We report measurements of the carbon-isotope composition (SlC value) of particulate organic carbon (POC) in the suspended sediment load of the Sanaga and Mbam Rivers, Cameroon. The results demonstrate that there is a seasonal cycle in 8°C value of 3.3%0 (-26.6 to-23.3%0) in the Sanaga River and 5.9%0 (-27.1 to-21.2%0) in the Mbam River that is directly related to seasonal changes in the discharge of the rivers. During periods of high discharge, S'C values of POC are high, reflecting an increase in the proportion of POC derived from C, plants, including C-derived carbon transported overland by wet season rains from savanna regions in the catchment hinterland. During periods of low discharge, the 8°C values of POC are low, reflecting derivation of the carbon primarily from C, plants growing close to the riverbanks. Results suggest that the prime determinant of POC 8°C values in tropical rivers that carry a significant suspended sediment load is the 6°C value of the catchment vegetation.
Geochemical data of fifteen Cretaceous sediment samples from Kumba area in the Douala sub-basin are presented to determine the provenance, source rock weathering, tectonic setting and paleo-oxidation conditions of the depositional setting of these rocks. For this purpose, the whole-rocks were analyzed for their major and trace element, including rare earth elements (REEs), contents by ICP-AES and ICP-MS methods respectively. On the basis of their major element composition, the rocks have been classified mainly as Fe-shale, shale, arkose and Fe-sandstone. For the provenance, the plot of Zr vs. 1.03. This is also confirmed by the values of Ni/Co (less than 7), U/Th (less than 1.25) and Cu/Zn (mostly less than 1). Tectonic discrimination diagrams (e.g., SiO 2 -K 2 O/Na 2 O and Th-Sc-Zr/10) show that these rocks were deposited mainly in an active continental margin setting, and in various tectonic environments. This reflects probably the recycling effect experienced by the samples studied.
In this study, clayey soils are characterized as backfill and potential fusible raw materials for engineering. Geotechnical tests (particle size distribution, Atterberg limits, densities) and chemico-mineralogical analyses (X-ray fluorescence, X-ray diffraction and Fourier transform infrared) were carried out on samples collected from field in the locality of Boulgou (North Cameroon) followed by the determination of mechanical properties of fired bricks (850–1200 °C). The excavations carried out have revealed a thick layer of clayey soils (~ 2 to 2.5 m) over a sandy layer. This clay formation presents some stratifications with limited influence variation in terms of mineralogy. Mean grain size distribution is dominated by sand (62–80%), clay (12–25%) and silt (6–9%). It corresponds to silty–clayey soils regarding their methylene blue values (3.3–5.6), with low plastic (13–22%) to high plastic (33%) characteristics. They are classified by USCS as clayey sand/silty clay, while one sample is a poorly graded sand (SP). Clay minerals observed are kaolinite (6–12%), montmorillonite (2–6%) and illite (8–10%). Those parameters associated with their fine nature and high compressibility make them suitable engineering applications for backfill material and barriers. From chemical analyses, relatively high contents in alkali and alkaline earth elements (~ 4 to 6%) to be used as potential fusible raw materials for fired bricks or gres ceramics were revealed. Bricks characteristics are varied: linear shrinkage (0.3 to 9%), bulk density (1.8 to 2.3 g/cm3), water absorption (19.7 to 1.3%) and flexural strength (0.3 to 17.4 MPa). Overall, the requirement for fired brick (< 20%) is met up by the water absorption values. As from 1050 °C, these soils are made suitable for brick-making with good characteristics (metallic sound, good cohesion and flexural strength).
Clayey materials from Sekandé and Gashiga localities in the northern part in Cameroon traditionally used for pottery were studied. Eight samples were collected and investigated by XRD, IR, XRF, physical and firing properties from 900, 1000 and 1100 °C. In term of mineralogy, studied clays are rich in smectites, illite, kaolinite, quartz, feldspar and mica. Physicochemically, results show large particle size variations with high plasticity (18–30%). Clay fraction (<2 μm) ranges from 18 to 38% and sand fraction from 40 to 53%. Si0
2
(46–55%) and Al
2
O
3
(19–21%) are major chemicals oxides, followed by Fe
2
O
3
(6.68–10.82%) and alcali and alcali-earth elements (8–10%). These characteristics govern their behavior on firing with temperature development. The color of specimens was predominantly red after firing. Between 900 and 1100 °C, their color ranged from reddish brown, red yellow or brown red to red. The linear shrinkage values vary from 0.5% to 7%, weight loss from 4% to 9% and bulk density from 1.74 to 2.21 g/m
3
. These values increased gradually for specimens fired from 900 to 1100 °C. The water absorption decreased from 17% to 14%. The evaluation of the studied clays based on their mineralogical, physicochemical and ceramic properties revealed that they are suitable for the manufacture of earthenware products like fired bricks.
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