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International audience; Xenoliths 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.

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.

An earthquake was felt in Kribi, southwestern Cameroon, on July 23rd 2002. It was recorded at 19h50 UT by two seismographs of the Mount Cameroon volcano observatory. A macroseismic survey was conducted in the area to place the event within its geological and seismological contexts and to evaluate the seismic risk in the region. The earthquake was felt with maximum intensity of IV+ MM in the city of Kribi and was accompanied by a sound related to the transfer of longitudinal elastic energy from the earth to the air. Analysis of the seismograms and macroseismic data show that the earthquake had a magnitude of 3.6 ± 0.4 and its epicenter is located in the Atlantic Ocean, 50–55 km west of Kribi. The earthquake originated from the oceanic part of the northern margin of the Congo craton and/or the Sanaga fault system, frequent reactivation of which has produced many historic earthquakes. Preliminary evaluation of seismic risk shows that Kribi city is the most risky zone in the area, but the risk is about 20 times less than in the Mount Cameroon region.

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