Sedimentology and geochemistry of carbonate bearing-argillites on the southeastern flank of mount Cameroon (likomba), Cameroon volcanic line (CVL).

Abstract

Sedimentological, geochemical and petrographic studies were carried out on carbonate-bearingargillites outcropping at the southeastern flank of Mount Cameroon (Likomba) to determine thelithofacies and their associations, major element geochemistry and mineralogy. This was in an attempt to establish their relationship with the Cameroon Volcanic Line (CVL), determine their provenance and propose the environment of deposition.. Outcrops and rock samples were carefully observed and described in the field. Major elements of the rocks were analysed using XRF technique. Thermal analysis, R-mode factor analysis and thin section studies were carried out accompanied with the determination of insoluble components of the carbonates. Studies revealed predominant carbonate and shale facies divided into five sub lithofacies including massive to faintly laminated shales (Facies I), laminated shales (Facies II) Carbonate interbeds (Facies III), shaly carbonate (Facies IV) and carbonates (Facies V). The shales predominantly consist of quartz, micas and clay while the carbonates are classed as biomicrites and consist of basically the iron carbonate mineral siderite, calcium carbonate and some subordinate pyrite. Geochemical results depict a broad variation in their concentrations with SiO2 and Fe2O3 showing the highest concentrations and Na2O and Mn2O3 with the least concentrations. R-Mode analysis discriminated two elemental associations including Fe2O3-MgO-Mn2O3 (72.56%) and TiO2-SiO2- Al2O3-K2O (23.20%), indicating both Fe-enrichment event, the subsequent formation of the siderite and the contribution of the continental sediments to the formation of these rocks. The rocks consist of cyclic iron-rich carbonates alternating with sideritic-shales and their marine fossil content suggest that they might have been formed as a result of variations in sea conditions and variation in sediment influx resulting from transgression and regression sequences occurring in a shallow to slightly deep marine environments. The rocks lie unconformably beneath the CVL and are highly fractured due to the overburden of the overlying igneous rocks.