Geochemistry of onshore deposits from Rio del Rey sub-basin of the western Atlantic margin of Cameroon (Coastal basin, Southwest Cameroon): provenance and environments of sedimentation
Tchouatcha, M.S.; Kassi, P.K.; Mbesse, C.O.; Noupa, R.K.; Mam, W.J.; Préat, A. (2022). Geochemistry of onshore deposits from Rio del Rey sub-basin of the western Atlantic margin of Cameroon (Coastal basin, Southwest Cameroon): provenance and environments of sedimentation. Environ. Earth Sci. 81(11): 321. https://dx.doi.org/10.1007/s12665-022-10440-7
In: Environmental Earth Sciences. Springer: Heidelberg; Berlin. ISSN 1866-6280; e-ISSN 1866-6299, more
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| Author keywords |
Geochemistry; Provenance; Sedimentation conditions; Cretaceous-Cenozoic; Rio del Rey sub-basin; Cameroon |
| Authors | | Top |
- Tchouatcha, M.S.
- Kassi, P.K.
- Mbesse, C.O.
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- Noupa, R.K.
- Mam, W.J.
- Préat, A., more
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| Abstract |
The Rio del Rey sub-basin belonging to the Cretaceous–Cenozoic coastal basins of Cameroon is studied with geochemistry (major and trace elements) associated to mineralogy, palynology and petrography. One dominant facies (calcareous shales/siltstones/claystones) occurs in the Cretaceous series and two others (calcareous fine- to coarse-grained sandstones and calcareous claystones/shales in the Paleocene series. Ratios of LREE/HREE (9.27–24.23), Cr/Th (2.24–12.60), Th/Sc (0.54–6.10), Eu/Eu* (> 1 on PAAS normalized and ˂ 1 on Chondrite normalized), Al2O3/TiO2 (10.42–112.93) plotted in the Ce vs. La/Yb, Zr vs.TiO2 and La/Sc vs.Th/Co diagrams indicate that the sediments derivate from felsic rocks associated with subordinate intermediate composition to mafic igneous rocks. CIA (Chemical Index of Alteration, 61.69–92.76), PIA (Plagioclase to Index of Alteration; 62.16–99.47) and K2O/Na2O ratios (0.08–22.13) suggest that the source rocks have experienced low to high weathering (during the Paleocene), high chemical weathering (at the Campanian–Maastrichtian transition) and moderate to high chemical weathering (during the Cenomanian). The Zr/Sc vs. Th/Sc diagram of sample groups reveals that the Paleocene coarse-grained sediments have higher zircon content. Al/Si ratios, low in the coarse-grained (0.04–0.06) and high in the fine-grained (0.2–0.58) sediments, behavior of Al/Si vs. CIA and some elemental concentrations, such as Zr, Hf, Ca, K, and Na, suggest that the geochemical composition is controlled by grain sizes. The petrographic and X-ray diffraction results point early to mesodiagenesis effects and an important role of sea level change on the environments of sedimentation. These latter vary from marginal to shallow marine during the Cretaceous and fluctuated between shallow marine/lagoonal and brackish/littoral settings during the Paleocene according to facies analysis and palynology, with marine species such as Dinopterygium cladoides and continental species such as Classopollis sp. The SiO2 vs. Al2O3 + K2O + Na2O plot suggests that a predominant semi-arid to arid climate with periodically semi-humid periods was the rule during the Paleocene, The Arc-Rift-Collision, with two sets of high and low-silica rocks and SiO2 vs. K2O/Na2O diagrams, indicates a Collisional or Active Continental Margin tectonic as also recorded in the Cretaceous and Paleocene deposits in the Douala coastal sub-basin and in the Cretaceous Campo coastal sub-basin in Cameroon. These tectonic events could reflect the Precambrian basement history linked to the Neoproterozoic orogeny. The geological history of the Rio del Rey sub-basin is similar to those of Nigerian and Brazilian East costal basins, with local variations of the sea level changes on both sides of the Atlantic Ocean and the sediments distribution which is related to the source rock lithology. |
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