• I A Oha

      Articles written in Journal of Earth System Science

    • Interpretation of high resolution aeromagnetic data over southern Benue Trough, southeastern Nigeria

      I A Oha K M Onuoha A N Nwegbu A U Abba

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      High resolution airborne magnetic data of parts of the southern Benue Trough were digitally processed and analyzed in order to estimate the depth of magnetic sources and to map the distribution and orientation of subsurface structural features. Enhancement techniques applied include, reduction to pole/equator (RTP/RTE), first and second vertical derivatives, horizontal gradients and analytic signal. Results from these procedures show that at least 40% of the sedimentary basin contain shallow (<200 m) magmatic bodies, which in most cases are intermediate to mafic intrusive and hyperbysal rocks, and may occur as sills, dikes or batholiths. Magnetic lineaments with a predominant NE–SW trend appear to be more densely distributed around the basement rocks of the Oban Hills and metamorphosed rocks around the Workum Hills. 3D standard Euler deconvolution and Source Parameter Imaging (SPITM) techniques were employed for depth estimation. Results from the two methods show similar depth estimates. The maximum depth to basement values for 3D Euler and SPI are 4.40 and 4.85 km with mean depths of 0.42 and 0.37 km, respectively. Results of 2D modelling of magnetic profiles drawn perpendicular tomajor anomalies in the study area reveal the existence of deep seated faults which may have controlled the emplacement of intrusive bodies in the basin. The abundance of intrusive bodies in the study area renders this part of the southern Nigerian sedimentary basins unattractive for petroleum exploration.However, the area possesses high potential for large accumulation of base metal mineralization.

    • Investigation of hydrologic inCuence of geologic lineaments in areas of the Lower Benue Trough, Southeastern Nigeria

      S N UKPAI C O OKOGBUE I A OHA

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      Stratigraphic formations, namely, Asu River, Ezeaku, Awgu and Nkporo Groups; belonging to Albian, Turonian, Coniacian and Campanian ages, respectively, underlie the studied region. The formations aredominated by groundwater problematic clastic sediments. This study is aimed at tracing fracture zones for groundwater prospects and delineating hydrological catchments for the watershed managementstrategy. It commenced with analyses of aeromagnetic and edge enhanced band 5 Landsat 7 ETM+ data, with application of Blters like reduction to equator (RTE), Brst vertical derivatives (1VD), total horizontal gradient (THG) and analytical signal. The THG of the RTE grids was combined with the edge enhanced Landsat data and utilized on-screen lineament discriminations. Results showed igneousintrusive representative lineaments in Asu River Group. Lineaments pinpointing ferruginous structures like ironstones stained the Nkporo Group. Further applications of edge enhanced Blters delineated lineaments as river beds, fractures/fault nodes and fold axes. The lineaments trending NW–SE depict fracture axes and river beds, whereas those trending NE–SW represent axial anticlines. Validation ofresults with electrical sounding veriBed the relevance of outcropping fractures as conduits through which groundwater discharges from the shallow water table at the northwestern hill range region; producingCuvial systems like river tributaries/catchments. Conversely, the rivers recharge the groundwater via fracture linking to deeper water table downstream.

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