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Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria 总被引：2，自引：0，他引：2
A. A. Adepelumi B. D. Ako T. R. Ajayi O. Afolabi E. J. Omotoso 《Environmental Geology》2009,56(5):927-933
Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration
into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic
system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity
(VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between
1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity
curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of
four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between
125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond
to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish
groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities
values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation
are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion
into the aquifers can be accurately mapped using surface DC resistivity method. 相似文献
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Reconnaissance soil-gas radon survey over the faulted crystalline area of Ile-Ife, Nigeria 总被引：1，自引：0，他引：1
Tropical rain forest areas are well known for problems with geological mapping because of the dense vegetation and thick overburden. The application of soil-gas radon measurements was carried out over known and suspected fault zones in the basement terrains of Ile-Ife, southwestern Nigeria. Radon concentration in the area ranged from 25.6 to 6,227.8 pCi/l, with distinct contrasts and overlap in concentrations among soil groups derived from various rock types. Radon concentrations in the soil exhibit a strong dependence on the local geology and reflect the bedrock geochemistry. Relatively high radon soil-gas concentrations of between 4,000 and 6,227.8 pCi/l were found directly on the axis of the known and suspected strike slip faults. The use of the radon-222 technique confirms its application as a useful tool in geological and structural mapping in basement terrains largely covered by relatively thick overburdens. 相似文献
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A.A. Adepelumi B.D. Ako T.R. Ajayi A.O. Olorunfemi M.O. Awoyemi D.E. Falebita 《Journal of African Earth Sciences》2008,52(4-5):161-166
Integrated geophysical methods involving magnetic and dipole–dipole resistivity (DDR) were conducted across a prominent zone of weakness clearly observable in Landsat MSS and SLAR images in the Precambrian basement complex of southwestern Nigeria. Up till now, the location and existence of this megascopic structure have not been confirmed using geophysical methods. With the objective of delineating this weak zone and its structural attributes, three traverses were established at 500 m intervals across it, and geophysical measurements were made at 10 m intervals along these traverses. Qualitative interpretation of the magnetic data obtained shows a diagnostic signature of a near-vertical fault, trending along a NNE–SSW direction. Also, the quantitative interpretation of the data using the non-linear least-squares regression technique indicates that the width of the magnetic anomaly ranges from 90 to 150 m, its dip angle varies between 75° and 85°; the anomaly is concealed by a regolith of approximately 15 m thickness. Furthermore, a 2D resistivity inversion of the field resistivity data reveals a three-layer model, representing thin resistive topsoil underlain by weathered bedrock, resistive bedrock with a distinct low resistivity zone located within the bedrock. The most plausible explanation for this low resistivity zone is that it was formed by shearing activities during Late Precambrian times. Conclusively, the integrated approach employed in this research confirms the existence of the supposed Ifewara shear zone (ISZ). 相似文献
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Emmanuel A. Ariyibi Samuel L. Folami Bankole D. Ako Taye R. Ajayi Adebowale O. Adelusi 《Arabian Journal of Geosciences》2011,4(1-2):239-247
The study area occupies a part in southern Ilesa and is located within the schist belt of southwestern Nigeria, which embraces undifferentiated schist, gneisses, and migmatites with pegmatites, schist and epidorite complex, quartzite and quartz schist, granite gneiss, amphibolite, pegmatised schist, granulite, and gneiss. The study is aimed at clarifying the potential source of mineralization dealt with before in regional studies. Sixty-one soil samples were collected and analyzed for identifying these elements: Pb, Fe, Ni, Cd, Cr, Cu, Zn, and Mn. Multivariate analysis was done to obtain the coefficients of principal components from the standardized variables The elemental associations from the principal components analysis that accounted for 85.34% variability of the total variance are: Fe–Mn, Pb–Cr, and Cd–Zn. Comparably, these are equivalent with the previous results in the amphibolites and added the extension of association region to involve the schist and epidorite complex, quartzite, and quartz schist. The metallic association ratio revealed high metallic concentrations and led to the mineralization trend in southern Ilesa. 相似文献
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The origin of the Benue trough has been a controversial subject. Previous workers in the area have evolved several theories ranging from a rift, with or without plate tectonic concepts (King, 1950; Wright, 1968, 1970; Burke et al., 1970; Grant, 1971; Olade, 1975) to a geosyncline (Lees, 1952) and a combination of both (Cratchley and Jones, 1965; Offodile, 1976) to explain the origin of the trough. One of the aims of the gravity survey, carried out in the middle Benue and discussed in this paper, was to attempt to resolve some of the problems associated with the origin of the trough as proposed by previous workers and in so doing to explain the geological peculiarities associated with the trough.
Interpretations of the gravity data along two north—south profiles in the survey area indicated the existence of a rift, of normal width (about 40 km) buried under the Cretaceous cover and located between the central axis (ridge) of the trough and the northern boundary of the trough. The gravity minimum which occurs south of the central axis of the trough, was also ascribed to another rift. Thus the Benue trough is considered to consist of two parallel rifts separated by the axial ridge which partly explains the abnormal width of the trough. The interpreted models also indicate a low-angle thrust fault, with a small displacement, which may be related to the folding of the sediments in the trough and also to the asymmetry of the trough. Furthermore, the gravity data suggest that oceanic crust might not have reached the ground surface in the Benue trough, as in the Red Sea, before rifting ceased. 相似文献
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Boreholes drilled in the crystalline rocks of Nigeria have a reputation of failures and low yields. The performance of 256 boreholes drilled in different parts of the crystalline rocks of SW Nigeria were reviewed to determine their failure characteristics. 100% success was claimed for 105 boreholes constructed by one driller. Out of 111 other borehole records supplied by three other drillers 35 were abortive, representing a failure rate of 32%. In contrast, 24 owners of 40 boreholes reported 24 failures representing a failure rate of 60%.The common causes of borehole failure in the crystalline rocks of SW Nigeria are seasonal variations in water level, improper casing of the overburden, damage to pumps and other system failures such as blocked pipelines and malfunctioning tanks. Non-penetration into the water bearing horizon also features as a cause of borehole failure in this study.It is suggested that proper construction, operation and maintenance of boreholes will reduce the incidence of borehole failures in crystalline rocks of SW Nigeria. 相似文献
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Babatunde J. Abiodun Zachariah D. Adeyewa Philip G. Oguntunde Ayobami T. Salami Vincent O. Ajayi 《Theoretical and Applied Climatology》2012,110(1-2):77-96
This study investigates the potential impacts of reforestation in West Africa on the projected regional climate in the near two decades (2031–2050) under the SRES A1B scenario. A regional climate model (RegCM3) forced with a global circulation model (ECHAM5) simulations was used for the study. The study evaluates the capability of the regional model in simulating the present-day climate over West Africa, projects the future climate over the region and investigates impacts of seven hypothetical reforestation options on the projected future climate. Three of these reforestation options assume zonal reforestation over West Africa (i.e., over the Sahel, Savanna and Guinea), while the other four assume random reforestation over Nigeria. With the elevated GHGs (A1B scenario), a warmer and drier climate is projected over West Africa in 2031–2050. The maximum warming (+2.5°C) and drying (?2?mm?day?1) occur in the western part of the Sahel because the West Africa Monsoon (WAM) flow is stronger and deflects the cool moist air more eastward, thereby lowering the warming and drying in the eastern part. In the simulations, reforestation reduces the projected warming and drying over the reforested zones but increases them outside the zones because it influences the northward progression of WAM in summer. It reduces the speed of the flow by weakening the temperature gradient that drives the flow and by increasing the surface drag on the flow over the reforested zone. Hence, in summer, the reforestation delays the onset of monsoon flow in transporting cool moist air over the area located downwind of the reforested zone, consequently enhancing the projected warming and drying over the area. The impact of reforesting Nigeria is not limited to the country; while it lowers the warming over part of the country (and over Togo), it increases the warming over Chad and Cameroon. This study, therefore, suggests that using reforestation to mitigate the projected future climate change in West Africa could have both positive and negative impacts on the regional climate, reducing temperature in some places and increasing it in others. Hence, reforestation in West Africa requires a mutual agreement among the West African nations because the impacts of reforestation do not recognize political boundaries. 相似文献