Geochemistry of Sedimentary Rocks from the Nkapa Formation, North Western Part of the Douala Basin, Cameroon: Implications for Provenance, Tectonic Setting and Paleoenvironmental Conditions

摘要

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. style="font-family:Verdana;">The clastic sediments were normalized using North American Shale Composite (NASC). The Ni/Co and V/(V style="font-family:""> style="font-family:Verdana;">+ style="font-family:""> style="font-family:Verdana;">Ni) ratios reveal that the sediments were deposited under variable conditions including euxinic, dysoxic and anoxic. style="font-family:Verdana;"> Overall, the evidence from discrimination diagrams using major and trace elements suggest style="font-family:"color:red;"> style="font-family:Verdana;">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 the style="font-family:Verdana;">m style="font-family:Verdana;"> 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.