Author(s)

Gabriel Ngueutchoua^1*, Leopold Darlus Ngantchu¹, Martine Youbi¹, Simon Ngos III², Véronique Kamgang Kabeyene Beyala³, Kevin Petsouonko Yifomju¹, Jean Claude Tchamgoué¹

¹Department of Earth Sciences, University of Yaoundé 1, Yaoundé, Cameroon.
²Department of Earth Sciences, University of Maroua, Maroua, Cameroon.
³Department of Earth Sciences, University of Dschang, Dschang, Cameroon.

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. TiO₂, Y/Ni vs. Cr/V, TiO₂ vs. Al₂O₃ diagrams, high LREE/HREE ratios (5.84 to 20.91) and negative and positive Eu anomalies (Eu/Eu*= 0.87 to 1.62) suggest that the studied rocks were mainly derived from felsic igneous rocks with lesser contribution of mafic components. The higher values of paleo-weathering indices such as Plagioclase Index of Alteration (PIA) and Chemical Index of Weathering (CIW), ranging from 79.63 to 99.90 and 87.57 to 99.92 respectively, suggest that the sediments and their potential source rocks experienced intense weathering. Whereas the variable Chemical Index of Alteration (CIA) values (63.01 to 99.50) coupled with high content of K₂O (up to 7.5) in most samples could be indicative of K-addition diagenetic processes. The A-CN-K plot also suggests a possible K-addition. The redox conditions during the sedimentation were suboxic to oxic as evidenced by the Ce anomalies of 0.88 to 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., SiO₂-K₂O/Na₂O 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.

Douala Sub-Basin, Provenance, Weathering, Oxic Condition, Tectonic Setting

Ngueutchoua, G. , Ngantchu, L. , Youbi, M. , Ngos III, S. , Beyala, V. , Yifomju, K. and Tchamgoué, J. (2017) Geochemistry of Cretaceous Mudrocks and Sandstones from Douala Sub-Basin, Kumba Area, South West Cameroon: Constraints on Provenance, Source Rock Weathering, Paleo-Oxidation Conditions and Tectonic Environment. International Journal of Geosciences, 8, 393-424. doi: 10.4236/ijg.2017.84021.