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Tectonic structures controlling mineralization in some parts of Southeast Nigeria were evaluated using airborne potential field data. High- and low-frequency filters and depth determination tools were adopted to evaluate short- and long-wavelength anomalies, resolve the spatial spreading of igneous intrusions, depths to geologic sources and basin topography. The high-frequency results exhibited high concentration of short-wavelength anomalies in the Obudu Plateau and Ikom–Mamfe Rift. The underlying main tectonics of the area elucidated by the low-frequency results caused the widespread occurrences of short-wavelength geologic structures that are revealed by the high-frequency maps. The study area is characterized by comparatively thin (~ 13.0 to < 3000 m) sedimentation. The observed thin thickness is as a result of the massive Precambrian basement outcrops in some locations in the Obudu Plateau and the proliferation of igneous intrusions within this part of the Lower Benue Trough. The 2-D models showed the undulating nature of the underlying basin topography, the location of intrusions, domal structures and related normal faults. The locations and neighbourhood of intrusions and/or short-wavelength structures are viable sites for lead–zinc–barite, brine and metallogenic minerals. [ABSTRACT FROM AUTHOR]

2D electrical resistivity tomography (ERT) data inversion and ground penetrating radar (GPR) techniques were used to investigate a cave in New Netim area, southeastern Nigeria. The aim of the research was to apply the non-destructive geophysical techniques in delineating a cave in New Netim. The Wenner electrode configuration was used during the electrical resistivity tomography data acquisition while the common-offset mode was used in the ground penetrating radar scanning. The ERT inversion and GPR results quantitatively show strong contrast in electrical resistivity and dielectric permittivity between the host rock (i.e., limestone) and the void. The differences in the electrical properties and dielectric permittivities of the top loamy soils, weathered limestone and the host rock (i.e., Mfamosing limestone) observed, in contrast to the response from the void were explored. The two combined geophysical techniques with their inversion results gave a reliable near surface geologic model, where both methods show relatively good correlation with regards to delineating the depth to top of the cave (~2.7 m). The joint interpretation of the ERT and GPR was effective in reducing the uncertainty associated with geophysical methods used in locating cavities on a standalone basis. The low cost, fast, environmental friendly and high resolving abilities though at shallow depths of the ERT and GPR techniques have continued to favour their usage in resolving near surface environmental and engineering problems. Generally, caves provide important geotourism attraction sites, hence certain recommendations were put forward that can guide further studies, like the application of Steiner's geostatistical inversion techniques and other post-exploration development strategies. [ABSTRACT FROM AUTHOR]

The surface resistivity method was used to appraise the protectivity of hydrogeological units and corrosivity of the top soil in Obot Akara County, southern Nigeria. A total of 28 vertical electrical sounding (VES) was undertaken in the area using the Schlumberger electrode configuration. The results of the VES data interpretation reveal 3 to 4 geoelectric layers in the study area. The resistivity of the first layer interpreted as the Motley top soil ranges from 34.7 to 929.7 Ωm with a mean value of 381.1 Ωm. The third layer, with a resistivity range of 99.4 to 2716.7 Ωm, constitutes the aquifer unit in most communities in the area, with an average thickness of 58.3 m, while the fourth layer penetrated in most communities has a resistivity range of 216.1 to 1475.7 Ωm with a mean value of 657.5 Ωm. The longitudinal conductance and resistivity reflection coefficient of the aquifer protective layers vary from 0.04 to 0.76 mhos and − 0.74 to 0.93, respectively. Analysis of these results shows that 89.3% of the hydrogeological units in the area is weakly/poorly protected, 10.7% has moderate to good protection, while 85.7% of the top soil at the sounding stations is noncorrosive and 14.3% is slightly to moderately corrosive. The implication of these results is that most of the hydrogeological units in the area are likely prone to contamination in particular by some ferrugenized materials from the overlying layers. Also, underground metal storage tanks and galvanized and steel pipes can be buried in the topmost layer in most communities in the area without any risk of failure. Although these findings are very promising especially in groundwater management and exploitation in the area, hydrogeochemical and microbiological analyses of groundwater samples from available boreholes are recommended to corroborate the results. [ABSTRACT FROM AUTHOR]

High-resolution potential field data were used to the study of Calabar Flank. The study is aimed at mapping the tectono-sedimentary framework, and determining depth to basement of the area. The smooth magnetic/gravity curves obtained from the 2-D models reflect thick sedimentary series and deeply buried basement rocks with no significant post rift tectonic events. Also, the main basement structures (that is, the horst and graben) and associated normal fault blocks of the Calabar Flank were properly delineated. Thickness of sedimentary series in some locations in the study area was observed to be ~7000 m, and the stacked models showed that the sediment thicknesses dip gently in the southwesterly direction. The models, particularly the joint gravity and magnetic model, validate the extant conceptual geological model for the area. [ABSTRACT FROM AUTHOR]

Groundwater potential of some parts of Cross River State, Nigeria, was assessed involving vertical electrical sounding (VES) and high-resolution aeromagnetic methods (HRAM). The VES and HRAM dataset were used to delineate the hydro-lithostratigraphic units and map the spatial distributions of geologic structures, respectively. The electro-stratigraphic sections revealed the various hydro-lithostratigraphic units composed of fractured/weathered crystalline basement, sandstones, siltstones, sandy shales, and highly baked and fractured shales occurring at different depths. Generally, the unsaturated top layer is composed of shales, marl, clay, silt, gravel and lateritic materials with resistivity ranging from ~ 3.0 to ~ 550 Ω m. This layer is underlain by various aquifer units like sandstones, siltstones, fractured shales and limestone/marl, and fractured/weathered basement occurring at different depths (~ 30 to ≤ 100 m) as revealed by the electro-stratigraphic sections obtained in the study area. In the Calabar Flank (CF), Oban Massif (OM) and Ikom-Mamfe Embayment (IME), the apparent resistivity for these hydro-lithostratigraphic units varied between ~ 8.50 and ~ 59.50 Ω m, ~ 120.2 and ~ 1562.6 Ω m and ~ 30.8 and ~ 277.2 Ω m, respectively. The enhanced total magnetic intensity maps and source parameter imaging result showed that the OM and IME are characterized by high concentration of short-wavelength anomalies, while the CF is dominated by relatively undisturbed thick sedimentation (~ 6217 m). HRAM results show that such areas are predominated by geologic structures like faults, fractures, fissure, dyke swamps, etc. caused by tectonics. Such geologic structures create secondary porosity and enhance permeability. From all the results obtained, OM and IME represent areas with moderate groundwater potential. The CF dominated by argillites with no significant tectonic activity is observed to have low groundwater potential. [ABSTRACT FROM AUTHOR]

Three-dimensional models of petrophysical properties were constructed using stochastic methods to reduce ambiguities associated with estimates for which data is limited to well locations alone. The aim of this study is to define accurate and efficient petrophysical property models that best characterize reservoirs in the Niger Delta Basin at well locations and predicting their spatial continuities elsewhere within the field. Seismic data and well log data were employed in this study. Petrophysical properties estimated for both reservoirs range between 0.15 and 0.35 for porosity, 0.27 and 0.30 for water saturation, and 0.10 and 0.25 for shale volume. Variogram modelling and calculations were performed to guide the distribution of petrophysical properties outside wells, hence, extending their spatial variability in all directions. Transformation of pillar grids of reservoir properties using sequential Gaussian simulation with collocated cokriging algorithm yielded equiprobable petrophysical models. Uncertainties in petrophysical property predictions were performed and visualized based on three realizations generated for each property. The results obtained show reliable approximations of the geological continuity of petrophysical property estimates over the entire geospace. [ABSTRACT FROM AUTHOR]

The electrical resistivity technique which involved the Schlumberger depth sounding method and geochemical analyses of water samples collected from boreholes was used to investigate the suitability of groundwater aquifers in Abi for drinking and irrigation purposes. Fifty randomly located electrical resistivity data were collected, modeled, and interpreted after calibration with lithologic logs. Ten borehole water samples were collected and analysed to determine anion, cation concentrations and some physical and chemical parameters, such as water colour, temperature, total dissolved solids, and electrical conductivity. The results show that the lithostratigraphy of the study area is composed of sands, sandstones (fractured, consolidated and loosed), siltstones, shales (compacted and fractured) of the Asu River Group, Eze-Aku Formation which comprises the aquifer units, and the Nkporo Shale Formation. The aquifer conduits are known to be rich in silicate minerals, and the groundwater samples in some locations show a significant amount of Ca2+, Mg2+, and Na+. These cations balanced the consumption of H+ during the hydrolytic alteration of silicate minerals. The geochemical analysis of groundwater samples revealed dominant calcium-magnesium-carbonate- bicarbonate water facies. Irrigation water quality parameters, such as sodium absorption ratio, percentage of sodium, and permeability index, were calculated based on the physico-chemical analyses. The groundwater quality was observed to be influenced by the interaction of some geologic processes but was classified to be good to excellent, indicating its suitability for domestic and irrigation purposes. [ABSTRACT FROM AUTHOR]

The character of the shallow subsurface materials in the landslide and flood-prone Agwagune Community has been investigated using geophysical (electrical resistivity), geological and geotechnical techniques. Arising from the continuous suffering of the people in the affected areas, high occurrence rate and the desire to characterise the surficial materials, two dimensional resistivity tomography, vertical electrical sounding, soil sampling and hydrodynamic monitoring were conducted. Results show that the surficial materials are dominated by two main lithologic units: thin sandy materials with resistivity >30 Ωm and thick argillaceous materials with resistivity <30 Ωm. Particle size analyses confirm the dominance of argillaceous: silty-clay (56.2 %) and very fine (55.3 %) over arenaceous (9.2 %) materials. Bulk and particle densities of the surficial materials vary from 0.99 × 103 to 1.40 × 103 and 2.06 × 103 to 2.50 × 103 kg/m3, respectively; pH, EC and porosity range from 4.46 to 6.68, 8.0 to 23.0 mS/cm and 34.0 to 60.0 %, respectively. Atterberg Limits vary from 15.82 to 38.70 for liquid limit and 18.10–24.00 for plastic limit. Plasticity index varies from 11.92 to 15.70 %. Shallow groundwater in the coastal area is always in hydrodynamic equilibrium with water inside the Cross and Efefa Rivers and pond fields. To sustain this equilibrium condition, excess water inside the Cross River is usually discharged into Efefa River through both surface and underground flow processes. However, when water inside the Cross River dries up, a new hydraulic gradient, which distorts the existing equilibrium, is formed. This results in the reversal of groundwater flow direction. Continuous flow of groundwater into the Cross River channel (CRC) without any corresponding recharge results in the formation of voids, which gravitational force, forces to collapse. The collapsed materials usually roll toward the CRC, resulting in landslides. Models illustrating the main cause of the repeated landslide problem and suggested measures to minimise its occurrence rate have been included. [ABSTRACT FROM AUTHOR]

In this study, the activity concentrations of natural radionuclides in soil and beach sediment samples collected from 15 randomly but uniformly distributed locations in the coastal area of Akwa Ibom (southern Nigeria) were measured using hyper pure germanium (HPGe) detector. The activity concentrations of 238U, 232Th and 40K varied from 9 to 44 Bq/kg, 3 to 72 Bq/kg and 35 to 250 Bq/kg respectively. These results are below the 1000, 1000 and 4000 Bq/kg upper limits of safety for 238U, 232Th and 40K respectively. Except 238U, 232Th and 40K show lower standard deviations than their mean values, which indicate that soils and sediments have high degree of uniformity. The spatial distribution of radionuclide concentrations is nearly uniform except at locations where carbonaceous materials and clay soils exist. Mean value of Th/U ratio across the area was ≤ 7, typical of reducing condition in the depositional environment, thus suggesting enrichment of carbonaceous materials and clays. Additionally, the concentration of 40K was observed to be slightly higher in locations where anthropic activities are prevalent. Apart from excess lifetime cancer risk (average concentration of 0.80 × 10−3), the average concentrations of other radiological parameters: radium equivalent (83 Bq/kg), absorbed dose rate (39 nGy/h), indoor annual effective dose equivalent (0.18 mSv/year), outdoor annual effective dose equivalent (0.05 mSv/y) and annual gonadal dose equivalent (259 μSv/y), are below permissible limits. Hence, the soils and sediments are safe and suitable for all purposes. [ABSTRACT FROM AUTHOR]

The contamination levels of soils and water resources in Calabar, Nigeria have been investigated using resistivity (vertical electrical sounding and electrical resistivity tomography), geochemical analyses of soil and water resources and textural analysis. Sixty randomly sited VES sites were investigated in two seasons while ERT investigations were performed along four profiles. The geochemical investigations were spread across seasons in order to track seasonal changes in physico-chemical parameters: hydrogen ion concentration (pH), electrical conductivity, total dissolved solids, chloride ion (Cl−), nitrate ion (NO3-), bicarbonate (HCO3-), sulphate ion (SO42-), calcium ion (Ca2+), sodium ion (Na+), potassium ion (K+) and magnesium ion (Mg2+). Additionally, concentrations of ammonium, aluminium and nitrite ions in soils were determined. Results show that ionic concentrations in the sand-dominated soils and water are within permissible limits and baseline standards. The resistivities follow known trends in the area. However, at the central waste disposal site, a localised thin (< 5 m), low resistivity (< 15 Ωm) anomaly suspected to be due to contamination by leachates was observed. Comparatively, the contaminated area is also characterised by marginal increase in ionic concentrations. Strong attenuation capacities of overlying and adjoining clay/lateritic sediments and optimal design of the waste dump site probably reduced the spread of contaminants. The contaminated zone need to be closely monitored so that it does not extend to the aquifers. Hence, all strategies presently being used in managing wastes in Calabar should be sustained. [ABSTRACT FROM AUTHOR]