberlite is therefore an appropriate term for the rock.
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3 (2), 273-293
A review of deposits in Tanzania is presented. The deposits like other similar deposits worldwide are characterised by their size, clarity, colour and shape. Tanzanian diamonds are of exceptionally high quality as exemplified by the world famous "Williamson pink" diamond. Statistics on size distribution from the Mwadui diamond mine over several years constitute the basis for predicting prices and experiments confirm that it is more satisfactory to use a single class boundary of -14 diamond screen mesh than to use the median value ranging between -17 + 3. Valuation of diamonds from five different locations are presented and it is demonstrated that diamond categories and value vary from one location to the other and from type to type.
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3 (2), 295-316
Graphite aggregates occur as octahedra and other forms of cubic symmetry within garnet pyroxenites in the Beni Bousera orogenic peridotite massif, N. Morocco. These aggregates have been interpreted as graphitised diamonds and their occurrence, together with a similar one at Ronda, S. Spain, is evidence that diamonds can form in the mantle away from cratons, possibly by recycling of crustal carbon via subduction zones. The tectonic setting of the Beni Bousera massif is clearly different to African diamond occurrences with obvious kimberlite parentage. This difference is also evident in the chemistry and age of the associated peridotites. The graphitic garnet pyroxenites at Beni Bousera bear some resemblance to eclogite xenoliths found in kimberlite pipes that commonly host diamonds. Subtle mineral chemical differences exist between these two rock types that may ultimately reflect fundamental differences in petrogenesis. However, the crustal isotopic signatures observed in some Beni Bousera pyroxenites and eclogite xenoliths in kimberlites imply that members of both suites may ultimately originate from subducted oceanic crustal protoliths plus sediment-derived material. Consideration of the physics of diamond graphitisation, the apparent absence of any remnant, ungraphitised diamonds, together with the thermal history of the Beni Bousera and other orogenic peridotite massifs suggests that diamond survival during emplacement is unlikely in similar massifs. If, as seems likely, many so-called "anomalous" diamond occurrences in continental collision zones originate from tectonically emplaced mantle fragments, their pressure-temperature-time trajectories must have been very different from that experienced by the Beni Bousera massif. However, the occurrence of graphitised diamonds within the pyroxenites at Beni Bousera provides new constrains on regional tectonic models and provides an important insight into diamond genesis in a non-cratonic setting.
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3 (2), 317-329
The River Sarabaya, a headwater tributary of the Niger drainage basin in SE Guinea, is diamondiferous throughout its length. Diamond is preferentially concentrated in fluviatile gravels found on the northern flanks of the valley as well as underlying low terraces and gravels associated with flood plains in the valley bottom. The valley has evolved under a long-term tectonic movement such that it has migrated progressively southwards. There has been a relatively recent increase in valley incision, possibly due to Quaternary climatic change, and the valley-bottom gravels contain higher concentrations of diamonds than those along the northern valley slopes. The Sarabaya has a unique population of diamonds which are thought to have been derived from local kimberlite dykes within its drainage basin.
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3 (2), 331-342
PANGIS network, supported by UNESCO, ACCT and bilateral French and Belgium cooperation since 1989, is a pool of African and European documentation centers working in the field of African Geology, all using the same tools for micro-computerized information management and connected together for data supply, information exchange, training support and publishing. PANGIS is also a micro-computerized bibliographic database co-compiled by the 31 members (11 new members in 1995) of the network gathering about 30.000 references (both published and unpublished documents) with analytical descriptions of documents. The material in this bibliography on Diamonds is available in the libraries mentioned at the end of each reference or at the library of CIFEG (see address above); CIFEG being the coordinating center of PANGIS.
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3 (2), 343-354
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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3 (3/4), 355-366
The Pan-African terrain of Eritrea has been known for its gold potential since at least the 17th century AD. However, over thirty years of warfare precluded the systematic geological investigations that relate mineralization with either tectonics or rock types so as to guide exploration programs. In an attempt to contribute to the solution of this problem, the available geological data have been assessed and integrated with new field observations. The Precambrian rocks of Eritrea consist of two major terrains. These are the Gneiss Terrain and the Metavolcano-Sedimentary-Ophiolite Assemblage intruded by calc-alkaline syn-, to post-tectonic granitoids. The nature and orientation of mesoscale gold-bearing quartz veins relates to regional scale N-S/NNE-SSW and NW-SE trending ductile to brittle-ductile Pan-African strike-slip shear zones. Two mineralized zones, the Ugaro and the Asmara zones are broadly located, respectively, within the releasing bends or transtensional sites in the major shear zones. This indicates that the vein-type hydrothermal gold and associated mineralization of Eritrea is largely tectonically controlled. Fluids accompanying late Pan-African and/or Tertiary granitization might have also played a role in concentrating and redistributing earlier mineralization.
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3 (3/4), 367-384
Based on extensive field and literature surveys together with radiometric dating evidence, the coastal geology of Kenya consists of the Karoo (Upper Carboniferous-Lower Jurassic) to Recent sedimentary sequences with minor local intrusions of igneous rocks of post-Jurassic age. The oldest sedimentary rocks found in coastal Kenya belong to the Karoo sequence and are exposed in the Mombasa coastal basin. In East Africa, the Karoo grabens were initiated by passive extensional regimes with normal-fault displacements being the extensional mechanism. In coastal Kenya, the Karoo graben was initiated in the Early Permian with the possible existence of pre-rift tillitic Dwyka equivalent sediments of Late Carboniferous sediments. The extensional regime of coastal Karoo basin terminated in the Jurassic when the basin was tectonically sealed off by the Late Jurassic faults which heralded the drifting away of Madagascar from the African continent. The Karoo basin is elongated in a broadly north-south direction and has a basin-fill of approximately 6,500 - 7,000 m comprising alluvial, fluvial and lacustrine sequences. The Karoo sediments in coastal Kenya constitute the Duruma Group which is equivalent to the Karoo Supergroup seen elsewhere in East Africa and they crop out onshore west of Mombasa town parallel to the coastline. The western boundary of the coastal Karoo basin is relatively more complex than the eastern margin, with both faulted and unconformable contact with the basement, which is of the Precambrian Mozambique Belt. The eastern margin of the basin is broadly defined by the post-Karoo Middle Jurassic marine limestones of the Kambe Formation. The limestone has both faulted and unconformable relationships with the underlying Duruma Group. The rest of the post-Karoo sediments are mainly prograding marginal to deep marine and shoreline sequences deposited in cycles separated by well-defined tectonic phases. The uplift of the eastern shoulders of the Tertiary East African Rift during the Pliocene led to downwarping of the Kenya coastal region resulting in the deposition of fluviatile sediments of the Marafa Formation. The coastal area emerged later in the Late Pliocene to Early Pleistocene, at which time dune sands of the Magarini Formation and other lagoonal sands were deposited. In the Quaternary period, coastal Kenya was the deposition of dune and lagoonal sands, and the growth of coral limestone, intercalated with continentally derived fluvial channel sands.
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3 (3/4), 385-393
A pedostratigraphic succession, consisting of a modem surface soil and two buried paleosols, was analyzed to determine if D/L (Dextrorotatory/Levorotatory) ratios of amino acids are useful for relative age determinations. The site, located in the Hagenia woodland of the Virunga Mountains at approximately 3000 m a.s.l., is considered representative of transported and residual regolith weathered during the late Pleistocene and Holocene. D/L ratios of aspartic acid and alanine from paleosols in this profile indicate relatively slow racemization rates that provide useful relative age controls. The variations in ratios for valine, leucine and glutamic acid were less but still useful in relative age determination. Valine and glutamic acid, which are known to behave erratically in tropical forest soils on Mt. Kenya, were not detected in the youngest soil, and show relatively low concentrations in the lower and older profiles. Phenylalanine was not detected in the Virunga soil and paleosols, and its absence is taken to indicate minimal aeolian contamination. When combined with other relative age indicators, such as stratigraphic position, strength of development and percent clay, amino acid D/L ratios for aspartic acid assist in refining age controls on buried paleosols. This is particularly true with older paleosols for which 14C ages are not available. Based on the data for aspartic acid, there is a considerable difference in age between the lower and upper buried paleosols, which are considered to separate LGM (Last Glacial Maximum) and Kalambo Interstade sediments from pre-LGM sediments.
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3 (3/4), 395-405
Three Mesozoic to Recent phases of distensive stress are observed in the Archaean Congo Craton of Continental Equatorial Guinea: a Neocomian phase with stress oriented N035E strike developed the Eastern Gabon Basin; an Albian phase oriented N120E developed the Douala Basin; and a Miocene to Recent phase oriented N-S developed the Uoro Rift Basin by oblique extension, and associated half-graben basins system formed along E-W faults dipping south. This third phase created the Uoro Rift; the associated half-graben basins are described for the first time in this paper. The Archaean foliation of the basal cratonic complex presents three prevailing strikes: N125E, N030E and N050E which coincide respectively with the strikes of the Eastern Gabon Basin, Douala Basin and Uoro Rift. With the exception of the half-graben system of the third phase, all the structures generated in the three Mesozoic-to-Recent extensional phases were controlled by the Archaean foliation.
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3 (3/4), 407-411
An area with several ductile faults of various importance has been recognized in the western part of Côte d'Ivoire. These accidents affect both Archaean rocks and formations of the transitional zone between Palaeoproterozoic and Archaean. They form a major South-North 2.1 Ga transpression structure.
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3 (3/4), 413-427
The Takoradi Shale Formation of the Sekondian Group (Late Ordovician to Early Cretaceous age) outcrops mainly along the coastal area of the Sekondi-Takoradi city in the Western Region of Ghana with an estimated thickness of 200 m. The formation has been dated as Devonian or Early Carboniferous age by various workers. The present study records a well preserved plant microfossil assemblage from the formation outcropping at Essipon beach. The miospore assemblages are assigned to three biozones namely Retispora lepidophya - Indotriradires explanatus (LE), Retispora lepidophyta - Verrucosusporites nitidus (LN) and Vallatisporites verrucosus - Retusotriletes incohatus (VI) biozones of the miospore zonation scheme established for the Tournaisian rocks of southern Ireland, dated as Late Devonian (Strunian) to Early Carboniferous (Lower Tournasian) age. The Devonian/Carboniferous boundary has been located within this section of the formation. From a phytogeographic point of view, some species from the formation imply some floral links with Europe, North America, South America, North Africa and Australia in their Late Devonian-Early Carboniferous palynoflora.
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3 (3/4), 429-437
Geochemistry of fluoride in Lake Natron is studied to elucidate processes controlling fluoride concentration and removal during brine evaporation. The range of fluoride concentrations (0.0004-2.75 g/l) in brines from Lake Natron is the greatest found anywhere. So fluoride ion increases by evaporation until saturation with respect to kogarkoïte is attained. Kogarkoïte Na3SO4F occurs in relatively considerable amounts about 4.5% in salt crust of Lake Natron. It has been identified by X-ray diffraction and scanning electron microscopy and it is the first occurrence recognized in the recent evaporitic deposits. The presence of the kogarkoïte salt can explain the behaviour of fluoride element in alkaline brines by evaporation.
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3 (3/4), 439-449
Results from a core sample (435) and grab samples 717 and 722 collected from the southern end of Lake Malawi indicate that rephosphatisation of bones from fish is taking place both at the sediment/water interface and below this interface. X-ray diffraction (XRD) and scanning electron microscope and electron microprobe (SEM/microprobe) results show that carbonate fluorapatite {Ca10(PO4)5(CO3)F.5(OH)} and carbonate hydroxyapatite Ca10(PO4)5(CO3)3(OH)2 at about 5% and 10% respectively are the dominant authigenic minerals at the sediment/water interface. These phosphatic minerals occur either in massive and microcrystalline forms coating clays or as endocasts of fish bone. Vivianite {Fe3 (PO4).8H2O), which occurs in both fibrous and rosette forms, is the dominant phosphate mineral at 7 cm beneath the sediment/water interface in core 435. Results from the two grab samples indicate a richness in biogenic material including fish bone, faecal pellets, molluscan shells, plant debris, fragmentary diatom frustules and arthropod exoskeletons while minerals include quartz, feldspars and clays. Several controls appear to be responsible for the formation of the phosphate minerals encountered in the present study which include: the presence of fish bone concentrates; prevalence of oxic or anoxic sedimentary environment; availability of crucial ions such as iron, bicarbonate and fluoride; and persistent mild alkaline water solution.
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3 (3/4), 451-459
In general the geologic formations of the crystalline basement of northern Côte d'Ivoire are unproductive because they have little or no primary porosity. They are useful aquifers only when a sufficient depth of weathered bedrock exists, or in some cases, in areas with intense open fracturing. A structural and geomorphological approach based on photo-interpretation is used to obtain a detailed description of the drainage networks and to observe fracture and lineament directions. The results show that fractures trending NE, NW and NS related to the Precambrian orogenesis of West Africa, are open fractures. Results also indicate that well productivity is only poorly related to geomorphological characteristics. The crossing of fractures can be used to suggest zones likely to provide high groundwater yields.
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3 (3/4), 461-470
The Ebrie lagoon system, a privileged place for human settlement (implantation) is a most extensive brackish environment in West Africa. It is composed of a central basin of 1 to 7 kilometres wide, orientated E-W and numerous arms or bay orientated N-S covering hundreds of square kilometres. This lagoon system which is the pride of the population of Abidjan is becoming asphyxiated by pollutants of diverse origins because of lack of adequate environmental protection policy. All urban effluents are thrown out into the lagoon without prior treatment causing severe consequences to both the ecosystem and the populations.
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3 (3/4), 471-484
Photogeological studies of the Younger Granites, in the North Eastern Desert of Egypt, between latitudes 27°00' and 28°40'N, using both aerial photographs and satellite images, revealed the separation of three successive phases of Younger Granites with different photogeological, radiometrical and geological characteristics. Photogeologically, the first phase plutons (YG1) are characterized by brown colour, dark tone, fine surface texture, low relief with gentle slopes, elongated ridges, large geomorphologic grains, and high density-dendritic to parallel-drainage patterns. They display high density and frequency of photo lineaments. The second phase plutons (YG2) are characterized by yellowish brown, light tone, moderate to coarse surface texture, moderate relief with deep slopes, elongated ridges, relatively smaller grains and moderate density trellis to dendritic-drainage patterns. Plutons of this phase display moderate density and frequency of photo lineaments. The third phase plutons (YG3) are distinguished by oval shapes, reddish brown colours, light white tone, smooth coarse surface texture, high relief with steep slopes and rounded peaks and low density dendritic to trellis-drainage patterns. They have low density and frequency of photo lineaments. Radiometrically, YG1 plutons display the lowest radioactivity (60-100 mR/h) while YG2 plutons display higher radioactivity (100-180 mR/h). YG3 plutons display radioactivity similar to the second phase but with anomalous zones with more than 180 mR/h. Petrographically, YG1 granites are composed of plagioclases (32.9%), K-feldspars (30.5%), quartz (26.6%), with 10% mafics (biotite & hornblende). Epidote, sphere, zircon and apatite are accessories. YG2 granites are usually composed of K-feldspars (39.5%), plagioclases (27.5%), quartz (26%) with average of 7% biotite. Accessories include allanite. Granites of YG3 phase are composed of K-feldspars (> 50%), quartz (30%), plagioclases (15%), with biotite and muscovite (< 5%).
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3 (3/4), 485-489
Groundwater borehole data as well as the results from Vertical Electrical Soundings were used to construct the contour maps of the elevation and depths of the groundwater rest level of Midwestern Nigeria, from latitude 5°15'N to latitude 7°30'N and from longitude 5°00'E to longitude 6°45'E.
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3 (3/4), 491-523
A compilation of the literature on the Cretaceous system in Nigeria is presented. A brief review of this work is included with accounts of particular importance being identified.
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3 (3/4), 525-535
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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3 (3/4), 537-549
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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4 (1), 1-138
As a follow up to two previous reference series on the inland continental basins of West Africa, the Iullemeden basin and the Chad basin, this issue is devoted to the geology of the Volta basin. This is a revised version of the DSc thesis of J.J. Drouet, carried out as part of the interuniversity cooperational programme between the University of Bourgogne in France and the University of Lomé in Togo. The basic geological framework of the Volta basin was studied by Affaton (1983) but the results presented in this issue represent the first detailed study of the sedimentary sequence of the basin. The absence of tectonism along the Togolese flank facilitated a detailed analysis of the sedimentary structures in spite of their Precambrian age. Although the Volta basin with a surface area of about 103,600 square kilometres is mostly situated in the Republic of Ghana, the results of the investigation carried out by Drouet along the Togolese flank are applicable to the entire basin as they represent the complete transversal section of the sequence. These impressive results include the detailed description of the sedimentary environments as well as the sedimentary and diagenetic processes. It is important to acknowledge the contributions of several reputable scholars to the successful completion of this study of the Volta basin and this special issue of the Africa Geoscience Review. Prof. Pierre Rat, Prof. (Mrs) M. Rat, Prof. J. Lang, Prof. L. Courel all of the University of Bourgogne, Dijon, France. Prof. F. Seddoh and Prof. P. Affaton of the University of Lomé kindly reviewed the manuscripts at different stages. It is obvious that the results published in this issue will stimulate further stratigraphic and tectonic investigations that will further increase our knowledge of this basin with its groundwater and possibly hydrocarbon-bearing potentials.


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4 (1), 139-151
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D., and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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4 (2), 153-175
A compilation of new gravity data for Southeastern Zaïre and published results for Zambia are presented. The Bouguer anomaly map reveals a large negative average of -140 mgal with a standard deviation of about 50 mgal. Referring to the Airy local compensation model, the relationship analysis between Bouguer anomaly and elevation shows that the crust in this region of Precambrian age is not in isostatic equilibrium. This interpretation seems to be unlikely, since the Katangan that is known as the last orogeny occurred in Late Proterozoic time. Combining data from Zaïre and Zambia with previous surveys in Western Malawi, Southern Kenya, Southwestern Tanzania, Burundi and Rwanda, a very low regional gravity anomaly of -140 mgal amplitude is defined. This regional negative anomaly with NE-SW axis, parallel to the trend of the known Upemba, Mwero, Luangwa and Lukusashi young rifts, cannot be explained by the properties of the crust but may result from a low-density upwelling asthenosphere, implying a model of thin lithosphere which is 123 Km thick. The classical incipient rifting southwestward from Lake Tanganyika and the recent uplift of topography with NE-SW axis may be due to this asthenospheric upwelling which is thought to begin during the Cenozoic rifting stage. The important consequence of the model, which is supported by structural, seismological and previous heat flow results, is that the main continental break-up of Africa south of 10°S may occur in the future through Southeastern Zaïre and Zambia rifting evolution dependent on the extent of the upwelling of the asthenosphere. A model of rifting evolution is proposed.
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4 (2), 177-283
The Central African Copperbelt of Zambia and the Democratic Republic of Congo (formerly Zaïre) is one of the great metallogenic provinces of Africa. It contains some of the largest and richest copper, cobalt and uranium deposits in the world. These deposits are hosted mainly by metasedimentary rocks of the Late Proterozoic Katangan Sequence. In addition to the Cu-Co and U deposits, there are also major deposits of Pb-Zn-Cu (± Ga, Ge) and Fe hosted by Katangan rocks. Other metals found in lesser abundance include Au, Ag, Pt, Pd, Mo, Se, Bi, V, Th and Ni. Metamorphism of the Katangan Sequence has given rise to deposits of talc and kyanite, while tropical weathering has produced many clay deposits. Katangan carbonate rocks, aside from being primary sources of agricultural and industrial lime, dolomite and gypsum, are also the major aquifers in Zambia and Katanga (formerly Shaba). The Katangan Sequence is thus the most economically important stratigraphic entity in Central Africa. It is found outcropping over an area stretching from the Haut Zambeze region of Eastern Angola, through the Lufilian Arc and Kundelungu Plateau of Katanga Province (formerly Shaba), Democratic Republic of Congo (ex-Zaïre), the Domes Region and the Copperbelt of Zambia, much of south-central Zambia, across the Mwembeshi Dislocation to the Zambezi belt of southern Zambia, and finally across the Zambezi rift to the Makuti Group of northwestern Zimbabwe. This comprehensive bibliography attempts to put together for the first time all the references dealing directly or indirectly with the geology and mineral resources of the Central African Copperbelt and the Katangan Sequence. The sources quoted include papers in scientific journals, popular (scientific and mining) publications, books, theses and dissertations (doctoral, master's and bachelor's), and conference abstracts, in a total of ten languages (English, French, Portuguese, Flemish, Dutch, German, Russian, Swedish, Italian and Japanese). Also included in the bibliography are unpublished reports of mining companies, Geological Survey Departments, universities, and other research institutions, which have been quoted in the published literature. Most of the unpublished reports dealing with the geology of the Katangan Copperbelt are available at the Bureau d'Etudes Géologiques, Gécamines, Likasi, Katanga, Democratic Republic of Congo, while unpublished reports dealing with the geology of the Zambian Copperbelt are available in the ZCCM Technical Services Library, Kalulushi, and in the library of the Zambian Geological Survey Department, Lusaka, Zambia. The bibliography aims at being exhaustively inclusive, and it spans the time range from 1830 (when the diary of Dr. José Maria Lacerda and Francisco João Pinto were published), to papers that were in the press in 1997. The diary of Lacerda and Pinto (1830) was the first published account of the mineral wealth of Katanga (especially copper), based on their 1798 expedition to the lands of Cazembe (south of present Lake Mweru, on the border between Katanga and Luapula Province of Zambia). The topics covered include geology, geophysics, geochemistry, geomorphology, soils, geobotany, remote sensing (aerial photography and satellite imagery), mineralogy, crystallography, stratigraphy, sedimentology, structural geology, tectonics, metamorphism, metallogeny, cartography, hydrology, palaeontology, geochronology, computerization, mineral economics, exploration, and the archaeology and history of the mines. Papers dealing with mining and metallurgy have also been included, if they have a bearing on geology or mineralogy. Papers dealing exclusively with technical aspects of mining and metallurgy (like ventilation, mechanical equipment, reagents, etc.) have been excluded. Many previous bibliographies on the geology of Zambia, Congo (Zaïre) and Angola have been consulted - these have also been referenced in the present bibliography. Some references are incomplete, because they are obtained from previous citations or bibliographies, or are in obscure publications (especially the early Belgian literature). [Annotations and editorial comments, such as this one, are given in square brackets]. During the period 1830 to 1997, which is covered by this bibliography, many name changes have occurred in Central Africa. The Democratic Republic of Congo (République Démocratique du Congo) is the re-instated name of the country that was known as Zaïre (1974-1997), and which was previously known as République Démocratique du Congo (or Congo-Leopoldville) (c.1961 -1974), and before that it was Congo Belge. In the 1890s and l900s it was known as the Congo Free State (État Libre du Congo, or Kongo Vrijstaat). The former Shaba Province of Congo (Zaïre) has reverted back to its old name of Katanga after the political upheavals of May 1997. In the 1880's, prior to Belgian occupation, Katanga was also known as Garenganze, and in some accounts, Catanga. In the Katangan copperbelt, the mining towns of Lubumbashi and Likasi were previously known as Élisabethville and Jadotville, respectively. The mines Kipushi and Musonoi were previously known as Mine Prince Léopold and Ruwe, respectively. Zambia was known as Northern Rhodesia before 1965. The Luanshya Mine was formerly known as Roan Antelope Mine. The Konkola Mine was known previously as Bancroft Mine. Zimbabwe was previously known as Rhodesia (1965-1980), and before that it was called Southern Rhodesia. Harare was previously called Salisbury (1893-1981). Some parallel uses are found, both in place names (Kirilabombwe/Chililabombwe), and in stratigraphic names (Mwashya/Mwashia). The Katangan Sequence has been variously referred to as the "Katangan", "Katangan Supergroup", "Katanga Supergroup", "Katanga Group", "Groupe du Katanga", "Supergroupe du Katanga", "Séquence du Katanga", "Katangienne", "Katanguienne", "Système du Katanga", "Katanga System", "Katangan System", "Systeem van de Katanga", etc. Because of the multinational and multilingual nature of this bibliography, users may find it helpful to have a basic vocabulary of key-words in several languages. These are listed below. Numerous other Late Proterozoic sequences of Central and Southwestern Africa have been correlated with the Katangan Sequence. These include the West Congolian sequences of Gabon, Congo, Bas Zaïre and NW Angola; the Lindian of Northern Congo (Zaïre); the Malagarasian of Burundi, the Bukoban of Tanzania, the Bushimay sequence of southern Kasai Province, Congo (Zaire); the Rushinga and associated sequences of the Zambezi Belt of NE Zimbabwe; and the Damara sequence of Namibia and Botswana. These correlated sequences were not deposited in the same basin as the Katangan Sequence, but were broadly contemporaneous with it. In some cases, e.g. Damara Belt of Namibia, Zambezi Belt of NE Zimbabwe, deformation and/or younger cover has obscured any connections these sequences may have had with the Katangan. For the benefit of any researcher who wishes to follow up on the correlative sequences to the Katangan, some key references are given in the following section, grouped by region.
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4 (2), 285-296
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community. Remarks, corrections and additions to the bibliography will be most welcome.
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4 (3/4), 297-324
The hydroclimatical situation of some sedimentary basins in Africa is reviewed and the importance of their fossil groundwater resources is emphasized. The geological and geomorphological framework of the basins are described with the peculiarities of the principal aquifers and their hydrogeology. The basement aquifers are discussed while those within the "Continental Intercalaire" (≈ Nubian sandstones) and the "Continental Terminal" are treated in greater detail because of their regional importance, covering large parts of the continent. The occurrence of complex hydraulic systems within some sedimentary basins is highlighted, as well as the preponderance of hydrothermal influences in certain areas. Water quality and reserves are discussed and it is recommended that experimental stations be established in all the basins in order to control the exploitation and improve the management of this often non-renewable resource.
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4 (3/4), 325-333
Shallow magnetic sources in the Upper Benue basin of Nigeria have been mapped in order to determine their structure, distribution and location at depth by employing techniques based on the Fourier analysis of aeromagnetic fields. Spectral depth determination to magnetic sources in the region yield two distinct magnetic depth ranges. Mean depth values in the range of 2.00 Km to 2.62 Km have been shown to correspond generally to the true basement surface, and indicates clearly the magnitude of the undulation of the basement topography in the region. Mean depths to shallower magnetic sources in the region vary between 0.07 Km to 0.63 Km, and may be attributed to shallow intrusive materials or some near-surface basement rocks. Some deeper intrusives occur within the basement at depths of up to 2.45 Km. The numerous shallow intrusions in the basin however occur substantially outside the basement. Depth results from the investigated blocks indicate that mean depths to the basement surface in the region show a gentle general southward increase with mean depth values ranging from 2.00 Km in the northern area to 2.62 Km in the south.
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4 (3/4), 335-342
The Quaternary glacial models for the Venezuelan Andes and Mount Kenya have many similarities. On Mount Kenya four pre-Würm/Wisconsinan glaciations have been identified and dated along with two Würm/Wisconsinan stades. There, the Last Glacial Maximum (LGM) ended about 15,000 yr BP; termination of the late glacial is less certain but was underway by 12,000 yr BP. In the Venezuelan Andes one pre-Würm/Wisconsinan glacial deposit has been identified and dates to ca. 300,000 TL yr. Two stades within the Würm/Wisconsinan are known from several catchments in Venezuela. The LGM is dated to 20,000 yr BP. The termination of the glacial-interglacial transition in both areas is considered to be ca. 10,000-12,000 yr BP.
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4 (3/4), 343-354
The water penury in the southern part of Morocco made it important to elaborate a mathematical model for an optimal groundwater management. This study covers the Turonian karstic of Errachidia-Boudnib basin. Geological, geophysical and well data enabled us to characterize the aquifer geometry and to define its physical limits. This aquifer spreads on more than 6700 Km², its thickness ranges from 40 to 150 m and it has the form of asymmetric synclinorium. By the mathematical model (Multic), the distribution of the hydraulic-heads in steady and/or non steady states, using the finite differences method, are calculated. Despite the considerable difficulties caused by the lack of data, the model permitted to reproduce the flow conditions and to adjust the hydrodynamic parameters which are: equivalent transmissivity: from 10(-1) to 10(-5) m²/s, storativity: from 5.10(-2) to 10(-4) and vertical permeability from 10(-6) … 10(-7) m/s. The model showed that the aquifer, submitted to an increasing exploitation, is more vulnerable in the west, whereas the central and oriental sectors, where the water-table is less fluctuating, constitute strategic groundwater reserves.
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4 (3/4), 355-360
The devaluation of the franc CFA has brought the governors of the countries affected to look for substitutes to imported products, mostly in the field of construction. The micro-concrete roofing tile is a material made basically with local raw materials (sand, broken granite, cement and oxide). The only imported component is the synthesised oxide, which gives the tiles a red colour. Its substitution by a local raw material will certainly reduce the cost prize of the final product. The partial substitution of the synthesized oxide by red sandy clay, a locally available raw material, improved the colour of the final product without changing its properties. We found that the substitution should not exceed 20% and that the red sandy clay actually gives a particular colour to the tiles which were formerly grey.
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4 (3/4), 361-371
The biostratigraphic analysis of Aptian-Albian successions of the Hameïma area allowed to distinguish three formations respectively dated Gargasian (Serdj), upper Gargasian to lower Clansayasian (Hameïma) and Clansayasian to Albian (Fahdene here studied). The taxonomy study and stratigraphic distribution of recognized Foraminiferal and Ostracode species in these deposits define more precise datings. On the paleoecological level, population study permitted to analyse with accuracy the repartition of the associations of Foraminifera and Ostracoda in function of the evolution of several types of paleoenvironments.
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4 (3/4), 373-380
Surface and subsurface studies realized in the Gafsa-Sidi Bonzid area enable us to point out the episodic activity of an old deep N120-140 fault corresponding to the Majoura-Mech tectonic trend. Outcrops of the Southern part of this system can be observed et the level of the Jebel Orbata and Jebel Bouhedma characteristic megastructures of the region. Its northward continuation corresponds in the sedimentary cover to positive flower structure in the Majoura area. This wrench fault system controls Mesozoic sedimentation inducing facies and thickness variations in the sequences as well as vertical and lateral subsidence inversions.
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4 (3/4), 381-393
The Upper Cretaceous Amman Formation and its stratigraphic equivalents are exposed in Jordan and adjacent areas. The formation consists of two subdivisions: a lower silicified limestone unit (30-100 m thick) and an upper phosphorite unit. The silicified limestone was deposited on a shallow carbonate platform along the fringes of the Tethyan seaway. Previous basinward studies have postulated a sill separating the open marine environment from the depositional site of the silicified limestone. If deposition occurred behind a sill, it must have been leaky because open marine waters are indicated by the faunal assemblage. The silica responsible for chertification of these and similar deposits has previously been attributed to four potential sources: silica-rich lakes, marine upwelling, fluvial input, and exhalation of subsurface fluids. The possibility of lacustrine sedimentation is negated by the great mass of silica present in this region (˜10(19)g SiO2), by the great regional extent of these deposits, by the lack of silica-rich rocks in the surrounding areas at the time of deposition, and by the dominance of marine fossils. The estimated average rate of silica deposition during the time of formation of these deposits (˜10(12)g SiO2/year) is comparable to the modern supply of silica by upwelling along the Chilean- Peruvian continental margin and to the fluvial input in modern Amazon subaqueous delta However, there is no sedimentologic or stratigraphic evidence of an Amazon-scale river having been present at the time of chert formation. Previous studies of the faunal assemblages within this unit reveal low diversity, presumably reflecting stressed conditions. Such stress is uncharacteristic of modern marine upwelling regimes. Moreover, the average ratio of chlorine/bromine in the chert is 30% smaller than the Cl/Br ratio in normal seawater. REE data reveal a slightly negative Ce anomaly which probably reflects the imprint left by carbonate and phosphate protoliths. Given this and previously published isotopic and tectonic data, the possibility of a deep-seated source of silicifying fluids merits consideration.
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4 (3/4), 395-403
The use of remote sensing by the numerical processing of satellite image over great Tunis bring up to delineate the regional lineamentary system. The joint analysis of outcrops and lineamentary data shows the coherence of results and their integration in the tectonic cutting out. The expression and distribution of lineaments to be proved link to neotectonic and tectonic significance. Recent tectonic activity of lineaments was detected from historic displacement of ancien hydrographic system. The epicenter distribution of historic and recent seismicity allowed to draw up a seismo-tectonic map of the area. This map proves the active character of some major lineaments and underline the real extent of earthquake risk zone.
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4 (3/4), 405-415
A new area of phosphate deposits is described. The study site is located SE of Irbid, Jordan and is a part of the Upper Cretaceous Amman Formation. The phosphate was apparently deposited in a shallow marine environment, ranging from low to high energy conditions. Chemical analysis shows signatures similar to those of other phosphates in Jordan. Cadmium concentrations are somewhat higher than other Jordanian phosphates.
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4 (3/4), 417-430
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community. Remarks, corrections and additions to the bibliography will be most welcome.
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4 (3/4), 431-450
Albo-Aptian lacustrine ostracodes have been studied in several intra-cratonic basins in West Africa and in Brazil: Bongor and Doba-Doseo in southern Chad, Harna-Koussou in northern Cameroon and Araripe in Northeast Brazil. As compared with the pre-salt series of the West African and Brazilian coastal basins of Barremian and older age, the ostracode faunas of these intra-cratonic basins are characterised by a clear domination of Cytheracean ostracodes with various species of Theriosynoecum, whereas the pre-salt series are clearly dominated by Cypridaceans (Cypridea, Sebastianites, Petrobrasia, Reconcavona...). The dominance of Limnocytherid Cytheraceans in these intra-cratonic lakes, as well as palynological, geochemical and sedimentological data support an interpretation of moderately alkaline lakes, in a hot climate with alternating humid an and seasons. Strong faunal similarities have been noticed especially between the late Aptian-early Albian faunas of the southern Chad basins and those of the lower member of the Santana Formation of same age of the Araripe Basin in Brazil, suggesting similar lake system. Of particular interest are the presence in both areas of Theriosynoecum silvai, as well as of a new species, Neuquenocypris berthoui n.sp. To be noticed is the presence in Chad of the genus Rosacythere, characteristic of south-European mid-Cretaceous lacustrine deposits, and of Metacypris polita and Frambocythere pustulosa, index species of the Albian of central Zaire. Relationships with Argentina are essentially expressed by the occurrence of the genera Neuquenocypris and Rayosoana.
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4 (3/4), 451-460
The Garoua E-W rift is the eastward extension in Northern Cameroon of the Benue trough which extends N50°E mainly in Nigeria. The Garoua rift is sprinkled with volcanic plugs and residual hills of sandstones showing intercalated clays. Lineament, dyke and fault orientations (N20°E, N70°E, N110°E; and N150°E) observed on aerial documents and on outcrops in the Garoua rift are consistent with those located in the neighbouring basement. This relationship underlines the control of pre-existing structures within the Precambrian basement on the genesis and development of this rift. Thick sequences of conglomeratic sandstones corresponding to proximal deposits outcrop close to the northern and southern basin limits. Numerous remains of silicified wood were observed in these sandstones. At the centre of the basin, numerous negative sequences are assigned to the installation of embankment deposits, in crevasses (fine-grained sandstones) in the flood plain (silt, clay). The magmatism display a great diversity, represented by basaltic, trachytic, phonolitic and rhyolitic plugs, lamprophyre and theralite dykes, and Kokoumi anorogenic complex, but is volumetrically restricted.
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4 (3/4), 461-473
Data from foraminifera and palynomorphs of Cretaceous marine series of Côte d'Ivoire sedimentary basin lead to precise the local biostratigraphical scale based on specific assemblages of these microfossils. This local scale comprising six cenozones based on foraminiferas and five on palynomorphs has been discussed and integrated in regards to the more general evolution frame of West African coastal basins related to the different opening episodes of the central Atlantic known in the northern Gulf of Guinea.
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4 (3/4), 475-479
In the Imsouane area (South Western of Morocco), all the fauna collected at the lower part of Talmest formation show a smaller size than normal occurrences. Two hypotheses can be proposed to explain the peculiarity of fauna studied: - firstly, the fossilised population is a thanotocenose from which all the big examples are excluded by a mechanical sorting; - secondly, an ecological factor prevented the normal growth of the fauna. In the sorting hypothesis, the fragility of spatangus test, the variable size of species and lithological nature make the possibility of such transportation hardly probable, leaving the hypothesis of a restrictive ecological factor. The smaller size of the collected fauna may be understood as the consequence of hard and disastrous biotope conditions. In summary, the size could be an extremely sensitive characteristic of biotopic variations sufficient to induce such a disturbance of the normal fauna growth. Several ecological factors may be evoqued to explain the reduced size of this fauna, but none of them can be considered determinant.
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4 (3/4), 481-497
A diverse and well preserved non-marine palynomorph assemblage consisting of pollen, spores and chlorococcalean algae was recovered from three outcrop localities of the Cocobeach Group, North Gabon Subbasin. The pollen/spore assemblages are dominated by Classopollis and Ephedripites and include Afropollis jardinus (Brenner) Doyle, Jardin‚ and Doerenkamp 1982, Uesuguipollenites callosus Dino 1994 and Alisporites sp. Several samples contain diverse assemblages of pteridophyte spores including Appendicisporites, Cicatricosisporites, Cyathidites, Dictyophyllidites, Gleicheniidites and Ischyosporites. Quantitative variations in pollen/spore type are believed to reflect the overprint of habitat differentiation associated with topography and climate in a rift valley setting. The palynofacies composition of these sediments can be related to organic geochemistry. Samples dominated by amorphous kerogen and fluorescing 'sheets' of unknown affinity (?algae or ?cuticle) also have the highest Total Organic Carbon (TOC) and Hydrogen Indices (HI). Samples containing abundant non-fluorescing, terrestrial ('woody') plant detritus and inertinitic ('coaly') material have the lowest TOC and low Hl. In most cases changes in palynofacies distribution probably reflects the interruption of lacustrine sedimentation by fluvial influence.
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4 (3/4), 499-510
Specimens of fresh/brackish water chlorococcalean algae have been recovered from two localities in both Peru and offshore Gabon. Samples from localities in Peru yielded Pediastrum and Botryococcus. Scenedesmus, Tetraedron, Tetrastrum and Botryococcus were recovered from samples of offshore Gabon wells. Quantitative and qualitative information indicates that the depositional environments for these algae range from freshwater to offshore marine. The latter occurrences are interpreted to represent chlorococcalean algae that were disseminated into marine environments by fluvial transport. Organic geochemistry indicates that these algae can produce long chain n-alkanes (> C22) which are major components of waxy oils normally associated with higher plants. This fact, in combination with sequence stratigraphy and biostratigraphy, is of importance in deciphering petroleum systems in the Mesozoic and Cenozoic of eastern South America and Western Africa.
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4 (3/4), 511-524
Rock exposures remain the most valuable tool to the geologist on which on-site studies can be conducted for better understanding of depositional systems, distribution and geometry of sand bodies and their petrophysical characteristics. These data sets provide the framework for modelling of subsurface reservoir bodies. An integrated sedimentological and biostratigraphic study was carried out on sediments of Eocene-Miocene ages which crop out on the fringe of the Niger Delta Basin. Various parameters have been used to define the systems tracts within the sections. These include the overall stratal stacking patterns of lithofacies, transgressive surfaces of erosion, marine flooding surfaces, inter-channel erosional surfaces, sedimentary structures and increasing bed thickness. Exposed sections of the Benin Formation exhibit channelised stratal geometry with mainly planar cross bedding to massive, loosely consolidated sandstones and siltstones with occasional clay in-fills and abandoned channel deposits and trace fossils. The sands are coarse-grained, largely texturally and mineralogically sub-mature. A range of sedimentary structures characterises this unit. The Nanka Sandstone represents a major channel fill comprising three (3) sand units separated by glauconitic shales. The sands are mineralogically mature, loose with sub-ordinate mudrocks and ferruginous sandstones with a clay matrix of about 5%. Sedimentary structures include ripple laminations, festoon structures, drag folds and discrete asymmetrical channel cuts with flat tops. Although the Ameki Formation shows variations in lithologies (sandstones, mudstones and heterolithics) across the northern fringe of the basin, the sections examined are all typified by marine facies containing foraminifera, gastropod and pelecypod shells and glauconite indicating major marine flooding events. These sections represent channelised to compound ribbon lateral distribution of lithofacies with bed contacts related to changes in base level. Distinct upward coarsening patterns typically begin with a mudstone base, grading through siltstones and heterolithics into sandstones. Depositional environments range from fluvial through tidally influenced nearshore inner to outer neritic conditions.
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4 (3/4), 525-536
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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5 (1-2), 1-9
Two different magmatisms are distinguished from morphological and geochemical (Zr/Hf) zircon data in differentiated volcanic rocks of the Gourougou massif, Eastern Rif, Morocco:
1* Fractional crystallization of a calc-alkaline series with shoshonitic affinity, generates cogenitic andesites, dacites and rhyolites, under moderate crystallization temperatures (respectively 850-750°C and 800-650°C for andesites dacites and rhyolites), and moderate to high water pressure.
2* Trachytes are differentiated from tensional within-plate alkaline series and crystallized from a dry and hot magma (≥ 900°C).
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5 (1-2), 11-22
The middle Drâa valley experienced long-term large-scale desertification sand formation. In order to arrest the situation, different desertification control measures were initiated. Some of the projects succeeded and others failed mostly because they did not consider the direction of movement of the sand. The present investigation of the dynamics of the sand reveal an association of an hydrous and eolin erosional origin. The search for the source areas using granulometric, morphoscopic and mineralogic analyses made it possible to specify the evolution of the sandy material, its nature and its components within the valley as well as the source.
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5 (1-2), 23-30
Lithofacies analyses of the carboniferous rocks of the N'Fis sedimentary domain reveal their compatibility with tilted blocks systems separated by a normal fault with a NW-SE inclination. The structure of the sedimentary domain and syn-sedimentary deformation are inferred from the activity of these paleofaults. Several volcanic manifestations are associated with these faults at different periods and in different blocks during the sedimentation. This orogenic system is generally found in the Mesetian domain, where the basement faults constitute structural limits dividing the pre-Hercynian shield into several sedimentary units.
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5 (1-2), 31-37
Several tectonic and metamorphic data permit the assumption of the existence of granitic intrusion within the N'Fis domain. The thermal evolution at a regional scale confirm an increased thermal gradient towards the N'Fis domain. In this domain, the senestral shear regime associated with a contact metamorphism is related to the Hercynian shear zones where many syntectonic granites are developed in western Moroccan meseta. The emplacement of this intrusion has previously been reported based on gravimetric data, but this hypothesis is now disputed because of the discovery of granitic enclaves in the late Hercynian basic dykes. This intrusive granite has similar lineament with those of the western Morocco Hercynian.
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5 (1-2), 39-48
On a "horsts and grabens"structured framework, the upper Lias-Dogger facies show an evolution of a diverse palaeogeography marked by a typical platform to the South and a deep basin to the North. This palaeogeography existed from the upper Toarcian until the lower Bajocian. During the middle Bajocian the palaeogeography was homogenic. The appearance of deep zones to the North (J. Tazgzaout) and resistant zones to the South (J. Izeft, Akka ou n'Oufij) confirm the existence of a new palaeogeography during the upper Bajocian. Once again a new carbonate platform of relatively thin but very homogeneous nature developed from topmost Bajocian to Bathonian pp. This uniform palaeogeographic situation corresponds undoubtedly to a stable tectonic regime announcing the end of the Jurassic sedimentary cycle.
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5 (1-2), 49-52
The Quaternary littoral formations along the Moroccan Atlantic coastline are subjected to intensive erosion along several sectors resulting in the withdrawal of the coastal cliff. The unstable shoreline was caused by factors related to the lithology of the deposits, their karstic geologic structure and neotectonic movements. These natural phenomena are enhanced by anthropic actions resulting mostly from excessive and irrational exploitation of natural resources. The impact of the anthropic actions are particularly evident in sectors where urban development results in very high population density.
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5 (1-2), 53-58
The northern terrane of Bou-Azzer consists of various rocks, such as lavas, tuffs and greywackes formed during the lower PII within a forearc basin. The evolution of this basin was controlled by normal faults with a NE direction and a NW dip. The early PIII basic dykes intrude the rocks above along lower PII normal faults. The basic magma intruded upward along the crustal normal faults initiating the early PIII distension.
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5 (1-2), 59-66
In the Atlantic coastal region of Larache, two principal marine Quaternary deposits separated by dunes systems are conspicuous. Mollusc shells from the Larache were dated by U-Series disequilibrium method. The ages obtained show the existence of two old sea-levels dated 130 Ky and 275 Ky respectively. These correspond to Ouljien and Harourien-Anfatien dates respectively. The first Quaternary marine deposits were overlain by six red paleosols of Tensiftien dates and the second Quaternary deposits are overlain by two paleosols of Tensiftien age. The development of the Larache coastal zone is confronted by several problems of different origins. Some are natural (e.g. those related to the advancement or withdrawal of the coastal cliffs due to erosion and sliding of the Quaternary deposits lying on clayey Mio-Pliocene substratum). Others are due to anthropic actions relating to a high rate of urban development.
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5 (1-2), 67-73
The Triassic-Liasic basaltic formation of the Argana basin shows a succession of superposed flows, sometimes intercalated by oxidized horizons, which can be continuous or discontinuous. The petrographic analyses reveal several facies which are distinct by their textural and granular aspect at the scale of each section. Their mineralogical composition is dominated by plagioclase and clinopyroxenes associated with secondary minerals.
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5 (1-2), 75-81
Contribution to a sedimentological study of Quaternary coastal deposits of Mohammedia-Aïn Sebaƒ area - In the Casablanca-Mohammedia region of the Atlantic coastal Moroccan belt, two geologic sections were investigated. One of the sections is located near Mohammedia Faculty of Arts and the other is in the neighbourhood of Sebaƒ in Casablanca. Three sea levels were identified in both sections. In the first section, they have been attributed to Maƒrifian, Anfatian and Ouljian dates whilst in the second section, they have been attributed to the Messaoudian, Maƒrifian and Anfatian dates. The morphostratigraphic and palaeoenvironmental evolution of the Mohammedia area during the Pleistocene period is described from sedimentologic analysis in this study.
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5 (1-2), 83-88
The Oued Oum Rbia valley presents varying morphology at different parts of the Doukkala basin. The geomorphology and its evolution (in space and time) is dependent on a number of factors, such as topography, lithology, tectonics, climate, eustasy and human activity. The sedimentological characteristics of the early Quaternary fluvial terraces (conglomeratic deposits) differ from those of the late Quaternary (silty deposits). With regard to the other factors, the nature of the detritic deposits is controlled by the dynamics, neotectonics and the climatic context.
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5 (1-2), 89-98
Detailed study of the lithostratigraphy, petrography and micromorphology of consolidate dunes complexes of Ras Kebdana Coastal region of northeastern Morocco revealed the existence of two systems, probably of different ages. The older system consists of calcarenites with level of calcrete developed near the top. Pedological and sedimentary studies of this calcrete suggest an interaction of pedogenic and sedimentologic processes during their formation, terminating with a laminar horizon. The younger system consists of calcarenites which fossilized under hot and humid conditions into four levels of paleozol.
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5 (1-2), 99-105
The Jurassic gabbros of central High Atlas (Morocco) present reactionary assemblages: (ol.+opx.+amp.+pl.), (ox.+bt.+amp.+pl.) and (bt.+amp.+pl.). They are produced during the late stage of site crystallisation, under low pressure conditions. The reactionary process was not isochimic at the studied site. The growth of the minerals was controlled mainly by the circulation of intergranular fluids.
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5 (1-2), 107-115
The description of halite crystals from Moroccan Late Triassic salt formations is not limited, as it is often the case, to the individualisation of milky and limpid halites and the recognition of some common crystalline facies, but it enriches the usual faciologic classification of new subdivisions that help to specify and qualify the reconstitution of the paleoenvironment and diagenetic processes. In addition to the fibrous halite, the limpid halite comprises five different types: vertically lengthened crystals, clastic halite, syntaxic and cementation halite, displacive halite and macrocrystalline halite. The milky halite consists of three types: skeletal hopper crystal, depressed-face halite cubes and chevron-cornet-zoned halite. These different types of crystals form three halitic facies: milky salt, muddy salt and clastic salt. The first has two varieties: the somber milky salt and the clear milky salt. The recrystallisation of these halitic facies led to a polygenic breccia with halitic cement.


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5 (1-2), 117-121
In the southern portion of the Bou-Azzer El Graara area, Precambrian I rocks outcrop. This cratonic rocks of Eburnean age have been affected by the major Pan-African deformation B1 (675 Ma) characterized by the development of several tectonic structures (schistocity, lineation, shear zone etc). Tectonic and microtectonic data reveal an heterogeneous and non-coaxial strain pattern.


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5 (1-2), 123-127
Geochemical analyses of core samples from uppermost alluvial deposits, from the Sebou River at the downstream direction immediately after the junction with the Fès stream, reveal the existence of mineralogic associations particularly Cr, Cu and Zn within lithochemical substrates. Analyses of the chemical fractions show that almost all the Cr is associated with iron and manganese oxides and hydroxides. Zn associates preferentially with carbonates and exchangeable cations (43%) as well as phases of Fe and Mn oxides (23%) and phases of Fe hydroxides and Mn (20%). On the other hand, Cu displays a strong association with the organic material (40%). The remobilisation of these metals is most probable since the phases discussed above are easily dissociable components with the slightest changes in physico-chemical conditions (pH, organic matter content).


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5 (1-2), 129-134
The Ikhourba fault represents a typical model of tectonic inversion because it had recorded different motions during the geological history of the Ida Ou Zal basin, as a normal syndepositional fault at the time of the opening of the Stephanian basin, then as a reverse fault at its closure and finally as a normal fault during the Triassic extension.


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5 (1-2), 135-144
The reef outcrop of Aghram Amallal (South-East of Fes) forms part of the reef formations of the southern side of the South Rifan Corridor. It is presented as a horizontally elongated lens (approximately 60 m long, 3 to 6 m thick). The bioconstruction is almost exclusively assured by the Tarbellastraea genera. The colonial morphologies are varied, and their spatio-temporal distribution has allowed the establishment of morphological zonations. The study of different distinguished morphological zonations and investigation of the accompanying fauna and flora as well as the analysis of the inter and intracolonial sediment reveal a rythmicity of the bioconstruction and the sedimentation. This rythmicity consists of two "regressive" sequences that are separated by a positive fluctuation of the sea level. The environmental conditions seem to characterize a "back reef" set and permit an interpretation of the studied reef as a "patch" that would integrate itself to an important marine platform. This would later develop in front of the El Aderj faults.


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5 (1-2), 145-149
Metasedimentary formation of lower Proterozoic age of the Irherm belt outcrops discontinuously, owing to the intrusion of the Eburnean granites. It is composed mainly of bedded schists rich in quartz, with fine quartzitic levels. This formation is affected by at least three phases of deformation: the S1 phase is related to the Eburnean orogenesis, whereas the other two phases (S2 and S3) are linked to the Pan-African orogenesis. From their geochemistry, the analysed rocks constitute a homogeneous set. They correspond to metagraywackes according to their MgO, TiO2 and Fe2O3 content, On the other hand, their Al²O³ and SiO2 contents show an intermediate position between metashales and metagraywackes, with a predominance of the latter.


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5 (1-2), 151-158
The structural and petrological study of viscous flow structures of monzonites from the Tamazert complex reveal microshear zones. These zones are distinguished by alignment and preferred orientation of orthose megacrysts. These structures are interpreted as originating from coaxial progressive deformation during the latter stages of monzonite solidification. This deformation is closely related to increasing viscosity during emplacement.


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5 (1-2), 159-171
Structural petrology and detailed mapping of the internal fabric of the Tamazert alkaline complex reveal the relative chronology of the emplacement of the intrusive rocks. This study is based on the studies of the nature and shape of the enclaves. The limits between the different rocks and the transboundary relations between the foliation structures of the different petrographic types was also investigated. The emplacement conditions of the different rocks are described.


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5 (1-2), 173-178
A sequential analysis of Liasic deposits in the northern margins of the High Atlas range at Béni-Mellal led to the identification of eight sequences of the third order for the Upper Sinemurian-Lower Toarcien interval. The age as well as the sedimentary characteristics of the deposits are described in this study.


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5 (1-2), 179-182
In the Foum Ikis Valley and in the Jaafar area located south of Midelt (central High-Atlas), several synsedimentary deposits resulting from sliding outcrop. All these gravitational sliding deposits (olistolith, intraformational breccias, turbidites and slumps) are due to tectono-sedimentary and tectono-eustatic events which took place during the Jurassic in the Midelt area in particular, as well as in all the central High-Atlas region in general.


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5 (1-2), 183-190
Geomorphological and sedimentological analyses of the Quaternary formations of the coastal Meseta between Oued Mellah and Oued Nfifikh (Mohammedia area), reveal the areal facies distribution of these deposits and the location of the Quaternary paleocoast lines. A lithostratigraphical subdivision is proposed for the Quaternary of the study area. It is no different from that established in Casablanca and is based on the stepping of dead cliffs, on sequence analysis and on the areal distribution of heavy minerals. This study shows that heavy minerals make good lithostratigraphic markers in the northern Moroccan coastal Meseta. Key words: Mohammedia, Quaternary, heavy minerals, sedimentology, geomorphology, paleocoast, stratigraphy.


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5 (1-2), 191-197
The Quaternary deposits of the Moroccan Atlantic coastal area between Casablanca and Al Mançouriya show yellowish fine-grained limestone intercalations with traces of root and calcareous incrustations. Morphological and paleontological arguments allow us to attribute these deposits to the Amerian. Sedimentological and paleontological data indicate that they formed in coastal, shallow lacustrine environments isolated behind an offshore bar. The climate was more humid than that which prevailed during the regressions.


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5 (1-2), 199-206
A small fluvio-lacustrine deposit has been discovered in the southwestern side Tiddas (Central Morocco) in a band outcropping between the Bou Regreg River in the East and Grou River in the West. The outcrops named "Aït Babout formation" consist of the following units from top to bottom: Bir Oughioul, Hançala, Zwirga and Bir Dallah units. The sedimentologic analyses of these continental deposits suggest a fluvio-lacustrian depositional environment. The formation reveal instability of the Central Moroccan Paleozoic basement during the Plio-Quaternary.


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5 (1-2), 207-215
At the ENE of the city of Gafsa, the analyses and comparison of the sedimentary series in both compartments of the Mech fault reveal two synsedimentary events during the Cretaceous. Combination of the results with those obtained from the analyses of the microtectonic structures at the boundary between both megastructures (Orbata and Bouhedma) confirm the existence of three syn-Cretaceous tectonic phases. The first phase is distensive and is of Lower Cretaceous age, whilst the second is also distensive but of lower Aptian age. The third phase is compressive and is post-lower Albian and Cenomanian age. The palaeogeographic reconstruction, based on the geometry of the sedimentary body on both sides of the Mech fault, shows that the fault is on a palaeoridge with a syasedimentary ascensional movement occurring during the Cretaceous. This palaeo-ridge resulted from diapirism of evaporitic facies of the Trias across the Mech fault within the subsurface. Key words: Synsedimentary tectonics, distension, compression, Mech's fault, "Palaeowrinkle", Cretaceous, Southern Tunisia.
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5 (1-2), 217-218
Les émissions volcaniques du Plateau d'Azrou (Moyen-Atlas) relèvent de deux lignées magmatiques alcalines, l'une sous-saturée en silice (Ne(norme) compris entre 4 et 19%) et l'autre saturée à légèrement sursaturée en silice (Hyp(norme) compris entre 0 et 17 %). Les roches de ces deux lignées se différencient par quelques caractères géochimiques typiques qui après correction des effets de la cristallisation fractionnée concernent en particulier les teneurs primaires en titane et vanadium: - TiO2 compris entre 1,8 et 2,2% et V entre 170 et 190 ppm dans la lignée saturée, tandis que les concentrations de ces deux éléments sont respectivement comprises entre 2,6 et 3,1% (TiO2) et 220 et 250 ppm (V) dans les produits de la lignée sous-saturée. La phase d'éruption finale du Jebel Boutagarouine, qui localement constitue le complexe volcanique le plus important, a produit des basaltes microlitiques primaires typiques de la lignée saturée (Morel et Cabanis, 1993). Des faciès hypovolcaniques, apparentés chimiquement à cette denières lignée, sont fréquemment rapportés en enclaves par les magmas les plus explosifs de la lignée sous-saturée. Malgré leur parenté chimique bien affirmée avec la lignée saturée, le doute pouvait subsister quant à leur âge; il pouvait en effet s'agir de roches plus anciennes ramonées par le volcanisme sous-saturé dâge quaternaire et daté (K-Ar sur roches totales) entre 1,8 et 0,50 Ma (Harmand et Cantagrel, 1984).
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5 (1-2), 219-232
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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5 (3), 263-273
Research interest in the Metlaoui carbonates of central Tunisia has been focused, in recent years, on the source and reservoir potential of the constituent facies. The nummulitic limestones of the El Gueria formation attain a maximum thickness of 160 m at Jebel Cherahil. They extend along a relatively broad zone that stretches from the Gulf of Gabes in the SE, through central Tunisia towards the NW and into the Medjerda valley. The general SE-NW orientation of this zone reflects the influence of the Kasserine "island" on early Cenozoic sedimentation. Various depositional models have been proposed for the nummulitic facies, but the general consensus has been for prograding nummulitic shoals over a NE-sloping marine shelf. Relationships between the El Gueria facies and its lateral equivalents may be seen at outcrop in Jebel Sfeïa, Jebel Afaïer, Kef El Guitoun, Jebel Ousselat, Jebel Serj, Blida and Faid. The lateral equivalent facies are also influenced by the NE-SW distensive tectonic framework at the basement of Ypresian.
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5 (3), 275-285
Recent sedimentologic study performed on the Upper Triassic mixed carbonate-evaporite-siliciclastic series in central Tunisia has led to characterize five major trangressive-regressive sequences. The basal carbonate terms of these sequences were deposited on retrogradational shallow marine platform during the Carnian and Rhaetian relative sea level rises. Conversely, the siliciclastic (shales and siltstones) and evaporitic terms linked to regressive episodes were deposited under transitional to margino-littoral condidons. The correlation of these sequences, mainly controlled by eustatic fluctuations, with the ABSAROKA global third order cycles (deposional sequences) reveals the presence, in central Tunisia, of an additional sequence within the Carnian time interval. Within the Carnian transgressive facies, organic-rich carbonates and shales were deposited during enhanced anoxic conditions. Their organic matter content is up to 7% of TOC and their residual petroleum potential is fair to good (up to 7 Kg of HC/t of rocks). These organic-rich facies of central Tunisia represent the sedimentary record of an Upper Triassic anoxic event on the southern Tethyan margin. In addition, these Carnian organic-rich facies represent a new oil- and gas-prone source rock in central-north Tunisia.
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5 (3), 287-295
The phyllite mineral suite distribution in the Jurassic, Cretaceous, Paleogene and Neogene sequence deposits, along the folded structures associated to the south Atlassic fault of Gafsa in Tunisia, fossilize the geodynamic events of this basin. The mineralogical variation along the stratigraphic series of Gafsa phosphatic basin is intimately connected with the eustatic and geodynamic events recorded in the basin. The Jurassic-Lower Cretaceous limit is marked by the inversion of the basin that is also accompanied by a mineralogical inversion. The Lower Cretaceous regressive clays are dominated by illite whereas the regressive Upper Cretaceous series are predominantly smectitic. The lowstand Tertiary sea level coincide with the abundance of palygorskite.
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5 (3), 297-311
In southern Tunisia several intriguing petroleum explorations have been conducted in the last decade, and there is therefore great interest in the hydrodynamic, geothermic and geochemical parameters of the Triassic reservoir. We collected and processed over one hundred petroleum well data, in the study area, and created contour maps describing the distribution of the parameters of interest of the Triassic aquifer. From these maps we deduced the main hydrodynamic, geochemical, and geothermic characteristics of the aquifer. The main recharge area is located in the Libyan territory where the groundwater diverges to the north and Northwest; other less important recharges could be mentioned since we deduce ascending vertical flow from the Paleozoic aquifers, and the pressure versus depth profile. Groundwater mineralization ranges from 3 to 250 g/l, depending mainly on the groundwater flow path; the lowest values are found in the principal recharge area; in addition, isolated lenticular clay strata have been located by identifying areas of high pressure and mineralization. At the aquifer roof, temperatures range from 30 to 90°C, and isotherm contours are clearly parallel to the Jeffara fault, evidence of the hydrogeothermic effect of the aquifer's structure on its temperature distribution.
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5 (3), 313-325
The Ouady el Khairat alluvium contain an aquifer system that extends to about 40 Km² with a thickness ranging from 10 to 100 m with a global groundwater resource of 6,5 M m³/year and a particularly low water mineralization. The Aïn Garci anticline subdivides this aquifer into two different non-communicating entities. There is a plan to construct a dam on this oued in the upstream part of the aquifer in order to protect Enfida town against inundations and to irrigate 3000 ha of cultivated lands. The floods of the ouady (about 9 M m³/year) furnish 92 % of the Aïn Garci aquifer. The modelling of the groundwater system confirms that the expected dam, which would collect about 7 M m³/year, should furnish at least 6 M m³/year in order to compensate the natural recharge of Aïn Garci and Enfida aquifers.
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5 (3), 327-338
The Gafsa fault belt represents the eastern end of the South Atlasic Accident, which extends in North Africa from Morroco westward, to Libya eastward. This fault belt acted as a megashear system of left and right lateral en echelon, during the Mesozoic and Cenozoic, respectively. The development of pull-apart basins and rhomb grabens and horsts is a result of this tectonic system. Previously, the Gafsa belt was considered to be an EW-trending system of en echelon anticlines and associated thrusts of the order of tens of kilometers. This study considers that the Gafsa basin was affected by strike-slip displacements along N120, N60 and N90 faults. These faults are responsible for reactivating existing structures during the Mesozoic (transtensional) period and Late Miocene (transpressional) period. A new interpretation is proposed for the Gafsa fault belt, based upon the analyses of geometric and kinematic evolution of the area.
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5 (3), 339-355
Anywhere, the assessment of hydrogeothermal resources needs mainly the adequate understanding of the thermal and chemical characteristics distribution, in addition to the petrophysic and hydrodynamic properties of the reservoir. Compilation and treatment of geological, hydrostratigraphic, geophysic and hydrogeothermic data led us to subdivide Tunisia into eight different hydrogeothermic units. Each of them is characterised by its extension, geology and hydrodynamism. The genetic relationship between temperature and hydrodynamism has been already demonstrated and shows that discharge areas are characterised by shallow hot water, high apparent geothermal gradient and low topography. Recharge zones are characterised by shallow cold water, low apparent geothermal gradient and high topography. Previously, a noticeable relationship was shown to exist between hydrodynamism, temperature and oil accumulations. Temperature is studied by considering either the deep oil information or the shallow hydrogeologic one. Temperature measurements are treated in a synthetic way for each identified basin. This also allowed the comparison of the relative importance and significance of the temperature data treatment and the proposition of a conceptual model as well as a synthetic diagram explaining the divers behaviours of thermal profiles in the investigated wells.
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5 (3), 357-366
In the southern Atlas of Tunisia, the structuration of Lower Cretaceous sequence deposits in subsurface is controlled by the reactivation of inherited faults which guide the deformation of basins and antiforms. The movements of fault corridors of south Atlassic system permit the ascension of Triassic salt. These tectonic dynamics are associated to the eustatic sea level changes. These are responsible for the distribution of sequence deposit system tracts in the basins of Moulares, Guettar and Ganntass. The sequences are delimited by uncorformities of downlap progradational and onlap aggradational and retrogradational surfaces. They are marked by variations of seismic facies, thickness and inversion of subsidence.
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5 (3), 367-372
The Medji-zir "Series" (Paleocene) is the upper member of the Tawilah Formation (Cretaceous-Paleocene) in the northern provinces of the Republic of Yemen (previously Yemen Arab Republic, = North Yemen), the lower member being the Ghiras (Cretaceous). Both members consist of similar sequences of sandstone and they were differentiated only an the basis of the occurrence of marine fossils in the Medji-zir. Therefore, they are considered to be informal units, and it is suggested to drop them from the stratigraphy of Yemen. The Medji-zir sequence is treated as a biostratigraphic unit within the Tawilah Formation, and it is named as Pulsiphonina prima Zone. Also, it is suggested to stop using the terms Tawilah and Ghiras Groups in the southern provinces of Yemen (previously Peoples' Democratic Republic of Yemen, = South Yemen), and to replace them with the new term Ahwar Group.
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5 (3), 373-384
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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5 (4), 385-483
A review is presented of current knowledge concerning the structure, stratigraphy and evolution of the Cretaceous sedimentary basins in Nigeria. Early Cretaceous rifting associated with the opening of the Equatorial Atlantic Ocean was accompanied by the widespread deposition of continental successions notably in the Benue Trough which originated at this time as part of the West and Central African Rift System. Middle to Late Albian, Late Cenomanian to Early Turonian, Upper Turonian to Coniacian and Late Campanian to Maastrichtian transgressive events variously affected the coastal and interior Nigerian basins. Late Santonian and latest Maastrichtian compressional events are recognizable; in the Benue Trough there was an intervening phase of renewed rifting.
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5 (4), 485-498
The Kunene Complex consists of mainly massive and minor laminated anorthosites. Structural and petrographic evidences suggest that laminated belts originated by a continuous deformation from hypersolidus (synmagmatic) to subsolidus conditions, in response to the slow growth of the igneous body. Within the complex, granitoid bodies of Kibaran age are elongated parallel to the structural grain of the complex. They are mainly contained in a belt that runs SW-NE from Pocolo to Dongue. Anorthosites on the NW and SE of this belt are clearly distinguishable by their chemical composition, being the southern anorthosites richer in Na, K and Sr. Collectively, geological and geochemical features suggest that the Kunene complex consists of at least two (but possibly several) individual plutons originated by intrusion of plagioclase-rich crystal mushes, possibly coeval with the Kibaran granitoids.
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5 (4), 499-506
The prominent NNE-SSW trending Ifewara fault in southwestern Nigeria is known to extend northward beyond latitude 8°N and southward to the Atlantic coast. An analysis of SPOT imagery lineaments in an area located east of Ilesha and containing part of this fault shows that the lineaments are directionally controlled by the fault. This has led us to conclude that the swarms of lineaments are in fact surface expressions of structures produced by early recumbent folds probably associated with nappes (D1) and a later episode of upright folds and mylonitic shear zones. It is therefore likely that the fault and the mapped fractures, together belong to a more extensive system of fractures located within the D2 shear zones.
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5 (4), 507-525
The Precambrian of Eastern Congo (Kivu region) is composed mostly of Kibaran belt; the Archaean formations are located in the northern part of the region. Metamorphism in Kibaran formations is intimately associated with the deformation of the belt. It can be subdivided into four episodes: the first two are medium-high-pressure metamorphism, and syn to late-phases of deformation D1 (1265±15 Ma) and D2 (1189±9 Ma) described in these terranes. The first metamorphic episode reached 565±5°C at 6.5±0.5 kb, whereas the second episode ranged from 350±20° to 810±5°C and 5 to 8 kb. The third is plutonometamorphism (540°C at 2 to 3 kb) and the last Kibaran metamorphic episode was a retrograde greenschist metamorphism associated with the uplift of the belt late-D2. Mineralogical studies enable us to constrain P-T conditions of metamorphism and to discriminate the metamorphic facies. Finally, regional consideration lend us to suggest that the Kibaran regional metamorphism changed with location, with lower pressures in external zones, and medium to medium high pressures in internal zones.
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5 (4), 527-535
Systematic measurements of the orientation of joints and faults within the main body of the Kenticha pegmatite deposit and statistical treatment of the data have revealed the internal structural features of these pegmatites. Analyses of the orientation of joints and faults in the pegmatites suggest that these pegmatites are formed by the magmatic differentiation, shearing, and push-up stress of the underlying rocks. The latter led to development of gently dipping and curving joints which produced ring-like fracture pattern and local faults within them. In addition to these, there are also regionally developed subvertical faults of different scales and orientations. The distribution of the rare metals and related radioactive elements in the pegmatite with respect to the internal structures within the body shows that it is structurally controlled.
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5 (4), 537-545
The morphological and chemical studies of gold particles from supergenous deposits from Ity show a relation between the granulometry of formations and the forms of the gold particles; xenomorphous and idiomorphous grains are linked with rough and fine formations, respectively. This correlation between the granulometry and the form of particles suggests a migration of the gold before the concentration. In addition, the spongy texture of some particles and the presence of secondary crystallises show evidence of dissolution and recrystallisation of gold during its supergenous cycle. This dissolution was due to chlorine as revealed by spectral analysis with a scanning electron microscope.
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5 (4), 547-555
The near surface plio-quaternary formations of the Rharb-Maâmora basin were deposited in lowland areas of the basin. Their hydrogeological investigation, notably the localization and mapping of aquifer reservoir formations (porous and permeable rocks) is difficult owing to their being deposited in continental environments where facies distribution is very complex and unpredictable. In order to by pass this problem and optimize the groundwater resources management within the basin, we compiled and interpreted a set of geophysical and well data, and paleogeographic maps. Results of this work allowed us to explain the modalities of the genesis of the aquifers in the basin, to identify these hydrogeological systems and to map the hydraulical producing areas of the basin.
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5 (4), 557-573
The Ashanti gold deposit is a mesothermal gold deposit in the Proterozoic Birimian Formation of Ghana. Chlorite from the alteration zones associated with gold mineralisation has been studied. Geochemical analyses showed that major differences exist in chlorite grains from the various ore bodies at the mine. Two chemically different types of chlorite were identified in the deposit. They are sheridanite and ripidolite. The former occurred in the shallow North Ramp ore body while the latter mainly occurred in the George Cappendell Shaft (GCS), Kwasi Mensah Shaft (KMS) ore bodies. The dose association between chlorite and sericite coupled with the observation that the former usually maintains the flow of the surrounding bedding structure may suggest that chlorite developed from earlier formed sericite. This may have occurred when Mg-bearing fluids, probably from above and to the NE of the deposit, interacted with Fe-bearing fluids generated from the surrounding host rocks. The process of fluid interaction may have aided gold deposition. Chlorite commonly replaces pyrrhotite and both minerals have not been observed in the quartz veins in this deposit. This places chlorite formation after the formation of earlier pyrrhotite. The main quartz vein emplacement may have post-dated pyrrhotite and chlorite formations.
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5 (4), 575-587
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the Library of the Geological Survey of Israel, which is accessible to the scientific community.
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6 (1), 1-13
The most significant coal deposits in Africa occur in the southern portion of the continent within continental Karoo basins. The Karoo deposits diminish northwards towards the equator and are virtually absent north of the Democratic Republic of Congo. In West Africa, Cretaceous and Tertiary coal, lignite and peat deposits occur in Nigeria, Bénin Republic, Niger and Sierra Leone. There exists a degree of variability in distribution, quality and thickness of the coal seams in different regions, but Southern Africa is undoubtedly one of the few areas in the world capable of producing and exporting large volumes of coal. Africa's coal deposits are utilized locally for the generation of electrical power, various metallurgy applications and for domestic energy.
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6 (1), 15-26
The majority of developing countries' populations are heavily dependent on wood and charcoal for energy. Virtually everywhere in the Third World natural forest is disappearing at an increasing rate. As a result of hardwood logging and fuelwood/charcoal making, an energy crisis will threaten the lives of over 1000 million people in the tropics during the next two to three decades. Peat, a renewable natural resource, like wood or biomass, should be considered in the energy context as a biofuel. African wetlands cover about 345 000 km² of the continent. Of this approximately 58 000 km² is considered to be peatlands. South Africa is estimated to have about 9000 km² of peatlands holding ± 250 x 10(6) tons of proven reserves. In this paper, peat will be presented as an alternative domestic energy source in parts of South Africa. The energy content of peat, expressed as its calorific value, varies between different peat types. African sedge/reed peats can be described collectively as medium-ash, high-volatile peats that are suitable to replace wood as domestic energy source as long as the moisture content is low enough.
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6 (1), 27-40
Sediment-petrographical studies have been carried out on lignites at two localities near Knysna, South Africa. A lithostratigraphic subdivision is proposed, formalising the sediments of the Knysna Formation and subdividing this formation into an upper sand and a lower lignite member. Based on sedimentological analysis and preliminary palynological investigations a non-paralic palaeo-environment has been suggested in which limnic and paludal conditions created the lignitic sand and lignite deposits respectively. The lignites appear to be of Miocene age.
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6 (1), 41-52
Lignites in South Africa are found mainly on the coastal plain and in offshore regions, and are dated Miocene and Jurassic/Cretaceous respectively. Only the lignites near Knysna were mined underground at the beginning of the 20th Century. None of the presently known occurrences is economically-viable for exploitation; because of the limited resources and poor quality. The seams are too thin, deep and irregular. Exploitation will also cause a negative environmental impact. Interest in lignites is mainly focused on the scientific aspects of dating and reconstruction of palaeoenvironments.
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6 (1), 53-64
Besides climatic factors, many non-climatic factors, such as tectonic movements, volcanism and land slides, have controlled the hydrology of mire basins. Therefore mire initiation and expansion has also occurred during dry climatic periods. The effect of climatic variations is more pronounced in the peat accumulation data. High accumulation rates correspond to periods of wet climate and low accumulation rates those of dry climate. However, many local factors may confuse this correlation. Long-term accumulation rates of dry matter range from 110 to 220 g m-2 a-1. The properties of minerotrophic peat vary from area to area and are affected by the local hydrology and nature of drainage basin. The most remarkable variations are in the ash content and in the chemical properties. A raised mire is an exception, having a low ash content and extremely low trace element concentrations. In the data as a whole, the water content, dry bulk density, ash content and net calorific value average 90.7%, 0.083 g/cm³, 12% and 19.1 MJ/kg respectively. The average carbon content is 54.0% and sulphur content 0.7%.
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6 (1), 65-70
Notable peat resources have been proven on Mbamou Island and around Pointe Noire. The Pointe Noire deposits also gave excellent results in horticultural tests and the size and location of the deposits render them eminently suitable for utilization and even export. Further preliminary studies also indicate major peatlands south into Cabinda and at various localities along the Congo coast from Pointe Noire northwards into Gabon and in the north of the country. However, the potential for fuel production has not yet been assessed and will only be done if the impetus for such action comes from within Africa. Cognisance should also be taken of the many other important applications of peat and peat derived products. Any management plan for alternative domestic energy supply will have to recognize the renewable nature of the resource and be executed accordingly on a sustainable basis.
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6 (1), 71-82
The coal resources of Nigeria are located mainly within the Benue Trough. In the lower Benue, sub-bituminous coals occur within the Maastrichtian Mamu Formation, High-volatile bituminous coals are found within the Turonian - Santonian Awgu Formation in the middle Benue while the upper Benue contains lignites and sub-bituminous coals in the Maastrichtian Gombe Sandstone Formation. Maceral analyses show that huminite dominates in the petrographic composition of the lower and upper Benue Trough coals and have vitrinite reflectance values that range from 0.30 to 0.63% Rm. In coals from the middle Benue, vitrinite macerals predominate and Rm values range from 0.74 to 1.25%. The sub-bituminous coals in the lower and upper Benue are ideally suitable for combustion, white the high-volatile bituminous coals in the middle Benue, apart from being suitable for liquefaction, are excellent as feedstock for coking in steel manufacture.
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6 (1), 83-101
Detailed sedimentological data in the Westphalian C of the Jerada Basin reveal the presence of proximal conglomeratic fluvial facies that passed laterally to distal silty sandy and coaly facies. In this lacustrine-deltaic series, two marine levels are interbedded. Sequential analysis leads to define several orders of stacked genetic sequences and to establish correlations within the Jerada Basin series. Eight coal seams developed in this paralic basin as distal facies passed laterally into proximal facies during retrogradational stages. These stages are related to base level rises that curtailed detrital influx and induced the development of swamps and the preservation of organic matter below anoxic water levels. The base level variations are related to active faulting along the basin margins and probably to sea level changes in the Paleo-Tethys.
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6 (1), p103
Major, economically important coalfields occur in the mid-Zambezi Valley of southern Zambia. The discovery of this coal in the mid '60s resulted in the first substantial surface and subsurface investigations of the coal-bearing sequence. This sequence is now known as the Gwembe Coal Formation, a Permian fluvial sequence within the continental Karoo Supergroup. Coal contained in a 5-12 m thick Main Seam of the Permian Gwembe Coal Formation is currently mined and indications are that, owing to block faulting, some coal-bearing sub-basins are buried and not yet discovered. This paper outlines coal deposits of the mid-Zambezi Valley Basin, describing the setting, geology, exploration effort, evaluation, reserves and usage. Depositional environments are highlighted with recommendations for further exploration.
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6 (1), 105-120
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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6 (2), 121-133
The Eburnian basement of the Iguerda-Taïfast inlier, located in central Anti-Atlas, has been crosscut by two swarms of doleritic dykes, during the Neoproterozoic. The first one is NW-SE and the second one is NE-SW to NNE-SSW. These dolerites are more or less altered during the tectonic Pan-African events. The primary mineral assemblage consists of plagioclase, clinopyroxene, ilmenite, apatite, micropegmatite (quartz and sodi-potassic feldspar), sometimes hornblende and rarely biotite. The first swarm (NW-SE) is richer in LREE, Zr, Th, U, Rb, Ba, Sr and P2O5 elements than the second one (NE-SW). The latter is also rich in V. Mineralogical and geochemical composition indicate that these dolerites belong to continental tholeiites. These swarms doleritic dykes have been emplaced in the course of extensional events in the Iguerda-Taïfast inlier, prior to Pan-African folding.
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6 (2), 135-140
Using the Rayleigh loop property of some members of the titanomagnetite solid solution series (1-x)Fe3O4xFe2TiO4 at room temperature, the composition of 285 rock samples from fourteen different sites of Biu Plateau was determined. Titanomagnetites with x = 0.56 were completely absent from these sites while those with up to x = 0.60 were fairly common. A few samples were found to have single domain magnetite {TMO(SD)}. The results indicate thee Biu Plateau basalt is a young basalt extending from mid-Tertiary to Recent times, and an ideal basalt suite for palaeomagnetic and rock magnetic studies.
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6 (2), 141-148
The sedimentological and geochemical analyses of surface sediments samples, from the western part of the Alboran sea (Moroccan Mediterranean margin) show that the repartition of the different sedimentary facies is essentially controlled by the nature of continental sediment input, the hydrodynamic factor and the morphostructural environment. Mineralogical studies of carbonates and clay minerals allow to distinguish between a marine and a continental origin. The study of some heavy metals (Cu, Zn, Al, Fe, and Pb) shows two groups of metallic elements with a different nature and origin.
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6 (2), 149-157
Geological and structural studies of the Bizerte-Bechateur area, along the extremity of the eastern flank of the Maghrebid chain, permit the recognition of tectonic blocks each evolving separately. The folded structures resulted from dextral and sinistral conjugated strike-slip faults. Two major blocks can be differentiated: - the Beni Meslem block, and - the Bechateur faulted block. The differentiation occurred along the major Ras Engela Fault, trending N150 by a drag movement of the Neni Meslem block towards the South against the Cape Bizerte fault in a N30 direction. The movement of the structures was produced during the Upper Eocene facilitating the installation of a gulf within which Jebel Seboa clays and coarse-grained sandstones of Oligocene age were deposited. The Bechateur block corresponds to an accommodation zone dominated by a brittle tectonic style exposing monoclinal structures affected by torsion and rotations. This tectonic edifice, active during the Upper Eocene, reveal the role of major faults in the evolution of basins and the origin of their structures. It provides a new perspective of the tectonic evolution of the Bizerte region.
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6 (2), 159-176
The study aims to clarify the origin of migmatites in the northern part of the Precambrian Arabian-Nubian shield, and combines whole rock chemical analyses of migmatites, garnet-biotite thermometry and fluid-inclusion microthermometry. The migmatites consist of quartz + plagioclase + biotite + muscovite + garnet; their mean composition is similar to that of diorite - granodiorite. Electron microprobe analysis reveals that the composition of plagioclase in the adjacent leucosomes and paleosomes is the same. Garnet core - biotite thermometry constrains the temperature of migmatite formation to be about 610-690°C. H2O-CO2±CH4±N2 fluid inclusions are restricted to the migmatite complex. Based on fluid inclusion data it is likely that a H2O-CO2 fluid with a H2O mole fraction of 0.3-0.6 participated in the migmatization. The calculated pressure during migmatization was about 2.5-4.5 kbar. Geochemical, thermobarometric and fluid inclusion evidence support the interpretation that metamorphic differentiation was the dominant migmatization process.
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6 (2), 177-196
An intense volcanism represented by basalts, andesites, dacites, rhyolites and ignimbrites occurred during the late Neoproterozoic in the Siroua area (central Anti-Atlas, Morocco). The ignimbrites are dacitic or rhyolitic composition and may be distinguished from other facies by specific characteristics such as vitroclasts, fiammes, lithophyses, vesicules and xenolites. The mineralogical and chemical characteristics of the rocks are typical of calc-alkalic orogenic magmatism linked to subduction of active margin type. The partial melting of a peridotite mantle, probably induced by fluids generated by dehydration of a lithospheric slab subducted during the Pan-African, generated basic magma enriched in rare-earth and incompatible elements. The presence of the ophiolites in the Siroua area conforms with this hypothesis. The ignimbrites and acidic rocks are interpreted as the products of crustal anatexies. An aerial to subaerial environment is suggested for the Siroua ignimbritic magma.
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6 (2), 197-211
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps. Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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6 (3), 213-246
The bauxite deposits in the Southern African Development Community (SADC) developed over different host rocks. In Malawi, the host rocks are syenogranitic and in South Africa and Zimbabwe they consist of dolerite dykes and sills. In Tanzania, the deposits are associated with gneisses and whereas in Mozambique and Zimbabwe some are associated with anorthosite complexes. The formation of these bauxite deposits has been attributed to several factors which include suitable host rocks, favourable climate, flat elevated undulating topography and high annual precipitation.
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6 (3), 247-269
The heavy-mineral sand deposits of the SADC are discussed in the light of ore reserves, grade, accessibility, existing infrastructure and amenability to exploitation. Detrimental factors affecting exploitation (mainly high clay content) are highlighted. The geological environment in the vicinity of the orebodies, the present geological setting, provenance for the heavy minerals and the geological processes which resulted in the concentration of these minerals are discussed. Promising heavy-mineral sand deposits are known to exist in Malawi, Mozambique, South Africa, Tanzania and Namibia. Titanium and related compounds which form the main products of heavy-mineral sand mining are briefly discussed and beneficiation and manufacturing processes used to produce the various titanium products as well as applications for these products and recent developments in pricing are described.
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6 (3), 271-282
Industrial mineral resources of Nigeria have been intensively explored in the last two decades as a result of the urgent need to economise foreign exchange by manufacturing products locally whenever possible. These minerals comprise a highly diverse group of often neglected though vitally important minerals that are used in a variety of applications ranging from every day products like floor tiles and drinking glasses to more highly sophisticated materials like fluorescent tubes. Industrial minerals are generally low-price high-volume minerals and are sold in bulk making their economic exploitation highly dependent on the cost of transportation and distance to the market. This article discusses the major types of industrial minerals in Nigeria. It confirms that with increasing demand for locally manufactured goods and intensified exploration, there is abundant reserves of a wide range of basic industrial minerals to meet the demand.
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6 (3), 283-289
In this study we have examined the behaviour of phosphorus ions in contact with sediments. We have also examined the desorption phenomen from sediment. These reactions (adsorption-desorption) affect considerably biological equilibrium in water system. The physico-chemical measurements have been carried out on sediments extracted from Sebou river in Morocco. The effect of pH, phosphorus and sediment concentration have been examined. Before all experiments, the sediment has been studied to determine specifically physico-chemical characteristics. We have also determined adsorbent power of sediment and the nature of over flow water. The results show that the water quality of Sebou river estuary is mainly influenced by the industrial and domestic waste water from Kenitra city agglomeration. The adsorbent power of the phosphate ions in one hour of the contact is approximately 60 to 80%.
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6 (3), 291-300
The metasomatic effect of carbonated fluids on the chemistry of Na-Fe clinopyroxenes is demonstrated from a melteigitic sample crosscut by a carbonatitic vein. The clinopyroxenes are progressively enriched in Na, Fe3+ and Si and depleted in Ca, Al and Ti. The comparison with the similar zoning observed in a pegmatitic sample without any metasomatic imprint, suggests that such normal zoning may be related to the increase of pCO2 during crystallization.
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6 (3), 301-314
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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6 (4), 315-329
All geological studies undertaken on the region of Tunis have emitted only some hypotheses concerning the nature and the installation of the different geological layers characterizing the underground of the capital. These works have not considered the precious geological and geotechnical information from geotechnical investigations carried out over several years at different sites of Tunis. The collection, structuring and management of these information within a Geological and Geotechnical Information System, the analyses and the restoration of these information under the form of geotechnical maps to be able to specify the geology of the underground of Tunis were carried out.
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6 (4), 331-359
Major, economically important coalfields occur in the mid Zambezi Valley of southern Zambia. The discovery of this coal in the mid 1960s resulted in the first substantial surface and subsurface investigation of the coal-bearing sequence. This sequence is now known as the Gwembe Coal Formation, a Permian fluvial sequence within the continental Karoo Supergroup. Coal contained in a 5-12 m thick Main Seam of the Permian Gwembe Coal Formation is currently mined and indications are that, owing to block faulting, some coal-bearing sub-basins are buried and not yet discovered. This paper outlines coal deposits of the mid-Zambezi Valley Basin, describing the setting, geology, exploration effort, evaluation, reserves and usage. Depositional environments are highlighted and recommendation for further exploration are given at the end.
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6 (4), 361-379
New lithostratigraphic, sedimentologic and geodynamic data on the Terminal Proterozoic and Lower Cambrian succession in the Western Anti-Atlas (Morocco) from analyses of outcrops exposed in Bas Draa, Anzi, Ait Abdallah, Ait Baha, Tighmi and the Kerdous northwestern border. Recognition of sedimentary environments based on the study of various lithofacies and many depositional environments and subenvironments are distinguished: alluvial fan, marine fan-deltas, fluvial system, lacustrine system, sebkha, shallow marine carbonates, offshore carbonates reefs, tidal dominated siliciclastic platform and offshore siliciclastic tempstites. The stratigraphic, sedimentologic and paleogeographic patterns are interpreted as the result of the infill rift basin generated in the western Anti-Atlas during a lower Paleozoic distensive event. The differential tectonics is the main control on basin structuration and consequently on rift basin architecture. Extensional events, during the synrift stage began at Anzi-Tighmi zone and the propagation of this distensional tectonics reached the northern and western border of Kerdous. The first event is represented by the Anzi group, wherease the second one is represented by the Asghrkyis group. Within the postrift succession the resulting vertical facies association shows a stack of two sedimentary groups. The Madaw group reflect an increased eustatic rise and a quiescence tectonic stage, while the Ait Abdallah group is the result of a tectonic subsidence and eustatic control on basin sedimentation and consequently sequential organisation.
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6 (4), 381-396
L'approche multidisciplinaire se montre intéressante pour subdiviser la Tunisie en grandes provinces hydrogéologiques. Cette subdivision constitue un document de base pour tout programme de recherche et de prospection des ressources du soul-sol. Le traitement intégré des informations brute et/ou interprétée fournies par les études multidisciplinaires a permis de subdiviser la Tunisie en neuf grands bassins hydrogéothermiques limités par des aires de recharge à l'amont et de décharge à l'aval pour l'eau souterraine. Le traitement des données par bassin hydrogéothermique a permis de tenir compte des caractéristiques hydrogéologiques et hydrodynamiques des nappes aquifères. L'examen comparatif des paramètres physico-chimiques des eaux des sources et des forages a mis en relief l'intérêt de l'exploitation par forage pouvant être mieux géré que la source plutôt aliénante. Ces eaux souterraines appartiennent à des faciès où dominent les chlorures, les sulfates, le sodium et le calcium. Les bassins hydrogéothermiques distingués vent caractérisés par une homogénéité chimique à l'exception des bassins du Nord dont l'hétérogénéité, aussi bien latérale que verticale, des formations géologiques influence la naturegéochimique des eaux souterraines. Ces eaux sont, en général, saturées vis à vis de la calcite, l'aragonite et la dolomite. L'évolution des indices de saturation par rapport à la force ionique, obéit à une équation linéaire suivant laquelle les eaux sont distribuées entre un pôle sous-saturé et un pôle saturé vis à vis du gypse (et de l'anhydrite). Ce résultat témoigne du lessivage des formations géologiques riches en ces minéraux depuis les zones de recharge jusqu'aux zones de décharge des bassins hydrogéothermiques; ceci correspond vraisemblablement à une acquisition de la minéralisation au cours du transit des eaux entre l'entrée et la sortie du système hydrogéologique.
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6 (4), 397-409
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.
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7 (1), 1-17
The palynological analyses of the 3000-6000' interval of the Ise-2 well (onshore SW Nigeria; easternmost part of the Benin Embayment) indicates a Lower Cretaceous age dating. The palynological associations are rich in age diagnostic species. They are compared with the palynozonations proposed in Gabon and NE Brazil, particularly those of the Potiguar Basin, adjacent to the Benin Embayment at that time. These results are integrated into the Lower Cretaceous geological frame work proposed offshore Benin and West Nigeria. Comparisons with the Potiguar Basin could be very important for the development of the deep offshore of the Benin Embayment.
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7 (1), 19-38
The Miocene to Quaternary succession exposed around Luanda is divisible into (from bottom to top): the pelitic sediments of the Quifangondo Formation, interpreted as deposited on a neritic ramp of Burdigalian age; bioclastic deposits of the Cacuaco Formation, characterised by "foramol"-type fossil assemblages pointing to a high-energy open shelf environment of Burdigalian age; terrigenous and carbonate sediments of the Luanda Formation referred to a transitional environment (lagoon, beach, estuary) of Miocene or Pliocene age; the alluvial deposits of the Areias Cinzentas Formation; and continental sediments of the Quelo Formation. These last sediments are locally overlain by dark grey to Wack shales of "Argillas Petras unit" interpreted as a solum related to the weathering of a pre-existing deposit, during the Holocene. The Tertiary succession records a 2nd order transgressive-regressive cycle, from offshore (the Quifangondo Formation) to infralittoral (the Cacuaco Formation) and to swamp or supralittoral deposits (the Luanda Formation), driven by tectono-eustasy. Since the end of this 2nd order cycle the study area was subaerially exposed as testified by the continental Quaternary deposits.
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7 (1), 39-53
The Paleozoic terranes of the Eastern High Atlas cropout mainly in Tamlelt inlier. They are subdivided into two structural units: northern and southern domains. The first which appears as an east-west-striking belt, was deformed during the Upper Devonian by D1 + D2 deformations (Eo-variscan phase ). NNE-SSW-trending isoclinal folds associated with low-grade metamorphism, are deformed again by a D3 deformation of Late Carboniferous phase (Namuro-Westphalian) age. The second domain corresponds to the central-southern part of the Tamlelt inlier, where the major D3 deformation is well expressed. The east-west-trending folded structures and late imbricate structures have a general southern vergence. Late orogenic shear zones are developed in the part of the second domain. This phase, called D4, developed eastwards overturned F4 folds.
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7 (1), 55-73
Geometry of Beglia Formation deposits (Middle Miocene) and their lateral equivalents in Tunisia and in Pelagian Block: sedimentology and depositional sequences. The analysis of some sedimentary structures in outcrops of Middle Miocene siliciclastic deposits (Beglia Formation), and the seismic record interpretation supported by the well log data compilation (Birsa and Nilde Formations) display a strinking lateral and vertical lithologic variations which could be related to the development during this period of a deltaic system. This system is influenced by the surge, the storm and the tide. The sequential subdivision proposed here shows that these deposits with those of Langhian stage are organized into three third order sequences which could be correlated with the global cycles TB. 2-4, TB.2-5 and TB.2-6.
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7 (1), 75-82
Fossil pollen studies from several wetlands in Maputaland provide information on the history of the expansions and the retreats of Podocarpus spp. in this region during the Quaternary period. Pollen data from a 45 000-year-old peat deposit at the Mfabeni peatland, on the eastern shore of Lake St Lucia, show that extensive swamp forest occupied the area between 45 000 and 41 000 years BP, which to the end of the Pleistocene, alternated with drought-tolerant vegetation. This alteration may suggest a drier and colder climatic phase. Pollen records from sediments in Lakes Teza and St Lucia, Sodwana Bay, Muzi catchment and Black Rock area give evidence of the occurrence of Podocarpus forest in the northern part of the coastal plain in the early and middle Holocene. The forest retreated from the area after about 5 000 years BP. In the region of St Lucia, the last occurrence of Podocarpus pollen was noted in samples dated at around 2450 years BP. In the Sodwana Bay area, there was no Podocarpus pollen in samples younger than 1410 years BP. Pollen from the northern part of Maputaland (Kosi catchment) shows that the forest retreated about 1390 years BP. The pollen data from the Mhlanga peatland on the southern margin of Maputaland indicate that, in the Holocene, Podocarpus forest was restricted only to the northern part.
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7 (1), 83-90
The Lega Dembi Primary Gold Deposit in southern Ethiopia occurs within Proterozoic N-S-trending volcano-sedimentary rocks, consisting of a sequence of biotite-feldspar-quartz schists, carbonaceous mica-schists, amphibolites and basic to ultrabasic rocks. This unit is separated from a foot wall high grade biotite gneiss by a major shear zone. The ore bodies are hosted in the volcano-sedimentary sequence and consist of swarms of quartz veins, lenses, and stockworks. The mineralization is defined by a complex paragenesis of gold in association with Cu- Pb-Zn-Fe sulphides, tellurides and sulphosalts. The presence of Ni-bearing minerals in amphibolites of the host sequence, together with the ore mineral association, suggests an origin related to mafic volcanism.
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7 (1), 91-100
Heavy metals distribution in core samples taken from the bed of the Yarmouk River, Jordan, has been studied for different grain-size fractions (clay fraction < 2 µm, silt fraction 2-63 µm, and non-detrital fraction > 63 µm). Lead and cadmium exhibit high concentrations both in the clay fraction (< 2 µm) and in the silt fraction (2-63 µm). Zinc, nickel and cobalt are enriched in the silt fraction. In the non-detrital fraction (> 63 µm) only cadmium, shows higher concentrations. The correlation matrix of heavy metals in the clay fraction suggests the importance of Cd, Cr, and Mn in their accumulation. Cr and Mn for silt fraction and Co for the non-detrital fraction. The enrichment factor is usually < 1 for almost all metals. The non-detrital fraction shows almost reasonable concentrations of all the elements, within the permissible limits, except for Cd, which shows concentrations between 0.3-1 ppm.
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7 (1), 101-113
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph.D. and M.Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community. Remarks, corrections and additions to the bibliography will be most welcome.
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7 (2), 115-185
Liberia and Sierra Leone are two West African countries that have been devastated by recent civil wars. Both countries are situated on the Archaean Man or Liberian craton, which is rich in minerals, such as gold, diamonds and iron ore. Ironically, it is this very mineral wealth, especially the diamonds, that has fuelled the civil wars, and has led to call for a boycott of West African diamonds (Doyle 1999a,b,c, 2000; Global Witness, 1999; Standley, 1999). More recently, the new unity government of Sierra Leone has suspended all licenses and has called for the cessation of all diamond mining activities, until they can be brought under the control of the central government, for the benefit of the whole country (Doyle, 2000b). Structure of the bibliography. This bibliography is designed to provide background material for renewed exploration activity which will follow the re-establishment of peace in the region. It has been structured in two main ways: by country (Liberia, the Ivory Coast, Guinea, Sierra Leone); and according to the following topics (for Liberia and Sierra Leone): General, Archaean, Palaeoproterozoic, Pan-African, Palaeozoic, Mesozoic, Cenozoic. Under the heading General are placed items such as books and articles dealing with the whole country, geological, geophysical and topographic maps of the country, etc.
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7 (2), 187-199
The Zeïda ore deposit is made up of a stratiform lead and barite hosted by Triassic arkosic series represented by a succession of arkose and marly interbedding showing several dynamic traces (oblique stratification, graded bedding). This formation, which is unconformable to the late-post Hercynian granites, was deposited in a shallow marine environment with a dominant fluvial sedimentation. The mineralizations are concentrated in paleochannels stratified or disseminated forms or as veins. The ore associations develop various facies which evoke mainly an epigenetic ore feature. To explain the ore deposit setting, we propose a system in relation with upwards hydrothermal fluids and a superficial descending water that leaches and mobilizes metal extraction from the basement. Once more, here, like anywhere in the Upper Moulouya district, the mineralization has occurred on the interface between hot hypogenic fluids hosting mineralizations and oxidized, cold supergenic fluids.
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7 (2), 201-209
Micro-concrete roofing tile is manufactured basically with local law materials (sand, broken granite, cement and oxide). The only imported component is the synthetised oxide. Its substitution with a local raw material will surely reduce the production cost of the products. This project consists in optimizing the colouring of roofing tiles with a clay identified in the region of Bonoua, Côte d'Ivoire. It has proved that with 10 % of this clay, it is possible to produce tiles with a colour very close to the colour (brown - dark orange)of burnt clay tiles. The characterisation of this clay has shown that it contains 20 % of iron oxide (Fe2O3) and is composed of kaolinite, illite and quartz. An economy of 18 % of the prize of the final product is obtained. The permeability test proposed by the Ivorian Standard cannot be the only test to justify the good quality of a tile.


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7 (2), 211-220
Many of the countries within the Economic Community of West African States (ECOWAS) possess a wide range of mineral resources which constitute a useful source of foreign exchange earnings necessary for national development. However, most of the resources are merely exported and the proceeds used for the importation of finished products derived from these exported raw materials. There appears to be an absence of a strategic medium- to long-term planning for the management of the exploitation of these non-renewable raw materials. It is evident that except for the oil producing countries like Nigeria, Equatorial Guinea, Cameroon and Côte d'Ivoire, the mining sector plays a very important role in the sustenance of the national economy of most ECOWAS countries. Despite this dominance, the contribution of mining to these countries' GDP is not impressive, averaging 7.0 % except in Guinea where it is 15.2 %. The presence of a wide range of mineral resources necessitates the formulation and implementation of policies for the establishment of industries to process some of these materials and maximise earnings from mineral exploitation for the establishment of the much needed infrastructures such as roads, telephone lines, electricity. A regional approach to mineral resources management could be a positive step towards the adaptation of management programmes that will facilitate research, exploitation of non-renewable mineral resources, and marketing of semi-processed products from these resources for the overall accelerated development of the region.


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7 (2), p221
Geophysical data can provide valuable geological information to assist mining operators develop proactive mine plans to address their exploration, engineering, environmental, and production requirements. Recent developments in geophysical instrumentation and interpretation software particularly in petroleum exploration are increasingly being modified and effectively applied in mineral exploration and exploitation. Several examples of mining operations from different parts of the world are discussed to demonstrate the important role of Geophysics in both mineral exploration as well as mining operations.


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7 (2), p223
This paper discusses the rare mineral deposits found in central Africa which are vital for the development of modern technology. The linkage between the civil wars and the mineral wealth in the region is highlighted.


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7 (2), p225
C'est un lieu commun de dire que le continent africain est riche en ressources minières. Celles-ci, objet de convoitise et d'une exploitation plutôt erratique, entraînent souvent violence et spoliation dans les pays producteurs. Comment peut-on lutter contre ce dangereux tandem? On note, en ce qui concerne l'Afrique subsaharienne, une désinformation chronique et persistante. En particulier, on a vite fait de donner aux conflits armés qui hantent l'Afrique des causes qui laissent de côte l'essentiel: la présence de richesses naturelles et la rapacité des uns et des autres à obtenir le contrôle de leur exploitation. On examinera le cas de l'Ogaden et celui de la Sierra Leone. Les richesses servent souvent à faire fructifier la vie industrielle et économique de pays qui ne les ont pas produites avec pour seule contre-partie sur place violence et mort. Ce détournement est encouragé par le fait que les données sur les ressources minières restent vagues et que leur mode de gestion permet toutes les fraudes, surtout à l'égard des populations qui, le plus souvent, ne bénéficient pas des richesses sur lesquelles elles vivent. Exploitation du pétrole au Nigeria, des mines de diamant en Afrique du Sud, de l'or au Mali, ces exemples vont nous aider à remettre en cause le mode de gestion des ressources minières. S'il est difficile de faire un retour en arrière sur la présence des multi-rationales, leur façon d'opérer doit cependant être révisée de manière à profiter aux populations locales en particulier par le traitement sur place du produit brut. D'autre part, il existe un mode d 'exploitation que l'on pourrait qualifier d 'artisanal qui ne profite guère plus à la population locale que celui des multinationales car il se fait souvent de façon sauvage, c'est-à-dire sans contrôle. Pour ce qui est de cette forme d'exploitation, il serait souhaitable d'envisager un regroupement des petites entreprises individuelles, peut-être en coopératif. On sait que la formule a donné de bons


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7 (2), p227
The Macalder - Migori area in western Kenya has been the focus of gold mining operations since 1941. The gold together with copper, lead, zinc and silver occurs in the Precambrian greenstone belts in fractured contact zones between the intrusive granites and basalts, greywackes and associated banded iron formations. Mining and processing of the ore-rich gossans has resulted in the discharge of groundwater of highly acidic and corrosive nature as a result of conversion of the pyritic ore into water soluble sulphates, leading to gross heavy metal pollution of the nearby rivers Migori and Kucha, with dire consequences to fish and other aquatic life forms. In addition, the quality of the surrounding soils has degraded due to their accumulated burden of heavy metals released from the mining operations. The old slime dams act as oxidation chambers where running surface water reacts with sulphur laden solutes. The slime dams contain highly stained ochreous material and are the sites where the ore-rich waste materials were deposited. Water pollution is attributed to extensive leaching and erosion of the dislodged overburden. Copper, chromium, zinc, cadmium, lead and arsenic in waters of the nearby Migori and Kucha rivers show elevated concentration levels that are several orders of magnitude higher than the permissible levels set for river water by international environmental agencies such as the World Health Organization. However, concentrations of these elements in soil decrease away from the mine site. Acid mine drainage is also not considered to be a serious problem in terms of the sulphide chemistry of the receiving waters. Again too, parameters such as pH and electrical conductivity were within acceptable ranges in the receiving waters, due to a dilution effect, but pervasion of the atmosphere by mercury vapour from the amalgam process continues to present a constant threat to the long term health of the alluvial artisans. The above observations are reviewed in relation to the sources, pathways and eventual fate of the toxicants. A risk assessment is presented and some measurements of exposure levels given, for the nearby population and those dependent on the Migori and Kucha for their domestic water supply. Practical guidelines for improving the quality of the receiving waters as well as measures for instituting an ecotoxicological monitoring system at the mine sites are also given.


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7 (2), 229-230
De la Conférence de STOCKHOLM (1972) à nos jours, on peut noter une nette évolution dans l'approche de la problématique de protection de l'environnement et de l'exploitation des ressources naturelles. Des voies se dessinent actuellement dans un esprit de coopération entre Société minières et organismes de protection de l'environnement qui tendent à intégrer les concepts de protection à long terme, en partenariat avec les communautés locales. On a noté par exemple que l'extrême pauvreté des populations riveraines des certaines aires protégées constituait une grande menace pour l'intégrité de ces sites. Un des moyens pour atteindre les objectifs de conservation résiderait dans une coopération fructueuse entre différents partenaires.


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7 (2), p231
Groundwater resources of Cameroon are limited with respect to quantity because more than 80% of the surface geology is Precambrian crystalline impermeable rocks. Documented groundwater quality is known only on thermal and mineral springs along the Cameroon volcanic Line. Around Ekondo-Titi, which is found in the NW flank of Mount Cameroon, the Lobe hot spring water was shown to be of a Na + K-Cl facies, with an ionic strength greater than 0.005 M. Thus rendering it brackish and unfit for human consumption. Meanwhile the quality of groundwater that is exploited in water wells for consumption by more than 80% of inhabitants of this area is unknown. Such a limitation renders water management for potability in such a rural area difficult and partly accounts for the very low percentage (EMBED Equation.3 10%) population with safe drinking water. Against this background, an evaluation of the quality of groundwater was carried out around Mount Cameroon, where potable water supply is a problem, especially in the NW flank. The results of groundwater quality in this flank of the mountain with volcano-sedimentary aquifers show that, although a water well had hardness of more than 75 mg/l as CaCO3 thus rendering it unsafe for drinking, the groundwater is of a Na + K-Cl facies, with ionic strengths less than 0.005 M; thus fresh and potable. These results do not reflect the brackish, though still dominant Na + K-Cl waters reported on the Lobe hot spring in the area. In the SW and SE flanks of the mountain, the volcanic aquifers here contain fresh potable CaMg-HCO3 dominant groundwater, which SUPERMONT is exploiting for commerce, but surface water are polluted at specific areas by nitrate ions from human activities. From these finding, it is hoped that similar detailed chemical evaluation of water resources in other rural areas needing potable water could be carried out because such work will be useful for the delineation and protection of fresh water aquifers and their sustainable exploitation in order to cope with the ever increasing demands and decreasing supplies.


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7 (2), p233
Les terrains affleurant en Guinée sont très variés, il témoignent d'une longue histoire depuis l'Archéen, jusqu'à nos jours (Quaternaire). Au Précambrien, la Guinée appartient au craton ouest-africain et plus particulièrement à sa partie sud appelée dorsale de Léo (ou de Man). L'histoire précambrienne est subdivisée en quatre périodes principales. La plus ancienne est l'Archéen dominé par une activité plutonique intense développée entre 3540 et 2600 Ma. Sur les terrains plutoniques archéens reposent des formations supra-crustales à quartzites ferrugineux, d'âge archéen à paléoprotérozoïque précoce et connues pour leurs gisements de fer (Nimba, Simandou). Intervient ensuite, au Paléoprotérozoïque, le cycle Birimien réputé pour sa fertilité en or. La période suivante correpond au Néoprotérozoïque (il n' y a pas de Mesoproterozoïque connu), elle est marquée, entre 1000 et 600 Ma, par les dépôts néoprotérozoïques tabulaires de la bordure sud du bassin de Taoudéni. Les événements archéens et Paléoprotérozoïques seront présents dans leur cadre géotectonique ouest-africains.


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7 (2), p235
Geological activity started in Cameroon from the Colonial period (1887-1960), when the Germans published an outline geology of Cameroon, just before the first world war. During the French colonial rule, the mineral policy had four orientations: encouragement of private sector, geological mapping of the national territory, creation of mining bureau, and training of Cameroonians. From 1960-2000 mining activity has been the work of the Department of Mines and Geology. It produced a mineral prospects map of Cameroon, which indicates that the territory is endowed with bauxite, rutile, iron (momelles), nepheline-syenite, casseterite (tin), gold, nickel-cobalt, disthene, uranium, diamonds, sapphire, rubis, lead, zinc, secondary clays, limestone, gypsum, corrundum and saltsprings. From 1988-2000, the economic crises discouraged foreign investors and in 1995-96, tens and hundreds of thousands tons of products from these minerals were imported. Although S new state universities were created in 1993, in a bid to reactivate geological training and explorations, the mining sector is still facing the following problems: the absence of a proper mining law, which is allowing among others, illegal small-scale mining practices with many impacts on the environment, the neglect of geological exploration in the country's economic policy, the absence of a national body specialised in mineral exploration, and the appointment of non-geologists in positions meant for geologists. These problems, which are destroying the geological culture in Cameroon, can be solved by creating institutions which will cater and encourage the mining sector, thus improving on the socio-economic development of the country.


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7 (2), p237
The pre-mining environmental map is a useful tool in the environmental management of a mining project. It constitutes an essential aspect of the Environmental Impact Assessment and can be prepared on a topographic or aerial photos base-map material. The scale of the maps will depend on the area and size of the mining project but a scale of 1:25,000 or 1:50,000 is appropriate. The map contains the following information on the pre-mining site: - topography indicating the surface contours and any existing excavation or disturbances as well as the elevation of important locations; - hydrological and hydrogeological details including locations of water courses and the position of the 1:50 year flood-line where the envisaged mining activities are within 100 m of a stream; - position of existing infrastructure including roads, railway lines, power lines, telephone lines and villages. The map is complemented with some supplementary notes which describe the geology of the area and the soil types that will be disturbed by mining. Surface wafer sources and water chemistry are described in detail and the land is classified into the classes of land capability and land-use before mining. There are still large portions of sub-Saharan Africa which are yet to be explored for mineral resources. Mineral exploration in these areas must be initiated by the preparation of the environmental maps which will ensure that mining activity is implemented in a conducive environmentally-friendly manner. Restoration or rehabilitation of the mine will also be facilitated by a well prepared map of the pre-mining environment.


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7 (2), p239
Dans le petit bassin versant de plateau de Samené (2,34 km³), appartenant au bassin de Bidi au Nord du Burkina Faso, le dispositif de mesures hydropluviométriques et piézométriques insta1lé, ainsi que la description détaillée des états de surface du sol pendant l'année 1995 montrent: 1) cinq unités hydrologiques regroupant dix-sept types de surfaces élémentaires réparties entre les champs de cultures sur sols sableux fins, argilo-sableux et limoneux (60 % de la superficie du bassin), les sols sablo-limoneux en jachère (27 %) et les sols dégradés gravillonnaires et cuirassés (13 %); 2) un coefficient de ruissellement de 74 % pour les zones hautes cuirassées et gravillonnaires en bordure du bassin; 3) un coefficient de ruissellement de 31 % en début de saison, pour les champs de cultures autour des habitations; 4) un coefficient d'écoulement mesuré à l'exutoire du bassin représentant environ 3 % de la pluie moyenne au sol dans le bassin estimé à 583 mm en 1985. Un modèle de terrain prenant en tenant compte les états de surface du sol, de la lame ruisselée en provenance de l'amont de la colonne de sol considérée et des paramètres hydrodynamiques (essai Müntz) a permis d'estimer la lame d'eau drainée à 1 m de profondeur. La comparaison en a été faite avec la lame d'eau atteignant la nappe d'eau phréatique dans des puits villageois en position morphologique et dans des situations d'états de surface différentes. Le battement de la nappe en 1995 est plus élevé sur les mi-versants que sur les haut-versants; dans cette zone, l'infiltration est favorisée au niveau des champs de cultures (situés juste à miversant) sarclés et billonnés avec des cordons pierreux isohypses, permettant ainsi une meilleure recharge de la nappe phréatique de la base des altérites latéritiques. Mots-clés: sahélo-soudanien ; bassin versant ; recharge ; modélisation ; piézométrie ; états de surface ; nappe superficielle


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7 (2), p241
Les gîtes aurifères du Paléoprotérozoïque du Burkina Faso peuvent être classés, en fonction de la nature et de la structure de la roche hôte du minerai et du degré et du mode de concentration de l'or, en deux types principaux: les gîtes à or concentré et les gîtes à or disséminé. Les gîtes à or concentré (6 à 8 gr/t), type le plus commun, correspondent à des filons de quartz déformés au sein de zones de cisaillement d'importance régionale. L'or apparaît directement associé à des sulfures ou à la tourmaline cristallisant aux extrémités des cristaux dans des zones d'ombre de pression ou/et dans des fentes de tension. Les données microthermométriques de la première génération d'inclusions fluides, biphasées et triphasées, indiquent une ou deux phases à CO2, pratiquement pur, avec une salinité moyenne autour de 3.0 % p. éq. NaCl; des traces de CH4 ont été détectées en spectrométrie Raman. L'homogénéisation de la phase carbonique se produit entre 17.2 et 30.9°C. L'homogénéisation de la phase vapeur se produit entre 280 et 330°C. Les gîtes à or disséminé (2 à 3 gr/t) correspondent à des listvénites et à des albitites apparaissant au sein des formations des ceintures de roches vertes, les listvénites au sein des roches ultrabasiques, les albitites au sein des métavolcanites et des métasédiments. Ces roches, plus compétentes que leur encaissant, subissent au cours des phases tectoniques une fracturation hydraulique développant en leur sein une succession de fentes de tension permettant la concentration des fluides à l'origine des minéralisations. L'étude du remplissage des fractures permet de mettre en évidence une succession de transformations marquée par: i) une métasomatose sodique, affectant l'ensemble des formations; elle résulterait de l'interaction entre les roches et un fluide de type eau de mer dans des zones contrôlées par la déformation; ii) une métasomatose carbonatée, développant les listvénites et se traduisant par la formation de magnésite ou d'ankérite dans


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7 (2), p243
The contribution of industrial minerals to the national economy has always been underestimated. This is particularly so because extraction is dominantly artisanal, with rare cases of semi-industrial exploitation. Extraction is mainly from igneous and metamorphic rocks which comprise about 70% of the major rock types found in Cameroon. The outcrop of the Loum quarry is migmatitic, characterised by gneisses, pockets of pink granites and white feldspathic veins, with the feldspars occurring between the gneisses and granitic bodies. The thickness of the feldspar veins range from less than 1 mm to above 10 cm. Compared with international standards for industrial minerals, the feldspars are good for glazing. Furthermore, their separation into veins makes their extraction very easy, hence augmenting their economic potential. Macroscopic investigation of the granites, which are the main igneous bodies in the migmatite reveal that they are very compact. This, in addition to their pink colour makes them very suitable for dimension stones and decorative slabs. Of abundant occurrence are the gneisses which are good for aggregates. In spite of this great economic potential, exploitation of this migmatititic outcrop is presently limited to aggregates. Such under-exploitation, besides generally having a negative impact on the national economy, reduces the number of jobs which would have created if all the component rocks of the Loum migmatite were appropriately exploited.


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7 (2), 245-246
The role of industrial rocks and minerals in the national economies of most African countries like Cameroon has always been underestimated. This is so because extraction is dominantly artisanal with rare cases of semi-industrial exploitation. As a result, quarrying of these rocks and minerals is usually placed under the informal sector of the economy, thus downplaying its economic importance. That notwithstanding, this informal activity contributes greatly to most national economies in Africa. Hence the need to economically and environmentally assess their exploitation in a bid to optimise their extraction within a sustainable environmental framework. Nine quarries located in various rock types in Cameroon were selected for this study based on the geology and extraction method. They include the Manjo, Yaounde and Pouma metamorphics, the Bamenda granites, the Batie weathered granites, the Ombe basalts, the Djoungou pyroclastics, the Muyuka sandy alluvial and the Buea volcano-sedimentary quarries.


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7 (2), p247
Un SIG concernant les GéoSciences du continent africain a été lancé en 1998 par le BRGM. Il a pour but de mettre en valeur à une échelle de synthèse le 1:2 000 000 ème, utile au développement durable, les excellentes données dispersées concernant (Géologie, Ressources Minérales, Eau, etc.). Un SIG GEOCARTES informant sur l'état des couvertures cartographiques ainsi qu'un exemple de SIG sur l'Afrique Centrale seront présentés. Ils constituent un par vers la création d'un réseau WEB de méta-données et de données harmonisées susceptible de contribuer aux actions de formation et d'aide à la décision institutionelles et industrielles.


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7 (2), 249-250
De Beers is currently exploring for diamonds in 9 African countries: South Africa, Botswana, Namibia, Zimbabwe, Angola, Tanzania, Gabon, Guinea and Mali. Besides these active projects, De Beers is also evaluating the possibilities of undertaking prospecting in the DRC, CAR, and Algeria and is about to embark in exploration in Mauritania. With an estimated 60 million carats produced in 1999, Africa remains the largest producing continent in the world. By value, last year's production is estimated at US$ 4.75 billions which represents ca 65% of the world's diamond value. Therefore, De Beers, through its mines and exploration ventures, remain largely committed to Africa. Diamond exploration always initiates with target selection, or, in other words, by establishing the nature and extent of Archaean cratons. These ancient and stable shields, which occur throughout Africa, present the best possible geological conditions for the formation of diamonds in the lithosphere and the emplacement of their host rocks (namely kimberlites and lamproites). Although this model is relatively simple and well proven, the definition of these cratonic areas is often very complex, especially in most parts of Africa where geological information and geophysical data is often scarce if non-existent. The cratonic and tectonic evolution and other important factors, such as levels of erosion, must also be taken into consideration when selecting targets for the prospecting of primary diamondiferous sources. The Man craton in West Africa represents undoubtedly one of such targets and, in principle, has all the requisites for the discovery of a "world class" primary diamond deposit. However, in spite of more than 40 years of exploration (by many ventures including De Beers), the Man craton has somehow evaded this "hope". De Beers commenced intensive diamond prospecting in Guinea at the end of 1995. The area targeted was the southeastern part of the country where alluvial diamonds abound and many kim


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7 (2), p251
The projected population of the African continent in this year (2000) is about 820 million and its average annual growth rate of the total population in this new millennium will be the highest (ca 2.5%) when compared to other continents. In the Africa's decade of rennaissance (1990-2000), its average positive economic growth rate was about 2-5%, but about 40% of its population in the sub-Saharan Africa falls into the absolute poverty category, according to the UN records. By 1995, the Africa's external debt burden amounted to about US$ 330 billion for which sub-Saharan Africa accounts for about US$ 231 billion. Africa has enormous earth resources. It has the world's largest reserves of strategic minerals such as Cr (82%), Co (54%), Mn (52%), Au (30%), U (29%), V (20%) and many undiscovered and underestimated earth resources. Development and sustainable management of these resources are necessary for poverty eradication in the continent. Hence, geosciences have a key role to play so as to increase the economic growth rate averaging 5-7% a year which is deemed necessary for poverty alleviation and eradication in Africa. Thus, geosciences in Africa and elsewhere have to provide solutions to societal or community problems. They have to contribute significantly to the socio-economic development of the peoples of the African continent. For Africa, geoscientific objectives in this new millennium have to be focussed at: (i) provision of sufficient earth resources (e.g., water, energy, minerals), (ii) provision and maintenance of quality education and research in geosciences, (iii) sound environmental management, timely assessment of natural hazards and mitigation of disasters; and (iv) advising and influencing politicians and decision makers on matters pertaining to the development and management of Africa's earth resources for sustainable socio-economic development of the continent.


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7 (2), p253
Les formations paléoprotérozoïques du craton de l'Arique de l'Ouest sont constituées par de ceintures de roches vertes aux limites de corps de granitoîdes représentant plus de 70% des affleurements. Les granitoïdes ont fait l'objet d'études pétrographiques, géochimiques, géochrologiques alors que les études stucturales sont plus limitées (essentiellement Pons et al., 1992 et 1995). Or la mise en place des granitoïdes apparait être un procesus fondamental dans la structuration de la croûte birimienne. Ce processus a été analysé dans la région du Liptako-Gourma à l'E du Burkina Faso où l'alignement plutonique Tenkodogo-Yamba (APTY), orienté NNE-SSW, 125 km de long, 25 km de large, constitué de granite à biotite se développe au sein d'un batholite composite de type TTG. Les structures de l' APTY et de son proche encaissant ont été définies par des données magnétiques en utilisant la technique de l'ASM dont les sites ont été situés sur une grille régulière de 2 km x 2 km. Les trajectoires des foliations de l'APTY apparaissent sigmoïdes et fréquemment sécantes sur les limites de l'alignement. Fortement pentées elles contiennent une foliation souvent subverticale. Ces données géométriques associées à l'étude des enclaves des composants du batholite au sein du granite de l'APTY et des caractères des déformations cristallines permettent de définir le mode de mise en place. Le granite à biotite de l'APTY se mettrait en place dans des structures dilatantes alignées ménagées par une tectonique transcurrente au sein d'un batholite de type TTG entièrement cristallisé et fortement refroidi. La fin du processus se traduirait par le développement des zones de mylonites régionales aux limites de l'alignement.


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7 (2), p255
Slope movements are a widespread phenomenon in the foothill areas of the Bamenda Highlands in the Northwest Province of Cameroon. This paper presents an overview of the causes and events that led to the occurrence of the Anjin landslide on the 15th of September, 1998 in the Belo-Subdivision that involved the sudden movement of over 1.5 x 10(6) m³ of rock and soil over a distance of about 400 m resulting in the death of two people. The approach included mapping of the landslide prone area, and the geological and geomechanical factors that resulted in the landslide were analyzed. In this study the database needed for a geotechnical characterization of the soils and empirical modeling to estimate the physico-mechanical parameters that aided in triggering the landslide were unavailable. In this respect, the geological and geomechanical properties of the rocks and the hydrogeology of the area were investigated along selected transects. The causes of the landslide were as a result of the complex geotectonic regime of the region that generates various instability conditions. The region is highly-fractured and traversed by multiple discontinuities of various directions on high angle slopes. These discontinuities are generally NWW-SEE-trending and are at variance to the dominant NE-SW trend of the Cameroon Volcanic Line which runs through the region. These zones of weakness generate unstable geotechnical conditions in the rock mass, which were accentuated by the growth of trees, the hydro-meteorological conditions and the frequent vibrations generated by machinery carrying out road construction in the area at the time. This article also formulates proper protection remedial measures of slopes, especially those close to residential areas.


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7 (2), p257
There has been a corresponding increase in construction of habitation to meet the demand of over half a million inhabitants of Bamenda as a result of the rapid increase of population in recent years. The principal locally available building material in the region is alluvial sand along the valley of River Menchum 50 km north of Bamenda. The sand originates from weathered granite underlying a section of the town. The method of exploitation is artisanal and the small scale miners operate as a cooperative enterprise. This paper reviews the artisanal mining method and suggests a more effective method using a water pump to disintegrate the sand and ensure a more consistent production.


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7 (2), 259-265
SEAMIC is a non-profit intergovernmental organisation established in 1977, under the umbrella of the United Nations Economic Commission for Africa (UNECA). The mission of SEAMIC is to promote socio-economic and environmentally responsible mineral sector development in the eastern and southern Africa sub-region, through the establishment of an independent and reliable mineral centre of knowledge, training, laboratory services, research and development, geoscience data processing and other services and products. The Centre was established out of the realisation that through co-operation and pooling of scarce resources together, its member States could establish a Centre of Excellence with a critical mass of highly trained experts, which could realise economies of scale, avoid duplication of efforts and repetition of mistakes, access in a cost-effective, efficient and focussed manner specialised mineral services and technology, and narrow the technology gap with the rest of the world. To-date SEAMIC represents a successful example of regional co-operation and it is an important player in mineral resources development in the region. It is a hub or a one-stop-shop for geo-information on the region, facilitates and provides a forum for scientific interaction and high-level specialised training, and provides good quality, accessible and competitive services to its customers. The importance of SEAMIC is more relevant in the field of industrial minerals development, because the Centre offers in one facility, services for laboratory testing and characterisation of raw materials, research and development on applications and product development including pilot manufacture of ceramic and other prototypes using a wide range of non-metallic minerals. Such combined assets are rarely found in the region.


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7 (2), 267-268
L'échantillon qui arrive sur le coin de la paillasse ou du bureau est-il bien "représentatif" du "lot" de matière dont la référence figure sur l'étiquette? Sauf s'il a été prélevé en respectant certaines règles, il n'y a aucun moyen de le savoir. Des tests faciles permettent de reconnaître un vrai diamant d'un faux: un faux billet de banque d'un vrai, mais on ne dispose d'aucun moyen qui permette de reconnaître un échantillon représentatif, digne de confiance, d'un spécimen sans valeur: l'échantillon n'a jamais aucune mémoire des outrages que, peut-être, il a subis et qui n'ont laissé en lui aucune trace. C'est un amnésique, dépourvu de patrimoine génétique est en outre souvent orphelin, car l'enseignement de la théorie de l'échantillonnage est encore "confidentiel". Les outrages subis par l'échantillon sont générateurs de biais (ou erreurs systématiques) et font de lui un simple spécimen sans valeur, car on ne corrige jamais un biais d'échantillonnage dont le plus souvent on ignore jusqu'à l'existence. L'échantillonnage que l'on qualifie de "primaire" se déroule en milieu industriel, souvent en plusieurs étages. Il donne naissance à un échantillon dit « de laboratoire » de masse aisément manipulable. La préparation de cet échantillon fait également intervenir des opérations d'échantillonnage que l'on qualifie de « secondaires » et qui alternent avec des opérations "de préparation", telles que des concassages, des broyages, des séchages, des mélanges, etc, Au laboratoire d'analyse on aboutit à une ou plusieurs "prises d'essai" qui sont soumises dans leur intégralité au processus analytique. Plusieurs questions se posent alors: Pourquoi échantillonner? Pour une raison simple et universelle: l'analyse est très coûteuse et souvent destructive. On substitue alors au lot un "echantillon qui le représente. On analyse ainsi le lot par procuration".


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7 (2), 269-270
The availability of good quality geological materials at affordable prices is crucial to the successful execution of construction projects. Geomaterials for Ghana's vibrant construction industry, especially crushed rock aggregates for road surfacing and concrete works, armour stones for coastal protection works and dimension stones for buildings, are often procured from granitic sources. As such, most engineering geological studies concentrated on these rocks to seek their suitability for effective use in the country's construction industry (Tsidzi, 1990). Although, vast amounts of these granitic rocks exist in the country, their geographical distribution is quite uneven. Construction works in those areas remote from the location of granitic rocks, therefore, tend to be costly due to the long haulage distances of procuring these materials. To resolve this issue, the work embodied in the paper seeks to determine the suitability of the major limestone deposits in (Fig. 1) Southern Ghana, namely, the Nauli Limestone and Oterkpolu Limestone for their effective utilisation in road construction, structural concrete manufacture, coastal protection works, production of dimension stones for buildings and other industrial applications. It should be noted that the industrial potential of these rocks has hitherto been limited because they have been inadequately characterised in engineering geological terms. The Nauli Limestone, which is near horizontally bedded Upper Cretaceous deposit in the southwestern portion of the country, is largely poorly exposed, having been covered by a mantle of Tertiary-Recent gravels, sands and clays. This grey shelly dolomitic limestone deposit with reserves estimated at 400 million tonnes was previously found to be suitable for the manufacture of portland cement and also for the production of lime for use in a local gold treatment plant (Kesse, 1985). Engineering tests performed on the rock material in this study have, however, indicated that the Na


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7 (2), p271
Geo-science is a critical constituent for further socio-economic development in sub-Sahara Africa and other developing countries. Geoscience plays a primordial role in the exploitation and management of a country's mineral wealth (including hydrocarbons, coal and underground water). Equally important is the role of geo-science to mitigate natural or man-made damage to our eco-system. Geo-science education in sub-Sahara Africa therefore must be viewed in the first place as 'Geo-science for Development'. Like the national Geological Survey Organisations, most universities in sub-Sahara Africa are under-staffed, under-financed and under-equipped. There exists a general need for institutional strengthening, capacity building and curriculum development. The solution is sought in regional co-operation - key words: pooling of scarce resources, critical mass, economy-of-scale, partnership for capacity building and south-south co-operation - and long-lasting 'twinning' relationships with universities in the North. A plan for the development of a number of regional MSc. Earth Science courses, to be located at different educational centres (to be selected) in West Africa, is presented. These courses will be developed under the umbrella of a regional network called 'GeoNet' comprising Earth Science departments from the region - the members - and 'twinning' partners in the North - supporting members. All courses are in the applied Earth Sciences and tailor-made according to the needs of the region. A professional course model is preferred over an academic model. Whereas the latter is "curiosity driven", the professional course model aims to educate to solve real problems. In order to fully comprehend the socio-economic impact of such courses, a distinction is made between courses that contribute to the creation of wealth and the ones that aim to preserve wealth and seek to maintain the well-being of peoples in the region. The first category includes the courses in mineral resource development (including water, hydrocarbons and coal). It is argued that it is the quality of the 'enabling environment' that determines whether West Africa will receive a substantial share of the world's mining investment funds. Without these, minerals will stay in the ground. Courses in mineral resource development contribute significantly to the so-called 'geo-infrastructure' which, in turn, defines to a large extent the 'enabling environment'. The relevance of other MSc. courses is also obvious. Water is most likely the most valuable and scarcest mineral resource of this century and the importance of a regional MSc. course in integrated and sustainable management of water resources needs hardly any justification. The second category includes regional courses in environmental geology, engineering geology, hazard mapping and coastal zone management. These courses aim to educate professionals to preserve wealth, to protect people and to help improve the civil infrastructure.


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7 (3), 273-287
To improve earthquake locations, regional seismic phases, i.e., Pn, Pg, Sn and Sg (Lg) have been studied in the region bounding the western branch of the East African Rift System between 1°N and 12°S. We analysed arrival time data from 56 regional earthquakes recorded by a local network (Mbeya network) in south-western Tanzania, consisting of five three-component digital stations. The earthquakes were located by adding data from 17 stations of the East and Southern Africa Seismic Network (ESASN). Calculation of phase parameters and earthquake locations result from an interactive inversion of data. The resulting crustal model is characterised by an average velocity of 6.32 ± 0.26 km/s and 3.61 ± 0.02 km/s for P and S waves, respectively. Upper mantle velocities corresponding to Pn and Sn phases are 8.11 ± 0.05 km/s and 4.67 ± 0.05 km/s, respectively. Achieved velocities are comparable to those obtained for the African Shield. The crustal thickness is estimated to be 41.3 ± 7.5 km assuming that the average focal depth of the studied earthquakes is 18.3 km. Twenty three of the studied earthquakes have also been located by the International Seismological Center. The reported epicentres are on average 29 ± 18 km away from our locations, which is of the same order of magnitude as the average radius of the area with a 95% confidence level. This coherency illustrates the ability of specialised local networks to reliably locate regional earthquakes in eastern Africa.


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7 (3), 289-306
Rifting, halokinesis and structuring of the Jurassic and Early Cretaceous subsurface peri-Tethyan basins of the Tunisian central Atlas (Galsa-Sidi Ali Ben Aoun region). In the Gafsa-Sidi Bouzid area, isopach-time and isochrone mapping, using seismic profiles and well data, are characterized by a network of deep-seated synsedimentary faults that have governed the genesis of the Jurassic and the Early Cretaceous basins. This network of faults comprises the strike-slip N-S Sidi-Ali Ben Aoun master fault ramified by the N060 Sidi Aïch and Souinia second order fault trends and the N120 strike-slip Majoura fault. Seismic sequence stratigraphy of the Jurassic and the Early Cretaceous deposits show the basin sedimentary infilling mechanisms associated with the tectonic fault system reactivated during the Tethyan rifting. Seismic lateral and vertical facies and thickness variations of the sequence system tracts on both sides of fault indicate the fault control during the Jurassic and the Early Cretaceous times. These faults inherited from the pan-African basement had been activated in transtensive movements during the rifting and the regional migration of the African plate toward the East and had induced Triassic salt and evaporite halokinetic intrusions along the faults creating thick rim syncline basins. The strike-slip faults are ramified in the sedimentary cover beneath the Sidi Aïch, Majoura and Souinia anticlines. This geodynamics creates Jurassic and Early Cretaceous platform rhomb basins, grabens and half grabens.


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7 (3), 307-314
Eastern Tunisia is characterized by its relatively high present seismic activity and its intensive neotectonic deformations. It is in the upper-middle Miocene to Tyrrhenian series of Eastern Tunisia that the existence of regional paleoseismic events extending from Cap-Bon to Sahel is identified out for the first time. These paleoseismic prints are induced by seismic shocks affecting the water saturated shaly-sandy sediments in defined structural settings. The discovery of these structures within Miocene to Tyrrhenian sediments extends our current knowledge of the seismic history of Eastern Tunisia, which is presently solely based on historical and instrumental seismicity data.


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7 (3), 315-325
The morphostructural setting of the Essaouira Basin (western High Atlas, Morocco) has been identified on topographic maps (scale 1/100 000) using geomorphologic markers associated to structural anisotropies (drainage anomalies, morphometric index of the thalweg network). The results of these analyses are compared with other available geophysical data (seismic profiles, gravimetric and magnetic maps). This comparison shows that the thalweg network is determined by the main structural directions identified by the geophysical and geological data. So it is possible to integrate all the data (field observations and cartographical remote sensing) into a synthetic morphostructural scheme.


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7 (3), 327-340
The Late Barremian to Early Aptian Bouzergoun Formation in the Agadir Basin, in Morocco represents wave-dominated deltaic and estuarine incised-valley fill depositional systems. The wave-dominated delta is represented by stacked thickening and coarsening upwards parasequences 5 to 15 m thick, formed during fifth or fourth-order regression and building a third-order highstand systems tract. Vertical facies transitions in parasequences reflect flooding followed by shoaling of diverse shelf environments ranging from lower shoreface/lower delta front (heterolithics to tabular-planar laminated sandstones and hummocky bedforms) to upper shoreface/upper delta front strand bars. The regional configuration reflects the progradation of a storm-influenced delta over an outer shelf facies. Early Aptian maximum sea-level fall led to the development of a sequence boundary that is an unconformity. The succeeding depositional sequence accumulated into an incised-valley and comprises a diverse assemblage of lithofacies that can be grouped into lowstand, transgressive, and highstand systems tracts. The lowstand systems tract is marked at its base by channels incised into the Upper Barremian shoreline deposits. Landward of the incised channels are fluvial conglomerates and pebbly sandstones that are enclosed in non-marine strata. As sea level began to rise, fluvial deposits were reworked into alternating couplets of moderately bioturbated tidally-influenced heterolithic sand and mud. The transgressive systems tract comprises the bulk of the estuarine fill and consists of a seaward and landward thinning wedge of tidally influenced fluvial, tidal flat, estuarine point bar and bay fill deposits. Highstand infilling of the valley was characterised by bayhead delta progradation.


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7 (3), 341-354
In the Bou Azzer El Graara inlier, the volcanic event of Jbel Boho, attributed to the Lower Cambrian, showed three major volcanic episodes of contemporaneous lower limestones deposition. The basic volcanic flows (basalt) constitutes the first volcanic episode, the second is made up of basic and intermediate types (trachy-andesites). The last is composed of acid types (trachytes and comendites). Geochemical analysis of the volcanic matter revealed alkaline affinity, and magmatic differentiation by fractional crystallization in an extensional geodynamic setting. This volcanism is ascribed to intraplate magmatism on the NW-Gondwanian margin.


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7 (4), 355-363
The tectonic affecting the sedimentary series of Chotts region shows some similarity in the architectural aspects of the basins. It also shows that the geometrical forms of basins existing in this region depend on the faults orientations. Almost all of the basins have their axes parallel to the adjacent faults. The depocenters of the basins must be the same during both Triassic and Lower Cretaceous ages.


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7 (4), 365-370
The Upper Cretaceous aquifer of the Essaouira basin constitutes a multi-layered system, fractured with a compartmentalised structure. The characterisation of its waters by the analyses of spatial variation of dissolved strontium concentrations indicates a discontinued aquifer, formed by an assembly of tectonic blocks separated by faults. These led to the deduction of the existence of only one water table within this system at each tectonic block. This aquifer structure favours mixing of waters from different origins. The Sr2+/Ca2+ ratio led to the determination of the evaporitic origin of the waters. According to this ratio, three different groups of water were identified: a group of Turonian (0.66 to 1‰), a group influenced by the Senonian waters (1.07 to 1.85‰) and a group marked at the same time by the Senonian and by the Cenomanian waters (2.16 to 10.59‰).


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7 (4), 371-381
The Cretaceous basin of Errachidia borders the calcareous High-Atlas ridge in the South. The low effective annual rainfall within the basin constitutes a problem as the different aquifers which are significantly drained by perennial springs cannot be recharged adequately. The hydrogeologic investigation of the Jurassic aquifers of the High-Atlas reveals a high level of evapotranspiration (ETP = 930 mm) compared to the low discharge rate from the springs and oueds. Despite the generally low piezometric level of the deep aquifers in the region, the significant discharge rate from the aquifers implies that there is an important reserve of fossil water in the underlying Senonian, Turonian end Upper Cenomanian deposits. This may be due to the fact that the aquifers are replenished from those within the neighbouring High-Atlas. Isotopic study and groundwater modelling of the aquifers from the massifs to the Cretaceous basin suggest that there is a link between the two domains.


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7 (4), 383-392
The El Madher plain is a sedimentary basin with a Miocene-Pliocene-Quaternary alluvial filling. It is located 15 km to the northeast of Batna city (in the northeastern part of Algeria) and constitutes one of its pumping areas. The characterization of this alluvial aquifer has contributed to the determination of the extent of the transmissivity zones and the water supply extracted underground. After a conclusive test on the imposed data, the model of the steady state flows using the finite differences method yielded a good agreement between the calculated piezometric curves, the observed curves, and the annual average hydrodynamic balance.


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7 (4), 393-400
The global balance of erosion-transport-sedimentation in the Inaouene drainage basin (Morocco) which was managed by the Idriss 1er barrage, has been derived by calculation of the average interannual solid contribution of three hydrological years (dry, humid and mean). The comparison between the fluvial transports during different flood events during the same year underlines the importance of hydrological processes in controlling mechanical erosion. The transport matter resulting from denudation would be, on the average, about 3.6 10(6) t/yr, corresponding to a specific denudation of 1286 t/km²/yr which is comparable to the value from Heusch and Millies-Lacroix (1971) model. The barrage would collect 94% of this solid load.


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7 (4), 401-413
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, Maps, Ph. D. and M. Sc. Theses, Reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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8 (1&2), III-VII

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The development of the Mining Sector in any developed or non-developed country is an integral part of the overall national development and must, therefore, be well structured to comply with a general economic plan. It is the responsibility of the government to formulate, disseminate and enforce the mining policy that be operational be it in a public or private system or the combination of both. Angola initially opted fore mining policy which gave led to the establishment of State-owned Mining Companies. The experience amassed over the last decades in applying this policy has helped to conclude that the combination of the public and private systems through gradual reduction of the State's monopoly offers better development prospects. Because of the internal instability and lack of specialized technical capability needed to promote the evaluation of mineral resources, the State has adopted a strategy under which companies with proven technical and financial capacity have been awarded reasonably-sized areas of their choice to undertake, at their expense, studies and prospecting operations for minerals that interest them. The State will benefit as it will gradually be more knowledgeable about the territory. In this way, information regarding the country's true mineral potential will be easily obtained. The study of the territory's geology and its mineralogical features has been compromised and hindered over many years by the military conflict and its attendant vicissitudes. As a consequence, Angola is placed in a very unfavorable position in comparison with some other countries within the continent and particularly in the region. Current worldwide consumption needs are focused on diamonds, precious metals and basic metals. Although our country needs industrial, agro-minerals and construction materials for the transformation of industry and agriculture, it also needs minerals and precious metals for foreign exchange earnings. I have been invited by the GeoLuanda 2000 Organizing Committee to address the participants to this event on the topic of geological mining activities in Angola. I have decided to tell you about the important steps we are now taking within the Angolan mining sector. I know that many of you are here for the first time. So, I think that by giving you an overview of the actions undertaken throughout the post-independence period, you will be in a better position to understand what the Angolan minerals potential is all about and how much work is still ahead in order to evaluate our mineral resources.

8 (1&2), 1-15
The Estrela (Star-fish) field, discovered in 1990, is located in offshore Angola Block 2/85, within the northern Lower Congo Basin. The 37° API crude oil is produced from Albian age Pinda carbonate shelf edge shoals. The field comprises two independent closures, which share a common structural spill point. Elongate, curvilinear-shaped reservoir fault blocks, termed A and B, are the result of basinward listric faulting and lesser shoreward compensatory displacement. The Estrela-1 discovery well encountered approximately 50 feet of porous, oil-bearing dolomite on the north-west flank of the field. Net oil pay thickness within the developed concession area averages 220 ft, reaching a maximum of 450 ft. A total of eight producing wells currently flow at a combined rate of approximately 17,000 BOPD. Ultimate cumulative reserves are estimated above 50 MMBO. Well control and 3-D seismic mapping indicate the presence of a saddle between the respective closures, coincident with listric fault interaction and a change in regional structural grain. Geochemical correlation of crude oil samples confirms that the northern Estrela A and southern Estrela B hydrocarbon accumulations lie in distinctly separate reservoir compartments despite the common spill point. The Middle Pinda prospective reservoir sequence comprises high energy, oolite-oncolite precursor grainstones, interbedded with less prospective lime mudstones. These sequences, particularly the grainstones, have undergone partial early dolomitisation, followed by later dissolution of remnant calcareous allochems. The resulting interconnected mouldic pore system is pervasive across stacked shoaling cycles. A 3-D reservoir model was built for the Estrela field, through an iterative process involving detailed geophysical interpretation of dipping dolomite layers truncated by an overlying erosional unconformity, multi-well log evaluation, and simulation to history match field performance. This paper discusses the geology of the Estrela field, and touches on how an iterative and integrated Geoscience and Engineering approach to the ongoing evaluation of the field has led to improved understanding of the mechanics of the field, and thus enhanced the operators ability to successfully manage this asset.


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8 (1&2), 17-27
Sequence stratigraphy concepts and the recognition of seismic facies patterns have been important tools in the successful exploration of the deepwater Miocene trend of Block 14, offshore Cabinda, Angola. Recent discoveries include Kuito field, the first field in this trend to be brought on production, and the Benguela and Belize fields that are presently in development planning. There is potential for additional fields in other discoveries and undrilled prospects that require further evaluation. The key to juxtaposition of effective reservoirs and trap seals for Block 14 hydrocarbon accumulations is the combination of lowstand turbidite sands overlain by highstand shales. The three fields, Kuito, Benguela and Belize all occur in slope valleys eroded during sea level lowstands. Massive basal sands dominate the early part of the sequence and generally thin upward during the waning stages of the lowstand. Deep-water marine shales cover the channelized sand deposits as the next highstand begins. Recognizable seismic facies patterns and sometimes direct hydrocarbon indicators are associated with the hydrocarbon accumulations in Block 14 fields. All fields have channel morphologies identifiable on horizon amplitude maps and in cross-section. Typically the seismic expression of these sandy submarine channels will include differential compaction, chaotic internal reflectors and amplitude anomalies. Direct hydrocarbon indicators occur as flat spots, AVO anomalies and turnoff of amplitude with depth. Overall reservoir parameters for the fields are excellent with average porosity ranging from 33% in the Upper Miocene to 23% in the Lower Miocene. Permeability is good to excellent ranging up to 5 Darcies. Reservoir continuity can vary from several hundred meters to several kilometers as a result of deposition in the submarine turbidite channel environment.


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8 (1&2), 29-36
Precision biostratigraphic analysis is the key to accurate stratigraphic correlation and sequence understanding in the Kuito Field, Block 14, offshore Cabinda, Angola The Miocene offshore Cabinda, Angola, has proven to be a highly prospective hydro carbon province. The Kuito Field discovery in 1997 by partners Chevron, Sociedade Nacional de Combustiveis de Angola (SONANGOL), AGIP Angola, TotalFinaElf Angola and Petrogal companies, is expected to produce 65,000 BOPD in 2002. We present a well correlation methodology for dynamic deepwater depositional systems. This correlation approach is dependent upon the integration of a multi-disciplinary team of biostratigraphers, sedimentologists, geophysicists, and geologists working to produce a cohesive stratigraphic logic. Palaeontological preservation offshore Angola is variable, and thus can obscure accurate correlation. A multidisciplinary approach utilising calcareous nannofossils, planktonic and benthic foraminifera provides a robust tool for sequence recognition. The predominantly endemic fauna and flora permit an intra-basinal scale correlation based upon event recognition and known chronostratigraphic markers. This approach is dependent upon consistent and precise biostratigraphic analysis. As a stratigraphic tool used in conjunction with complementary geological and geophysical data this approach facilitates a continuous iteration process towards a systematic stratigraphy.


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8 (1&2), 37-48
Diatom-rich layers were encountered in offshore Angola (block 3) in sediments of the upper Malembo Formation (upper Miocene) drilled by Elf Aquitaine in the Pacassa and Veado wells. The diatom assemblages are composed of a mixture of marine and freshwater taxa The marine diatoms are mostly littoral; true oceanic forms are rare. Freshwater diatoms, which are often very abundant in the samples, are likely to have been transported by the Congo River and are contemporaneous and/or older than the marine assemblages within which they deposited. They offer a very interesting insight on what the freshwater diatom flora was in western Africa during the Late Miocene. DSDP Site 362 (Walvis ridge) was studied as a reference section (upper Miocene through Quaternary) for this area. Our results suggest that the age of the diatom-rich interval in block 3 wells is late Tortonian, ranges between 8.8 and 7.4 Ma, and corresponds to a period of high-latitude cooling and increased coastal upwelling along the Benguela Margin.


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8 (1&2), 49-55
Wide angle seismic data collected on land in Northern Angola, during the March-April 2000 Zaiango seismic experiment, provide the first information concerning the Northern Angolan margin crustal and upper mantle features, where reflected and refracted arrivals, are observed. Multichannel data were acquired by the R/V le Nadir (IFREMER) using a single bubble air-gun array and a new digital 4.5 km long streamer, and coincident wide angle data were recorded on land by three broad band three-component seismic stations. The data collected on land for some selected seismic lines, together with the results of processing and a first rough modelling are here presented. Travel times of P-refracted arrivals and prominent crustal and mantle reflectors are observed to offset of over 200 km. However, only speculative models can be tested for the moment.


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8 (1&2), 57-66
Around Benguela, the Mesozoic-Tertiary succession of the southern part of the Kwanza Basin show characters markedly different from the coeval deposits exposed in the remaining part of this basin. The most remarkable ones occur in the Upper Cretaceous deposits. These sediments can be related to a series of Cretaceous (post-early Cenomanian) tectonic events and have been interpreted as evidences of a peculiar type of extensional tectonics (raft tectonics). Carrying on our researches on the tectono-sedimentary reconstruction of this part of the Kwanza Basin, the Upper Cretaceous deposits widely exposed in the surroundings of Benguela, Dombe Grande and Cuio consist of dominant silty-arenaceous shales, subordinate limestones, sandstones and polymictic conglomerates. This is interpreted as a deposition in a terrigenous shelf with occasional carbonate levels with foramol-type composition that pass on (near Dombe Grande) to continental alluvial deposits grading into tidal flat deposits. We propose for these deposits the new formation name Tchipupa Shale Formation. New data from the calcareous nannoplankton datation allow us to attribute these deposits to the Campanian-Maastrichtian. The most significant successions of the Tchipupa Formation show the different stratigraphic relationships with the substrate (especially the frequent overlap on fault scarps) that suggest that significant tectonic events occurred during the pre-sin - post deposition of this formation. Furthermore, there are evidences of a long lasting subaerial exposure of the deformed substrate.


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8 (1&2), 67-78
Near Cabo Ledo village, a Burdigalian succession named Quifangondo Formation was investigated in terms of stratigraphy, sedimentology and petrology. This succession consists mainly of shales and silts with cm-thick interlayers of calcilutites, with marked dominance of fine-grained deposits referable to ramp facies. In the study area, some sedimentological characters suggest the occurrence also of slope facies of moderate depth in the upper portion of Quifangondo Formation. The area has been subdivided into two sectors: 1) southern and central sector, constituted by slump deposits and low-density turbidite facies characterized by traction-plus-fallout deposits; 2) northern sector, constituted by bioclastic arenaceous and arenaceous-conglomeratic turbidites with a sandstone/pelite ratio >1, alternating with layers of pelites. These turbidite sediments have been subdivided in 5 1ithofacies. The sedimentary structures suggest deposition by hyperconcentrated flows for lithofacies 1 and sandy high-density turbidity current for lithofacies 2-5. Petrographic analysis was performed only on 5 out of 15 collected samples. The studied samples can be classified as arkosic arenite. The remarkable increase of the terrigenous input observed in the upper part of the succession suggests that the continental shelf was episodically fed with a large amount of coarse sediments of fluvial origin. These extra sedimentary input, probably linked to tectonic events, were delivered to the shelf margin/slope break area by large channels. This local tectonic event, has been correlated with an Early Cretaceous magmatic intrusion. It is reasonable to infer that the age of the tectonic event can be somewhere between the Late Cretaceous and the Miocene.


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8 (1&2), 79-88
Recently-acquired field data from excellent outcrops in the Benguela, Lobito and Catumbela sectors of the South Angola margin record: 1) the lateral transition from the proximal Albian platform in the East to the distal carbonate platform in the West corresponding to the layers of the Catumbela Formation. The proximal domain is characterized by the vertical succession of the lagoonal claystones and carbonates of the Binga facies, overlain by the mottled claystones and fluviatile sandstones of the Tuenza facies. The distal domain exhibits spectacular clinoforms where upper shoreface carbonates prograded over alternating offshore marl-limestone strata (Quissonde Formation), 2) structures associated with gravity sliding of the carbonate platform over the Aptian salt strata (Loeme Formation). The eastern domain of the platform features a series of extensional synsedimentary structures (tilted blocks, divergent onlaps, roll-overs) while the western domain is characterized by compressional structures (syn-sedimentary 1 kilometer wide synclines and anticlines) reactived by normal faulting. These features are related to a negative inversion tectonics. This study details a spectacular field analogue of the extensional and compressional structures related to the Albian salt tectonics. These structures were initiated by the Albian tilting of the southern Angolan margin related to the post-rift stage of the thermal subsidence. The field observations are compared and contrasted with subsurface data displaying similar structures of the same age in the Kwanza basin.


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8 (1&2), 89-99
The classical basin modelling approaches with fluid flow modelling on the present day geometry of the carrier surface may give a poor overall description of the petroleum system. In this study we have worked with an area where the structuring and trap formation coincides with active generation and migration of hydrocarbons from multiple sources. The main scope of this work has therefore been to develop a workflow for performing secondary oil migration modelling on structurally reconstructed maps, and thereby investigate the migration patterns through time. The results of the simulations using structurally reconstructed maps have been compared to the results we obtained performing the migration on simple decompacted horizons. We have also investigated how differences in the timing of hydrocarbon expulsion affect the resulting hydrocarbon migration and accumulation.


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8 (1&2), 101-126
The Upper Albian deposits (CXIIb-c, 103-96 Ma) in the study area of the Congo coastal basin are of mixed sedimentary types: carbonates, terrigenous clastics and evaporites. Subtidal, intertidal to supratidal and sabkha depositional environments were identified by lithological analysis and petroleum borehole logging and characterised in terms of their sedimentary dynamics. Facies are arranged in elementary lithological sequences a few tens of metres thick that are comparable to parasequences in genetic stratigraphy. This depositional pattern corresponds to: (i) regressive episodes of several metres, to several tens of metres, with a sometimes progressive sometimes sudden transition from subtidal to intertidal or supratidal environments; (ii) transgressive episodes, often featuring a sudden return to a subtidal environment. This staccato pattern of sedimentary dynamics is related to the evolution of the passive margin of the South Atlantic, which is set in its climatic context in relation to the position of the equator in Albian times (humid tropical climate).


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8 (1&2), 127-140
A siliciclastic-carbonate mixed succession, named Luanda Formation, has been investigated in terms of stratigraphy and sedimentology. The analysed succession is well exposed around Luanda From the study of 4 stratigraphic-sedimentological sections, it is evident that the Formation can be subdivided into several lithotypes that are related to transitional evironments (alluvial, lagoonal, coastal and baymouth littoral). Several samples have been collected for biostratigraphic analysis. Abundant foraminiferal and ostracodes assemblages were found in only two sections. The species found include Globorotalia crassaformis and Dentoglobequadrina altispira. This suggests an Early-Middle Pliocene (PL1 partim-PL4 Zone) age for the lower-middle section of the Luanda Formation.


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8 (1&2), 141-147
The Southern Outeniqua basin is an untested frontier area of deepwater acreage off the south coast of South Africa of about 20 000 km² in extent. The basin forms the southern extension of the Bredasdorp, Pletmos, Gamtoos and Algoa Basins. As no boreholes have been drilled in this frontier area, maturity levels and source rock occurrences within the Southern Outeniqua are unproven. However, drilling data and hydrocarbon analyses from boreholes on the periphery provide most encouraging indications that multiple potential source rock intervals can be expected within the Southern Outeniqua Basin. Seismic amplitude anomalies, which correlate with known source intervals in the peripheral basins are also associated with some of the major unconformity surfaces that have been mapped on a regional scale across the Southern Outeniqua Basin. Geohistory models, calibrated using data from surrounding wells, were constructed on a grid across the basin. The models show that these various source rocks are at suitable levels of maturity to produce either oil or gas across the vast majority of the basin.


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8 (1&2), 149-155
Biostratigraphical and paleobiogeographical significance of echinoids distribution in Iullemmeden Basin (Niger, West Africa) during the Maastrichtian and Paleocene. - the Uppermost Maastrichtian deposits indicate significant relations between Brazil, the Iullemmeden Basin and the coastal basins of Senegal and Morocco; - the Paleocene deposits contain evidence of exchanges with the Caribbean (Cuba-Jamaica). The occurrence of the endemic genus Mauritanaster and endemic species Paleostoma rocki in the Paleocene fauna of Morocco raises the intriguing question of how they became isolated paleogeographically from the trans-Saharan seaway.


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8 (1&2), 157-168
A. Géosystèmes margino-littoraux, littoraux et de plate-forme: enregistrement sensible de la migration des lignes de rivage et des fluctuations du niveau marin. B. Géosystemès continentaux et margino-littoraux: enregistrement sédimentaire, discontinuités et changements climatiques globaux. C. Facteurs déterminants et contraintes du signal stratigraphique à l'échelle des bassins. A. Margino-littoral, littoral and platform geosystems: records of coastline migration and sea-level fluctuations. B. Continental and margino-littoral geosystems: sedimentary record, discontinuities and changes in global climate. C. Determining factors and constraints on the stratigraphic signal at basin scale.


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8 (1&2), 169-193
The Mouka-Ouadda Formation forms a vast subhorizontal plateau of approximately 40 000 km² in the East and the Northeast of the Central African Republic. It is characterized essentially by siliciclastic deposits (sandstone conglomerates) whose maximum thickness is under 500 m and whose present limit corresponds to erosion. The sedimentary figures and structures are characterized by fluviatile formation. Probably dating from the Cretaceous period, and overlay in angular discordance either the Precambrian basal complex, or the Paleozoic glacio-fluvial formation of the Kombélé whose reworked glacial deposits (proglacial fluviatile) are difficult to distinguish from the outcrop in the absence of characteristic figures and structures. A preliminary study of the formations earlier than that of the Mouka-Ouadda (Paleozoic glacio-fluvial and Precambrian basement) so as to establish petrographical and mineralogical relations with the Mouka-Ouadda Formation is studied within the context of an essentially braided fluviatile system. The petrographic and mineralogic analyses, notably the exoscopy of quartz grains and the study of heavy minerals, are in favour of a source of detritic material of mostly southern origin. This hypothesis is supported by the main direction of the Paleocurrents towards the NNE and NE. The detritic material comes mainly from erosion of Precambrian schisto-quartzitic complex as well as the Paleozoic glacial formation of the Kombélé. The Precambrian granito-gneissic complex did not make up an important source of detritic material because it was probably peneplaned while being deposited. The study of the climatic and geodynamic contexts of the Mouka-Ouadda Formation, at the level of Central Africa, supports the case of a Cretaceous period for the Mouka-Ouadda Formation. The Mouka-Ouadda Formation is a reservoir rock of the diamond which is exploited in the Quaternary alluvial deposits stemming from the erosion of the Mouka-Ouadda Formation. The primary kimbe


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8 (1&2), 195-208
Sequence stratigraphy concepts and the recognition of seismic facies patterns have been important tools in the successful exploration of the deepwater Miocene trend of Block 14, offshore Cabinda, Angola. Recent discoveries include Kuito field, the first field in this trend to be brought on production, and the Benguela and Belize fields that are presently in development planning. There is potential for additional fields in other discoveries and undrilled prospects that require further evaluation. The key to juxtaposition of effective reservoirs and trap seals for Block 14 hydrocarbon accumulations is the combination of lowstand turbidite sands overlain by highstand shales. The three fields, Kuito, Benguela and Belize all occur in slope valleys eroded during sea level lowstands. Massive basal sands dominate the early part of the sequence and generally thin upward during the waning stages of the lowstand. Deep-water marine shales cover the channelized sand deposits as the next highstand begins. Recognizable seismic facies patterns and sometimes direct hydrocarbon indicators are associated with the hydrocarbon accumulations in Block 14 fields. All fields have channel morphologies identifiable on horizon amplitude maps and in cross-section. Typically the seismic expression of these sandy submarine channels will include differential compaction, chaotic internal reflectors and amplitude anomalies. Direct hydrocarbon indicators occur as flat spots, AVO anomalies and turnoff of amplitude with depth. Overall reservoir parameters for the fields are excellent with average porosity ranging from 33% in the Upper Miocene to 23% in the Lower Miocene. Permeability is good to excellent ranging up to 5 Darcies. Reservoir continuity can vary from several hundred meters to several kilometers as a result of deposition in the submarine turbidite channel environment.


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8 (1&2), P209
The poster illustrates three different potential scenarios of structural development of the SOB and its southern margin, the DMFR. The origin and composition of the DMFR is a widely debated issue. Orogenic uplift of the Cape Supergroup along the southern margin of Godwana resulted in the formation of the Cape Fold Belt (CFB) from 278-230 Ma. Major erosion of the Cape Supergroup followed in the present-day offshore areas of the South Coast as well as the reconstructed Patagonia/Falklands/Maurice Ewing Bank plates, leading to crustal thinning. Inversion and active rifting took place from Late Jurassic, resulting in the following Mesozoic basins: Bredasdorp, Pletmos, Gamtoos, Algoa, as well as the deep-water Southern Outeniqua Basin, the latter which does not follow the structural grain of the CFB like the other shallow water basins. Rifting ceased during Late Valanginian and an intracontinental strike-slip fault resulted in the separation of the Patagonia/Falklands/Maurice Ewing Bank plates from the African Plate. This Agulhas-Falklands Fracture Zone (AFFZ) became an oceanic transform fault. The origin of the DMFR, a prominent feature 300 km long and 30 km wide, is a contentious issue. Three models are illustrated in this poster. Firstly, it has been considered to be an old basement pre-rift feature, comprising either Cape Supergroup sediments or volcanics, which was later transacted by the AFFZ. (Ben-Avraham et al., 1993). A second model illustrated the DMFR to consist of pre-Cape sediments exposed by erosion after the Cape Orogeny. The DMFR is interpreted as a flanking structural high bordering the diverging plates during rifting and the early stages of ocean spreading diagonally across the grain of the CFB. The in situ rotation of Falkland microplate south of the African continent was the result of this tectonic process. Continued ocean spreading was then overwritten by a strike-slip regime, which culminated in the AFFZ, along the axis of rifting (i.e., weakened crust direction) and the westward movements of the Falklands/Maurice Ewing Bank plates. Thirdly, a model proposed by M. Jones of Ranger Oil (petroleum exploration company operational in the area), depicts the Southern Outeniqua Basin to be Jurassic to Early Cretaceous transtensional basin bounded by intra-cratonic strike-slip faults active from the ?Middle Jurassic onwards. Latest movement on these faults coincided with end of rifting in the Late Valanginian when all movement transferred to the AFFZ. Major vertical movement occurred on all faults at this time causing major subsidence of SOB but leaving the DMFR as a basin margin high It is therefore not believed to be an inversion structure so much as a remnant high. Seismic evidence suggests that the DMFR consists of synrift sediments overlying basement.


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8 (1&2), 211-222
The Northwestern border of the African Craton has known an intense distensional tectonic. This tectonic that began in the Permian age was reactivated in the Liassic, from the first stages of the Atlantic central rifting. Thereafter, basins of collapse were created. Basins bearing this structural device became traps for organic matter. This organic matter was preserved and constituted (when physicochemical conditions allowed) a good source rock. The Middle Atlas basin (in Morocco) is a typical example of these basins of collapses of the Northwestern border of the African Craton. During the lower Liassic, the Middle Atlas basin was affected by an heterochronous tectonic event, which reached its paroxysm during the Domerian-Toarcian, and led to the formation of a collapse basin. The fossilisation and preservation conditions of the organic matter was best in deeper zones. TOC values can attain 10%. The preserved organic material was affected by a thermal digenesis to produce a very good oil source rock, with a very good petroleum potential which can reach 27 of HC/ ton of rock. During the Domerian-Dogger interval, the oil source rock underwent very important burial, responsible for the thermal maturation of the organic matter. Burial decreases from the center of the basin towards its margins. The extent of the burial (> 3000 m) was translated by an early hydrocarbon generation in the Domerian source rock. The beginning of generation is estimated at the end of Jurassic age. The expulsion of hydrocarbons could have occurred just after their generation.


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8 (1&2), 223-237
In this paragraph we present a brief introduction to the geology of the area that we will visit during the excursion. These short notes on the geological setting of the Luanda-Benguela area are partly drawn from the literature and partly from our own unpublished field-data. Our synthesis does not differ substantially from the classical schemes proposed recently by geologists working mainly in the oil companies. Nevertheless we present some new data and a new and more dynamic view of the tectono-sedimentary evolution of the Kwanza Basin. Our original contribution is based essentially on our field-work, in some localities of the central and southern part of the Kwanza Basin. In particular we could visit and study the surroundings of Luanda, Cabo Ledo, Sumbe (from the Binga folls to S;Filomena Beach), and Benguela (from the Rio Hanha to Cuio).


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8 (1&2), 239-255
This field-trip guide stems partly from our field-work during the last ten years. Unfortunately, lack of adequate financial support and impossibility to get access to most of the subsurface data, lack of good-quality topographic maps and aerial photographs, all concurred to make our work highly discontinuous and incomplete. In fact, to get a more complete knowledge of the geology of the area, we should have produced geological maps of adequate scale at least for the areas most significant from the stratigraphic and tectonic point of view. We could, however, study a certain number of stratigraphic sections in the localities where the most complete successions crop out. Excellent exposure and lateral continuity sometimes allowed us to trace beds and structures for many kilometers. Therefore, we can propose a hopefully convincing reconstruction of the tectono-sedimentary evolution of a significant part of the Kwanza Basin. This work is dedicated to the memory of Dr. Pas Pinto, a friend, the founder and director of the National Museum of Archeology, and the staff of the Museum for facilitating our stay in many ways in Benguela.


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8 (1&2), 257-269
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, Maps, Ph. D. and M. Sc. Theses, Reports, etc. Special emphasis is given to local material which does not reach international bibliographies or phases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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8 (3), 271-288
The Precambrian basement of Ethiopia exposed in four geographically separate zones has been traditionally classified into three stratigraphic units: the Lower Complex, the Middle Complex and the Upper Complex. Recent geochronological, thermochronological, geochemical and lithotectonic data, however, revealed that this three-fold classification of the Precambrian basement of Ethiopia is highly oversimplified and even possibly wrong. Based on a thorough review of existing data to date on the Ethiopian basement, it is here proposed to abandon this three-fold stratigraphy, ratifying former proposals based on local studies. Moreover, there is confusion and little agreement in the application of the terms Pan-African orogeny, Arabian Nubian Shield (ANS) and Mozambique Belt (MB) to the Ethiopian Basement. Compilation and review of existing data on magmatic rocks (particularly granitoids) indicate that the MB and the ANS correspond to contemporaneous events of the Pan-African Orogeny, at least in Ethiopia, but with a difference in their tectonic evolution and degree of later denudation.


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8 (3), 289-302
A sedimentological study of the Ordovician sequence in eastern Meseta, Morocco, revealed new information concerning the mineralogic composition of the sediments as well as their sources, facies and environment of deposition. The vertical sequences and their lateral evolution have been established based on palaeontological data and palynological datations. Factors affecting sedimentation are discussed.


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8 (3), 303-308
The study of Birrimian formations of the Afema conducted in Jonction and Toliesso areas disclose the existence of a Paleobasin which exhibits from the bottom to the summit, metamorphic rocks (green schist facies) with sedimentary, volcano-sedimentary and volcanic origins, oriented along the Birrimian direction (N30°) with an isoclinal folding gently sloping south-eastwards. The auriferous mineralisation displays a composite nature: an hydrothermal and epigenetic mineralisation removing a primary mineralisation with volcano-sedimentary syngenetic character. At least three factors (lithological, tectonic and chemical) monitor this mineralisation which, in addition, is associated with pyrite and mispickel.


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8 (3), 309-324
In the maritime Jeffara, a region of southeastern Tunisia, undifferentiated topography and the presence of Quaternary terrains complicate conventional morphostructural analysis. This problem which is more acute in lagoons and submerged lands was resolved by analysing Digital Elevation Models (DEM) and drainage pattern. The drainage pattern morphometric analysis automatically extracted from DEM completed by a morphogenic analysis of the hydrographic pattern allows a morphostructural study of the area and an understanding of the relation between present morphology and subsurface structures. The monotonous and calm aspects of this region apparently conceal structures related to faults and/or ductile tectonics which were initiated since late Jurassic.


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8 (3), 325-336
Geoelectrical investigations in the central portion of the Saïss coastal plains revealed the boundaries of the different geological formations and facilitated the construction of longitudinal and transverse sections as well as isobath maps of the top of the Lower Jurassic (Lies) resistant substratum. This study also revealed the global complex structure of the Saïss hydrogeologic basin.


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8 (3), 337-350
Structural evolution of the Prerifan ridges (Morocco) Meknes area influence of the Mesozoic extension over the Miocene-Pliocene thrusts, contribution of seismic and well data. Prior to the Late Miocene-Pliocene shortening phase responsible of the Prerifan ridges thrusts, the Mesozoic sequence and the underlying basement underwent an extensional tectonic activity. The tectonic and sedimentary markers of the extension indicate that the Mesozoic half-graben system geometry resulted from two main events: a NW-SE Triassic-Liassic extension related to the opening of the central Atlantic, and block collapsing induced by gravity gliding. Structural and kinematic analysis of the Miocene-Pliocene structures, based on the seismic and borehole data show that NE-SW reverse faults present a strike-slip component and constitute the lateral ramps of the overthrust units. Two structural units showing a differential movement and separated by a common lateral ramp were distinguished. The ridges that constitute the "External ridges" result from the western unit movement and form the "Western Arc". On the other hand, the ridges that constitute the "Internal ridges" result from the eastern unit movement and form the "Eastern Arc". The displacement direction of these two units followed the previous normal fault directions that localized their lateral boundaries. Hence, the western unit and its lateral ramps were deflected to the west.


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8 (3), 351-364
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, Maps, Ph. D. and M. Sc. Theses, Reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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8 (4), 365-378
A statistical reduction based on a simple correlation between topography and gravity can provide a close approximation to the complex solution of direct gravity problem involved with terrain correction. The statistical anomaly (ΔGs) is the difference between the gravity field (g) and the correlation correction (gcor). The gcor is derived from the regression equation for the g values and station elevations. The efficiency of the statistical reduction is successfully examined in the eastern Caucasus, where geological structure is well documented. We also applied the statistical reduction for the analysis of the ΔgB (Bouguer) and Δf.a. (free-air) anomalies recorded in Sinai and southern Israel. The Δgs map produced shows an enhancement of the NW-trending positive anomaly in western Sinai parallel to the Gulf of Suez, and a chain of positive anomalies, which extends north-eastward from south-western Sinai into southern Israel. This map also displays the known negative fields associated with the Gulf of Suez and the Gulf of Elat. Combined analysis of rock density data, geometry of the Δgs anomalies and magnetic field data, suggests that the positive NE-trending anomalies are probably related to gabbroic bodies within the Precambrian basement, whereas the NW-trending zone along the Gulf of Suez possibly reflects the composite effect of basic and metamorphic rocks.


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8 (4), 379-390
Isotopic and chemical characterization of groundwater in North-West Côte d'Ivoire: recharge of discontinuous aquifers in the Odienné region. Chemical analysis carried out on groundwater showed low mineralization water with an acid character. That acidity is due to intense biological activity which results in the liberation of biogenic CO2 which in turn contributes to release of H+ and HCO3(-) ions. The comparison of water pH and bicarbonate contents showed intense geochemical activity and the ionic exchanges or dissolved substances between different aquifers present and in contact with the atmosphere as well as the possible connections between these aquifers. Stable isotopes (18O and 2H) confirmed the periodical recharge of aquifers of the region by rainwater and lateral inflow from neighbouring reservoirs. Tritium results showed the recent character of the waters and the role of hydraulic regulation played by the lateritic horizons in the transfer of groundwater.


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8 (4), 391-402
The Middle and Upper Eocene continental deposits in the Bou-Anguer basin were calcitised into calcrete and later silicified into silcretes. Macroscopic and microscopic study revealed that silicification was due to the deposition of silica within the voids resulting in the epigenesis of carbonates by silica. This epigenesis was isovolumic and preserved the shape and size of the calcite crystals. Dissolution of calcite occurred during the deposition of silica. The field observation of the facies variation and the result of microscopic investigations suggest that the silicification is associated with ground-water regiments. The epigenetic modalities and the origin of the silica are discussed.


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8 (4), 403-412
Dans les dépôts du Viséen de la région d'Aguelmous, des différences d'épaisseur, de granulométrie et de faciès appuyées par des indices de mouvements syasédimentaires nous permettent de déterminer une tectonique en blocs basculés. Cette tectonique se continue et s'accentue au Namurien par l'ouverture du bassin de Fourhal.


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8 (4), 413-423
Investigation of coarse-grained continental shelf sediments (> 63 µm) off the coast of Côte d'Ivoire revealed the following characteristics: the sediments are well-sorted and mostly fine-grained beach sands; the mixed component consists of poorly-sorted, fluviatile sands predominantly fine-grained and positively skewed. The morphologic complex of the continental platform portrays an heterogenous granulometric repartition. The convex morphobathymetric profiles are predominantly fine-grained and represent the muddy domain with recent sedimentation at the mouth of rivers. The concave profiles occur within sandy belts particularly in recent zones of sedimentation and often show slope ruptures which correspond to location of ancient sand barriers or beach rock obstructing sediment transport and responsible for the poor sorting displayed in the morphobathymetric profiles. Intermediate bathymetric profiles exist between the convex and concave prof lest They are also associated with recent zones of sedimentation with abundance of fine grains in the middle and outer continental platform.


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8 (4), 425-435
In the low plain of the Seybouse, the storage of the industrial metallic products and refuse on top of the alluvial reservoir produced an infiltration of two heavy metals: the chromium (Cr) and the tin (Sn) towards the aquifer. High concentrations of both elements (Cr 1.28 mg/l and Sn: 0.24 mg/l) were observed in the well MP5. In order to know the precise origin of these two elements as well as their evolution with time, a monthly monitoring of in situ water chemistry, measuring physical and chemical parameters: pH, redox, T, conductivity, O2 and complete analysis of chemical elements in the laboratory {Ca2+, Mg2+, Na+, K+, Cl-, SO4(2-), HCO3(-), NO3(-), Sr2+, Si4+, Cr(total), Sn(total)} have been performed at this well during one water-year from February, 1999 to December, 1999. The results obtained show a good linear correlation between Cr and Sn (Cr = 5.292 Sn + 0.0239, r = 0.976), indicating a common origin for these two elements, originating from electroplating residues. The chemical evolution of these two elements versus time shows the existence of several parameters (pH, Eh, rain value and the pumping which occurs intervenes in the dissolution of these elements and the alteration of their chemical speciation. Plotting the water points on the Eh-pH equilibrium diagram indicates that chromium appears in the aquifer water under two complex forms, trivalent Cr(OH)3, and hexavalent CrO4(2-), on the other hand, tin appears under a stable form: Sn(OH)6(2+).


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8 (4), 437-450
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, Maps, Ph. D. and M. Sc. Theses, Reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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9 (1), 1-17
A major part of the Irumide belt in northern Zambia consists of granitic rocks, which on the basis of field relationships are distinguished into several distinct suites. The oldest suite of granites consists of medium-grained homogeneous leucocratic granite gneiss. A second suite consists of weakly deformed, porphyritic biotite granites, which contain abundant xenoliths of the earlier granites and metasedimentary rocks. The third group consists of homogeneous medium-grained undeformed biotite granites. Preliminary zircon SHRIMP dating on the suite of porphyritic and medium-grained granites, indicates an intrusion age of ca. 1020 Ma. An attempt to date the older granite gneiss yielded a wide range of ages from ca. 2020 Ma and ca. 900 Ma, indicating the presence of inherited zircon populations and U-Pb loss during subsequent metamorphism. The major element chemistry of the granites indicates that the rocks are meta- to peraluminous. The granites from the different suites have markedly similar major and trace element characteristics exemplified by high K2O and HFSE contents, relatively flat HREE and moderate to steep LREE patterns as well as pronounced negative anomalies on Nb, Ti, P and Sr. A moderate negative Eu anomaly in the REE patterns suggests plagioclase fractionation to be an important process in the genesis of the granite suites. Teutonic discrimination on the basis of trace clement pasterns indicates that the granitic suites are syn- to post orogenic. The geochemical features shown by the granitoids are interpreted to indicate that petrogenetic processes remained uniform through the different tectonic stages shaping the belt, and that all of these processes involved, to a lesser or greater extent, melting of a calc-alkaline lower crustal source.


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9 (1), 19-37
L'analyse microtectonique de la déformation récente, les sondages électriques et l'étude sismologique en Tunisie nord-orientale (région de Sidi Khalifa et ses environs), a permis la mise en évidence de certaines zones à risque sismique et la coexistence de déformations compressives et extensives. Ceue coexistence observée en surface, a également été démontrée par le calcul des mécanismes aux foyers. L'étude sismotectonique de la Tunisie nord-orientale révèle l'existence de plusieurs zones qui se caractérisent par une sismicité relativement intense. Plusieurs zones ont été définies et rattachées aux principaux accidents tectoniques actifs de cette région: - la sismicité de la région de Kechabta-Messeftine est liée aux joux de failles préexistantes telles que la faille de Messeftine (FM) et la faille de Kechabta-El Alia (FKA); - la sismicité de la région de Monastir et ses environs est en grande partie liée au décrochement N-S de Skanes-Monastir; - la sismicité de Kalaâ-Kébira et ses environs est liée essentiellement à des failles normales préexistantes réactivées; - la zone de Zaghouan-Sidi Khalifa constitue un secteur actif qui présente une importante séismicité historique. La faille de Sidi Khalifa qui constitue la bordure sud du fossé de Bou Ficha, correspond à un accident profond ayant rejoué à maintes reprises. Elle constitue une source séismogénique importante puisqu'elle affecte les dépôts récents et historiques. Mots-clés: Tunisie Nord-Orientale, zonation séismotectonique, microtectonique, mécanismes aux foyers, sondage électrique.


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9 (1), 39-46
L'aire géographique concernée par la carte des gradients géothermiques est comprise entre les parallèles 33 et 37° et les méridiens 8 et 12è. Elle couvre la totalité de la Tunisie orientale (on-shore et off-shore). Selon la subdivision de la Tunisie en unités structurales, la région étudiée correspond au domaine de la marge orientale. Ce domaine se distingue par des nombreuses sebkhas et des vastes plaines où affleurent des séries miocènes, pliocènes et quaternaires. La monotonie apparente de ce domaine masque une grande complexité de soul-sol mise en évidence par les études géophysiques. Cette marge est en effet structurée selon des couloirs de failles profondes limitant des bassins de grabens et des plates-formes mésozoïques et cénozoïques. Les valeurs avec lesquelles a été établie la carte des Gradients Géothermiques dérivent du traitement, selon une méthodologie appropriée, des données de température relevées des puits pétroliers qui parsèment la région. Ce traitement consiste essentiellement en la correction des valeurs de température prises dans la boue de forage (Bottom Holl température: BHT). Sur cette carte les gradients géothermiques montrent une moyenne de 32°C/km (degré Celsius par kilomètre). Elle présente des zones à anomalie géothermique positive (gradients supérieurs à 40°C/km), entre le Sahel et le golfe de Gabès au Sud et le golfe de Hammamet au Nord et des zones à anomalie géothermique négative (gradients inférieurs à 30°C/km) jalonnant les structures de l'axe nord-sud. On montre que la répartition des gradients géothermiques est doublement influencée d'une part par la structuration profonde de couloirs de failles et du magmatisme des bassins sédimentaires et d'autre part par l'hydrodynamisme des aquifères que logent ces bassins. Ces résultats peuvent aider à suivre des domaines à intérêt pétroliers.


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9 (1), 47-55
The present study is devoted to highlighting the upconing and ascending of deep water via fractures zones feeding the alluvial aquifer in north El-Minia district. Twenty groundwater samples were collected from ten locations in the study area, two each (the same position at each locality is sampled in the shallow and deep horizons. The samples were analysed for isotopic and chemical composition. The radiocarbon age was determined for two wells with different depths. The mineralization (TDS, hypothetical salt assemblages, saturation indices of relevant salts) of the deep wells are more developed than the shallow ones. Oxygen-18 and deuterium have values almost lower than those of the Nile River and irrigation canals, around new El-Minia, and the depletion becomes higher in the deep wells than in the shallow ones. The distribution of the data points on the conventional delta oxygen-18-delta deuterium diagram is compatible with the mixing trend between Nile water and pluvial times meteoric water. The proportion of each of the two sources in the groundwater composition was calculated, based on binary model of mixing. The percentage of paleowater is of considerably higher values in the deep wells (average 18.5 %) than in the shallow ones (average 9.6 %). The radiocarbon age of the deep well at Brdtoha locality (36 m depth) is about 4000 years older than that of the shallow well which is typically of modern age. The isotopic (oxygen-18, deuterium, and carbon-14) and hydrochemical composition of the alluvial aquifer in north El-Minia district confirm that it receives higher saline water upconed from deep aquifers (Eocene carbonates and upper - lower Cretaceous Nubian sandstone) and this must be taken into consideration for exploitation management.


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9 (1), 57-73
The significance of structural control on fluvio-deltaic sedimentary dynamics during the Visean: the formation of Guezouman (Arlit region, Niger). The paleo-drainage pattern on the eastern edge of Tim Mersoï basin displays an overall braided channel arrangement with the main streams oriented N80°E with N30-40°E tributaries. In the vertical plane is a typical sequence of deposits of fluviatile character with frequent erosion surfaces within the middle part of the formation. In the vicinity of the In Azaoua-Arlit fault further West, toward the basin center, sedimentary dynamics are characterized from the beginning of the Guézouman deposits, by channel disruption and frequent flooding, a common process in river delta environments. During the early Tagora episode, the structural control of sedimentation west of the Aïr is related to the In Azaoua-Arlit fault, which was activated in sinistral strike-slip mode, causing the formation of "en echelon" folds grading into sigmoid folds or even folds parallel to the fault. These structures which form barriers in places presumably diverted certain streams southward, causing flooding as they meandered, as is observed in delta environments. This is a delta of structural origin, differing from the classical models by the absence of visible marine influences although many studies assume open marine conditions West of the In Azaoua-Arlit fault, which has yet to be proved. This delta is comparable with the present-day Okavango delta of northern Botswana; the main stream guided by faults flows into a graben where it branches forming an inland delta with no connection with the sea.


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9 (1), 75-92
The Triassic-Liassic volcanic rocks of Morocco: example of the Tasraft ridge (Central High Atlas). Petrological, geochemical data and geodynamical implications. A petrographic study of the Upper Triassic-Lower Liassic volcanic rocks of the Tasraft ridge (Central High Atlas) shows two facies with the pyroxene and plagioclase as the main components: i) doleritic basalts and ii) microlitic porphyritic basalts. These volcanic rocks, which were emplaced during five main episodes under thinning water trench, constitute a pile of volcanic lava. The geochemical data (major and trace elements) reveal a distensive geodynamic context (anorogenic volcanism) and an intra-plate tholeiite affinity (continental tholeiite). The multi-elements spectral analysis of the Triassic-Liassic basalts suggest that the basaltic magma formed from the interaction of a mantle plume with the sub-continental lithosphere. The basaltic rocks as well as the important thickness of the sedimentary series in the studied area was related to crustal thinning due to the intracontinental rifting preceding the Central Atlantic opening. The volcanic rocks of the Tasraft ridge and their equivalent in other parts of Morocco constitute one of the main subprovinces known as the "Central Atlantic Magmatic Province".


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9 (1), 93-105
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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9 (2), 107-117
The Northwest of Tunisia is a domain which offers very important emergence of the Paleogene lithostratigraphic series. The emergence is formed by very diversified clays levels, which are intermixed during the transport and their sedimentation. The associations of clays minerals vary with time. Indeed, the Paleocene fraction under 2 µm is characterized by the presence of kaolinite and rarely of the smectite. However, those of Eocene and Oligocene are series marked by the predominance of kaolinite, illite and irregular interstratified illite/smectite. The non-clays minerals are essentially calcite (dominant), quartz, very few feldspaths, dolomite and gypsum. The geochemical analysis of the total rock of clays samples reveals some variable silica (SiO2) and aluminina (Al2O3) contents, with some relatively weak proportions of Fe2O3, CaO and MgO. The loss to the fire is 20% for the majority of the samples. The results of the geotechnical analysis reveal the presence of few plastic clay. Cationic exchange capacities for raw clays are low. The clay minerals (fraction under 2 µm) are included between 20 and 80 %, according to the stratigraphic position. The ceramic tests based on the results of the analyses above show that the Paleogene clays of Northwest Tunisia can be manufactured into earthenware stones in the presence of necessary additives.


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9 (2), 119-134
Sequence analysis of Upper Miocene clastic series, within the central part of the Rharb basin, has been carried out using data from forty wells drilled on the supra- nappe sequence. Data from well logs and cuttings characterize the vertical facies change mainly represented by siltstone sediments interbedded with shale. Facies analysis reveals sandy sequences interbedded with shaly sequences, and the relationship between these sequences and the eustatic curves of Vail et al. (1987) suggest a depositional environment for the Upper Miocene clastic sediments.


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9 (2), 135-142
Marine deposits of Visean age are well-exposed in Middle Atlasic Causse depressions (Bhalil, Imouzzer du Kandar and El-Hajeb). They overlay in unconformity the Devonian beds. Biostratigraphic datings, based on foraminifers, algae and pseudo-algae, indicate a Late Visean V3b(gamma) for the oldest deposits of this area. They are characterized by Ungdarella uralica, Forschia sp., Endothyranopsis ex gr. crassa, Pseudoendothyra sp., Paroarchaediscus spp. at the concavus stage). Tournaisian and Early and Middle Visean are completely lacking. After the marine transgression of the V3b(gamma), the whole area is occupied by a carbonate platform, characterized by bioclastic and reefal limestones, and calcareous and sandy tempestites. In latest Visean the new morphology of the basin received a detritic sedimentation composed of meter-thick olistolites (quartzitic sandstones, limestones, conglomerates) and prograding deltaic deposits at Imouzzer du Kandar, and finally of sandy turbidites of deep-sea fan at El-Hajeb.


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9 (2), 143-156
To establish a diagnosis of the metallic contamination at the Oum Er Rbia estuary, geochemical (Al, Mn, Fe, Pb, Zn, Cu, Cd, Cr, Hg and organic carbon) and grain-size analyses were performed on the fine fraction (below 63 µm) of surficial and cored sediments. Heavy metals and organic carbon contents show that the Oum Er Rbia estuary is moderately contaminated. However, in the urban discharge areas of the cities of Azemmour and Sidi Ali, the degree of contamination is higher particularly for Pb, Zn and Cu. The organic matter plays an important role in the accumulation of these metals. The vertical profiles of metals analysed along a core acquired from the urban discharge area of Azemmour show that the metals are distributed into two groups. The first group contains Pb, Zn and Cu which demonstrate an enrichment at the top of the core end probably originate from urban discharges. The second group contains Al, Fe, Mn, Cr, Cd and Hg which do not demonstrate any significant variation at the top of the core and probably originate from natural sources. Although, the estuary of Oum Er Rbia could be considered less contaminated than other coastal ecosystems in Morocco (estuaries of the Sebou, the Bou Regreg and the Moulouya) and in Europe (estuary of the Scheldt, Gulf of Fos and North of the Adreatic Sea), precautionary measures should be taken to preserve this ecosystem.


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9 (2), 157-170
Detailed mapping and structural analysis of the Stephanian-Autunian formations of the Ida-Ou-Zal and Ida-Ou-Ziki areas (Menizla basin, western High Atlas, Morocco) reveals several superimposed tectonic events. The first is a late Stephanian-Autunian syndepositional extension, with a NW-SE dominant trend. The second event is a (early?) Saxonian subequatorial compression responsible for the main folds and faults trending N-S. The third event is a (late?) Saxonian, NE-SW compression generating left-lateral strike-slip faults which shared the basin into two parts. The Alpine tectonics is represented by the Triassic extension and the Tertiary compression (post-Eocene in the area). The collected data suggest that the original basin was created by collapse of the Hercynian chain, in a way that is comparable to the Stephanian-Autunian basins of western Europe.


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9 (2), 171-181
Role of polyphase brittle deformation (from the upper Miocene to the present time) in the genesis of the hydrographic layout of the Wadi Aggay and the origin of Sefrou basin (NW margin of the Middle Atlas, Morocco). Systematic analysis of the deformation to macroscopic scale (faults with striation, stylolithes, tension gashes) allowed the tectonic reconstitution of Sefrou graben. Indeed the separation of the superimposed tectonic phases founded at the same time on qualitative and quantitative criteria led to the distinction of five states of palaeostresses having affected the zone during the Neogene and the Quaternary time: (1) an upper Miocene NE-SW extension, (2) a lower Pliocene NW-SE compression, (3) a mid - upper Pliocene NNW-SSE extension, (4) a lower - mid Quaternary states of stress where σ1 is directed N030 or vertical, and σ3 is directed N120 and (5) a mid - upper Quaternary last state of stresses where G1 is vertical, G2 is directed N170 and G3 is directed N080 (with permutation σ1-σ2). The superposition of these palaeostresses is the cause of the reactivation of the inherited faults and creation of a new faults. The cumulated effects of those faults determined the genesis of the hydrographic layout of the present Wadi Aggay valley, the formation and the contribution to morpho-sedimentary evolution of the subsiding Sefrou basin.


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9 (2), 183-197
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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9 (3), 199-210
A method of determining the frequency-magnitude relationship and estimating the maximum possible earthquake magnitude m(max) for a seismotectonic zone from a combined catalogue of micro-seismic data, and regional and historical data is introduced in this paper. The method assumes that, if the earthquake characteristic within a seismotectonic zone is uniform and if the micro-seismic network is situated inside the zone, then the micro-seismic data, and regional and historical data sets display the same characteristic breakdown in self-similarity. Hence, by examining the same characteristic in the regional and historical data set and in the set recorded by the micro-seismic network, m, and its associated return period can be estimated. The method is applied to the seismotectonic zone called the Cape Low Province (without clusters of high seismicity) in the southern part of the Republic of South Africa, after the cumulative frequency-magnitude earthquake data sets have been normalised to per annum and corrected for differences in the monitoring area. A m(max) of ML = 5.7 is obtained, this is compared to the hazard parameters as calculated by the maximum likelihood method of Kijko and Sellevoll (1989 and 1992) on the combined catalogue of micro-seismic data, and regional and historical data.


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9 (3), 211-224
Three-staged glacis generations of Pleistocene age are found on the west piedmont of Jebel Bargou. Each one bears an incrusted detrital cover. The morphological and the petrographical study of these formations provide information concerning rhexistasic conditions and the morphogenic dynamics during the Quaternary. It also reflects the biostatic environment and the pedogenetic dynamic, which prevailed during the development of calcareous incrustings.


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9 (3), 225-243
Synthesis of geophysical studies of the Essaouira basin, corresponding to the intermediate zone between High Atlas and Atlantic margin, combined with data deduced from classical concepts elaborated according to the evolution of various wrench faults systems indicate a model of geodynamical evolution of the Essaouira basin. Analysis of gravimetric, magnetic and isopachs maps showed that the geodynamics of the basin is governed by episodic rejuvenation of the basement faults in transtension or transpression. So the basin has evolved a large wrench fault corridor cut up in moving rigid blocks, separated by wrench faults due to the tectonic heredity of the Hercynian and tardi-Hercynian discontinuities of the basement. Analysis showed that the geodynamic evolution was determined by sinistral strike-sliping of en echelon N80°E master faults corresponding to the Essaouira and the Chichaoua wrench faults and dextral strike-sliping of N160°E, conjugated faults which are more active onshore to the North of the Essaouira-Chichaoua strike-slip faults. Salt tectonics has influenced the accumulation and the differentiation of the system tracks. If the halokinesis is reduced and even absent in the Eastern part of the basin, it has been more active to the West and the diapiric structure shows the existence of flower structures determining a corridor-oriented N 160°E, bounded by rim synclines.


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9 (3), 245-253
The distribution of surficial sediments on the bay of Tangier is controlled by hydrodynamics and morphology of this area. It shows a decrease of grain-size distribution from the shore to the open sea which depends principally on the direction of E-W littoral drift. The repartition of silt fraction is mainly controlled by the NE waves, by the nature of continental sediment and by bathymetry. Sedimentological and mineralogical analyses of surficial sediments are suggestive of a distribution of sedimentary facies consistent with the continental origin from the western Rif formations.


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9 (3), 255-263
This contribution presents new tectono-sedimentary and volcanic data concerning late Neoproterozoic (PIII) in south-east of Kerdous Precambrian basement (western Anti-Atlas, Morocco). Several cross sections in conglomeratic PIII series of Tafeltast and of the western part of "Tagragra d'Akka" inlier, show some lateral variations of thickness and facies. These series are limited by basement-inherited faults with normal component, active during the late Neoproterozoic. Slope deposits with thick blocks of the basement and syn-sedimentary structures attest this dynamic. This sedimentation is also associated to an important volcanism with rhyolitics glowing ash cloud, ignimbrites and volcanic matrix breccias. We suggest that these characters are the witness of the late Proterozoic distension that controls the western Anti-Atlas rifting as it was already demonstrated in neighbouring domains.


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9 (3), 265-278
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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9 (4), 279-288
The transformation and dispersion of mercury in the southwest Lake Victoria goldfields in northern Tanzania was investigated through field and laboratory studies in order to evaluate the environmental impacts and human health risks due to mercury contamination associated with small-scale gold mining operations. Gold-ore tailings, river sediment, fish, and lichens were analyzed for mercury to determine the contamination levels. Mercury concentrations in the tailings from the Rwamagaza mine were in the range of 165-232 mg kg-1, whereas at the Mugusu mine the maximum concentrations were 5-6 mg kg-1 (dry weight) in the river sediment contaminated with the tailings. The dispersion of mercury along the Mabubi River downstream of the gold-ore processing site at the Mugusu mine decreased rapidly to less than 0.5 mg kg-1 at a distance of 4 km, and less than 0.1 mg kg-1 at 9 km close to the Lake Victoria Nungwe Bay. Granulometrical analysis of mercury distribution indicated highest mercury concentrations to be associated with the grain size fraction < 212 µm in the sediment. Mercury levels in eight fish species from the Nungwe Bay ranged from 2 to 34 µg kg-1 (mean 13 µg kg-1, wet weight), which reflected low background concentrations. Gold extraction by amalgamation in the SW Lake Victoria goldfields has not caused elevated mercury concentrations in the fish. On the basis of these and previous results, fish consumption from the Nungwe Bay does not seem to pose any significant human health risks in terms of mercury or methylmercury exposure. Mercury uptake levels by fish in a laboratory model of an aquatic system contaminated with metallic mercury from gold-ore tailings indicated low bioavailability of mercury from such system; this was consistent with field findings.


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9 (4), 289-311
This study provides an assessment of seismic hazard and seismic risk for Tulbagh, located about 90 km N-E from Cape Town, where the strongest and most damaging earthquake known in the earthquake history of South Africa took place. The study contains two parts: assessment of seismic hazard and seismic risk. The applied procedure for the assessment of seismic hazard is known as the "Parametric-Historic" procedure. This method permits the combination of both historical and instrumental data. The historical part of the catalogue contains only the strongest events, whereas the complete part can be divided into several subcatalogues, each assumed complete above a specified threshold of magnitude. In the analysis, the uncertainty in the determination of the earthquake was taken into account by incorporation of the concept of "apparent magnitude". The technique has been developed specifically for the estimation of seismic hazard at individual sites without the subjective judgement involved in the definition of seismic source zones, when the specific active faults have not been mapped or identified, and where the causes of seismicity are not well understood. The Parametric-Historic procedure being parametric in nature, consists essentially of two steps. The first step is applicable to the area in the vicinity of Tulbagh and requires an estimation of the parameters specific to that area, otherwise known as the area-specific parameters. In this case, these parameters include the mean seismic activity rate, the Gutenberg-Richter parameter, and the maximum regional magnitude. The second step is applicable to the Tulbagh site, and consists of parameters characteristic of the site and is referred to as the site-specific parameters which are the parameters that give the distribution of the amplitude of peak ground acceleration (PGA). The results of the hazard assessment are expressed as probabilities that specified values of PGA will be exceeded during the chosen time intervals. A worst case scenario sketches the possibility of a maximum PGA of 0.30 g. The second part of our study concentrates on the probabilistic seismic risk analysis. It includes a comprehensive introduction to the problems associated with the estimation of seismic damage to buildings. This is followed by the methodology for the estimation of expected damage from a probabilistic point of view. The work closes with an application of the described methodology to a site in the vicinity of Tulbagh.


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9 (4), 313-323
Malawi lies on the Western Branch of the East African Rift System (EARS). The country is within the most seismically active belt of the EARS. Strongly felt earthquakes have been reported in various parts of the country although damage to property and loss of life has been minimal. This could have been due to sparse population and types of housing structures in the past. The situation has rapidly changed due to the increasing population and acceleration in urbanisation in the country's main cities. Urban drift combined with low incomes in cities has resulted in a large population living in poorly constructed houses. Hence most of the population in Malawi today lives in houses that are very vulnerable to ground movement even of moderate size. With these developments, the country is more prone to dangers of earthquakes than it were a few years ago. Earthquake hazard estimations for hard rock sites have been calculated for three major cities of Mzuzu, Lilongwe and Blantyre where industrial development is focused. The calculations were done following a probabilistic hazard analysis approach. In cities of Mzuzu, Lilongwe and Blantyre, peak ground acceleration (PGA) values of 80-130 cm/s2 have been estimated for return periods of 50-100 years. These PGA values correspond to Modified Mercalli Intensity (IMM,) of VI-VII. The anticipated intensities would cause tremendous damage to buildings and would have adverse social and economic impacts in Malawi. This is due to the fact that the building code of Malawi has no consideration for earthquake ground motion. If site effects were taken into account, the expected ground motion levels would be more than the results presented here. Malawi is still developing, hence it is expected that vulnerability to earthquakes will continue to increase with time. Efforts are being made to put in place proper earthquake disaster mitigation programmes to reduce earthquake risk.


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9 (4), 325-335
The Cameroon Volcanic Line is a dominant structural and morphological feature on the African continent, responsible for the main uplands in Cameroon and Nigeria. Landslides are common hazard along this line and occur mainly in the hilly terrain situated in the coastal region where there is high precipitation. Case studies of over sixty landslide events around Mt. Cameroon, the Rumpi Hills, the Batie Hills, and the Bamenda Highlands (where 64 people have been killed in 11 events between 1988 and 2001) indicate that the steep gradients, high precipitation, human intervention, and earthquakes, are the main factors which trigger these events. Field studies indicate that the nature of sliding varies: from rotational and soil fall to normal sliding, depending on the geology, tectonic setting, and slope gradient. Analysis of slide surfaces indicates an association of the landslides with fault zones which run N45°-55° E, parallel to the direction of the Cameroon Volcanic Line, and also along antithetic faults to this direction. The study area is geologically varied and consists of Precambrian and Cretaceous granites, Cretaceous and Tertiary sediments and Tertiary volcanics (basalts, trachytes, rhyolites and pyroclastic material). Analysis of the timing of these hazards, their frequency, as well as geological and structural considerations derived from the case studies are used to propose prevention and mitigation approaches which may be used in future to reduce the loss of life from these hazards.


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9 (4), 337-341
The presence of elevated levels of cerium, in conjunction with a deficiency of magnesium, in cardiac tissues of patients with Endomyocardial Fibrosis (EMF) in Kerala in India provided a model for environmental exposure to these elements. The assessment of Cc and Mg concentrations in soil, water and foodstuff in the Mukono area in southern central Uganda, where EMF is common, yielded only slightly elevated levels of Ce, but markedly low Mg levels in water and foodstuff. The intake of large quantities of Cc may therefore be related to the direct ingestion of soil, i. e., the practice of geophagy, a behaviour common among children of this region.


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9 (4), 343-350
Disasters (floods, earthquakes, hurricanes, wildfires, hazardous spills, public unrest, famine, epidemics, etc.) are spatial events. Emergency disaster management requires response, incident mapping, establishing priorities, developing action plans, and implementing the plan to protect lives, property, and the environment. Mapping and information acquisition is therefore vital for disaster management. Preparation of risk maps is essential for planning effective preparedness and response measures. Available technologies such as GIS and remote sensing provide analysis of environmental factors for the identification of potential geohazards and disasters. Under the UNESCO project entitled "Geosites" of the International Geological Correlation Program, the Division of Earth Sciences, Nairobi Office has envisaged to produce a geological atlas of Africa. The atlas contains geological overview maps for 55 African countries plus a set of regional maps for understanding the general stratigraphic features and events of the continent. For each country, a brief description on geology, stratigraphy, tectonics, economic geology, geohazards and geosites is included. The atlas aims to promote sustainable development in the continent through system analysis, prospective studies, and evaluation of performance indicators. It is the contention of the authors that there should be more efforts directed towards the development of an integrated information system amongst various agencies that will help to minimise the effects of disasters.


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9 (4), 351-367
The aim of this study was to find out environmental hazards, which occur as a result of beach erosion in Shanzu-Barnburi area, Kenya. In August to November 2001 a case study of Shanzu-Bamburi area in Kenya was carried out. Among the study objectives was to assess the potential for erosion and accretion within the study area noting the degree of severity. Methods used included interpretation of aerial photographs, bench-mark measurements, beach-width measurements, hydrographic charts interpretations and visual observations. Results from aerial photographs, hydrographic charts, and bench-mark measurements indicate this beach to be eroding. The implications for this beach erosion are that a lot of land is being lost. Seawalls, groins and revetments have been constructed in this area, just to end up in accelerating erosion. Building of breakwaters is suggested but only after long-time studies have been successfully carried out in the area. This paper thus gives the result of this study and further attempts to bring out the options available in the study area to respond to beach erosion as an environmental hazard.


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9 (4), 369-375
The paper explores a number of possibilities from the eminent danger identified in the case of Lake Nyos. It is the assertion of the authors that any dam failure will lead to thousands of people in Cameroon and Nigeria directly being affected from flooding. The reduction of hydrostatic pressure will then lead to a new gas disaster with serious effects. It is proposed that fortification of the natural dam to mitigate on the floods is an absolute urgent need. Mapping of the risk zones and mass education of the population on the impending catastrophe should be carried out.


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9 (4), 377-384
The use of plants in analysis of toxic metallic elements in the biogeochemical environment is presented considering the challenges and types of biogeochemical samples. Whereas plants respond differently to varying subsurface conditions, the need to identify indicator species is paramount in detecting elevated concentration of metallic elements in the environment. Of equal importance is the biogeochemical availability of pathfinder elements, associated with particular mineral deposits or point source emissions, to the indicator plants. Thus, in this way the metallic elements are absorbed into the plants, making them a suitable sampling medium for geobotanical detection of anomalous concentration of potentially hazardous metallic elements in the biogeochemical environment. The results from a geobotanical case study undertaken around the fluorite mineralization in Kimwarer Location in Kerio Valley, Kenya, demonstrates the usefulness of plants in analysis of elevated concentrations of metallic associated elements. Indicator plants species identified as suitable indicators for detecting hazardous elemental concentrations around the fluorite mineralization include Vangueria acutiloba, Croton dichogamus, Harrisonia abyssinica, Acalypha fruiticosa, Acacia tortilis, Euclea davinorum, A. amara, E. davinorum, Balanite aegyptiaca, and Nandi flame. These plant species show elevated concentrations of the fluorite pathfinder elements.


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9 (4), 385-395
In the Tala-Kangundo area, located approximately 50 km ENE of Nairobi, Kenya, quarrying of volcanic tuffs for building stone is causing a serious environmental degradation. Agricultural land is being destroyed at an alarming rate by the careless scraping off the top rich soil to pave way for quarrying. After excavation, there is little or hardly any rehabilitation work program in place to restore the land for resumed fanning purposes. Furthermore, good grazing lands with beautiful landscapes and aesthetic values are either interfered with or lost completely through the haphazard quarrying activities. Further environmental degradation is reflected by the quarry sites having become an eyesore with extensive and numerous heaps of dumps of unused quarry rock fragments. Secondly, these open and unguarded quarries pose dangers to both animals and human beings, especially to playful children in their vicinity. Thirdly, some of he quarries are filled with stagnant waters, thereby becoming breeding grounds for vector borne disease carriers. Fourthly, recreational land for parks and playgrounds is being destroyed in the absence of proper planning of the planning of the quarrying activities. The authors recognize that good management of these quarries is required and more detailed, explicit and strict policy guidelines on the exploitation of the rock resource and rehabilitation procedures on the disused quarries are needed. As a result, the quarry owners will not only reap maximum economic benefits by avoiding the middlemen (brokers) exploitation, but will also maintain a clean and healthy environment for themselves and for posterity.


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9 (4), 397-399
Over the years attempts have been made to predict the occurrence of landslides in time and space, but with little or no success. A combination of certain factors, commonly cited as increase in slope angle, removal of lateral support at the toe of the slope, added weight at the top of the slope, earthquakes and other shocks and vibrations, removal of vegetation, and high rainfall followed by increased water-pore pressure, are necessary to trigger the slump-type landslide. A recent study of landslides in Kenya suggests, however, that in expansive soils, the rate of expansion of the soil when exposed to moisture plays a critical role in triggering the slurp-type landslides. This critical role played by the rate of expansion of the soils can be used as a factor to predict potentially where and when a landslide is likely to occur, if the critical conditions of slope and moisture availability have been met. Residents of areas prone to landslides can be trained to recognize precursory conditions that portend landslide danger and therefore take appropriate precautionary measures.


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9 (4), 401-407
Mozambique has more than 50 % of its territory covered by international river basins and shares 9 rivers with its neighbors draining to the Indian Ocean. Major floods have been recorded in all these rivers in 1976, 1977, 1978, 1981, 1984, 1985, 1996, 1997, 1999 and 2000. The 2000 catastrophic floods were the most destructive and affected the southern and central region of Mozambique. They were caused by intense and unusual heavy rainfall within a short span of time resulting from a nucleus low pressure and by Eline and Gloria tropical cyclones. Historically, Mozambique is prone for floods but this event was also influenced by poor river basin management. The severe flood event has set back the economic development of Mozambique for many years. In fact 800 people died, 550.000 were displaced and 27 % of total population of Mozambique was affected. Additionally, 10 % of arable land was destroyed as well as basic infrastructures. Floods are part of the process of nature and human societies must live with floods. Therefore structural and non-structural measures must be taken to minimize the negative impacts. Prevention and management of geohazards must be supported by research on disaster risk reduction.


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9 (4), 409-412
No two African volcanoes are exactly alike in their habits or histories: from some, hot lavas pour out quietly and spread over wide areas (e.g., Nyiragongo), from others, material is blown out violently in a series of explosions. Some volcanoes are quiescent for long intervals while others have been active at shorter time intervals. In spite of their individuality, African volcanoes are believed to share a common cause and certain features. The original magma that supplies them all is similar at the depths from which it starts towards the surface. All are actuated by gas pressures, though some zones are typified by tectonic movement and volcanic eruptions.


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9 (4), 413-418
Maputo is situated along the coast and has a rapidly increasing population growth and an increasing demand for land use resulting in environmental problems such as informal settlements with construction along steep slopes. Maputo was built on Pliocene to Pleistocene dunes composed of fine red sands. On the eastern and southern sections it is bounded by a slope 20-40 m high with 20°-40° inclination. Unusual but intense and brief rainstorm occurred in February 2000 and a precipitation of 400 mm was registered in four days. This rain saturated the water table and the steep slope resulted in flooding that caused landslides, slope instability as well as deep gully failures. Besides the intensive rainstorm, other factors contributed to the disaster. These include the rapid growth in urbanization, poor drainage system, geologic and topographic factors, absence of land use planning as well as poor legislation and institutional framework. The disaster caused displacement of hundreds of families who lost their houses and possessions. Basic infrastructures such as roads, drainage, water supply, communication and electricity systems were destroyed. Good land use planning, better drainage system and the enforcement of legislation within the context of well established institutional framework should limit the effects of such disasters in the future. This paper emphasises the fact that prevention and management of geohazards can only be enhanced by research on disaster risk reduction.


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9 (4), 419-427
A significant portion of the natural environment in African countries with major mining activities (e.g., Zambia, South Africa, Zimbabwe, Ghana, Mali, etc.) has been negatively altered. To correct these negative effects on the environment and reduce the hazards of mining activities, monitoring and rehabilitation programmes must be associated with mining projects. An environmental management approach adopted by some major mining companies in the continent is "Best Available Technology Not Entailing Excessive Cost (BATNEEC)". Each mine site has particular characteristics that will influence the environmental rehabilitation programme. These characteristics may be obvious but critical differences exist and can be identified after careful investigation. Rehabilitation of mines must be conducted according to the local social structure with respect to ecological sustainable development. The goal must be the achievement of improvement in the total quality of life both in the present and the future. There must be sustenance of the ecological processes on which life depends. The majority of harmful effects on the environment can be minimized through careful pre-mining planning and conscientious management of mining activities. It is mostly in cases where there has been an absence of a pre-mining environmental management plan (EMP) that severe degradation occurs. Reversal of the harmful effects on mining is usually prohibitively expensive. It is therefore advisable to prepare and execute an Environmental Management Plan and monitor the situation throughout the entire mining cycle (Figure 1).


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9 (4), 429-432
Geoenvironmental hazards and disasters arise from natural phenomenon. However, there occurs an interface stage in which man either through omission or commission induces accidents of disastrous proportions. One of the human-induced disasters with profound environmental consequences is mass population displacements or refugee emigration. This paper considers an example of a man-made environmental hazard - Kakuma Refugee Camp. The camp was established in 1992. The climate of Kakuma is generally arid and the vegetation type in the area is mainly bush composed of acacia species. The camp is about 12 km2 and currently has a population of 85,000 refugees. In addition to these, there are agencies' workers and UNHCR staff. There has also been a marked influx of locals around the camp and Kakuma centre. Given its population, the camp essentially represents an unplanned urban settlement in a fragile rural setting without the necessary settlement facilities. The concentration of such a large population in an area that previously supported a small population impacts negatively on the camp environment and surrounding area. This is exemplified by the fact that the camp is not a planned settlement. In a fragile environment such as Kakuma, the impacts are typified by degradation of vegetative cover leading to loss in bio-diversity, increase in soil erosion, problems of waste disposal, pollution etc. This paper, based on a baseline survey of the refugee camp examines the environmental impacts that arise from settlement of large numbers of displaced persons in a small fragile area, notes the environmental problems and makes recommendations towards sound environmental management and suggestions for the establishment of refugee settlements in future.


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9 (4), 433-446
The Current Bibliography of Middle East Geology contains recently published material on the geology of the region (including Egypt). The bibliography lists books, articles, abstracts, maps, Ph. D. and M. Sc. theses, reports, etc. Special emphasis is given to local material which does not reach international bibliographies or databases. Most of the material in the bibliography is available at the library of the Geological Survey of Israel, which is accessible to the scientific community.


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