Lithotectonic setting, paleoweathering, maturity, sediment recycling and paleoredox conditions of quaternary alluvium from Mayo Sina (Tchad). A geochemical approach.

The alluvial material in the two PITs of the Mayo Sina in the southern part of Chad, were subjected to a geochemical analysis in order to determine the source rock lithological composition, tectonic context, degree of weathering, type of climate at the period of weathering, and cycles of sedimentation and maturity. Plotting source lithology charts with values of La/Sc, Th/Sc, La/Co, and Cr/Th indicated that the sediments originated from a felsic source rock composition. The Enrichment of LREE/HREE and a negative chondrite Eu anomaly confirm the felsic source rock composition. A passive tectonic context for the source rock of the sediments is revealed by binary charts (SiO2 versus K2O/Na2O) in conjunction with innovative discrimination plots (DF 1 and DF 2 (Arc-Rift-Col)M1, DF (A-P)M, and DF (A-P)MT). The exceptional degree of plagioclase removal and weathering is demonstrated by the results of the Plagioclase Index of Alteration (PIX) and Chemical Index of Alteration (CIX). The proportion of SiO2/Al2O3 and the new index of compositional variation (ICVnew), which exclude iron and calcium oxides from the formula, indicate that the sediments are immature to mature. Schematic representations of K2O/Na2O ratio indicate that the sediments have undergone both primary to secondary phases of sedimentation.

Geochemical dataset of alluvial sediments in the Mbiame floodplain (NW Cameroon): Implication for provenance, paleoweathering, and maturity.

To identify potential heavy minerals in the Mbiame floodplain in the Northwestern region of Cameroon, geochemical and petrographical data from alluvial deposits were utilized. The grains are mixed with inclusions of zircon and ilmenite, and the megacrysts come from felsic to intermediate igneous rocks like old basalt-andesite and magmatic gneiss. The Mbiame region lies between latitudes 6° 8' and 6° 24' N and longitudes 10° 39' and 10° 57' E, East of Mount Oku. One of the principal volcanic massifs on the Cameroon Volcanic Line (CVL), Mt. Oku is situated over a basement composed of migmatites, biotite diorites, and Pan-African granite-gneisses that date back to 600 Ma. The Mbiame Floodplain is located in the Pan African Fold Belt, which is made up of the Benin-Nigeria belt, which is a component of the Central African Fold Belt, and the Trans-Saharan belt. Between the Congo and West African cratons is a heavily eroded and deformed combination of Neoproterozoic plutonic and volcanic arcs and Paleoproterozoic micro-continents. The Central Cameroon Shear Zone serves as the primary lineament for the Pan African Orogeny, which is structurally separated into the Northwestern Cameroon Domain (NWC), the Adamawa-Yade Domain (AYD), and the Yaounde Domain (YD) in Cameroon. The field work was carried out during the dry season. During the field campaign, numerous bulk sediments were sampled from three (03) pits of vertical lithological succession along the left terrace of the Mbiame plain and twelve (12) were selected for laboratory analyses. The criteria for sample collection were based on texture (grain size) and color parameters. To identify the heavy minerals in the sediments and to understand the source of the sediments, the selected 12 bulk samples from the different layer of the pits were dried and sieved for heavy mineral determination. Heavy mineral separation was performed on about 2 g of the concentrate using bromoform liquid and the retained heavy minerals were mounted and observed under a petrographic microscope for optical properties identification. Twelve (12) bulk sediment samples weighing 100 g each were ground up in a mild steel pulverizer before being examined for major and trace elements. At Acme Analytical Laboratories Ltd., Vancouver, Canada, the geochemical study was carried out utilizing a combination of mass spectrometry (ICP-MS) for trace elements and inductively coupled plasma emission spectrometry (ICP-ES) for significant oxides. Lithium metaborate/tetraborate (LiBO2/Li2B4O7) flux was combined with 0.2 g of sample in crucibles, and the mixture was fused in a furnace. After the beads cooled, they were digested in ACS-grade nitric acid and then subjected to ICP-MS analysis. To calculate loss on ignition (LOI), a sample split at 1000 °C was ignited, and the weight loss was then measured. Data of this paper are further presented and discussed in Etutu et al. [1].

Geochemical balance of the mineral fraction and statistical analyzes of the Ebolowa municipal lake's sediments (central Africa): Implication for early diagenesis process.

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.

Provenance, paleoclimate and diagenetic signatures of sandstones in the Mamfe Basin (West Africa).

Petrography, heavy mineral and trace element geochemistry have been used to unravel the tectonic setting, source area lithology, diagenesis and paleoclimate conditions of the Mamfe sandstones. Quartz exists as monocrystalline (79%), and polycrystalline grains (21%). Orthoclase and microcline are the most dominant feldspars in the rocks. Heavy minerals such as zircon, tourmaline, kyanite, augite, garnets, hornblende, epidotes, diopside, muscovites, biotites, and opaque minerals were disclosed by the samples after bromoform separation. These sandstones are mineralogically and texturally immature and have been classified as arkose on the basis of the QFR diagram. QtFL plot indicates derivation mainly from a transitional continental region of continental block provenance with trace elements geochemical data pointing to a felsic source. The felsic sources are related to the Precambrian granitic/gneissic rocks which formed the basement and margins of the basin. The bivariant log-log Qt/F+R and Qp/F+R plot and the nature of quartz grains of the studied sandstone specimens indicate a semi-humid climatic condition prevailed at the time of deposition in a fluvial environment. The sandstones display deformation of mica, cementation, replacement, and albitization with some having an imprinted reddish brown color indicating a redoxmorphic, locomorphic and phyllomorphic diagenetic stages associated to early, burial and uplift diagenetic processes.