Mineralogy and geochemistry of sands of the lower course of the Sanaga River, Cameroon: implications for weathering, pro
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ORIGINAL ARTICLE
Mineralogy and geochemistry of sands of the lower course of the Sanaga River, Cameroon: implications for weathering, provenance, and tectonic setting Marie The´re`se Nanga Bineli1 • Vincent Laurent Onana1 Yves Robert Bikoy1 • Georges Emmanuel Ekodeck1
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Sylvie De´sire´e Noa Tang2
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Received: 22 April 2020 / Revised: 24 July 2020 / Accepted: 23 September 2020 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This study focuses on the mineralogy and bulk chemical composition of 19 sediment samples, collected from the Sanaga River bed, between Nanga-Eboko and the Atlantic Ocean in Cameroon, to infer provenance, weathering, and tectonic setting. The textural analysis revealed that these sediments are mainly coarse-grained sands. X-ray diffraction and heavy mineral analyses show that these sands are made of quartz, microcline, plagioclase, muscovite, ilmenite, anatase, magnetite, opaques, and epidote. The Index of Chemical Variability values (1.07–2.68) indicates that the sands are immature. The Chemical Index of Alteration (53–66 %), Plagioclase Index of Alteration (PIA; 57–75 %), and Mafic Index of Alteration (54–67 %) values revealed a moderate intensity of weathering for these sediments. According to the compositional maturity diagram, the sands are mainly litharenites. The studied sands show enrichment in light rare earth elements relative to heavy rare earth elements and a negative anomaly in Eu (Eu/Eu* = 0.32–0.83). These sands were derived from felsic metamorphic rocks dated Meso to Neoproterozoic from the Pan-African (700–1000 Ma) domain of south Cameroon. Th/U ratios (mean = 5.40; n = 19) reveal that these sands originating from felsic source rocks and are low to moderately recycled. On the tectonic discrimination diagrams, all the samples are plotted in the
& Vincent Laurent Onana [email protected] 1
Department of Earth Sciences, Faculty of Science, University of Yaounde´ I, P.O. Box 812, Yaounde´, Cameroon
2
Department of Geology, Higher Teacher’s Training College, The University of Yaounde´ I, P.O. Box 47, Yaounde´, Cameroon
rift and passive margin domains, which is consistent with the tectonic history of Pan African in southern Cameroon. Keywords Central Africa Sanaga River sediments Heavy minerals Major and trace elements Source rocks Rift and passive setting
1 Introduction Rivers are natural flowing watercourses that carry eroded materials from continental areas to oceans and seas. The sediments they transport make it possible to understand evolution processes at the continental interface. Rivers cover large parts of continental surfaces and constitute geological and environmental records of the tectonic and climatic conditions in a river basin. The textural and mineralogical changes induced by weathering and fractionation phenomena during sedimentary processes lead to geochemical heterogeneity of river sediments during their genesis, transport, and deposition within sedimentary basins. Howeve
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