The Importance of Diagenetic Processes in Sandstones Facies of the Hamakoussou Sedimentary Basin in North Cameroon: Influence on Reservoir Quality.

Published studies in the Hamakoussou reservoir sandstones are very few and the characterization of the reservoir quality including diagenesis is unknown. In this paper, after lithological reports, classical petrographic techniques have been used to study the diagenesis and reservoir quality of the Hamakoussou sandstones: Diagenetic processes within and around detrital grains show that early cementation by calcite come from volcanic veins and late cementation originating from silicification. Diagenetic phenomena (early cementation, compaction, fracturation and late cementation) show that these sandstones have a low porosity due to the blockage of intergranular pore spaces by cement. Intense volcanic activity associated with the circulation of fluids (silica and calcite) as well as the dissolution along the contacts of quartz grains are the principal sources of early and late cements which are responsible for the decrease in porosity observed in these sandstones. The immediate consequence is the sudden drying up of boreholes drilled for water supply

First palynostratigraphical evidence for a Late Eocene to Early Miocene age of the volcano-sedimentary series of Dschang, western part of Cameroon and its implications for the interpretation of palaeoenvironment

International audienceThe volcano-sedimentary infill of the Dschang basin in the Western part of Cameroon is poorly known. The present study provides the first biostratigraphical data of the volcano-sedimentary sequence and allows constraining the age and the position of this basin within the regional context of Central Africa. The studied sequence is composed of three depositional units. The first unit is a fining-upwards sequence of coarse-grained sandstone that gets finer towards the top, passing to thick layers of fossiliferous claystone. The second unit is strongly affected by volcanic activity and consists of a volcano-sedimentary sequence. The third unit is marked by basaltic volcanism and covers the series. Diverse and well-preserved palynomorphs were recovered and are used to provide valuable information for age determination of the Dschang volcano-sedimentary sequence, namely to be of late Eocene- Early Miocene age. The recovered spores, pollen, green algae and fungal remains from the bottom of the sequence include Bombacidites spp., Clavainaperturites cf. clavatus, Crototricolpites sp., Perfotricolpites digitatus, Proteacidites spp., Psilastephanocolporites minor, Psilastephanocolporites spp., Retitrescolpites spp., Retitricolporites irregularis, Retitricolporites spp., Retitriporites sp., Spirosyncolpites bruni (probably synonymous to Spirosyncolpites spiralis), Striatopollis bellus, (considered synonymous to Striatopollis catatumbus), Striatopollis sp., Tetracolporites quadratus, Tetratricolporites sp., ?Verrutricolporites rotundiporis, Cyathidites sp., Laevigatosporites spp., Polypodiaceoisporites spp., Verrucatosporites usmensis, Verrucatosporites spp., Botryococcus sp., Tasmanites sp., and fungal remains.The samples are assigned to the Verrucatosporites usmensis Zone of Salard-Cheboldaeff (1979). The palynological assemblages are similar to those of other Late Eocene to Early Miocene palynological records from the West, Central and Northern African basins. Study of the organic matter by pyrolysis Rock-Eval 6 (Types I, II and III), the sedimentological setting, the palynofacies and the palynomorph assemblages show evidences of tidal influence (presence of the prasinophyte Tasmanites) in an active continental margin (semi-arid to humid lacustrine depositional environment). The Ngoua sedimentary sequence is fluvio-lacustrine, and believed to have witnessed some occasional marine incursions possibly during the opening of the Central Atlantic Ocean (CAO) and strongly disturbed later by intense volcanic activity

Hydrocarbon potential, palynology and palynofacies of four sedimentary basins in the Benue Trough, northern Cameroon

Organic geochemical, palynological and palynofacies analyses were carried out on 79 selected samples from four sedimentary basins (Mayo-Rey, Mayo-Oulo-Lere, Hamakoussou and Benue) in northern Cameroon. Rock-Eval pyrolysis and Total Organic Carbon results indicate that most of the samples of the studied basins are thermally immature to mature. The organic matter consists of terrestrial components (peat, lignite, bituminous coal, and anthracite) associated with organic matter of marine origin. Based on the appraisal of multiple parameters: Total Organic Carbon (TOC), maximum Temperature (T-max), Hydrogen Index (HI), Oxygen Index (OI) and Production Index (PI), some samples are organically rich both in oil and/or gas-prone kerogen Type-II, II/III and III. The source rock quality ranges from poor to very good. The source material is composed of both algae and higher plants. Samples from these basins yielded palynological residue composed of translucent and opaque phytoclasts, Amorphous Organic Matter (AOM), fungal remains, algal cysts pollen and pteridophyte spores. Abundance and diversity of the palynomorphs overall low and include Monoporopollenites annulatus (¼ Monoporites annulatus), indeterminate periporate pollen, indeterminate tetracolporate pollen, indeterminate tricolporate pollen, indeterminate triporate pollen, indeterminate trilete spores, Polypodiaceoisporites spp., Biporipsilonites sp., Rhizophagites sp., Striadiporites sp., Botryococcus sp. (colonial, freshwater green algae), and Chomotriletes minor (cyst of zygnematalean freshwater green algae). Age assigned confidently for all these basins the palynological data except for one sample of Hamakoussou that can be dated as Early to Mid- Cretaceous in age. Callialasporites dampieri, Classopollis spp., Eucommiidites spp. and Araucariacites australis indicate, an Aptian to Cenomanian age. The other pollen and spores recovered may indicate a Tertiary or younger age (especially Monoporopollenites annulatus), or have arisen from modern contamination. Geochemical data show that sediments are wackes, arkose, iron-sandstone and ironshale. The Chemical Index of Alteration (CIA-K) is low moderate to high, suggesting a shorter exposure time and fast erosion and transport. The studied sequences cover various depositional settings ranging from wetlands to dry environment inside island arc, passive margin or active continental margin. This study reveals new data and the economic potential of this part of Cameroon