Abstract:This study investigates the provenance, paleoweathering, and paleoclimate of the Ossa lake sediments, based on the mineralogy and geochemistry data. Ossa lake sediments are characterized by silt and clay with high content of total organic carbon (TOC). Clay minerals are identified as kaolinite and illite types. Other dominant minerals identified are quartz, zircon, rutile, goethite, gibbsite, feldspar, and accessory vivianite. The major, trace, and rare earth element concentrations indicate that the sediments … Show more
“…The surface sediments from the surrounding streams and in the sedimentary rocks of the watershed area show a similarity in distribution spectra with a dominance of the sandstone from the Douala Sedimentary Basin (DSB). The sedimentary rocks (especially the sandstones) of the DSB (Ngueutchoua et al 2019 ), the sediments of river Sanaga (Nanga Bineli et al 2021 ), and the sediments of Lake Ossa (Ekoa Bessa et al 2021 ) all near the study site have similar spectral signatures to the sediments in this study. Even the sediments of river Dibamba (Sonfack et al 2021 ) that are further away from the study site are completely similar to the sediments in this study (Fig.…”
Section: Discussionsupporting
confidence: 64%
“… Fig. 3 PAAS-normalized REE patterns of the Douala sub-basin (DSB; Ngueutchoua et al 2019 ), Sanaga River (Nanga Bineli et al 2021 ), Ossa Lake (Ekoa Bessa et al 2021 ), Dibamba River (Sonfack et al 2021 ) and average of waters and sediments from this study …”
Section: Resultsmentioning
confidence: 88%
“…Overall, the different spectra of REE in surface waters such as the depletion of some REE (Nd to Dy) in the waters and a slight negative anomaly of Eu in the river waters, are likely due to the variation in pH (5.08 to 7.62) and TDS (233 to 1259, mg/L) between the river, effluent, and well hydrochemical compartments. It appears that high pH and reducing conditions favor the adsorption/precipitation of REE in the still environment (Ekoa Bessa et al 2021 ). Low pH and TDS in river water increase the solubility of REE.…”
The concentrations and distribution spectra of 14 stable rare earth elements (REE) were studied for surface waters (
n
= 30) and sediments (
n
= 30) of the tropical zone Mgoua watershed in southwest of Cameroon. Samples were analyzed using the inductively coupled plasma mass spectrometer (ICP-MS) method. The ∑REE concentrations of the surface waters vary from 0.11 to 6.60 µg/L with an average value of 1.18 µg/L. This average is 150 times lower than the average values of the Post-Archean Australian Average Shale (PAAS). In the sediments, the concentrations range from 282.12 to 727.67 ppm with an average value of 550.05 ppm, making it 2.5 times higher than the PAAS. Rare earth spectra normalized to PAAS are spread out and show heavy rare earth enrichment; positive Eu anomalies; negative, low, or no Ce anomalies; and a gradual decrease in heavy earths in river and well waters and sediments, but are sawtooth with strong negative Ce anomalies in effluent waters and sediments. A low rare earth fractionation is noted in river and well waters [(La/Yb)
N
~ 0.35–1.19], while it is high in effluent waters [(La/Yb)
N
~ 0.42–56.99]; a slight depletion of rare earths in all environments [(La/Sm)
N
~ 0.69–2.35], as well as a depletion of heavy rare earths [(Gd/Yb)
N
~ 0.58–1.94]. In the sediments, the same characteristics are found with elemental ratio values differing slightly [(La/Yb)
N
~ 1.15–1.99]; [(La/Sm)N ~ 0.75–1.36]; and [(Gd/Yb)
N
~ 1.15–2.01]. This study shows that the Mgoua watershed does not have a high concentration of REE, although in the sediments they are well above the average PASS value while they are insignificant in the waters.
“…The surface sediments from the surrounding streams and in the sedimentary rocks of the watershed area show a similarity in distribution spectra with a dominance of the sandstone from the Douala Sedimentary Basin (DSB). The sedimentary rocks (especially the sandstones) of the DSB (Ngueutchoua et al 2019 ), the sediments of river Sanaga (Nanga Bineli et al 2021 ), and the sediments of Lake Ossa (Ekoa Bessa et al 2021 ) all near the study site have similar spectral signatures to the sediments in this study. Even the sediments of river Dibamba (Sonfack et al 2021 ) that are further away from the study site are completely similar to the sediments in this study (Fig.…”
Section: Discussionsupporting
confidence: 64%
“… Fig. 3 PAAS-normalized REE patterns of the Douala sub-basin (DSB; Ngueutchoua et al 2019 ), Sanaga River (Nanga Bineli et al 2021 ), Ossa Lake (Ekoa Bessa et al 2021 ), Dibamba River (Sonfack et al 2021 ) and average of waters and sediments from this study …”
Section: Resultsmentioning
confidence: 88%
“…Overall, the different spectra of REE in surface waters such as the depletion of some REE (Nd to Dy) in the waters and a slight negative anomaly of Eu in the river waters, are likely due to the variation in pH (5.08 to 7.62) and TDS (233 to 1259, mg/L) between the river, effluent, and well hydrochemical compartments. It appears that high pH and reducing conditions favor the adsorption/precipitation of REE in the still environment (Ekoa Bessa et al 2021 ). Low pH and TDS in river water increase the solubility of REE.…”
The concentrations and distribution spectra of 14 stable rare earth elements (REE) were studied for surface waters (
n
= 30) and sediments (
n
= 30) of the tropical zone Mgoua watershed in southwest of Cameroon. Samples were analyzed using the inductively coupled plasma mass spectrometer (ICP-MS) method. The ∑REE concentrations of the surface waters vary from 0.11 to 6.60 µg/L with an average value of 1.18 µg/L. This average is 150 times lower than the average values of the Post-Archean Australian Average Shale (PAAS). In the sediments, the concentrations range from 282.12 to 727.67 ppm with an average value of 550.05 ppm, making it 2.5 times higher than the PAAS. Rare earth spectra normalized to PAAS are spread out and show heavy rare earth enrichment; positive Eu anomalies; negative, low, or no Ce anomalies; and a gradual decrease in heavy earths in river and well waters and sediments, but are sawtooth with strong negative Ce anomalies in effluent waters and sediments. A low rare earth fractionation is noted in river and well waters [(La/Yb)
N
~ 0.35–1.19], while it is high in effluent waters [(La/Yb)
N
~ 0.42–56.99]; a slight depletion of rare earths in all environments [(La/Sm)
N
~ 0.69–2.35], as well as a depletion of heavy rare earths [(Gd/Yb)
N
~ 0.58–1.94]. In the sediments, the same characteristics are found with elemental ratio values differing slightly [(La/Yb)
N
~ 1.15–1.99]; [(La/Sm)N ~ 0.75–1.36]; and [(Gd/Yb)
N
~ 1.15–2.01]. This study shows that the Mgoua watershed does not have a high concentration of REE, although in the sediments they are well above the average PASS value while they are insignificant in the waters.
“…The study area is considered to be the “promotor” and “amplifier” of the opening of this part of the Atlantic Ocean, which has long been the ideal region for geological studies (e.g., Fairhead 1988 ; Guiraud and Maurin 1991 , 1992 ; Pletsch et al 2001 ). Previous studies suggest that the Western African margin expanded like a “zipper” from south to north, but did not extend into Cameroon until the Barremian-Aptian period (Manga 2008 ; Ekoa Bessa et al 2022 ). With the occurrence of the oceanic strike-slip fault and subsequent margin expansions in the mid-Aptian, the Cameroonian margin underwent considerable structural reconfiguration, involving the fragmentation of the margin rift features (Benkhelil et al 2002 ).…”
Section: Study Area and Geological Settingmentioning
The paleoweathering, provenance, and tectonic setting of the source region were determined with compositional and geochemical analyses of sediments obtained from the beach locations of Yoyo, Mouanko, and Mbiako along the central coast of Cameroon. The beach sediments are medium to coarse-grained and are brown to light brown. Their mineralogy is dominated by quartz and clay minerals with a medium amount of feldspars, rutile, goethite, hematite, and calcite. Moreover, their petrography is made up of quartz and feldspars, with low proportions of augite, apatite, biotite, and zircon. The sediments are classified as sublitharenite, and they are mostly made up of felsic rocks derived from the adjacent Neoproterozoic magmatic and gneissic basement rocks. Weathering indices such as the chemical index of alteration (CIA) and plagioclase index of alteration (PIA) indicated that in this study, the source area’s weathering intensity was moderate. The index of chemical variability (ICV) indicates a low maturity. The geochemistry data revealed passive and rift settings for the beach areas, which are congruent with the local geology.
“…Clastic sediments can be derived from a variety of tectonic settings and have distinct geochemical signatures due to parent rock geochemical composition. The unique discriminant function graphs rely on the major oxides that have been adjusted to 100% volatile-free [22]. For the low-silica tectonic discrimination [(SiO2)adj= 52.88-70.33% (m2)]sediments, discrimination diagrams were proposed [28] [29].…”
Section: Provenance and Tectonic Settingmentioning
A detailed sequential analysis which included thin section petrography, X-ray diffraction, and X-ray fluorescence was applied to investigate the mineral, chemical classifications, provenance, paleo-weathering, paleoclimate, and maturity features of such Zubair oil shale in the Rumaila oilfield in southern Iraq. In core samples and thin sections, the analyzed shales are primarily silty, flaky to subflaky, micaceous, calcareous, well-sorted, poorly cemented, and weakly to moderately compacted silt-grade sandy mudstone. According to XRD analysis, the main mineral is quartz, which is followed by kaolinite, while calcite and dolomite are less common and Illite, Illite/smectite, and pyrite are rarely abundant. Petrographic analysis of the Zubair shales revealed four lithofacies: silty clayey laminated mudstone lithofacies, mica-rich mudstone lithofacies, clay-rich siliceous mudstone lithofacies, and clay-bearing calcareous mudstone lithofacies. Major and trace element concentrations reveal that the oil shales have been formed from felsic rocks such as granodiorite, tonalite, and granite. A passive margin setting was revealed by the tectonic discrimination diagram. Weathering index values like the (CIA) chemical index of alteration, the (PIA) plagioclase index of alteration, and the (CIW) chemical index of weathering imply extensive chemical weathering in the source area. Zubair shales' K2O/Na2O ratio and (ICV) index of compositional variation are uniform with their high maturity. The compositions of mineral and trace elemental ratios, as well as the climatic index "C," indicate a warm to humid subtropical climate with deposition in a shallow oxic and dysoxic environment.
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