TITLE:
Geochemistry of Sedimentary Rocks from the Nkapa Formation, North Western Part of the Douala Basin, Cameroon: Implications for Provenance, Tectonic Setting and Paleoenvironmental Conditions
AUTHORS:
Florence Njinto Kwankam, Christopher Mbaringong Agyingi, Josepha Foba-Tendo, Cheo Emmanuel Suh
KEYWORDS:
Geochemistry, Sedimentary Rocks, Nkapa Formation, Provenance, Depositional Environment
JOURNAL NAME:
International Journal of Geosciences,
Vol.12 No.9,
September
1,
2021
ABSTRACT: The Douala sedimentary basin in Cameroon is the main gas prospective
basin in the country and has witnessed a number of investigations in this
regard. The Nkapa Formation is one of the basin’s principal rock units and here
we analyzed samples from sediments comprising this formation in order to
constrain their provenance, tectonic setting and depositional environment using
geochemical traits. Major and trace elements were analyzed by inductively
coupled plasma mass spectrometry. Elemental ratios provide information on
geochemical signatures of Eu/Eu ratios of the sandstones and shales, suggesting
the provenance of the sediments was felsic from continental rock protoliths.
Calculated K2O/Na2O ratios > 1 is reminiscent of
quartz-rich sediments deposited in passive margin (PM) environments with
significant terrigenous input. The elemental ratios La/Sc, La/Ca, Th/Sc, and
Th/Co suggest that the sediment sources are felsic and mafic in nature. The clastic sediments were normalized using North
American Shale Composite (NASC). The Ni/Co and V/(V + Ni) ratios reveal that the sediments were deposited under variable
conditions including euxinic, dysoxic and anoxic. Overall, the evidence from discrimination diagrams using major and trace
elements suggest that the sediments were derived from mostly Passive margins (PM) and
continental island arc (CIA) with minor Oceanic island arch (OIA) sources.
Limestones from the studied area at Kompina, rich in calcium carbonate above
98.5% make them suitable for use in the chemical industries. In addition the felsic and
mafic source rocks can lead to formation of light and dark colored minerals
which can be of economic value.