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Shallow groundwater resources, especially in hard rock environment, constitute an important part of urban water supply in developing countries, appropriate to the low level of economic development. However, increasing urban population and dependence on shallow groundwater systems make it imperative to evaluate the availability and the contamination of these resources, and define new strategies of water exploitation taking into accounts these findings and constrains. This study has been carried out on the shallow groundwaters of Yaounde, central Africa. Based on head slug-in tests, chemical and isotope analyses, we demonstrate the importance of geomorphological and geological settings that constrain hydrogeology, urban occupation and therefore, water exploitation and contamination. Slug test results show spatial variability of well recovery rates with higher values recorded in the valleys compare to the hills, presenting saturated hydraulic conductivity of 10-6-10-8 m/s. Groundwater evolves from recharge zone as Ca-HCO3 in the hillside lateritic system to discharge zone in the slope/valley colluvium/alluvium system as NaK-NO3. The groundwater composition dominated by silicates/water interaction in the hillside lateritic system, and anthropogenic processes in the slopes and valleys. δ15N and δ18O of nitrates indicates that nitrate pollution of groundwater is mainly from sewage and human waste. Shallow groundwater in the hillside/new urban district and to a lesser extent slopes should therefore be protected and prioritised for usability and sustainability of the resources while ensuring the abstraction of the deeper part of the shallow aquifer in the valley/central districts due to the presence of denitrification. The proposed conceptual scheme for Yaounde can then be used as a guide in the development, exploitation and management of local wells in hard rocks system of Africa.

The coastal flanks of Mt Etinde is wedged between the sea and the southwestern slope of Mt Cameroon. The only fresh water resources available for multipurpose uses in this area are mountain springs and streams that drain volcanic materials. To access the sources, processes and assess the ecological risk associated with hydrochemicals and heavy metals in these mountain water resources, 18 water samples were collected in different seasons at 4 locations between may 2009 and december 2010 for major ions and heavy metals determination. The sampled waters ranged from neutral to slithly alkaline, weakly mineralized and dominated by Ca–Mg–HCO3 water type irrespective of season. The hydrochemical ratios revealed ions chemistry mostly influenced by geogenic source of silicate rock weathering and atmospheric inputs. Sampled waters had low concentration of heavy metals which are less mobile in the aqueous phase, controlled by hydraulic condition. Geochemical processes of mineral dissolution and reverse ion exchange coupled with hydrodynamic processes of flushing at the weathering front and soil leaching are the main controls on the water chemistry in the area. Despite agricultural and other anthropogenic activities, quality indices in the study area indicate the absence of anthropogenic inputs. Key words: Major ions, heavy metals, rocks weathering, soil leaching, water quality assessment.

L’histoire de la subsidence et de l’évolution thermique du sous-bassin de Kribi-Campo situé dans le Golfe de Guinée a été contrainte à l’aide de 10 puits en mer en utilisant la technique de délestage après décompaction. Quatre principales phases de subsidence ont été discriminées : la première, du Barrémien à l’Aptien (130–112 Ma); la deuxième, de l’Albien au Sénonien (112–65 Ma); la troisième, s'étendant du Paléocène au Miocène (65–5 Ma); et la quatrième du Pliocène au Pléistocène (5–2 Ma). Les cartes de quantité et de vitesse de subsidence et de sédimentation montrent une grande zone subsidente dans la partie ouest du bassin autour de Kribi. Le facteur d’extension β pour le modèle d’extension uniforme correspond à des valeurs allant de 1,04 à 1,06. Graphiquement, les courbes de subsidence tectonique apparaissent encadrées par les courbes correspondant à β = 1,03 et β = 1,09. Les pentes des courbes linéaires de la subsidence tectonique par rapport à la racine carrée du temps, t, ont permis d’avoir des paléotempératures des sédiments ainsi que des gradients géothermiques en parfait accord avec les valeurs observées dans les puits. Par exemple, un gradient de température de 35,316 °C·km−1 a été calculé avec les températures maximales tandis que celui obtenu à partir des puits est de 35,554 °C·km−1. La comparaison des valeurs calculées de la réflectance de la vitrinite Ro avec les valeurs mesurées montre une bonne correspondance. Ces valeurs de la vitrinite indiquent que les roches-mères d’âge Crétacé et Tertiaire inférieur ont probablement atteint la maturité thermique.

Sedimentary features such as channel sands and submarine fan sequences are important hydrocarbon reservoirs throughout the world and may be interpreted from bed thickness trends and log motifs. The log motifs of four well logs were employed during this study to delineate reservoir architectural depositional features and environment, determine their lithological attributes, and evaluate reservoir properties. Gamma ray log signatures were utilized to infer depositional features, discriminate litho-units, and define depositional environment; resistivity log was employed to identify reservoir zones and formation fluids, while the combined density and neutron logs aided in the estimation of reservoir porosity and lithological typing. Results of analysis show seven laterally discontinuous reservoirs: one in Well X (X2), three in Well Y (Y1, Y2, Y3), and three in Well W (W1, W2, and W3) with thicknesses of 6.2 m, 19.2 m, 7.6 m, 78.7 m, 100.9 m, 38.1 m, and 41.6 m, respectively. Reservoirs architecture reveal distributary channel sands, submarine fan lobes, and deep tidal channel-fills deposited within the deep marine mud-rich N’kapa Formation. Average porosity, water saturation, and hydrocarbon saturation values of Well X and Well Y reservoirs are 20.8%, 30.8%, 69.2%, and 40.2%, 18.3%, 81.7%, respectively, indicating moderate-to-good reservoir quality. Also, the permeability values are moderate to good (74.89–12,584 md), except for Y3 and Well W reservoirs whose well log-derived permeabilities were unreliable due to their non-irreducible nature. Density-neutron crossplots indicate heterogeneous reservoir lithologies comprising of limestone, dolomite, and sandstones, with predominant calcite and subordinate dolomite as mineral matrix. Crossplot of water saturation and porosity revealed grain-size variation ranging from fine-grained to silty sediments with bulk volume water values suggesting Well X and Y reservoirs to be homogeneous and will produce water-free hydrocarbons, while Well W reservoirs are heterogeneous water-prone reservoirs.

The P10 well is located offshore, in the Northern part of the Rio Del Rey basin in southwest Cameroon. Although the Rio Del Rey basin is the most prolific coastal basin in Cameroon given the production results from several fields in the southern part, yet it remains very little explored in its northern part. This work evaluation the petroleum potential in the northern part of the Basin using a combination of the "Quick Look" interpretation of the logs recorded in well P10 and "complex matrix" facies analysis of the different lithofacies through the neutron porosity - bulk density (NPHI-RHOB) and delta time sonic - bulk density (DT-RHOB) diagrams. The composite log includes the Gamma Ray log; Caliper log; Deep Resistivity log; neutron porosity log and bulk density log. In addition to this composite log, a geological end of well report is completed to refine the results. Ten (10) near sand/sandstone reservoirs were delineated between 950 and 1803 TVD m (true vertical depth in meter) with very good porosities (12%

International audience; he Rio Del Rey basin located in the Gulf of Guinea is one of the two basins lining the Cameroonian coast. It evolved since the Cenozoic in a tectono-magmatic and seismic complex setting. During the Miocene, this evolution was controlled by tectonics, relative sea level changes, basin filling and mantle dynamics. Two deposit megasequences of second order, MS1 and MS2, were pointed out. MS1 (lower Miocene), aggradational and corresponding to the Isongo turbidites deposited during a period of relative sea level drop registered two sequences of third order differentiated by the degree of channel incision: S1a (Aquitanian-Burdigalian), hardly incised and S1b (Serravallian), moderately incised. A double extension along N-S (Burdigalian) and NE-SW (Serravallian) directions responsible for a set of horsts and grabens, high subsidence and depocentres trending NW-SE affected these sequences. MS2 (middle to upper Miocene), progradational and corresponding to deltaic alternations deposited during a period of creation of available space were controlled by the tilting, wrenching, a second stretching phase and low sedimentary filling. MS2 recorded three cycles of 3rd order: S2a (lower Tortonian), S2b (upper Tortonian) and S2c (Messinian) differentiated by their morphology in ramp for S2a and S2b and slope for S2c. The formation of grabens and horsts and the tilting of the margin coincide with the high activity of the Cameroon volcanic line interpreted as a result of deep mantle dynamics affecting the inner Congo craton lithosphere. This architecture, which differs from those of the other basins of the Gulf of Guinea, partly explains the low oil production of this basin.

Studies for the characterization of hydrocarbon reservoirs using well logs have been carried out in the M-Field of the Douala Basin to evaluate the hydrocarbon prospectivity, delineate hydrocarbon zones and determine the petrophysical properties of the identified reservoir rocks. Data from two wells comprising gamma ray, resistivity, neutron, density logs were used. Gamma ray log was used for lithologic discrimination; resistivity log was employed to identify formation fluid based on electrical responses of reservoir formations, while combined density and neutron logs were used to estimate reservoir porosity, as well as ascertain hydrocarbon type where present. Four hydrocarbon bearing reservoirs were delineated in the study area; one in Well-X (X 2) with a thickness of 6.2 m and three others in Well-Y (Y 1, Y 2, Y 3) with thicknesses of 19.2 m, 7.6 m and 78.7 m, respectively. Neutron–density crossplots indicate heterogeneous reservoir matrix comprising of sand, limestone and dolomite. The reservoirs were correlated using gamma ray log and were found to be discontinuous across the wells. The petrophysical parameters of the reservoirs evaluated indicate porosity, water-saturation and hydrocarbon-saturation values of X 2 to be 20.8%, 30.8% and 69.2%, respectively, and the average porosity, water saturation and hydrocarbon saturation of the Well-Y reservoirs to be 40.2%, 18.3% and 81.7%, respectively. The porosity value indicates medium–high formation porosities and oil as the dominant hydrocarbon type. The crossplot of water-saturation and porosity revealed that the grain size variation of the reservoirs ranges from fine-grained to silty sands. The bulk volume water (BVW) values for the M-Field reservoirs suggest that they are homogeneous and at irreducible water saturation (Swirr) and hence will produce water-free hydrocarbons.

International audience; Dinosaur trackways have rarely been reported in Cretaceous strata across the African continent. To the exception of ichnological occurrences in Morocco, Tunisia, Niger and Cameroon, our knowledge on the composition of Cretaceous dinosaur faunas mostly relies on skeletal evidence. For the first time, we document several dinosaur trackways from the Cretaceous of the Mamfe Basin in western Cameroon. Small and medium-size tridactyl footprints as well as numerous large circular footprints are present on a single horizon showing mudcracks and ripple marks. The age of the locality is considered Cenomanian-Turonian and if confirmed, this ichnological assemblage could be younger than the dinosaur footprints reported from northern Cameroon, and coeval with or younger than skeletal remains reported from the Saharan region. These trackways were left in an adjacent subsiding basin along the southern shore of the Benoue trough during a time of high-sea stand when the Trans-Saharan Seaway was already disconnecting West Africa from the rest of the continent. We predict that other similar track sites may be occurring along the margin of the Benoue trough and may eventually permit to test hypotheses related to provincialism among African dinosaur faunas.

Investigations were carried out on the Tertiary sedimentary sequences from west Cameroon, namely the Mamiwater well (from 268 to 828 m), the Pungo well (from 731 to 1338 m) and the Yatou well (from 700 to 1402 m). These intervals correspond to the Souellaba Formation (SFm) of the Douala sub-basin according to the well final report produced by the National Hydrocarbons Corporation of Cameroon (NHC). The aim of this study was to characterize the lithofacies, the palynological zones, and characterize the depositional environments based on palynomorphs and palynofacies. The studied intervals are dominated by shale interbedded with limestone and siltstone; a few beds of claystone, fine to medium and coarse-grained sandstone (limited to the Pungo well) and rare marl layers are also observed. Three main palynozones were identified in each well and each zone is named. The palynological composition of the assemblages is marked by the abundance of spores and pollen grains and several stratigraphic markers in the three wells such as Cicatricosisporites dorogensis, Perigrinipollis nigericus, Proteacidites cooksonii, Zonocostites ramonae, Magnastriatites howardi, Loranthacidites nataliae, Brevicolporites molinae, Triporotetradites hookenii, Marginipollis concinnus and Adhenantheridites simplex. The dominance of the latter over dinoflagellate cysts in the Souellaba Fm indicates a high continental influence. The high percentage of angiosperms pollens grains, which are dominant in the assemblages, indicates the proximity of terrestrial sources associated with oxygenated environments. Moreover, the dominance of terrestrial palynomorphs and the relative abundance of marine palynomorphs are interpreted as indicating shallow marine environments of deposition close to terrestrial source. This marine condition is confirmed by the presence of foraminiferal test linings. The abundance of plant debris within the palynofacies indicates a climatic control on the parent vegetation and suggests the proximity to fluvial inputs. The organic matter analysis reveals type III kerogen. The relatively high number of opaque phytoclasts suggests combustion events.

Major and trace element composition of iron duricrusts including clayey material samples and biostratigraphy of the Missole I outcrop from the Paleocene–Eocene N’Kapa Formation in the Douala sub-basin of Cameroon were used to infer the palaeoenvironment and relative age of the iron duricrusts. Iron duricrusts and clayey materials are essentially kaolinitic and smectitic and are generally siliceous and ferruginous (iron duricrusts) or siliceous and aluminous (clayey materials). These materials have high Chemical Indices of Alteration (CIA = 86.6–99.33%). The negative Eu anomalies with high (La/Yb) N shown by iron duricrusts and clayey sediments are essentially derived from silicic or felsic parent rocks when fractionated chondrite-normalized REE patterns also indicate felsic or silicic parent rocks. The Missole I iron duricrusts have a post-Thanetian age according to the relative age of claystones (Thanetian) and were formed after the deposition of sedimentary materials in an anoxic low-depth marine environment with eutrophication of surface water, and may have been exhumed and oxidized under arid climate.

The quick-look and gas chromatography analyses were used for formation evaluation of four depth intervals in a well (well A) located within the offshore of the Rio Del Rey basin. The results show 3 water reservoirs (R1 to R3) and 1 hydrocarbon reservoir (R4). The quick-look reveals that the hydrocarbon (oil and gas) reservoir is a shaley sandstone or a radioactive sandstone located between 4898-4932 Mmd which is filled by oil and gas and with a good porosity. The chromatographic gas ratio analysis reveals that the hydrocarbon reservoir is filled by a productive gas which may be a wet gas. The result provided by the gas chromatography is a false result probably due to its limitation which is that the hydrocarbon component must exist at the gaseous phase (C1-C5) to be detected and analyzed. The gas chromatography based its analysis only in the C1 to C5 range, in oil we have from C1 to C8.

International audience; Missole facies description and sequence stratigraphy analysis allow a new proposal of depositional environments of the Douala sub-basin eastern part. The sediments of Missole outcrops (N’kapa Formation) correspond to fluvial/tidal channel to shallow shelf deposits with in some place embayment deposits within a warm and semi-arid climate. Integrated sedimentologic, palynologic and mineralogical data document a comprehensive sequence stratigraphy of this part of the Douala sub-basin. Five facies associations occur: (1) facies association I is characterized by Floodplain deposits; (2) facies association II is Fluvial to mouth bar deposits; (3) facies association III characterise Shallow Shelf deposits; (4) facies association IV represents Distal bay or Lacustrine déposits; and (5) Facies association V is made of Fluvial channel deposits. Six depositional sequences were identified. These sequences are composed of four progradational sequences and two retrogradational sequences containing a fluvial channel portion represented by lag deposits at the base of retrogradational sequences. These deposits represent the outset of the relative sea level rise period. In the study area, the N’kapa Formation is composed of non-marine/coastal aggradational deposits representing the early stage of the regressive period. The occurrence of the estuarine/bay deposits with paleosols development is interpreted as evidence of climate change with significant relative base level fluctuation. The study of key minerals associated to sequence stratigraphy as well as palynology demonstrated that sequence architecture has been controlled mostly by climate evolution and outcrops are dated Paleocene – early Eocene.

Major and trace element concentrations of clay deposits of the Missole II and Bomkoul respectively from the Paleocene-Eocene N’Kapa Formation and the Miocene-Pliocene-Matanda-Wouri Formation in the eastern part of the Wouri River in the Douala sub-basin of Cameroon have been investigated to identify the parent rocks. To carry out this study, X-ray diffraction, inductively coupled plasma–atomic emission spectrometry (ICP/AES) and inductively coupled plasma–mass spectrometry (ICP/MS) were performed to determine respectively the mineralogical and chemical data of Missole II and Bomkoul clayey materials. Clay sediments are essentially kaolinitic and illitic, and kaolinitic and smectitic respectively in both sites. They are generally siliceous, aluminous with small iron and bases (MgO, CaO, Na 2 O, and K 2 O) contents. Samples of Missole II profiles are more siliceous than those from the Bomkoul grey and dark grey clayey materials. Clayey materials have high Chemical Index of Alteration (CIA = 80–99.34) which suggests that they are strongly weathered under humid tropical climate before and after their deposition in the coastal plain. The value of Eu/Eu * (0.48–0.61), La/Sc (2.15–20.50), Th/Sc (0.74–2.25), Th/Co (1.08–8.33), and Cr/Th (5.24–13.55) ratios support essentially a silicic or felsic parent rocks. Total REE concentrations reflect the variations in their grain-size fractions. Chondrite-normalised REE patterns with LREE enrichment, flat HREE, and negative Eu anomaly are attributed essentially to silicic or felsic parent rocks like those from weathered materials developed from the gneisses around the coastal plain in the littoral part of Cameroon ( Noa Tang et al., 2012 ), main characteristic of Paleocene-Eocene and Miocene-Pliocene clay sediments of Missole II and Bomkoul areas.

International audience; The South Namibian Plateau, which belongs to the South African Plateau, is situated between 25°‐29°S and 15°‐20°E. This study examines the relationships between this portion of the plateau and the development of planation surfaces and scarps bounding the plateau. Geomorphological analysis through morphometric indices extracted from a DEM (90 m) and its derived maps as well as field observations supported by the literature data permit the demonstration that tectonics, climate and base level are the main factors that control the formation and evolution of the planation surfaces and scarps that separate them. From west to east, the South Namibian Plateau consists of four main morphological provinces: the coastal province and the intermediate, upper and Kalahari provinces in the interior plateau. These provinces include five Cenozoic planation surfaces that are differentiated by their elevations, regional slopes, relative reliefs and erosion processes. These surfaces have been formed by etchplanation and pediplanation. The drainage pattern and river length profiles show that the coastal province evolved differently than the interior plateau. The development of the coastal province is controlled by eustasy and tectonics, whereas climate-related processes and tectonics control that of the interior plateau. The presence of several scarps separating these surfaces, the most degraded and older of which are inside the plateau, reflects a polyphase evolution. This evolution can be highlighted by two models: (1) an eastward migration mantle dynamics causing a slight uplift and rejuvenation of the system by destabilizing the coupled weathering/erosion equilibrium and (2) an internal propagation of isostatic rebound induced by the retreat of the western scarp leading to a significant flattening in the central part of the plateau.

A geological study carried out in the Bomkoul area (Douala sub-basin, Cameroon) has revealed the presence of heterogeneous clayey materials on hills (80–120 m altitude). The clay deposits are thick at the upper slope where sandstones and sandy-clay overlying clay layers, and thin at the middle and lower slopes where weathered clays overlying clay layers. Clayey materials identified are grey, dark-grey and mottled in color, with sandy-clay, clayey-silt, silty-clay and clay textures. Raw materials are mostly made up of fine particles ranging from 52 to 82% clay and silt in the mottled clayey material, 50 to 82% clay and silt in the dark-grey clayey material and 70 to 85% in the grey clayey material. Their chemical composition is characterized by silica ( 2 ), alumina ( 2 O 3 ) and iron (1 to 16% Fe 2 O 3 ). The main clay minerals are disorganized and poorly crystallized kaolinite and few smectite. The physical, mineralogical and geochemical properties of these materials presented and discussed in this work show that the clayey raw materials of the Bomkoul area have a good potential for pottery as well as brick, tile and soil sandstone manufacture.

International audience; The Kribi-Campo sub-basin is composed of an Early to Mid Cretaceous series from West Africa's Atlantic coast and is located in southern Cameroon in the Central African equatorial rain forest. It is the smallest coastal basin in Cameroon and forms the southern part of the Douala/Kribi-Campo basin known as Douala basin (s.l.). Until now, no detailed sedimentological studies have been carried out on the outcrops of this basin located in the Campo area. The aim of this study was to characterise the depositional environments, vertical evolution and tectonic context of these Lower Cretaceous series in order to make a comparison with adjacent basins and replace them in the geodynamic context. Facies analysis of the Lower Mundeck Formation (Lower Cretaceous) indicates the presence of four major, interfigered facies associations, that are inferred to represent elements of an alluvial to lacustrine­ fan delta system. The clast lithologies suggest proximity of relief supplying coarse-grained sediment during the deposition of the Lower Mundeck Formation at Campo. The general dip and direction of the bedding is approximately 10 ­12 NW, which also corresponds to the orientation of the foliations in the underlying metamorphic basement. The main sedimentary succession is characterised by a major retrogradational/progradational cycle of Late Aptian age, evaluated at about 3 Ma, with a well-developed progradational trend characterised by fluctuations of the recognised depositional environments. Fluctuations in lake level and sediment supply were possibly controlled by active faults at the basin margin, although climatic changes may have also played a role. The consistently W­WNW palaeoflow of sediments suggests that the palaeorelief was located to the east and could be oriented in a NNE­SSW direction, downthrown to the west. Local outcrops dated as Albian, both north and south of the main outcrop, display some marine influence. These deposits are cut by 040­060 faults parallel to the oceanic transform. Similarly, the Lower Mundeck Formation of the Campo outcrops is considered to be associated mainly with the early drift period of Late Aptian­Albian age. This study is also the first step of knowledge of these African margin deposits, to realise in the future the correlations between outcrops and offshore data.

Lacustrine and alluvial fan facies from the Lower Mundeck Formation (Barremian ?–Aptian) cropping out in the southern part of the Kribi-Campo sub-basin (Cameroon) have been characterised for their oil potential, using both Rock-Eval pyrolysis and palynofacies analyses. The shaly facies show good potential as oil-prone source rock, with TOC content around 4.4% and some intervals with an optimum potential to yield 45 kg hydrocarbons/t of rock. Along the studied outcrops, these organic-rich facies represent approximately a third of the total thickness. Although the studied samples come out from immature thin organic-rich beds within sand dominated beds, it is reasonable to think that these oil-prone facies increase in thickness and maturity in the offshore area, making this part of the southern margin of Cameroon of special interest for petroleum exploration.