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Search Results: 1 - 10 of 466886 matches for " Olivier A. Njoh "
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Aptian-Late Cenomanian Fluvio-Lacustrine Lithofacies and Palynomorphs from Mamfe Basin, Southwest Cameroon, West Africa  [PDF]
Olivier A. Njoh, Miriam B. Nforsi, Junie N. Datcheu
International Journal of Geosciences (IJG) , 2015, DOI: 10.4236/ijg.2015.67064
Abstract: The sedimentary sequences in the Mamfe Basin are generally thought of as continental (fluvio-lacustrine) in origin. But the wide spread occurrence of salt springs and salt accumulations and in places gypsum, often puts to question the exclusive continentality throughout this basin’s history. The sequences studied portray a wide range of complex lithologies and lithofacies relationships and include basal and intra-formational conglomerates, sandstones, shales, carbonaceous, carbonate and halite facies respectively. All these are well exposed at several outcrop sections distributed all over the basin with some measuring up to and above 30 m in height.Sedimentary structures include: parallel aligned imbricated prismatic pebbles, plannar to trough-cross stratifications, fining upward grain size distribution and thin frequently alternating sandstone-shale beds. Palynological data have been obtained for the first time from the shally and carbonate intervals and integrated with five lithofacies associations, permitting the determination of the ages and paleo environmental reconstruction. The palynomorphs are characterized by pteridophytic spores dominated byCicatricosisporitessp.,Cyathiditessp. andDeltoidsporasp., pollen grains include gymnosperms dominated byClassopollis annulatus
Shallow Marine Cretaceous Sequences and Petroleum Geology of the Onshore Portion Rio del Rey Basin, Cameroon, Gulf of Guinea  [PDF]
Olivier Anoh Njoh, Agbor Junior Taku
Open Journal of Marine Science (OJMS) , 2016, DOI: 10.4236/ojms.2016.62014
Abstract: Extensive thickly folded sedimentary sequences are exposed onshore of theRio del ReyBasin contrary to previous reports of their rarity. Shales predominate, frequently intercalated by marlstones, sandstones, mudstones, limestones and marls and have been intruded in places by volcanic rocks of the Cameroon Volcanic Line (CVL). An integration of lithostratigraphic, paleontologic, granulometric and petrographic data generated from field and laboratory studies, permitted the identification of eleven (11) lithofacies which were subsequently grouped into three facies associations to facilitate the reconstruction of the paleo-depositional environment. Graphic logs constructed from the different outcrops studied revealed general coarsening upward sequences. Mega body fossils recovered from these sediments include severely altered, ferruginized fish and turtle-like heads, bivalve shells and moulds. Two bivalve taxa were identified:Exogyra ponderosa(Roemer) and members of theVenericardiinaesub-family. Textural and mineralogical details were obtained from granulometric and thin sections (microscopy). Interpretation of these data inferred an open relatively deeper marine, probably middle neritic to near shore transitionalintertidal environments into which these sediments previously dated as Lower to Upper Cretaceouswere deposited. Elements of a possible petroleum system: source and reservoir rocks, migratory pathways and
Carbonate Enrichment in Volcanic Debris and Its Relationship with Carbonate Dissolution Signatures of Springs in the Sabga-Bamessing, North West, Cameroon  [PDF]
Raymond Beri Verla, Germain M. M. Mboudou, Olivier Njoh, Gilles Nyuyki Ngoran, Aloysius Ngambu Afahnwie
International Journal of Geosciences (IJG) , 2014, DOI: 10.4236/ijg.2014.51012
Abstract:

Sabga-Bamessing is a part of the Bamenda Mountains, an extinct volcanic center of the West Cameroon Highlands along the Cameroon Volcanic Line (CVL). The pristine volcanic rocks of the Sabga area are alkali mafic to felsic (basanites, phonolites, trachytes and rhyolites). Some weathered sections of a heterolithologic debris flow with a suppositious primary chemistry of the original volcanic rocks prior to weathering have shown significant calcium carbonate enrichment. CaO and LOI values of up 61.31% and 41.72% respectively show corresponding enrichment of 16.54 and 10.88, when compared with average fresh volcanic rocks. Na+ normalized molar ratios computed from the chemistry of springs and rivers show carbonate dissolution signature which is contrary to silicate dissolution expected in acid volcanic rocks. Saturation indices (SI) calculated with PHREEQC reveal that brackish to saline springs are supersaturated with Calcite (CaCO3), Aragonite (CaCO3), Dolomite (CaMg(CO3)2 and Hydroxyl apatite (Ca5(PO4)3OH). Recharging contributions to spring water chemistry deviate from those produced by rock weathering, precipitation and evaporation/crystallization. An enrichment process

Characterization of Alluvial Gold Bearing Sediments of Betare Oya District-East Cameroon, Implication for Gold Exploration and Recovery  [PDF]
Germain Marie Monespérance Mboudou, Kennedy Folepai Fozao, Olivier Annoh Njoh, Christopher Mbaringong Agyingi
Open Journal of Geology (OJG) , 2017, DOI: 10.4236/ojg.2017.711115
Abstract: Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional conditions revealed a characteristic fining upward sequence in all the sections of 08 Au-pits within the Betare Oya basin. A typical profile is 2.5 to 4.5 m thick and is composed of a 30 to 50 cm organic topsoil layer, underlain by a 1.5 m thick reddish brownish gold free saprolite, which is underlain by 1.5 m sandy section. From litho-stratigraphic investigations and grain size analysis results a quartz dominated gravelly 1.4 m thick layer consisting in boulders (275 mm), cobbles (2-<20 mm) and subrounded pebbles (28 - 38 mm) mixed with sand grains (0.9 - 1.5 mm) and silt (0.01 - 0.02 mm). Pyrite, chalcopyrite and arsenopyrite are minor minerals and could be referred as to Au pathfinders (As, Fe, Cu). This layer overlays paleo-Proterozoic basement rocks (Nyong series) and is overlain by a poorly sorted sandy layer containing rounded whitish quartz grains and plagioclase fractions (Ca, Na), minor silts (0.02 - 0.2 mm), gravel and feldspar (K) leached from granitic plutons along shear zones in the area. The saprolite horizon overlaying the sandy layer derives from weathering and leaching of basement rocks under warm-humid climatic conditions. From gold grain count, the gravelly layer is the main productive horizon. Its upper layer (0.5 m) yields 02 Au grains per Kg of sampled materials while the 1 m-tick lower layer contains up to 34 Au-grains per sample and 13 g rains in 1 Kg of sampled materials. The sandy layer follows with averagely 02 Au grains per Kg as indication of partial leaching of primary mineralized rocks. Au concentration at depth (sandy and gravelly layers) is due to physical and chemical remobilization of Au in the secondary environment of deposition. Au is lithologically controlled and could be an important exploration factor in the study area. The calculated aspect ratios for pebbles from the gravelly and sandy layers disclosed two polynomial trends: 1) y = 0.0148x2 + 1.2187x + 2.0344, R2 = 0.6929 (sandy layer); 2) y = 0.0617x2 + 1.0849x + 0.8097, R2 = 0.8694 (gravelly layer); and y > R2 is satisfied in both cases. This implies that Au recovery from these layers could be effective
Comparison of Physicochemical, Organoleptic and Nutritional Abilities of Eight Sweet Potato (Ipomoea batatas) Varieties  [PDF]
Emy Njoh Ellong, Corinne Billard, Sandra Adenet
Food and Nutrition Sciences (FNS) , 2014, DOI: 10.4236/fns.2014.52025
Abstract:

In Martinique (F.W.I.), biodiversity of vegetable varieties remain unexploited due to public unawareness or supply problems. To further enhance the sweet potato, physicochemical, sensory and nutritional characteristics of eight varieties of sweet potato were established. The eight sweet potatoes cultivars were noticeably diverse with phenotypic, sensory, physicochemical and nutritional characteristics which were very varied. The eight cultivars grown in Martinique were advantageously positioned in relation to the globally identified sweet potato, regarding fibre, starch, potassium, copper, vitamin B1, B3 and B9 contents. Compared to the ordinary potato, Martiniquan sweet potatoes have a much better nutritional potential. Energy value and vitamin C levels were twice as much as in normal potatoes. Martiniquan sweet potatoes cultivars were also richer in minerals and vitamins, with 2.7 times more vitamin B9 and 63 times more beta-carotene than the ordinary potato.

Physicochemical, Nutritional, Organoleptic Characteristics and Food Applications of Four Mango (Mangifera indica) Varieties  [PDF]
Emy Njoh Ellong, Sandra Adenet, Katia Rochefort
Food and Nutrition Sciences (FNS) , 2015, DOI: 10.4236/fns.2015.62025
Abstract: Physicochemical characteristics of four varieties of mango (Julie, Bassignac, Green and Moussache) from Martinique (F.W.I.) were examined at three ripening stages. All ripening protocols studied showed an evolution in parameters between the harvesting and the expandable stage. Fruit and pulp firmness, starch and vitamin C contents decreased whereas pulp pH and carotenoids content increased. Only fruit size and polyphenols content were the same during the ripening. Bassignac and Julie varieties were richer in vitamin C, polyphenols and carotenoids. Moussache variety was the most energetic with important carbohydrates content. The Green variety differed significantly with a light-coloured pulp, low fruity odour and mango flavour, and a specific slightly sweet, very sour, bitter and astringent taste. Moussache and Bassignac varieties had a very sweet taste unlike the Julie variety with a specific slightly sweeter taste. Different processing methods were tested for each variety. Mangoes technological ability processing had been validated.
Polyphenols, Carotenoids, Vitamin C Content in Tropical Fruits and Vegetables and Impact of Processing Methods  [PDF]
Emy Njoh Ellong, Corinne Billard, Sandra Adenet, Katia Rochefort
Food and Nutrition Sciences (FNS) , 2015, DOI: 10.4236/fns.2015.63030
Abstract: Thirty-five fruits and seventeen vegetables from Martinique were evaluated for total phenol content (TPC), Vitamin C and carotenoid content. TPC, Vitamin C and carotenoid contents ranged from 11.7 to 978.6 mg/100g, 0.1 to 2853.8 mg/100g and 9.7 to 9269.7 μg/100g respectively. Fruits and vegetables from Martinique have equivalent or higher TPC, Vitamin C and carotenoid contents than fruits and vegetables from temperate climates. Cashew apple had high values for all three parameters (55.8 mg/100g of Vitamin C, 603 mg/100g of TPC and 924 μg/100g of carotenoids). Bassignac mango and mamey apple had the highest carotenoid contents, with 3800.3 and 3199.7 μg/100g respectively. Acerola had the highest Vitamin C and polyphenol contents with 2853.8 μg/100g and 727.4 mg/100g respectively. Pigeon peas had high values for all three parameters (569.2 mg/100g of Vitamin C, 978.6 mg/100g of TPC and 364.3 μg/100g of carotenoids). Pumpkin and watercress had the highest carotenoid content, with 9269.7 and 4339 μg/100g respectively. TPC, Vitamin C and carotenoid content were significantly impacted by processing techniques. TPC, Vitamin C and carotenoid contents decreased by up to 75.78%, 100% and 70.18% respectively, depending on the processing technique used.
The effect of crop residue layers on evapotranspiration, growth and yield of irrigated sugarcane
FC Olivier, A Singels
Water SA , 2012,
Abstract: A layer of harvest residues from the previous crop can reduce wasteful evaporation from the soil surface and thereby increase the efficiency of use of limited water resources for agricultural production. The practice of harvesting sugarcane green and leaving crop residues in the field, as opposed to burning the residue, has been re-adopted in many sugarcane industries worldwide. However, a better understanding of the dynamic impacts of residue layers on various aspects of the cropping system is required to (1) enable the formulation of sets of best management practices for specific production scenarios, and (2) promote the use of residue layers in areas where it is desirable and has not been adopted, such as irrigated sugarcane production in South Africa. The objective of this study, therefore, was to quantify the effect of 2 different types of residue layers on crop growth, cane yield and evapotranspiration of fully irrigated sugarcane. A layer of cane tops and dead leaves (Trash) and a layer of green tops (Tops) were applied to the soil surface of sugarcane crops (plant crop and first ratoon crop of variety N14) grown on lysimeters at Pongola, South Africa. Observations of crop growth (stalk population, stalk height, canopy cover), cane yield and evapotranspiration for these treatments were compared to that of a bare soil treatment. The data were also used to derive values of crop evaporation coefficients for different development phases and these were compared to FAO56 recommendations. Initial stalk population in the plant crop and radiation capture in the plant and ratoon crop were affected negatively by crop residue layers, but without significantly reducing final stalk population and cane yield. Peak stalk population occurred later in crops grown in residue layers, but peak and final stalk populations were unaffected. Evapotranspiration was reduced by both residue layers, mainly due to a slower developing canopy (reduced transpiration) and reduced evaporation from the soil, during the pre-canopy phases. Increased drainage was observed under residue layers, emphasising the importance of accurate irrigation scheduling to avoid water logging. The FAO56 methodology for calculating crop evaporation coefficient values for the initial, development and late season phases are supported by the results obtained here. Crop evaporation coefficient values were significantly reduced by residue layers. It is important that irrigation scheduling practices be adjusted to realise the potential water savings of sugarcane production systems that make use of residue layers. This study provides the information required to do that. The information could also be used to improve the ability of the crop models to accurately simulate crop growth and evapotranspiration in a residue layer cropping system.
L'Europe vue de la Lituanie.
Olivier Vila?a
EspacesTemps.net , 2003,
Abstract: L'Europe vue de la Lituanie : une représentation équilibrée mais arbitraire Cette carte de l'Europe est tirée d'un manuel scolaire lituanien contemporain, destiné aux élèves de huitième. Si elle ne surprend pas au premier coup d'oeil, c'est que sa simplicité, son harmonie graphique et notre propre expérience de la cartographie trahissent vraisemblablement notre sens critique. Pourtant, en y regardant de plus près, on se rend rapidement compte de ...
Les lignes de faille de l’Europe.
Olivier Vila?a
EspacesTemps.net , 2005,
Abstract: Lignes de faille de l'Europe, Norman Davies, 1996 La référence est un exercice essentiel, mais parfois délicat, de la pratique scientifique. Se référer à une carte peut poser problème dans la mesure où la carte a les défauts de ses avantages. En effet, elle ne correspond pas seulement à un outil de synthèse. C’est aussi un outil scientifique dont la lecture permet de valider ou d’infirmer des hypothèses, voire d’en imaginer de nouvelles. Cette puissance lui a d’ailleurs ...
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