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Los datos de alta resolución aeronáutica (HRAM) de la costa de Abigi-Ijebu en la parte oriental de la cuenca Dahomey en el sudoeste de Nigeria se filtraron, transformaron, mejoraron, analizaron e interpretaron en términos de estructuras, geometría del basamento y espesor sedimentario, para evaluar el potencial de prospección petrolera de este sector de la cuenca Dahomey, así como proporcionar información relevante que podría apoyar la campaña de exploración de hidrocarburos del descuidado brazo oriental de la cuenca Dahomey, que recientemente ha demostrado ser prolífico con el descubrimiento de yacimientos de petróleo Aje y Ogo en la parte costera de la cuenca . Los datos de HRAM se filtraron para eliminar el ruido cultural y de fondo, continuaron hacia arriba para suprimir los efectos de fuentes poco profundas y mejorar el efecto de roca del sótano que emana de fuentes relativamente más profundas. Los datos también se redujeron al polo a baja latitud para simplificar las anomalías magnéticas y para enfocar los picos de las anomalías positivamente simétricas con respecto a las fuentes geológicas correspondientes. Se aplicaron filtros derivados para detectar y mejorar las firmas magnéticas alineadas de forma preferencial que reflejan el marco estructural del área de estudio. El análisis espectral radial y las técnicas de ponderación de profundidad de Euler se emplearon para determinar la profundidad de las fuentes magnéticas que generaron la topografía del basamento y, por lo tanto, el espesor de las rocas sedimentarias que cubren las rocas cristalinas. Los derivados y filtros derivados de inclinación mejoraron y delinearon varias estructuras regionales lineales, algunas de las cuales tienen más de 15 km de longitud y una tendencia principalmente a lo largo de la dirección NE - SW. El análisis espectral y las soluciones de ponderación de profundidad de deconvolución de Euler 3D indican que la profundidad en la parte superior de las anomalías magnéticas varía desde alrededor de 100 m por encima del dato de referencia de Minna hasta más de 2,0 km por debajo del dato. La topografía del basamento revelada por las parcelas de solución de Euler indica rocas del basamento de la corteza gradual y suavemente deprimidas que pueden ser ayudadas por fallas regionales que gradualmente descendieron o deprimieron las rocas de la corteza hacia el sur para aumentar el acomodo de los sedimentos. Por lo tanto, esto sugiere un aumento en el potencial de prospección de hidrocarburos hacia el sur del área de estudio, especialmente en el mar abierto y más profundamente en el Océano Atlántico. doi: https://doi.org/10.22201/igeof.00167169p.2019.58.4.2057

Very Low Frequency Electromagnetic (VLF-EM) and hydrogeochemical studies have been integrated to measure ground conductivity and also determine the concentration of leachate derived contaminants in the groundwater around Abeku dumpsite in Ibadan, southwest Nigeria. Ten (10) VLFEM profiles were occupied within and around the dumpsite fence. Water sample from wells were also analyzed to determine the concentration of pollutants in the study area. Qualitative interpretations of VLF-EM results indicate relatively high ground conductivity within the dumpsite, which decreases away from the actual waste dump phase of the dumpsite. Ground conductivity is relatively higher in the south and east of the dumpsite which are located downhill of the groundwater hydrostatic head when compared with the north and west of the study area situated uphill of hydraulic gradient. Hydrogeochemical analyses present NO3−, SO42− and PO42− ions concentration in the range of 9.24 – 13.64 mg/L, 3 – 12 mg/L and 0.33 – 1.07 mg/L respectively. The SO42− and PO42− ions concentrations are within permissible limits, while the NO3− ion concentration is slightly above the Federal Ministry of Environment’s standard for potable water in Nigeria.

High-resolution airborne-magnetic data acquired over the Yola extension of the northern Benue Trough, northeastern Nigeria, were analyzed to delineate rock distribution, define basement geometry, determine sedimentary thicknesses, and highlight structural framework among others for the hydrocarbon prospect evaluation of sub-basins in the extension. Filtered and refined magnetic intensity data were subjected to Analytic Signal, Horizontal and Vertical Tilt Derivatives and Euler deconvolution depth weighting analyses to enhance various geological features requisite for petroleum prospect evaluation. Sedimentary rock units flanked the northeast and south widely occur in the central part with volcanic rock intrusions delineated within the sedimentary terrain. Extracted lineaments (less than 5 km and up to 45 km) were observed to dominantly follow the established Benue Trough and Yola sub-basin evolutionary trend along the NEeSW and ESEeWNW directions, respectively. Three prominent subbasins with sedimentary thicknesses in excess of 3 km and width of more than 60 km, separated by basement highs of mostly volcanic intrusions origin, were identified. The occurrence of relatively thick and extensive sub-basins which are underlain by structurally active basement rocks suggests relatively high geothermal gradient for generation of hydrocarbon from organic matter rich source rocks while the generated oil and gas are preserved within intra-sedimentary structural traps created when the basement fractures were reactivated. [ABSTRACT FROM AUTHOR]

The petroleum prospect of the Nigerian sector of the Dahomey Basin is evaluated with high resolution aeromagnetic data. The aim is to delineate the basin topography, deduce the presence of sufficient thickness of sediments and identify the presence of subsurface structures that can form hydrocarbon trapping mechanisms. The total field data was subjected to noise filtering, anomaly transformation and enhancement, with a view of performing geologic discrimination of the subsurface, map rock lineaments and determine basement depths. Radially averaged power spectrum was used to evaluate the noise-signal amplitude-frequency range of the data, which assisted with noise and regional field removal with Butterworth filter. Data processing also include removal of the IGRF field, downward continuation and reduction to pole. Generation of the derivatives, analytic signal, Euler depth solution and lineament maps form the basis of geological and structural mapping, including evaluation of basin architecture. Depth estimates from the total field power spectrum range from less than 1 km to 12 km, while 3D Euler Deconvolution indicates depth to basement range from < 500 m in the northern zone and up to 6000 m in the southern region, with a NE-SW trending relatively shallow region of maximum depth of 1500 m separating the western Dahomey Basin from the Eastern Niger Delta. The presence of up to 3000 m thickness of sediments and presence of fractures whose reactivation can form traps, suggest the potential for untapped resources in the unexplored parts of the Nigerian sector of the Dahomey Basin. [ABSTRACT FROM AUTHOR]

The airborne Time-domain electromagnetic data acquired over the Ilesha Schist Belt in southwestern Nigeria were filtered, enhanced and analysed to generate ground conductivity responses at different time gates and employed to characterise the subsurface in terms of rock distribution, structural framework as well as evaluate the gold and base metal mineralisation potential of the region. The near-surface sensitive early time gate conductivity responses (EMZ1 – EMZ3) indicate relatively high subsurface conductivity distribution (60–120 mS/m) in amphibole schist and pegmatite terrain in the west while medium to low-conductivity (<5 mS/m) values were recorded in the east underlain by granitic rocks. Major and minor linear/sub-linear conductive features having conductivity in excess of 2 mS/m and trending NE-SW, NNE-SSW, NNW-SSE and ENE-WSW directions were delineated on the mid conductivity time gate responses (EMZ3 – EMZ5). One of which presents geometry and pattern consistent with the well-reported Ifewara – Iwaraja fault system that runs through the entire Ilesha Schist Belt. Very high anomalous conductivity (160–300 mS/m) responses at late conductivity time gates (EMZ10 – EMZ13) with characteristic long decay curves were obtained over isolated zones, especially along fractures and veins suggesting the occurrence of structurally controlled gold and base metal mineralisation. [ABSTRACT FROM AUTHOR]