Rainfall Variability along the Southern Flank of the Bambouto Mountain(West-Cameroon)

This paper presents the rainfall variability along the southern flank of the Bambouto mountain. Data were collected from rain gauges, while spatial variability was estimated through daily recorded data. Monthly and annual data were used to draw isohyetes via the triangular method, with linear interpolations between observation points. Results show that rainfall is highly variable along the slope. Daily rainfall amounts range from 0.1 mm to 120 mm. Mean yearly rainfall is 1918.1 mm. Rainfall amount does not have a linear relationship with altitude. Dschang is characterised by abnormally high rainfall. Following a North-South direction, rainfall decreases from Dschang to a Melang-Loung-Djuttitsa axis. From this axis, the gradient reverses as rainfall increases rapidly towards the Mélétan mountain. The existence of the relatively dry zone within the hillside seems to be due to the influence of two air masses. The first is cold and very wet which moves from the Mamfe basin to the summit zone where it starts to warm up as it flows towards Melang and Loung where temperature increases. The second comes from the south to south-east monsoon which is also impoverished during the ascension to higher altitudes. It is also likely that a third air mass from the dry harmattan is involved depending on the position of the ITCZ

New Discriminant Functions and Geochemistry of the Mamfe Cretaceous Formations (South West Cameroon)

Major and trace element geochemistry have been used to unravel the tectonic setting, source rock composition, and depositional environment of sedimentary rocks in the Mamfe formation. Field studies reveal both sub tabular and tabular outcrops indicating a post tectonic sedimentary activity for the subtabualar outcrops. Major element geochemistry reveals a moderate to high proportion (50-75wt %) of silica for the analyzed samples. New discriminant diagrams constructed for usage of adjusted major elements shows samples plotting on collision, arc and rift. Another discriminant plot for adjusted major element combined with trace elements shows samples plotting on active and passive tectonic setting.  Ratios of highly immobile trace elements such as Cr/Th, Th/Sc, Th/Co, and La/Sc conclude a felsic source rock for the studied rocks of the Mamfe formation. Trace elements ratios for redox conditions and marine-continental discrimination such as Ni/Co, U/Th, V/Cr, Th/U, and Y/Ho show that the sedimentary rocks of the   formation were deposited in a shallow oxygenated continental fluvio-lacustrine environment

Computational applications in secondary metabolite discovery (caismd): An online workshop

We report the major conclusions of the online open-access workshop “Computational Applications in Secondary Metabolite Discovery (CAiSMD)” that took place from 08 to 10 March 2021. Invited speakers from academia and industry and about 200 registered participants from fve continents (Africa, Asia, Europe, South America, and North America) took part in the workshop. The workshop highlighted the potential applications of computational meth‑ odologies in the search for secondary metabolites (SMs) or natural products (NPs) as potential drugs and drug leads. During 3 days, the participants of this online workshop received an overview of modern computer-based approaches for exploring NP discovery in the “omics” age. The invited experts gave keynote lectures, trained participants in handson sessions, and held round table discussions. This was followed by oral presentations with much interaction between the speakers and the audience. Selected applicants (early-career scientists) were ofered the opportunity to give oral presentations (15 min) and present posters in the form of fash presentations (5 min) upon submission of an abstract. The fnal program available on the workshop website (https://caismd.indiayouth.info/) comprised of 4 keynote lec‑ tures (KLs), 12 oral presentations (OPs), 2 round table discussions (RTDs), and 5 hands-on sessions (HSs). This meeting report also references internet resources for computational biology in the area of secondary metabolites that are of use outside of the workshop areas and will constitute a long-term valuable source for the community. The workshop concluded with an online survey form to be completed by speakers and participants for the goal of improving any subsequent editions

Morphotectonic of Regolith Landsurfaces in Cameroon (Central Africa): Weighting the Evidences of Late Cretaceous Uplift and Climatic Deep Weathering and Stripping

International audienceIn the last few decades, a range of regolith-related issues highlighted their usefulness on assessing landform dynamics for better understanding and quantifying earth surface processes. A model for the evolution of weathered landsurfaces in Cameroon is developed using available data on their morphology and petrogeochemical patterns, tectonic evidences, geophysical anomalies and sedimentological data. On deformed orogens, the model demonstrates the pivotal role of uplift, consequent volcanic cover and rheology-dependent gravitational collapses in inducing large scale compartmentalization. In areas of tectonic quiescence, it enhances a well known predominance of deep weathering and striping resulting in morphogenetic sequences similar to that of climate-dependent dynamics on the West African craton. These schemes in accordance with regional correlations allow assuming four regolith landsurfaces recognizable with their actual relicts and their specific petrogeochemical patterns. These are the high glacis, the widespread Intermediate ferricrete, the African bauxitic surface, and the modern bauxites developed on Neogene volcanics across the so-called Cameroon Volcanic Line. These findings provide a unique geomorphic record resulting in interplay between late Cretaceous epeirogeny, heterogeneity of uplifted basement, and climate variability. It stands as an input in understanding the dynamics of the complex geomorphic system of the African tropical belt, and specifically in Central Africa where no tectonic input were considered in old issues. It is also a basis for assessing denudation rates and their comparison with weathering-limited steady cratonic denudation of West Africa, and to investigate Cenozoic drainage rearrangement and stabilization as a consequence of uplift

Morphotectonic of Regolith Landsurfaces in Cameroon (Central Africa): Weighting the Evidences of Late Cretaceous Uplift and Climatic Deep Weathering and Stripping

International audienceIn the last few decades, a range of regolith-related issues highlighted their usefulness on assessing landform dynamics for better understanding and quantifying earth surface processes. A model for the evolution of weathered landsurfaces in Cameroon is developed using available data on their morphology and petrogeochemical patterns, tectonic evidences, geophysical anomalies and sedimentological data. On deformed orogens, the model demonstrates the pivotal role of uplift, consequent volcanic cover and rheology-dependent gravitational collapses in inducing large scale compartmentalization. In areas of tectonic quiescence, it enhances a well known predominance of deep weathering and striping resulting in morphogenetic sequences similar to that of climate-dependent dynamics on the West African craton. These schemes in accordance with regional correlations allow assuming four regolith landsurfaces recognizable with their actual relicts and their specific petrogeochemical patterns. These are the high glacis, the widespread Intermediate ferricrete, the African bauxitic surface, and the modern bauxites developed on Neogene volcanics across the so-called Cameroon Volcanic Line. These findings provide a unique geomorphic record resulting in interplay between late Cretaceous epeirogeny, heterogeneity of uplifted basement, and climate variability. It stands as an input in understanding the dynamics of the complex geomorphic system of the African tropical belt, and specifically in Central Africa where no tectonic input were considered in old issues. It is also a basis for assessing denudation rates and their comparison with weathering-limited steady cratonic denudation of West Africa, and to investigate Cenozoic drainage rearrangement and stabilization as a consequence of uplift

Geotechnical Suitability of Soils in Road Construction for Sustainable Development in Tropical Africa: Case of Lateritic Graveled Soils of Bandjoun (West, Cameroon)

The environmental impact of the exploitation of geomaterials and their relatively high cost, coupled with the increasingly low financial capital in developing countries, are pushing road actors to turn to inexpensive local ecological materials. The present study is conducted on lateritic graveled soils of Bandjoun (LGSB) in the West Cameroon Region. The aim is to determine whether lateritic gravel soils, particularly those in Bandjoun, can be an ecological and economical alternative to rock aggregates in road construction, considering their geotechnical parameters and environmental impact. These soils were described in the field and were also subjected to complete geotechnical identification in the laboratory. The LGSB presents Californian bearing ratio indices ranging from 26% to 83.3%, a plasticity index of 10.11%, a fines content of 12.05%, an average methylene blue value of 4.25, a water content at the Proctor optimum of 27.6% and a dry density of 1.75 g/cm3. They are silty or clayey gravels and sands of subgroup A-2-7 according to the Highway Research Board classification; sandy and gravelly soils with fines of class B according to the classification of the Road Construction Guide; and silty gravels according to the classification of the Central Laboratory of Bridges and Highways. These soils can be used naturally in pavement layers, in particular in subgrade for all traffic classes and in subbase for low traffic. The tonnage of these soils has been estimated at 18,389 t. The global warming index shows that the use of these soils (18,389 t) in road construction can reduce 31,629–62,706 kg of carbon emissions. The use of lateritic soils in road construction is a very interesting alternative to reduce the environmental impacts associated with the manufacture of rock aggregates. So, lateritic soils should be used instead of rock aggregates for cleaner, more environmentally friendly road construction. The present work presented a specific evaluation of the geotechnical properties and ecological impact of lateritic graveled soils for road construction, as well as their potential for ecological and economic utilization

Distribution of duricrusted bauxites and laterites on the Bamiléké plateau (West Cameroon): Constraints from GIS mapping and geochemistry

International audienceEstimation of the mineral resources potential is an important issue for most of developing countries. The spatial distribution of bauxites and lateritic land surfaces on the Bamiléké plateau (West Cameroon) has been investigated with a Boolean modeling process into a GIS environment on the basis of geological constraints such as elevation, rock and soil types, and landscape morphology. Field observation and SRTM (Shuttle Radar Topographic Mission) data allowed the differentiation of two lateritic land surfaces separated by a minimum altitude difference of about 60 m. These surfaces constrained by favorable rock types, slope steepness and soil types provided a potential lateritic bauxitic area of 381 km 2 (17.2% of the total study site). Field validation and the integration of legacy spatial data resulted in an area of 60.1 km 2 for potential bauxitic ores, i.e. obviously duricrusted bauxitic surfaces (with 47.8 km 2 in the upper surface and 12.3 km 2 in the lower surface). Alumina contents obtained from duricrust samples were analyzed by geostatistical methods and classical kriging interpolation to discriminate between bauxitic and ferruginous laterites. This highlighted a geochemical trend from higher alumina values on the upper surface (40–66 wt.%) to lower values on the lower surface (13–44 wt.%). Finally, our study documents two duricrusted lateritic surfaces arranged in a staircase manner and having different geochemical characteristics. The total bauxitic-rich surface is distributed in five spots throughout the study area and covers 56.2 km 2 , while ferruginous laterites occupy a spot of 3.9 km 2. GIS mapping approach of lateritic land surfaces, accounting for reliable constraints, might be promising for larger scale investigations of mineral resources in Cameroon

Lateritic landsurface-regolith differentiation on Pan-African granitic basement of Adamaoua highland, Cameroon

International audienceThe aim of this paper is to describe and discuss the laterization pattern and the structuration mode of landsurfaces formed over the Pan-African granitic basement of Adamaoua highland. Paleocene to mid-Eocene epeirogeny compartmentalized the regional topography of Adamaoua on which lateritic landsurfaces have been formed over granitoids of comparable geochemistry. Regional scale geomorphological observations and petrogeochemical characterization of lateritic duricrusted regolith allow to distinguish three distinct lateritic landsurfaces, which are compared to lateritic surfaces from West Africa. Regolith of the upper and middle landsurfaces incorporate composite lateritic duricrusts including old bauxites and ferricretes, which are petrologicalheritages from former regolith of etch-plain type Paleogene African Surface. On Pan-African granitic basement of Adamaoua, the upper and middle landsurfaces formed on granitoids before mid-Miocene basaltic-andesitic outpourings that locally cover them, while the lower landsurface also formed on grantic rocks has been mostly shaped over late Neogene. The geochemical compositions of lateritic duricrusts of upper and middle landsurfaces are clearly distributed between aluminous, ferruginous and kaolinite poles that typifies lateritic regolith of thebauxitic and (Fe-rich) intermediate etch-plains surfaces similarly as lateritic regolith of the Paleogene West- African sequence. Geochemical compositions of lateritic regolith on lower landsurface are mostly distributed between silica, kaolinite and iron, suggesting that more or less evolved or duricrusted horizons have been exposed by differential erosion of this landsurface. Lateritic regoliths of the three landsurfaces are also typified and differentiated by their index of laterization (IOL) and fractionation patterns of some trace (Cr, V, Zr, Ti, Nb, Th, Y, Ta, Ga) and rare earth elements (HREE, Eu/Eu*, (Gd/Yb)N). Though Neogene volcanic epirogenic uplift effects on landscape cannot be totally excluded, erosion and down-wasting of Paleogene landscape mostlyevolved to a degraded lateritic etch-plain and late formation of a lower pediplain on Pan-African basement of Adamaoua highland under long-lasting per-humid climatic conditions over Cenozoic

Differentiated Neogene bauxitization of volcanic rocks (westernCameroon): Morpho-geological constraints on chemical erosion (vol 194,104685, 2020)

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