TITLE:
Sedimentology and Geochemical Evaluation of Lignite-Argillite Sequences in a Named Basin in Bali Nyonga, Northwest, Cameroon
AUTHORS:
Roger Ngong Ngia, Christopher M. Agyingi, Josepha Foba-Tado, Germain M. M. Mboudou, Anita Nshukwi, Victorine N. Beckley
KEYWORDS:
Lignite, Bali Nyonga, Argillite, Clay Minerals, Cameroon Volcanic Line (CVL), Lacustrine Basin
JOURNAL NAME:
International Journal of Geosciences,
Vol.6 No.8,
August
31,
2015
ABSTRACT: The sedimentology and
geochemistry (major and trace element compositions) of lignite and argillite
(carbonaceous shale and claystone) sequences in a Basin in Bali Nyonga, west of
the Bamenda Mountain have been investigated to determine their sequences and
the prevailing environmentalconditions
which control their formation. Ten representative samples were obtained
fromtrenches, pits, and river and stream valleys in the study area. These
samples and their ashes were subsequently examined using X-ray fluorescence
spectrometry (XRF), inductively coupled plasma spectrometry (ICP), and X-ray
diffraction analysis (XRD). The geochemical results revealed that thelithophile,
chalcophile and siderophile elements were dominantly epigenetic in origin,
mainlyfrom detrital sources
supported by high silica and alumina concentrations in all the samples. The
mineral phases identified were quartz, kaolinite, illite, pyrite, hematite, and
minor phases of feldspars,pseudorutile. The relatively high silica (54.10 wt%)
and alumina contents (27.77 wt%) in thesesamples
can be explained by high detrital input during peat formation. The low contents
of MgO and CaO in the analysed samples agree very much with the continental
setting of the peat formating basin. A clayey microband derived from alkaline
volcanic ashes was identified in the lignite and the dominant composition of
these clayey microbands was mixed-layer clay minerals of illite and kaolinte,
which were interlayered with organic bands. The modes of occurrence of ash
bands indicated that the volcanic activities were characterized by multiple
eruptions, short time intervaland
small scale for each eruption during peat accumulation. The ratios of
redox-sensitive traceelement (V/Cr versus Ni/Co and V/V + Ni versus Ni/Co),
Sr/Ba, and major oxides ratio (CaO + MgO + Fe2O3)/(SiO2+ Al2O3) from
the analysed samples from Bali Nyonga indicate a terrestrial, reductive (oxic),
littoral to brackish water environmental conditions which are characteristics
of paludal-lacustrine basin that is filled by Tertiary volcanic materials.