ABSTRACT
The Ebolowa Municipal Lake (EML) (South Cameroon) in order to identify the early diagenesis processes taking place in the lake and the factors influencing them. To this end, 21 samples were collected. In situ, hydrogen potential, redox potential, conductivity, dissolved oxygen content, and turbidity were measured. In the laboratory, the samples were subjected to mineralogical analysis by X-ray diffraction, geochemical analysis by X-ray fluorescence and ICP-MS, and statistical analysis. The coefficient of variation (Qi) was calculated from the geochemical data. In the water column, OD > 2 mg/L, pH > 7 and Eh < 0 mV. In sediments: pH < 7, Eh values are lower. The contents of 2.08 ≤ TOC ≤ 12.65%. The mineralogical procession consists of quartz, kaolinite, gibbsite, goethite, and siderite. The latter is only present in the EML. The sediments are dominated by SiO2 (60.44-89.47%), Al2O3 (6.55-18.17%), and Fe2O3 (1.15-6.21%). The Qi values range from 0.73 to 2.31. The Mn/Fe ratio values are below 0.40. Qi > 1 for Al, Fe, Mn, Mg, K, Na, P, Ni, Co, Zn, Pb, Cd, Cu, Ba, and V, and Qi < 1 for Si; Qi = 1 for Ca. The hierarchical cluster analysis shows two groups: the first one includes the samples from the central and western parts, while the second one includes those from the eastern and southern parts of the lake. The water column is subject to oxic conditions, while the sediments are anoxic. The rapid consumption of oxygen is due to organic mineralization, which is the main diagenesis observed in the lake. This phenomenon is more accentuated in the western part of the lake.
ABSTRACT
The present study focused on evaluating the contribution of both organic and inorganic component to the chemistry of Cretaceous black shales in the Mamfe basin, Sw Cameroon by performing inductively couple plasma spectrometry analyses with the data analysed using multivariate statistical analyses. The shales are classified as calcite enriched (Ca/Mg > 1) and calcite depleted (Ca/Mg < 1). Major elements such as K, Ti, and Al shows significant correlations (>0.71) among themselves and negative correlations with total organic carbon (TOC), total organic nitrogen (TON) and total organic sulphur (TOS) indicating that they were control mainly by inorganic factors. The positive correlation between phosphorus (P) and TOC, TOS, TON maybe due to absorption by organic fraction into the lattice of the shales. Selected both biophilic (Ba, Co, Ni, and Sc) and terrigenous (Zr) trace elements were correlated amongst themselves and with organic components. Zr show negative correlation (-0.36) with organic components and correlates negligibly with Co, and Ni (0.04, 0.16) indicating these elements were derived from organic matter with exception to Ba and Sc which shows positive correlation with Zr (0.77) and negatively correlated with TOS (-0.34, -0.13), carbon (-0.25, -0.17) and TON (-0.17, -0.06). The enrichment of light rare elements over heavy rare earth elements positive europium anomaly on PAAS normalise diagrams and an insignificant to negative correlation with TOC, TOS, and TON indicating their derivation from mainly an inorganic factor. Statistical analyses by hierarchical classification ascending (HCA) and principal component analyses (PCA) confirms solely an inorganic contribution to the chemistry of the studied black shales in the Basin. The positive correlations portray by some elements with organic components maybe due to their absorption by organic fractions into their lattice. Further indirect/direct methods such as sequential extraction and FTIR is required throw light on the origin of the chemistry of black shales in the Mamfe basin.