Dynamic interaction in tropical Africa: IGCP-616Y and IGCP 646 projects and events

The scientific objectives and research program of the IGCP-646 project (2015–2018) cuts across many disciplines and includes various aspects of continental basement geology, resource exploration (mineral, water and hydrocarbons), geohazard mitigation, and climate change, all of which are of critical importance to developing countries, particularly in parts of West Africa where population pressures are on the rise. Considerable emphasis was placed on capacity building, creation of opportunities for young scientists to undertake higher degrees programs, knowledge transfer and training. The SIDA-funded “pilot project” IGCP-616Y (started in 2012), focused on three objects (i) crustal architecture, tectonic evolution and regional geology of Central Africa and the connection with NE Brazil; (ii) the Mesozoic continental rifting and breakup leading to a better integration of the onshore and offshore geology; (iii) clarification and quantification of the links between basement structures, neotectonics, climate change and landscape evolution. The IGCP-616Y and IGCP-646 projects consisted of over 250 researchers, from different countries. In the course of the projects, six annual meetings, four field trips/workshops, as well as several training sessions were organized. Here we provide a summary of the scientific targets of the projects and a summary of the organized activities

The Importance of Diagenetic Processes in Sandstones Facies of the Hamakoussou Sedimentary Basin in North Cameroon: Influence on Reservoir Quality.

Published studies in the Hamakoussou reservoir sandstones are very few and the characterization of the reservoir quality including diagenesis is unknown. In this paper, after lithological reports, classical petrographic techniques have been used to study the diagenesis and reservoir quality of the Hamakoussou sandstones: Diagenetic processes within and around detrital grains show that early cementation by calcite come from volcanic veins and late cementation originating from silicification. Diagenetic phenomena (early cementation, compaction, fracturation and late cementation) show that these sandstones have a low porosity due to the blockage of intergranular pore spaces by cement. Intense volcanic activity associated with the circulation of fluids (silica and calcite) as well as the dissolution along the contacts of quartz grains are the principal sources of early and late cements which are responsible for the decrease in porosity observed in these sandstones. The immediate consequence is the sudden drying up of boreholes drilled for water supply

Ten golden rules for optimal antibiotic use in hospital settings: the WARNING call to action

Antibiotics are recognized widely for their benefits when used appropriately. However, they are often used inappropriately despite the importance of responsible use within good clinical practice. Effective antibiotic treatment is an essential component of universal healthcare, and it is a global responsibility to ensure appropriate use. Currently, pharmaceutical companies have little incentive to develop new antibiotics due to scientific, regulatory, and financial barriers, further emphasizing the importance of appropriate antibiotic use. To address this issue, the Global Alliance for Infections in Surgery established an international multidisciplinary task force of 295 experts from 115 countries with different backgrounds. The task force developed a position statement called WARNING (Worldwide Antimicrobial Resistance National/International Network Group) aimed at raising awareness of antimicrobial resistance and improving antibiotic prescribing practices worldwide. The statement outlined is 10 axioms, or “golden rules,” for the appropriate use of antibiotics that all healthcare workers should consistently adhere in clinical practice

Paléoenvironnements et diagénèse dans un réservoir gréseux d'âge crétacé du Fossé de la Bénoué au Nord Cameroun (les grès de Garoua)

Le fossé de la Bénoué qui débute au niveau du golfe de Guinée se divise en deux branches dans sa partie septentrionale: la branche de Gongola qui va jusqu au Niger et la branche de Yola-Garoua qui se prolonge en territoire camerounais et dans laquelle de part et d autre du fleuve Bénoué se trouvent les buttes de grès dits grès de Garoua . En dépit de son importance en termes de réservoir, les travaux antérieurs, très peu nombreux dans la partie camerounaise, n ont pas souligné les paléoenvironnements, la lithologie, la minéralogie, les événements diagénétiques et les déformations ayant affecté ces grès. Des études faciologiques, pétrographiques, minéralogiques et géochimiques y ont été conduites afin de reconstituer les paléoenvironnements de dépôts à partir des informations tirées de la succession lithologique, de caractériser les différentes sources d apports, d évaluer l intensité les processus d altération chimique ayant affecté ces grès depuis la sédimentation et enfin de dresser un répertoire des événements et mécanismes des processus majeurs de la diagenèse. Sur le plan faciologique, il s agit des quartz-wacke pour la plupart associés à une faible proportion d arkosique wacke et de mudstone, issus de blocs continentaux matures et immatures et de formations orogéniques recyclées. Ces faciès consolidés sont à stratifications entrecroisées et/ou obliques avec une alternance de niveaux grossiers et fins souvent intercalés par des lits de conglomérats plus épais dans les chenaux. Les niveaux argileux laminés de faible épaisseur se retrouvent sous forme de lentilles et de galets mous ou simplement en lits fins intercalés dans les grès grossiers. Les éléments figurés sont pour la plupart constitués de quartz, de feldspath de micas, de minéraux lourds (zircon, rutile ) et des fragments de roche du socle (granite) dans les conglomérats. Les phénocristaux sont pour la plupart sub-émoussés tandis que les cristaux plus petits sont sub anguleux à anguleux. Les quartz et les feldspaths potassiques (microcline avec des reliques de macles polysynthétiques encore conservées dans certains cas) sont ubiquistes dans la plupart des secteurs étudiés. On note l absence de feldspaths dans les secteurs de Tinguelin, Douli et Mourbeli. La série est traversée par des roches volcaniques et des intrusions plutoniques et repose de façon discordante sur le socle granitique visible à Hosséré Tinguelin dans la partie Nord du bassin. Les lithofaciès décrits ici traduisent l évolution des paléoenvironnements de type fluviatile sous influence tidale. Les évènements diagénétiques recensés en pétrographie intègrent la compaction (contacts entre les grains de quartz), la cimentation (carbonate, silice et hématite), la dissolution des feldspaths, la transformation et la néoformation de certains minéraux argileux (kaolins et illites) et la micro-fracturation. La présence d oxydes de fer dans les micro- fractures et autour des éléments figurés ainsi que les surcroissances de quartz attestent la circulation des paléofluides dans les sédiments au cours de la diagenèse. L analyse des éléments majeurs, mineurs et traces montrent que les grès de Garoua ont été alimentés par des produits d érosion d un socle granito-gneissique appartenant à une marge passive donc la composition est celle des roches acides ou felsiques et qui ont donné des wackes, des arkoses, des litharénites et de grès ferrugineux parcourus par des fluides chauds au cours de la diagenèse. La porosité primaire est réduite par la calcite, la silice et les minéraux argileux par dissolution des feldspaths. Cette dissolution, ainsi que la corrosion des quartz et la fracturation sont responsables de la mise en place de la porosité secondaire. La présence de la smectite dans les secteurs à activité volcanique a un lien possible avec ce volcanisme. L illitisation des kaolinites bien que discrète, la dissolution des feldspaths partielle ou totale, les contacts entre les grains de quartz (plans, concavo-convexes plus ou moins stylolithiques) ainsi que la présence de la dickite sont révélateurs d une diagenèse d enfouissement. Ceci montre que les grès de Garoua ont atteint probablement un stade avancé de la diagenèse avant de connaître à nouveau une diagenèse d exhumation avec des phénomènes d oxydation et de kaolinisation généralisés. Ces observations confortent l hypothèse d un taux d enfouissement relativement important pour un gradient géothermique moyen avec des températures avoisinant les 100 C.The Benue Basin is the northern bifurcated extremity of the Golf of Guinea. The Gongola arm extends into Niger, while the Yola arm prolongs into the Cameroonian Territory aligned with present existing sedimentary buttes (Garoua sandstones) protruding on either side of the Benue River. Little work has previously as been carried out with regards to its reservoir importance. Meanwhile, neither lithological, diagenetic nor deformation of these sandstones been studied. Faciological study, petrography, mineralogy and geochemistry have led on one hand in order to rebuild paleoenvironments of deposits based on information derived from the lithological succession, to characterize the different terrigenous sources with the aim to evaluate the intensity of chemical weathering processes that have affected these sandstones since their sedimentation, and finally, on the other hand to develop an inventory of events and major diagenetic processes. These include well consolidated, planar cross-stratified wacke, arkosic wacke and mudstone coming from mature and immature continental blocks and recycled orogenic formations. These facies are consolidated to cross-bedding and / or oblique with alternating coarse and fine levels often interspersed by thicker beds of conglomerates in channels. Thin argillaceous beds are found interbedded with coarsed-grained sandstones. The most frequent sediment clasts constitute quartz, feldspars and basement fragments within conglomerates. The phenocrysts are quite often sub-rounded, while smaller clasts are often angular to subangular (heteroclastic). Quartz and potassic feldspars (microcline with polysynthetic twins is still visible in some cases) are widespread in some sedimentary butte vestiges, while feldspars in other cases exist as traces. The series is cross-cut by volcanic rocks and magmatic intrusions. These sandstones are deposited unconformably on a granitic basement that is visible at Hossere Tinguelin found in the northern part of the basin. The lithofacies described here depict fluviatile-type of palaeoenvironments. The diagenetic events diagnosed from petrographic studies incorporate compaction, cementation (authigenic carbonate and silica), dissolution of feldspars, transformation and neoformation of some clay minerals (Kaolin and Illite) and fracturing. The presence of iron oxy-hydroxides within some facies and along microfractures, quartz overgrowth and hematite attests the circulation of palaeofluids within the sediments during diagenesis. Analysis of major, minor and trace elements show that Garoua sandstones were fueled by acidic or felsic rocks products coming vi from granite and gneissic basement belonging to a passive margin and have given wackes, arkoses, litharénites and ferruginous sandstone passed through by hot fluids during diagenesis The occurrence of interstitial calcite, silica and hematite has greatly contributed in the reduction of primary porosity. The dissolution of feldspars, corrosion of quartz and fractures has enhanced secondary porosity and neo-formation of kaolinite. The occurrence of smectite within the volcanic areas shows a possible link with volcanism. Neoformation of illites from kaolinites and the appearance of dickite reveal a higher diagenetic intensity. More of quartz with planar, convexo-concave to more or less stylolithic grain contacts compared to the absence of feldspars that have totally been dissolved or transformed in some formations shows that the Garoua Sandstones have attained a higher stage of diagenesis prior to a new diagenetic phase of exhumation with the phenomenon of oxidation and generalized kaolintisation. These observations support the hypothesis of a considerable burial depth with an average geothermal gradient at temperatures close to 1000C.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Les xénolithes comme preuve de l'infiltrations magmatiques alcalines sous le lac Nyos (ligne volcanique du Cameroun, Afrique de l'Ouest)

International audienceXenoliths enclosed in Lavas of the Nyos volcano (Cameroon Volcanic Line, continental sector) range from fertile lherzolites to harzburgites. One spi- nel-free wehrlite has been also sampled. The occurrence of phlogopites and pargasites in some harzburgites together with specific textural rock-type (lher- zolites transitional porphyroclastic to equigranular), including major and trace element compositions both in peridotites bulk rocks and minerals point out interactions between the mantle and basaltic magmas responsible for the for- mation of wehrlites beneath the Nyos volcano. Hydrous minerals (phlogo- pites and pargasites) and metasomatic events are their main petrogeochemi- cal signatures different from group 1 samples which are characterized by spoon-shaped REE patterns. Later on, hydrous phases, Ti-rich Cpx, CaO rich Ol, Ti, and V rich Ol wehrlite precipitated from melt enrichments due to the percolation of the mantle by basaltic magmas of alkaline affinity. The meta- somatic liquid which percolates the Nyos mantle column was a dense alkaline silicate rich in volatile, displaying low HFSE abundances in the metasomatic hydrous melts compared to the LILE. It is suggested that Nyos mantle perido- tites have experienced: 1) variable metasomatic events related to the perco- lating of the depleted mantle by a alkaline silicate liquid, 2) the spinel-free wehrlite is a group 2 sample corresponding to a cumulate of a similar melt, 3) amphibole may be a potassium-bearing mineral instead of or in addition to phlogopite at shallower levels of Nyos upper mantle and 4) transitional tex- tural rock facies express also the fingerprint of rising mantle plume which were percolated by alkaline magma during their transit to the surface

First palynostratigraphical evidence for a Late Eocene to Early Miocene age of the volcano-sedimentary series of Dschang, western part of Cameroon and its implications for the interpretation of palaeoenvironment

International audienceThe 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

The Garoua Formation of the Upper Benue Trough (Cameroon), as a potential lateral extension of the Bima Formation (Nigeria): evidence from geomorphology, facies analysis, petrology and geochemistry

The Garoua Formation of the Upper Benue Trough in Northern Cameroon crops out as buttes or tabular hill cut by various deep valleys. They are similar to features widespread in the Upper Bima Member of Bima Formation in Nigeria. The numerous outcrops consist of East–West oriented sandstone (Hossere) hill. Angular to sub-angular quartz and potassic feldspars represent the main components. Feldspar is subject to diagenetic transformation into kaolinite. Clay mineral analysis of Garoua Formation reveals the abundance of kaolinite and smectite, along with illite and chlorite, which are scarce and occur in low proportions. The intergranular matrix consists of a mixture of microcrystalline quartz, clay and iron oxides. Diagenetic fluid circulation contributed to infill fractures of quartz grains and feldspar. The geochemical signature of wacke, arkose, litharenite and ferruginous sandstone of the Garoua Formation consists of more than 50 Wt % SiO2 followed by Al2O3 and Fe2O3 making less than 20 Wt %. They occur as residual hills and must have been affected by Neogene tectonic movements in Africa. The Garoua Formation known as Cretaceous yielded little palynological residue with few fungal remains of the Rhizophagites type, little amorphous organic matter (AOM) and few translucent phytoclasts, insufficient for age dating at the current stage of the research. The Garoua Formation is tentatively interpreted as an extension of the Upper Bima Member known from the adjacent Nigeria territory, based on the geomorphological, lithostratigraphic, petrographic, mineralogical and geochemical similarities.</p

Eruption history and petrogenesis of rocks from Nyos volcano (NW Cameroon): Evidence from lithostratigraphy and geochemistry

Even though ca 1746 people and over 3000 cattle were killed in 1986 by sudden release of about 800 million m3 of CO2 from Lake Nyos volcano in northwest Cameroon, the lake's formation history is not known. Here we report results of a lithostratigraphic and petrogenetic study of Nyos volcano that allows us to confirm its phreatomagmatic (maar) origin. Eruptive products are divided into 2 units, the phases of each of which are closely related in time. Unit A comprises 4 phases, the last (A-4) represents the cataclysmic phreatomagmatic formation of Nyos maar and may have been triggered by collapse of the vent system of the previous (A-1 to A-3) phases, and/or reactivation of basement faults. After a repose period, activity shifted NE of the maar to form Unit B products. The B-1 phase of this unit deposited the scoria now covering most of the Lake Nyos area. Unit B-2 constructed the Fon's cone. A small lava flow (Unit B-3) represents the latest phase of volcanic activity of Nyos volcano. Based on area-thickness estimation methods, a total of ca 0.8 km3 of eruptive material was produced from the volcano. Geochemical data suggest that magma of the 2 units probably formed by melting of the same garnet-bearing OIB-like asthenospheric mantle source, and evolved mainly by crustal contamination and fractional crystallization in independent magma batches that erupted without mixing. Our results provide a basis for advice on general hazard mitigation in the Lake Nyos area

Major elements, trace elements and Sr-Nd-Pb isotopes form lavas of lakes Nyos, Wum, Elum and Oku sampled in the Oku Volcanic Group of the Cameroon Volcanic Line

Lake Nyos is located at the summit of a stratovolcano in the Oku Volcanic Group (OVG) along the Cameroon Volcanic Line. The sudden release of magmatic CO2 trapped at the bottom of Lake Nyos in August 1986 caused historical casualties of 1750 people and over 3000 cattle. New geochemical data of volcanic rocks from the Nyos volcano and the first available data for volcanic rocks from other maar-bearing volcanoes (Lakes Elum, Wum and Oku) in the OVG are presented and compared. Lavas from the Nyos, Elum and Wum volcanoes show similarities in major and trace elements and Sr?Nd?Pb isotopes, suggestive of a similar mantle source. However, this source is slightly different from that of the Oku volcano. The samples from Lake Oku have lower alkali, higher TiO2 and more depletion and enrichment in most incompatible trace elements than those from the Nyos, Elum and Wum volcanoes. These differences and those observed in the Sr?Nd?Pb results are consistent with a heterogeneous source for lavas in the OVG. Trace element compositions suggested the presence of garnet in the source (< 6% garnet) and modelled melting results indicate < 2% partial melting of the source material. Isotope data plot within the focal zone, extending towards enriched mantle 1 (EM1; e.g. Lakes Oku and Nyos samples). This indicates the involvement of at least three mantle components: depleted mid-ocean ridge basalt mantle, high-µ and EM1 components in the magmatism of the lavas studied. The contributions of these components in different proportions, originating from asthenospheric and subcontinental lithospheric mantle sources, can account for the observed variations in geochemical characteristics. The geochemical characteristics of the studied lavas indicate that the magma source need not necessarily have an abnormal CO2 concentration to pose a potential threat. Degassing of an ordinary magma chamber and the migration of gas to the bottom of the lakes through cracks and faults can lead to the accumulation of CO2 in lake bottoms. This is controlled by tectonic parameters (fractures and faults) that enhance degassing from the magma chamber to the lake bottom and physical parameters of the lake (e.g. size, depth, temperature and solubility) that control CO2 stability

First 2D and 3D interpretative models of sedimentation in the Cretaceous Hama-koussou sedimentary basin: Litho-bio-stratigraphy and palaeoenvironment records

The Hama-Koussou Basin is one of the offset structures of the eastern end of the Benue Trough in Northern Cameroon. This sedimentary basin is an asymmetrical syncline whose axis is strongly shifted towards the East, filled predominantly with Cretaceous deposits, The basin has experienced at least three (3) phases of sedimentation during its geological history: two (2) fluvial phases with one at the top and the second at the bottom consisting of conglomerate, micro-conglomerate, and sandstone, sandwiching one fluvio-lacustrine phase consisting of fossiliferous claystones and marlstones with intercalations of siltstones and carbonate cemented fine sandstone. Numerous sedimentary structures including planar, oblique, and cross stratifications, convolute bedding, desiccation cracks, ripple marks and loadcast have been recorded. The mineral assemblage is dominated by quartz, plagioclase, mica and microcline, accompagnied by diagenetic phases (iron oxide, silica and carbonate). Clay minerals consist of kaolinite, illite and chlorite/smectite. Palynofloral analysis reveals various taxa indicative of a fluvio-lacustrine environment: These include Classopollis sp., Eucommiidites sp., Concavisporites sp., Cicatricosisporites sp, Araucariacites australis, Callialasporites dampieri, Callialasporites microvelatus. The occurrence of Callialasporites microvelatus confirms the Cretaceous age whereas age determination for all other samples was uncertain due to scarcity in palynomorphs. Low numbers of bisaccate, grass, and other angiosperm pollen grains may be indicative of a Cenozoic or younger age, although contamination by modern pollens cannot be excluded.The region experienced volcanism represented by explosive and effusive phases, recorded as sills and dykes. Plutonism is characterized by the establishment of intrusive granite. The East-West elongation observed in the HSB is the same in the Mayo-Oulo-Lere and Babouri Figuil basins and can be interpreted as the result of the same tectonic event linked to the opening of the Atlantic Ocean resulting in the formation of the Benue Trough and adjoins basins