Provenance and depositional history of Mesozoic sediments from the Mamfe basin and Douala sub-basin (SW Cameroon) unraveled by geochemical analysis. (October 2019)

• Record Type: Journal Article
• Authors: Ngueutchoua, Gabriel; Eyong, John Takem; Ekoa Bessa, Armel Zacharie; Azanji Agheenwi, Zita Bih; Maschouer, Alain Emane; Kemteu, Christel Sobdjou; Dzoti, Yannick Lontchi; Hamadou, Touda; Ongbassouek Baboule, Bibiche-Mabel; Kenfack Nguemo, Gatien Romuald
• Is Part Of: Journal of African earth sciences. Volume 158(2019)
• Publication Date: 2019-10
• Subjects: Geochemistry -- Weathering -- Provenance -- Mamfe basin -- Douala sub-basin; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2019.103550
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: Mineralogical and geochemical analytical methods were employed to characterize sediment samples from the Mamfe basin (MB) and Douala sub-basin (DSB) in order to constrain the provenance, weathering, paleoclimate, and depositional history of rocks from both basins. Sediments under study are classified as shales, wackes, and arkoses and are essentially derived from felsic rocks which likely correspond to nearby extensive Neoproterozoic migmatitic and gneissic basement rocks. The A-CN-K plot indicates that the K-metasomatism may have affected the bulk composition of most of the studied rocks. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and (A-K)-C-N plots suggest that the intensity of weathering was higher for DSB relative to MB samples. This differentiation can be related to active tectonism during the deposition of the MB sediments. The SiO2 /Al2 O3, Al2 O3 /Na2 O, and K2 O/Na2 O ratios, and the Index of Chemical Variability (ICV), indicate a low compositional maturity for MB compared with DSB samples. The values of U/Th, V/Cr, Ni/Co, and authigenic U suggest an oxic depositional condition for all studied samples. The average Sr/Ba ratios for the MB (0.31 ± 0.12 and 0.59 ± 0.25, for the Okoyong and Nfaitok-Yawo areas, respectively) and DSB sediments (0.31 ± 0.08 and 0.20 ± 0.09, for southern Kumba and western Mbanga areas, respectively), suggest a depositional paleoenvironment with low salinity. The average Rb/Sr ratios for the MB (0.62 ± 0.36 and 0.17 ± 0.06, for the Okoyong and Nfaitok-Yawo areas, respectively) and DSB sediments (0.53 ± 0.11 and 0.73 ± 0.29, for southern Kumba and western Mbanga areas, respectively) are low, suggesting warm and humid condition during the deposition of MB and DSB sediments. Multi-element tectonic diagrams indicate passive and rift settings, which are consistent with the local geology, but also a collisional setting, which is probably linked to the tectonic evolution of the Neoproterozoic metamorphic source rocks. Highlights: The Mamfe basin and Douala sub-basin sediments were derived mainly from felsic igneous rocks. The Mamfe basin sediments underwent low degree of chemical weathering, relative to Douala sub-basin sediments. Sediments from both basins were deposited under warm and humid paleoclimate. They experienced K-addition processes during diagenesis, and oxic condition during sedimentation.