Aeromagnetic data over the Mamfe Basin have been processed. A regional magnetic gridded dataset was obtained from the Total Magnetic Intensity (TMI) data grid using a 3 × 3 convolution (Hanning) filter to remove ...Aeromagnetic data over the Mamfe Basin have been processed. A regional magnetic gridded dataset was obtained from the Total Magnetic Intensity (TMI) data grid using a 3 × 3 convolution (Hanning) filter to remove regional trends. Major similarities in magnetic field orientation and intensities were observed at identical locations on both the regional and TMI data grids. From the regional and TMI gridded datasets, the residual dataset was generated which represents the very shallow geological features of the basin. Processing this residual data grid using the Source Parameter Imaging (SPI) for magnetic depth suggests that the estimated depths to magnetic sources in the basin range from about 271 m to 3552 m. The highest depths are located in two main locations somewhere around the central portion of the study area which correspond to the area with positive magnetic susceptibilities, as well as the areas extending outwards across the eastern boundary of the study area. Shallow magnetic depths are prominent towards the NW portion of the basin and also correspond to areas of negative magnetic susceptibilities. The basin generally exhibits a variation in depth of magnetic sources with high, average and shallow depths. The presence of intrusive igneous rocks was also observed in this basin. This characteristic is a pointer to the existence of geologic resources of interest for exploration in the basin.展开更多
The Mamfe Basin has been the subject of many studies,but some debates persist,especially concerning the stratigraphic nomenclature,corundum origin,and marine transgression.The aims of this work are(1)to propose a new ...The Mamfe Basin has been the subject of many studies,but some debates persist,especially concerning the stratigraphic nomenclature,corundum origin,and marine transgression.The aims of this work are(1)to propose a new lithostratigraphic nomenclature of the Mamfe Basin formation based on new field observations,(2)to determine the source rock distribution and the origin of gem deposits and(3)to correlate the Cameroon section of the Mamfe Basin with the Nigerian deposits.The main results show that the name Manyu River Group is more appropriate as the Manyu River crosses all the facies in the Mamfe sedimentary Basin belonging to the Manyu Division.According to the facies analysis,the age of deposition,the mineralogic and geochemical data such as the V vs.Al2O3andΣREE vs.Al_(2)O_(3),TiO_(2)MgO,Na_(2)O,P_(2)O_(5),and CaO diagrams,this Group is composed of at least five Formations,including four Cretaceous Formations,from bottom to top:the Etoko Formation(alluvial and fluvial channel to fluvio-lacustrine deposits),the Nfaitok Formation(lagoonal deposits),the Bachuo Ntai Formation(fluvial braided channels or fluvio-deltaic environment)and the Eyumojock/NsanaragatiFormation(fluvio-lacustrine deposits)and the new Cenozoic Formation named Bakebe Formation(fluvio-lacustrine deposits).The gem minerals such as corundum,rutile,or tourmaline in the Cretaceous deposits of the Mamfe Basin are mainly detrital as indicated by the presence of worn shapes and fragments of these minerals.The presence of sapphire in the AlboCenomanian deposits indicates a Precambrian age of the felsic source rock,likely the plutonic rocks such as granite or pegmatite as indicated by the abundance of tourmaline and high LREE/HREE ratios(14.81–34.29)and slightly negative and positive Eu anomalies(0.85–1.15).This marine incursion in the Mamfe Basin was probably from West Nigeria,according to the geographic location of the Mamfe Basin and the general palaeogeographic evolution of the Benue Trough.展开更多
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 put...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 by?Cicatricosisporites?sp.,Cyathidites?sp. and?Deltoidspora?sp., pollen grains include gymnosperms dominated by?Classopollis annulatus?and?Classopollis todosus?and angiosperms represented by?Retitricolpites?sp. and?Retimoncolpites?sp., fungal remains include some hyphae and?Fusiformisporites?sp. Only a few dinoflagellate cysts dominantly?Spiniferites?were encountered at Nfaitok outcrop, suggesting a proximal sea water influence. A fluvial, lacustrine-deltaic and an anoxic deep bottom lake setting sub-environments were reconstructed with no marine strata encountered. The brines are here suggested to have originated from sea water splay over a barrier and complimented by the chemistry of the drained surrounding country rocks. The palynomorph assemblage suggests an Aptian-Turonian age for the studied sequences and a chronostratigraphic sequence in which the Nfaitok and Satom Bridge units are both Late Cenomanian-Turonian (lateral equivalents of each other) are younger and overlie the Aptian-Early-Cenomanian Okoyong sandstone unit.展开更多
Groundwater studies in parts of the Mamfe basin are sparse and the Mamfe area has the highest population density in the Mamfe basin. An in-depth study of groundwater rock interaction and groundwater quality is of vita...Groundwater studies in parts of the Mamfe basin are sparse and the Mamfe area has the highest population density in the Mamfe basin. An in-depth study of groundwater rock interaction and groundwater quality is of vital importance. This same part of the basin is the economic centre and as such development of businesses in this area requires knowledge of the groundwater quality. Therefore, this study was undertaken to determine the input of the rock formations on the groundwater solute chemistry and groundwater domestic-agro-industrial quality using hydrogeochemical tools and physicochemical parameters: Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters, in the rainy season, pH ranged from, 4.3 - 8.6;EC, 3 - 1348 μS/cm;Temperature, 24.4℃ - 30.1℃? andTDS, 2.01 - 903.16 mg/L and in the dry season, pH ranged from 5.5 - 9.3;EC, 6 - 994 μS/cm;Temperature, 25℃?- 38.6℃?andTDS, 4.02 - 632.48 mg/L. Forty groundwater samples: 20 per season, wet and dry were analysed. The major ions fell below WHO acceptable limits for both seasons. The sequences of abundance of major ions were: Ca2+ > K+ > Mg2+ > ?> Na+, Cl- > ?> ?> ?> NO3 in wet season and Ca2+ > Mg2+ > K+ > Na+, ?> Cl- > ?> ?> ?in dry season. Ion-exchange, simple dissolution and uncommon dissolution processes determined groundwater character. Groundwater ionic content was as a result of ion exchange from rock-weathering. Water types are: CaSO4 and MgHCO3 in both seasons. Hydrogeochemical facies are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3. SAR for wet season 0.05 - 0.06 and dry season 0.00 - 0.05, %Na wet season 3.64 - 16.59 and dry season 1.22 - 10.97, KR wet season 0.01 - 0.02 and 0.00 <span style="font-size:10pt;展开更多
Backscattered electron BSE-CL images,U-Th abundance,and U-Pb ages were obtained for zircons from the Nkogho granitic basement rocks cropping out in the Mamfe Basin(SW Cameroon).These data are used to characterize and ...Backscattered electron BSE-CL images,U-Th abundance,and U-Pb ages were obtained for zircons from the Nkogho granitic basement rocks cropping out in the Mamfe Basin(SW Cameroon).These data are used to characterize and classify each zircon,elucidate their geochemical traits.They were also used to formulate a model of their host composition to ascertain the source,and document any preserved postemplacement events.These zircons mainly form long to short prisms that are pyramidal to dipyramidal in shape.They typically exhibit complex oscillatory growth zoning,as well as exhibit sector zoning.These features are mainly compatible with igneous zircons,although a few examples have metamorphic signatures.The U(30 ppm–6380 ppm),Th(4 ppm–1280 ppm),and Pb(12 ppm–648 ppm)contents show core to rim variations with most values fall within the range of crustal granitic zircons.The Th/U ratios(0.08–1.23),with core to rim differences mainly encompass values typical of magmatic zircons with a few values characterizing metamorphic zircons that grew in equilibrium with an anatectic melt.The U-Pb ages(108.4±1.7 to 988.4±19.0 Ma)with some core and rim age differences date Early Neoproterozoic,Cryogenian–Ediacarian,Early Cambrian–Ordovician,Devonian–Carboniferous,and Aptian–Albian events.The arc-like Nkogho I-type granitoid crystallized from granitic magma during Cryogenian to Ediacarian times and was later affected by post-Ediacarian Cambrian to Albian magmatic events.Aptian–Albian ages probably reflect opening of the Mamfe Basin.展开更多
文摘Aeromagnetic data over the Mamfe Basin have been processed. A regional magnetic gridded dataset was obtained from the Total Magnetic Intensity (TMI) data grid using a 3 × 3 convolution (Hanning) filter to remove regional trends. Major similarities in magnetic field orientation and intensities were observed at identical locations on both the regional and TMI data grids. From the regional and TMI gridded datasets, the residual dataset was generated which represents the very shallow geological features of the basin. Processing this residual data grid using the Source Parameter Imaging (SPI) for magnetic depth suggests that the estimated depths to magnetic sources in the basin range from about 271 m to 3552 m. The highest depths are located in two main locations somewhere around the central portion of the study area which correspond to the area with positive magnetic susceptibilities, as well as the areas extending outwards across the eastern boundary of the study area. Shallow magnetic depths are prominent towards the NW portion of the basin and also correspond to areas of negative magnetic susceptibilities. The basin generally exhibits a variation in depth of magnetic sources with high, average and shallow depths. The presence of intrusive igneous rocks was also observed in this basin. This characteristic is a pointer to the existence of geologic resources of interest for exploration in the basin.
文摘The Mamfe Basin has been the subject of many studies,but some debates persist,especially concerning the stratigraphic nomenclature,corundum origin,and marine transgression.The aims of this work are(1)to propose a new lithostratigraphic nomenclature of the Mamfe Basin formation based on new field observations,(2)to determine the source rock distribution and the origin of gem deposits and(3)to correlate the Cameroon section of the Mamfe Basin with the Nigerian deposits.The main results show that the name Manyu River Group is more appropriate as the Manyu River crosses all the facies in the Mamfe sedimentary Basin belonging to the Manyu Division.According to the facies analysis,the age of deposition,the mineralogic and geochemical data such as the V vs.Al2O3andΣREE vs.Al_(2)O_(3),TiO_(2)MgO,Na_(2)O,P_(2)O_(5),and CaO diagrams,this Group is composed of at least five Formations,including four Cretaceous Formations,from bottom to top:the Etoko Formation(alluvial and fluvial channel to fluvio-lacustrine deposits),the Nfaitok Formation(lagoonal deposits),the Bachuo Ntai Formation(fluvial braided channels or fluvio-deltaic environment)and the Eyumojock/NsanaragatiFormation(fluvio-lacustrine deposits)and the new Cenozoic Formation named Bakebe Formation(fluvio-lacustrine deposits).The gem minerals such as corundum,rutile,or tourmaline in the Cretaceous deposits of the Mamfe Basin are mainly detrital as indicated by the presence of worn shapes and fragments of these minerals.The presence of sapphire in the AlboCenomanian deposits indicates a Precambrian age of the felsic source rock,likely the plutonic rocks such as granite or pegmatite as indicated by the abundance of tourmaline and high LREE/HREE ratios(14.81–34.29)and slightly negative and positive Eu anomalies(0.85–1.15).This marine incursion in the Mamfe Basin was probably from West Nigeria,according to the geographic location of the Mamfe Basin and the general palaeogeographic evolution of the Benue Trough.
文摘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 by?Cicatricosisporites?sp.,Cyathidites?sp. and?Deltoidspora?sp., pollen grains include gymnosperms dominated by?Classopollis annulatus?and?Classopollis todosus?and angiosperms represented by?Retitricolpites?sp. and?Retimoncolpites?sp., fungal remains include some hyphae and?Fusiformisporites?sp. Only a few dinoflagellate cysts dominantly?Spiniferites?were encountered at Nfaitok outcrop, suggesting a proximal sea water influence. A fluvial, lacustrine-deltaic and an anoxic deep bottom lake setting sub-environments were reconstructed with no marine strata encountered. The brines are here suggested to have originated from sea water splay over a barrier and complimented by the chemistry of the drained surrounding country rocks. The palynomorph assemblage suggests an Aptian-Turonian age for the studied sequences and a chronostratigraphic sequence in which the Nfaitok and Satom Bridge units are both Late Cenomanian-Turonian (lateral equivalents of each other) are younger and overlie the Aptian-Early-Cenomanian Okoyong sandstone unit.
文摘Groundwater studies in parts of the Mamfe basin are sparse and the Mamfe area has the highest population density in the Mamfe basin. An in-depth study of groundwater rock interaction and groundwater quality is of vital importance. This same part of the basin is the economic centre and as such development of businesses in this area requires knowledge of the groundwater quality. Therefore, this study was undertaken to determine the input of the rock formations on the groundwater solute chemistry and groundwater domestic-agro-industrial quality using hydrogeochemical tools and physicochemical parameters: Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters, in the rainy season, pH ranged from, 4.3 - 8.6;EC, 3 - 1348 μS/cm;Temperature, 24.4℃ - 30.1℃? andTDS, 2.01 - 903.16 mg/L and in the dry season, pH ranged from 5.5 - 9.3;EC, 6 - 994 μS/cm;Temperature, 25℃?- 38.6℃?andTDS, 4.02 - 632.48 mg/L. Forty groundwater samples: 20 per season, wet and dry were analysed. The major ions fell below WHO acceptable limits for both seasons. The sequences of abundance of major ions were: Ca2+ > K+ > Mg2+ > ?> Na+, Cl- > ?> ?> ?> NO3 in wet season and Ca2+ > Mg2+ > K+ > Na+, ?> Cl- > ?> ?> ?in dry season. Ion-exchange, simple dissolution and uncommon dissolution processes determined groundwater character. Groundwater ionic content was as a result of ion exchange from rock-weathering. Water types are: CaSO4 and MgHCO3 in both seasons. Hydrogeochemical facies are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3. SAR for wet season 0.05 - 0.06 and dry season 0.00 - 0.05, %Na wet season 3.64 - 16.59 and dry season 1.22 - 10.97, KR wet season 0.01 - 0.02 and 0.00 <span style="font-size:10pt;
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)Discovery Grant to Prof.David R.Lentz(UNB)。
文摘Backscattered electron BSE-CL images,U-Th abundance,and U-Pb ages were obtained for zircons from the Nkogho granitic basement rocks cropping out in the Mamfe Basin(SW Cameroon).These data are used to characterize and classify each zircon,elucidate their geochemical traits.They were also used to formulate a model of their host composition to ascertain the source,and document any preserved postemplacement events.These zircons mainly form long to short prisms that are pyramidal to dipyramidal in shape.They typically exhibit complex oscillatory growth zoning,as well as exhibit sector zoning.These features are mainly compatible with igneous zircons,although a few examples have metamorphic signatures.The U(30 ppm–6380 ppm),Th(4 ppm–1280 ppm),and Pb(12 ppm–648 ppm)contents show core to rim variations with most values fall within the range of crustal granitic zircons.The Th/U ratios(0.08–1.23),with core to rim differences mainly encompass values typical of magmatic zircons with a few values characterizing metamorphic zircons that grew in equilibrium with an anatectic melt.The U-Pb ages(108.4±1.7 to 988.4±19.0 Ma)with some core and rim age differences date Early Neoproterozoic,Cryogenian–Ediacarian,Early Cambrian–Ordovician,Devonian–Carboniferous,and Aptian–Albian events.The arc-like Nkogho I-type granitoid crystallized from granitic magma during Cryogenian to Ediacarian times and was later affected by post-Ediacarian Cambrian to Albian magmatic events.Aptian–Albian ages probably reflect opening of the Mamfe Basin.
