Geochemical characterization of the metasedimentary rocks of the Yaounde Group within the southernmost North Equatorial tectonic belt:insights into geodynamic evolution

The Proterozoic metasedimentary rocks of the Yaounde Group on the northern edge of the Congo Shield in Central Africa were investigated to understand their provenance and depositional environment.Petrography,geochemistry,and field evidence helped to subdivide the metasediments into paragneiss,mica schist,chlorite schist,and quartzite which were derived from greywacke,shale,quartz arenite,litharenite protoliths.They are immature with some mature samples,moderately weathered and reworked Neo-and Post-Archean metasediments.Rare earth element signatures(Chondrite Eu/Eu^(*)≤1),enrichment of light rare earth elements over the heavy ones,and the La/Sc ratio(>0.7)are compatible with those of the intermediate and felsic sources from the upper continental crust.These metasediments were deposited in the continental arc setting and have evolved during Proterozoic times according to the Wilson cycle to form the West Gondwana including NE Brazil.

Displaying Water Table Levels, Flow Direction for Predicting Construction Techniques Using Geographic Information: Case Study of Kumba (South West, Cameroon)

The rapid economic growth of the town present the matter of water issue as a problem to human life human life, construction life, agriculture, etc. This study is to predict techniques of foundation construction through the displaying of the water table at the flow direction in the town of Kumba and GIS. It is characterized by a significant research question which is the level of fall and rise in groundwater levels within the town of Kumba and this influence on choice of types of foundation in construction. This study is directed to decision makers, and technicians of the construction field to develop policies facilitating the supervision when building construction foundation by informing about water level depth and its flow direction in the town. To achieve this, depths of static water levels were measured in over 200 randomly selected hand-dug wells in Kumba, after their geolocation and data were collected during the dry season (November and March 2017) and during the rainy season (between April and October 2017). Data were analyzed and treated using Microsoft Excel and GIS software us as Golden Surfer, Global Mapper, and ArcGIS. The results show variations of water level and those areas that may threaten foundation construction. Quarter as Kumba Station, Mile 1, Bulletin Street (Fongong Quarter), and parts of Fiango show that water table is to deep water and proper for the shallow foundation but very hard for water supply through borehole. Groundwater flow direction was revealed to be towards the south and southeastern parts of Kumba. The significant of the study is to propose to the technician the direct application on the field of chosen types of foundations according to the quarter and proposed groundwater supply possibilities.

Lithostructural controls in Douala-Buea Region landscape (SW Cameroon margin):Insights from morphometric analysis

The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimentary cover,was explored in order to evaluate the lithology and tectonics controls on its landscape usingthequalitativeandquantitative geomorphological analyses based on 30 m resolution Digital Elevation Models(DEM)and field evidences.This area displays an uneven and complex landscape differentiated into four morphological units:Douala,Nkondjock,Kumba and Buea Units.The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Camposedimentarybasin.The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement.The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau.The Buea Unit corresponds to the Mount Cameroon stratovolcano.The relief analysis through mountain-front sinuosity(Smf,1.19–1.43)and relative relief ratio(Rr,0.10–2.31)vary from one unit to another.The drainage network analysis including drainage patterns,stepped longitudinalriverprofiles,theassociated morphometric indexes,notably the concavity index(IC,0.56–0.88),deviation(D,267–2912 m),basin asymmetry factor(A_(F),6.37–42.12),hypsometric integral(HI,0.10–0.29),valley floor width to valley height ratio(V_(f),0.36–2.75),elongation ratio(R_(e),0.30–0.50),watershed slope(S,6.88–88.88)and stream length gradient index(SL,0–3332)vary from one basin to another too.These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics.The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points,asymmetric basins,and fault reactivations,and highlights the tectonics activity that used to occur through the time and their control on the morphology.Together,they document the lithostructural controls on the DBR landscape evolution,extendable in the whole SW Cameroon margin.

Post-orogenic transients and relict landforms of the Bafoussam–Mamfe region(West-Cameroon Highland margin)

The Bafoussam-Mamfe Region(BMR)belongs to the Western Cameroon Highland margin,an amalgam of transient landscape that evolved from the interactions between tectonics,lithology and climate forcings.This area is tectonically active and shows differential tectonic uplift,contrasting relief,variations in erosion rates,in river incision,and in channel gradient.In order to appraise the BMR tectono-geomorphic evolution,it is essential to understand relationships between internal and external processes and their geomorphic expression at a river basin scale.For this purpose,we use drainage texture(Dt),stream frequency(Fs),drainage density(Dd),asymmetry factor(AF),the transverse topographic symmetry factor(TTSF),the mean of mountain front sinuosity per unit(Smf),concavity factor(Cf),hypsometry integral(HI)and streamlength gradient index(SL-index)based on 30 m Digital Elevation Models(DEM)and field survey.The results reveal considerable variations in geology,relief,topography and geomorphic indices values differentiated into three geomorphic units;the Mamfe unit developed on the Mamfe Cretaceous basin,the Nguti and Bafoussam high plateau units build up on the Precambrian granito-gneissic basement overlaid by a volcanic cover.The stepped(longitudinal and normalized)river profiles and complex hypsometric curves show the lithostructural control of the hydrographic network.Dt(from~1.21 to~4.59),Fs(from~0.26 to~1.91),Dd(from~0.66 to~1.71)geomorphic indice values indicate a part of lithologic control on this morphology while the AF(from~1.16to~24.91),TTSF(from~0.20 to~0.71),Smf(U2=1.11 and U3=1.19),Cf(from~-20.91 to~78.93),HI(from~0.12 to~0.52)and SL-index designate the active tectonics as the main factor that had controlled the morphology of this same area.Above results pinpoint the combined post-Pan-African to Recent tectonic features,lithologic heterogeneities and the differential erosion processes as main factors that have controlled the BMR landscape.These results highlight how the Central African surface and the West African passive margin evolved since Proterozoic time.