Institute for Geological and Mining Research IRGM

Yaoundé, Cameroon

Institute for Geological and Mining Research IRGM

Yaoundé, Cameroon
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Moise B.,Institute for Geological and Mining Research IRGM | Moise B.,University of Geneva | Victor H.J.,Institute for Geological and Mining Research IRGM | Burkhardt S.F.,University of Geneva | And 8 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2017

The volcano-sedimentary infill of the Dschang basin in the Western part of Cameroon is poorly known. The present study provides the first biostratigraphical data of the volcano-sedimentary sequence and allows constraining the age and the position of this basin within the regional context of Central Africa. The studied sequence is composed of three depositional units. The first unit is a fining-upwards sequence of coarse-grained sandstone that gets finer towards the top, passing to thick layers of fossiliferous claystone. The second unit is strongly affected by volcanic activity and consists of a volcano-sedimentary sequence. The third unit is marked by basaltic volcanism and covers the series. Diverse and well-preserved palynomorphs were recovered and are used to provide valuable information for age determination of the Dschang volcano-sedimentary sequence, namely to be of late Eocene- Early Miocene age. The recovered spores, pollen, green algae and fungal remains from the bottom of the sequence include Bombacidites spp., Clavainaperturites cf. clavatus, Crototricolpites sp., Perfotricolpites digitatus, Proteacidites spp., Psilastephanocolporites minor, Psilastephanocolporites spp., Retitrescolpites spp., Retitricolporites irregularis, Retitricolporites spp., Retitriporites sp., Spirosyncolpites bruni (probably synonymous to Spirosyncolpites spiralis), Striatopollis bellus, (considered synonymous to Striatopollis catatumbus), Striatopollis sp., Tetracolporites quadratus, Tetratricolporites sp., ?Verrutricolporites rotundiporis, Cyathidites sp., Laevigatosporites spp., Polypodiaceoisporites spp., Verrucatosporites usmensis, Verrucatosporites spp., Botryococcus sp., Tasmanites sp., and fungal remains.The samples are assigned to the Verrucatosporites usmensis Zone of Salard-Cheboldaeff (1979). The palynological assemblages are similar to those of other Late Eocene to Early Miocene palynological records from the West, Central and Northern African basins. Study of the organic matter by pyrolysis Rock-Eval 6 (Types I, II and III), the sedimentological setting, the palynofacies and the palynomorph assemblages show evidences of tidal influence (presence of the prasinophyte Tasmanites) in an active continental margin (semi-arid to humid lacustrine depositional environment). The Ngoua sedimentary sequence is fluvio-lacustrine, and believed to have witnessed some occasional marine incursions possibly during the opening of the Central Atlantic Ocean (CAO) and strongly disturbed later by intense volcanic activity. © 2017 Elsevier B.V.

Ozawa A.,Mitsubishi Group | Ueda A.,University of Toyama | Fantong W.Y.,University of Toyama | Fantong W.Y.,Institute for Geological and Mining Research IRGM | And 6 more authors.
Geological Society Special Publication | Year: 2017

A large amount of CO2 is stored in the deep waters of Lake Nyos, a volcanic crater lake in Cameroon. The lake is meromictic and thus anoxic in the deeper areas, where dissolved iron exists as Fe2+. Since 2001, a controlled degassing of the lake has been underway. The degassing brings deep water containing Fe2+ to the lake surface as a fountain. This resulted in the formation of Fe(OH)3 precipitates and turned the lake surface red-brown. This coloration was accelerated after the addition of two further degassing pipes in 2011. The Fe(OH)3 precipitates sink to deeper parts of the lake, re-dissolve and are reduced back to Fe2+, which is thought to be precipitating as siderite. The rates of dissolution and precipitation of siderite in Lake Nyos were examined. Fragments of siderite crystals were covered with gel (Epikote) and placed in lake water for 54 h at several depths characterized by chemical features. The change in the thickness of the crystal surface before and after the reaction was analysed by an interferometer in the laboratory. The siderite dissolves at a rate of -0.09 μm a-1 for samples placed at a depth of 50 m, whereas precipitation took place in deeper waters. The precipitation rate of siderite increased by 0.29 μm a-1 with an increase in depth from 100 to 200 m, and decreased to 0.25 and 0.09 μm a-1 at depths of 208 and 210 m, respectively. However, the calculated saturation indices of siderite in the lake waters increased with depth. The objective of this study is to examine the observed rates of dissolution and precipitation of siderite and to compare them with the saturation index of siderite calculated from the chemistry of the lake water. We also discuss the change in Fe species from the oxidation of Fe2+ to Fe3+ at the surface and reduction to Fe2+ and consequent precipitation as siderite in deeper parts of the lake by degassing of CO2 from bottom water in Lake Nyos. © 2017 The Author(s).

Issa I.,Tokai University | Issa I.,Institute for Geological and Mining Research IRGM | Aka Tongwa F.,Institute for Geological and Mining Research IRGM | Mouliom A.G.,University of Yaounde I | And 8 more authors.
Journal of Limnology | Year: 2014

Based on geo-anthropological and geochemical studies, catastrophes similar to the unprecedented gas explosions in the mid-1980s from the Cameroonian killer lakes Nyos and Monoun, might occur in any of the 37 other lakes located along the Cameroon Volcanic Line (CVL). Because people could suffer loss and desolation from predictable catastrophes in the future, monitoring/surveillance policies must be established. Due to their location, crater lakes integrate the geochemical processes that develop in the Earth’s crust due to magmatic activities. Therefore, monitoring the surface manifestations of those deep seated and/or hydrothermal processes might reveal increases/decreases in magmatic activities. The anomalous changes in a volcanic lake induced by mixing with exogenous fluids that have a specific δ18O and δD compositional fingerprint (magmatic, metamorphic, etc.) could be utilized to predict volcanic hazards. If the steady state of a lake environment and the external and intrinsic parameters that control its hydrodynamics are clearly identified and reasonably understood, the anomalous evolutionary processes that compromise its stability can be identified. This study attempts to collect the δ18O and δD data from 17 Cameroonian lakes to help establish a volcano-related monitoring/surveillance network. This work identifies the processes that control the isotopic composition of the lakes and assesses the intra-/inter- and spatial δ18O/δD variations. Almost all of the lakes contain meteoric water. These lakes are mostly isotopically stratified; epilimnia is generally more positive than the hypolimnia. However, although the rainfall is gradually depleted in heavy isotopes when moving from the South to the North due to the latitude effect, the lakes become more enriched (0.6‰/100 km) due to evaporation. The evaluated impact of several parameters on the isotopic variation suggests that the hydrological setting may play an important, albeit not preeminent, role relative to the other factors. Consequently, the interplay between climatology, phytogeography, hydrology and morphometry might help shape the isotopic composition of the lakes. © 2015 J. Limnol All rights received.

Itiga Z.,Institute for Geological and Mining Research IRGM | Bardintzeff J.-M.,Cergy-Pontoise University | Bardintzeff J.-M.,University Paris - Sud | Bardintzeff J.-M.,French National Center for Scientific Research | And 3 more authors.
Arabian Journal of Geosciences | Year: 2013

Tchabal Gangdaba (TG) volcanic massif, which is a part of the continental sector of the Cameroon Volcanic Line (CVL), is dated between 34.4 and 25.1 Ma. It displays mafic lavas (picrobasalt and basanite, 41–43 wt % SiO2) and felsic lavas (rhyolite, 68–73 wt % SiO2). The lack of intermediate rocks evidences a pronounced Daly gap between 43 and 68 wt % SiO2, which corresponds to an important time span of 3.4 Ma. It is interpreted as due to extensive fractional crystallization under peculiar thermodynamical conditions. Felsic lavas yield strong negative anomalies in Ba, Sr and Eu (0.1 < Eu/Eu* < 0.3) reflecting alkali feldspar and plagioclase fractionation and in Ti reflecting titanomagnetite and ilmenite fractionation. All TG rocks are enriched in LREE and mildly fractionated, which suggests enriched mantle sources. Sr initial isotopic ratios ranging from 0.7033 to 0.7059, εNd from +2.89 to +4.64 and Pb isotopic ratios of 18.988 < 206Pb/204Pb < 19.998, 15.592 < 207Pb/204Pb < 15.673 and 38.948 < 208Pb/204Pb < 39.648 are typical of an enriched mantle source close to HIMU and FOZO. A discrete Sr crustal leaching is evidenced. © 2013, Saudi Society for Geosciences.

Guemene Dountio E.,Environmental Energy Technologies Laboratory EETL | Guemene Dountio E.,Institute for Geological and Mining Research IRGM | Njomo D.,Environmental Energy Technologies Laboratory EETL | Fouda E.,Institute for Geological and Mining Research IRGM | Simo A.,Institute for Geological and Mining Research IRGM
Solar Energy | Year: 2010

This study deals with comparison of Cameroonian ground based measurements with estimations done using satellite images, by applying the second version of the HELIOSAT method, as computed by the web tool HELIOCLIM of the SoDa project. Measurements and satellite resources were chosen for the same period of the year 1985, on ten Cameroonian locations, distributed with mean spatial resolution of 200 km between two neighbouring stations. Correlations curves are constructed between daily irradiation estimates from satellite data and from measurements. The consequent regression equations are established, using the least square method. Finally, a brief discussion is carried out on the spatial distribution of errors observed on results. Similarly to previous studies this study confirmed the capability of the method to produce good results for the Garoua location, and established its extension on other sahelian sites, comparatively to the poor agreement observed on southern sites. Furthermore, even if the study was not done on a long period, it brought out the necessity to correct the HELIOSAT results for many Cameroonian locations, to march the experimental results. © 2010 Elsevier Ltd. All rights reserved.

Olinga J.B.,Institute for Geological and Mining Research IRGM | Mpesse J.E.,University of Douala | Minyem D.,University of Yaounde I | Ngako V.,Institute for Geological and Mining Research IRGM | And 2 more authors.
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2010

The Pan-African deformation of the Awaé - Ayos group (southern segment of the Neoproterozoic fold belt of Cameroon, Central Africa) is controlled by thrust tectonics and late strike-slip shear zones: the thrusting of the Pan-African Nappe over the Congo Craton (D2 deformation phase) is followed by a strike-slip shearing trending ENE-WSW (D3 deformation phase). During these stages deforming conditions were ductile to brittle-ductile. The dominant structural features of the D3 phase are penetrative foliation steeply dipping N or S, an associate ENE-WSW trending stretching lineation, and an N-S to NE-SW directed folding. Deformation criteria in the distinguished rock units indicate dextral sense of shear. An overall dextral transpressional model is assumed to explain these thrust and shear movements. © 2010 Schweizerbart'sche Verlagsbuchhandlung. Stuttagrt. Germany.

Ako A.A.,Hydrological Research Center | Shimada J.,Kumamoto University | Hosono T.,Kumamoto University | Kagabu M.,Kumamoto University | And 7 more authors.
Journal of Hydrology | Year: 2013

We used environmental tracers (δD, δ18O, 3H and chlorofluorocarbons (CFCs)) to establish the groundwater flow system within the Mount Cameroon area: a 4090m high active entirely alkaline volcano located within a humid equatorial region. Seventy-five ground and surface water samples (68 spring samples, 6 borehole samples and 1 stream sample) were collected around the volcano during the wet (October-November 2010) and dry seasons (January-February 2010) as well as 10 rain samples in June-September 2010 in order to establish recharge elevations, apparent ages (residence times) and groundwater flow system in the fractured volcanic (basaltic) aquifers. The δ18O and δD composition of rainwater and groundwater in the Mount Cameroon area fit the Douala Local Meteoric Water Line (DLMWL). The recharge elevations of the individual springs were calculated from their δ18O-values and the equation of the altitude gradient (-0.16‰ δ18O/100m) of precipitation on the mountain. For springs sampled during the two seasons, dry season samples have higher recharge elevations than rainy season samples. Seasonal variation exists in the tritium values as rainy season samples systemically are higher than those of the dry season samples This implies the input of new water from the rain causing the groundwater system to rejuvenate. Apparent ages for the Mount Cameroon springs calculated from CFCs based on the Piston Flow model range from 10 to approximately 57years. CFC apparent ages for rainy season samples are systemically younger than those of dry season samples. There is seasonal variation in groundwater flow system in the Mount Cameroon area and also along the different flanks of the volcano. The groundwater flow system is conceptualized by 2 models; a Bypass/piston flow model for the flow system during the rainy season and a binary mixing/piston flow model characterizes the flow system during the dry season. © 2013 Elsevier B.V.

Marzoli A.,CNR Institute of Geosciences and Earth Resources | Aka F.T.,Institute for Geological and Mining Research IRGM | Merle R.,Curtin University Australia | Callegaro S.,University of Padua | N'ni J.,Institute for Geological and Mining Research IRGM
Lithos | Year: 2015

At Mt. Bambouto, a continental stratovolcano of the Cameroon Line, magmatic activity lasted for over 20. Ma and was characterized by at least two caldera formation events. Here we present detailed mineral and whole-rock compositions of Mt. Bambouto basanites, hawaiites, trachytes and phonolites, with emphasis on caldera related volcanic rocks. These data show that differentiation took place within a complex magma plumbing system, with magma chambers occurring at different depths within the crust. Though differentiation was chiefly dominated by fractional crystallization, chemical mineral zoning of olivines, clinopyroxenes, and feldspars is also indicative of open-system processes such as magma mixing and magma chamber recharge. Chemical zoning is evident mainly in the outer 100 microns of the analyzed crystals, suggesting that magma mixing occurred shortly before eruption. The last caldera collapse at about 15. Ma also marked a clear change in the magma plumbing system. Before caldera collapse, Mt. Bambouto was characterized by a dominant production of peralkaline quartz trachytic magmas in shallow magma chambers. During this phase, evolved basic magmas (hawaiites) and strongly evolved alkaline magmas were formed in middle and upper crustal magma chambers, respectively. After emptying of the shallow quartz trachytic magma chamber and caldera collapse, magmas from the deep magmatic plumbing system were mobilized and partially mixed. This triggered eruptions of magmas on the caldera rims. © 2015 Elsevier B.V.

Nagao K.,University of Tokyo | Kusakabe M.,University of Toyama | Yoshida Y.,Yoshida Consulting Engineer Office | Tanyileke G.,Institute for Geological and Mining Research IRGM
Geochemical Journal | Year: 2010

He, Ne and Ar isotopic ratios and concentrations of noble gases in different depths of Lakes Nyos and Monoun in Cameroon, West Africa, were investigated. Samples were collected in November 1999, January 2001 and December 2001. Improved sampling method applied in 2001 enabled us to detect detailed isotopic distribution in the lakes. Concentrations of Ne and Xe in the lake waters were low by factors of-10 and ∼3, respectively, compared with those of air saturated water (ASW), whereas in CO2 gas they were depleted by 2 orders of magnitude compared with those in air. In contrast, He was strongly enriched in lake water by more than three orders of magnitude compared to ASW. 3He/4He ratios of 8 × 10-6 (Lake Nyos) and 5 × 10-6 (Lake Monoun) indicated recharge of magmatic gases of mantle origin to the lakes, though the ratios were lowered by the addition of radiogenic 4He from crustal rocks. A small contribution (<2%) of MORB-like Ne was detected in both lake waters. A simple mixing between two end members, i.e., atmosphere and gases from a deepseated reservoir, can explain the noble gas signatures. Depth profile of He concentration in Lake Nyos showed a clear layered structure with a maximum at 190 m, 20 m above the lake bottom. Below this depth, 3He/4He ratio decreased slightly, suggesting that the fluid from the deep-seated reservoir is supplied to the lake mainly at ca. 190 m. C/3He ratios were 1.5 × 1010 and 0.6 × 1010 in deep and shallow layers of Lake Nyos, respectively. The C/3He ratio was 1.7 × 10 10 at Lake Monoun. A gas recharge model to explain the observed layered structure in Lake Nyos is presented. Copyright © 2010 by The Geochemical Society of Japan.

Aka F.T.,Institute for Geological and Mining Research IRGM | Aka F.T.,Ministry of Scientific Research and Innovation MINRESI | Yokoyama T.,Tokyo Institute of Technology
Natural Hazards | Year: 2013

Scientific visits to Lake Nyos in Northwestern Cameroon in the aftermath of the gas disaster that killed over 1,750 people in 1986 revealed the presence of a pyroclastic natural dam in the northern border of the lake. This dam is being affected by back erosion. Collapse of the dam could cause a flood that would affect inhabited areas over a 220 km distance. Timing of dam collapse has been hotly debated based on vastly different carbon-14 and potassium-argon formation ages. In previous work, we used uranium series disequilibria to suggest a formation age of > 5,000 years. Detailed comparison of uranium series and trace element data for lavas of Lake Nyos and Mt. Cameroon, both belonging to the Cameroon Volcanic Line, suggests that Lake Nyos basalts erupted with an initial radium-226/thorium-230 ratio that is two times higher than lavas erupting on Mt. Cameroon today. This information is used to infer an age of 8,750 ± 490 years, which we suggest is the formation age of the Lake Nyos dam. The erosion rate deduced from this age does not indicate that collapse of the dam from back erosion alone and the attendant potential flood disaster are as eminent and alarming as previously thought. However, other factors militate for action to secure the dam. Work is underway to reinforce it by engineering methods. © 2012 Springer Science+Business Media Dordrecht.

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