Geochemical approach to depositional setting and organic matter accumulation of lower cretaceous shales of the Mundeck formation, Kribi-Campo sub-basin (South Cameroon)

Abstract

In order to deduce the origin, depositional setting and factors of organic matter accumulation, the Kribi Campo shales were examined for total organic carbon and geochemical analysis. The results show that the average total organic carbon concentration in the six studied sites are greater than 1 (3.58–12.26 w. %), suggesting they are good source rocks. The studied shales reveal V/Ni values of 1.88–4.26 indicating that the organic matter in the shales were sourced from marine origin and mixed terrestrial marine origin. The Al, Zr and Zr/Al diagrams, indicate that the terrigenous debris influx was relatively high in the Lower Formation and fluctuates from relatively constant to relatively decreasing and increasing manner in the Upper Formation. The Ni/Co, V/Cr, U/Th ratios range from 1.39 to 3.21, 1.22–1.81, 0.18–0.45 respectively, and an average Y/Ho ratio of 26.37–28.71 ppm, indicate the shales were deposited in a continental environment. The paleoproductivity proxies (P/Ti, Babio, Cu/Al, and Ni/Al), shows that in both Formation the P/Ti average ratio value (0.27 and 0.29), indicates moderate rate of paleoproductivity. Ba_bio average concentration in the studied sites of the Upper Mundeck Formation is higher than that of the Lower Mundeck Formation, indicating the authigenic barium sulfate was stored in variable quantities in the different studied sites of both Formations, its values vary from 322.94 to 2335.22 ppm, indicates a low to moderate paleoproductivity. The organic matter was preserved as a result of rapid deposition, high sedimentation and lesser exposure time.