Geology, Palaeodeposition and the Involvement of Rhyolite Melts in the Petrogenesis of the Tabenken Coal Seam in the North West Region of Cameroon

The discovery of patches of a coal deposit and other associated sedimentary and volcanic rocks in Tabenken North West Cameroon has raised the question of the geology and palaeoenvironment of that area. This Region, which is predominantly characterized by a granitoid basement of Precambrian age is in most parts overlain by Cenozoic basalts, hawaite, mugearite, trachyte and rhyolites. Volcanic outpours modified the geomorphology of the area into a series of hills and valleys. We investigated the geological setting in view of reconstituting the palaeodepositional environment of the Tabenken Coal Seam. Field studies show that the coal occurs in form of inclusions within sandstones, high grade coal bed, massive beds exposed by landslides and in alkali rhyolites. The results of Ultimate analyses of the coal indicate bituminous coal with 58% Carbon, sulfur content as low as 0.12% and ash content of 17%. The occurrence of a well stratified dark volcanic ash bed in the area is interpreted to be an interactive product of the explosive volcanic activity and weathering. Field examination of the area suggests that it was a micro-continental sedimentary palaeo-basin which was later infilled with Cenozoic volcanic outpours which probably modified the chemistry of the coal to meta-anthracites. The actual ages of the coal as well as the associated sedimentary units have not been established, meanwhile, the volcanism started some 31 ma ago.

Organic Matter Characterization and Palynological Evidence of Mid-Ordovician to Pennsylvanian Age of the Tabenken Coal,Northwest Cameroon

In this work,we intend to investigate the kerogen composition of the Tabenken coal hence,its palaeo-depositional environment and age.Tabenken is one of the three areas in the continental sectors of the CVL(Cameroon Volcanic Line)where coal occurs in between a granitic basement and volcanic outpours.Samples of coal from this seam were studied to determine the organic matter richness,maturity,depositional environment and its age through organic geochemical techniques such as Rock-Eval pyrolysis and palynological studies.HI(Hydrogen Index)obtained is less than 200 mgHC/gTOC for most of the samples indicating Type III kerogen for these samples(gas prone)and terrestrial source of the original peat-forming organic matter.One sample presents a HI of 462 mgHC/gTOC indicating organic matter type II,prone to producing oil.Palynological studies reveal the presence of hydrogen-rich AOM(Amorphous Organic Matter)indicating preservation under dysoxic-anoxic conditions.High values of TOC ranging from 0.29 to 1.98 are suggestive of AOM of terrestrial origin.The remarkable absence of pollen suggestive of deposition before the Pennsylvanian during which the earliest forms of flowering plants first appeared displays a relative abundance of spores in the organic residue suggestive of deposition from the mid-Ordovician.Careful interpretation of palynological data suggests the coal was laid down from the mid-Ordovician to the Pennsylvanian age.