Heliyon 7 (2021) e07205

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Heliyon

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Research article

Structural architecture of the Middle Niger Basin, Nigeria based onaeromagnetic data: An example of a non-volcanic basin

Naheem Banji Salawu a,c,*, Silas Sunday Dada b, Julius Ogunmola Fatoba c,Olusola Johnson Ojo d, Leke Sunday Adebiyi c,e, Abayomi John Sunday f,Toyin Yusuf Abdulraheem a

a BS Geophysical and Consultancy Ltd., Ilorin, Nigeriab Department of Geology and Mineral Sciences, Al-Hikmah University, Ilorin, Nigeriac Department of Geophysics, Federal University Oye-Ekiti, Oye-Ekiti, Nigeriad Department of Geology, Federal University Oye-Ekiti, Oye-Ekiti, Nigeriae Department of Physical Sciences, Landmark University, Omu-Aran, Nigeriaf Department of Science Laboratory Technology, Kwara State Polytechnic, Ilorin, Nigeria

H I G H L I G H T S

� Boundaries of basement areas with the basin are marked by systems of lineaments.� Delineated lineaments offer target areas for follow-up mineral investigation.� FVD map reveals possible lack of volcanic rocks within the basin.� Internal geometry of the basin is revealed based on SPI depth solutions.

A R T I C L E I N F O

Keywords:Middle Niger BasinRiftAeromagnetic dataShear zone

* Corresponding author.E-mail address: salawubanji@yahoo.com (N.B. S

https://doi.org/10.1016/j.heliyon.2021.e07205Received 30 June 2020; Received in revised form 12405-8440/© 2021 The Author(s). Published by Els

A B S T R A C T

The Middle Niger Basin is located within the west-central half of Nigeria, as a NW-SE trending Campano-Maastrichtian depo-centre which extends from the southern end of the Sokoto Basin west of Kainji reservoirsouthwestwards to the convergence of the Benue and Niger Rivers at Lokoja. The aeromagnetic anomaly data ofthe Middle Niger Basin was interpreted to characterize the structural architecture and depth to the magneticbasement of the basin. This is to expand the current knowledge of the region. The analysis of the data has beenfacilitated by the application of derivative and source parameter imaging techniques. The results from theapplication of total gradient to the aeromagnetic data provided here signify a rift origin of the basin and NW-SEtrending fault systems in the surrounding basement complex terrain. The absence of magnetic highs on the firstvertical derivative of the reduced-to-pole aeromagnetic data reveals lack of volcanic rocks within the sedimentarylayers of the basin. Additionally, the consistent NW-SE trending source parameter imaging depth solutions withinthe basin confirm the internal geometry and NW-SE orientation of the basin with sediments not more than 1100 mthick.

1. Introduction

The Middle Niger Basin, which extends northwesterly from theconvergence of the River Niger and River Benue at the Lokoja/Dekinaaxis, is flanked on both sides by the basement complex of northwesternand southwestern Nigeria (Figure 1). It equally separates the basin fromthe early Cretaceous to late Jurassic Illo and Gundumi Formations of the

alawu).

7 November 2020; Accepted 31evier Ltd. This is an open access

Sokoto Basin by a narrow geologic formation considered to be crystallinebasement around the Kainji reservoir area (Adeleye and Dessauvagie,1972; Kogbe 1989; Rahaman et al., 2018). The Middle Niger basin isfairly elliptical with an orientation that is virtually perpendicular to theBenue Trough in Nigeria. The basin is roughly 350 km long with a widthbetween 75 km and 150 km (Zaborski 1998). The Middle Niger Basin isdifferent from other basins in Nigerian because of the absence of

May 2021article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Figure 1. Simplified geological map ofNigeria and its surrounding areas showingthe location of the Middle Niger Basin,which is indicated with a yellow polygonon the map. (Adapted from Salawu et al.,2021). The Abbreviation used: KZISZ -Kalangai-Zungeru-Ifewara shear zone. Reprinted bypermission from [the Licensor]: [SpringerNature] [Geomechanics and Geophysics forGeo-Energy and Geo-Resources] [Structuralgeometry of Ikogosi warm spring, south-western Nigeria: evidence from aero-magnetic and remote sensing interpretation,Salawu et al., (2021), [COPYRIGHT] (2021).Journal website: https://www.springer.com/journal/40948.

Figure 2. Total magnetic intensity anomaly mapof the entire Middle Niger Basin and surroundingbasement complex terrane. At low-latitude areassuch as the studied region, magnetic sourcebodies are usually characterized by low aero-magnetic anomalies. The dotted lines representthe boundary of the Middle Niger Basin. Solidblack lines: major shear zones from previousstudy of Salawu et al. (2020). Abbreviations: AYI– Anka-Yauri-Iseyin shear zone; KZI –

Kalangai-Zungeru-Ifewara shear zone.

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carbonate rock. The regional structural evolution of the basin has been asubject of debate for long and satisfactory clarification about itstectono-stratigraphic evolution is still in contention (Rahaman et al.,2018).

Several researchers that investigated the Middle Niger Basin havereported contradictory thicknesses for the sedimentary pile. A possiblemaximum depth value of Middle Niger Basin sediments has been esti-mated to be generally around 1000 m (Kogbe et al., 1983). Ojo (1990),based on aeromagnetic investigation, reported basic intrusive rocks atdepths between 4000 m–6000 m well below the base of the sedimentary

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formations of the Middle Niger Basin, which he suggested to be notmore than 2000 m thick. Udensi and Osazuwa (2004) carried outmagnetic investigation of the central and southern portion of the MiddleNiger Basin using spectral analysis. Their results reported a sedimentarythickness of about 3500 m within the investigated segment of the basin.Megwara and Udensi (2014) used aeromagnetic data to investigate thesouthern portion of the Middle Niger Basin and concluded that thedepths to the magnetic sources along established aeromagnetic dataprofiles range from 10 to 510 m with an average depth value of 128 m.Salawu et al. (2020) integrated remote sensing and aeromagnetic

Figure 3. Reduced-to-pole aeromagnetic anomaly map of the Middle Niger Basin with surrounding basement complex terrane. The continuous dotted lines representthe boundary of the Middle Niger Basin. Solid black lines: major shear zones from previous study of Salawu et al., (2020). Abbreviations: AYI – Anka-Yauri-Iseyin shearzone; KZI – Kalangai-Zungeru-Ifewara shear zone.

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methods for the investigation of structural features and possible depthto magnetic sources of the northern segment of the Middle Niger Basinwith a view to unravel the sedimentary thickness and lineaments of thestudied region. The results of their investigations revealed a maximumsedimentary thickness of 950 m within the northern portion of the basinand also showed that the boundaries of the basin are marked by seriesof faults.

Since a general understanding of sedimentary basin features can beachieved through the interpretation of aeromagnetic anomaly data (Farhiet al., 2016; Mohamed et al., 2020), we have deployed geophysical datato provide further information needed to address the internal geometryof the basin. This is with the aim of locating structural features andestimating depths to magnetic sources by various processing techniquesthat have been established to aid the interpretation of magnetic data suchas the estimation of source depth with the aid of source parameter im-aging method (Thurston and Smith 1997). Furthermore, the applicationof first vertical derivative technique (Evjen, 1936) and total gradientmethod (MacLeod et al., 1993; Nabighian 1972; Roest et al., 1992) whichare well adapted to locating structural features (intrusions, faults, con-tacts) have been deployed in this study.

In view of the discrepancy in estimated depth values of the MiddleNiger Basin, we present the structural features and sedimentary thick-ness data of the Middle Niger Basin using high resolution aeromagneticanomaly data. The objectives of the study are: (i) delineation of preciseboundary of the basin using first vertical derivative, (ii) investigation ofvolcanic and structural features within the basin utilizing total gradient,(iii) possible depths to magnetic basement estimation using sourceparameter imaging technique. This study is aimed at providing impor-tant clues about the origin and internal geometry of the Middle Nigerbasin which are essential for further exploration activities within thebasin.

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2. Geologic setting

The studied area is located within 4� 300 to 8� 000 E and 8� 000 to 11�

000N in the central-western half of Nigeria (Figure 1). The Middle Nigerbasin (Figure 2) is presumed to be a north-westerly prolongation of theAnambra Basin (Akande et al., 2005). The sedimentary fill of the basinconsists of a NW-trending belt of Upper Cretaceous sedimentary rockunits which were deposited due to faulting of blocks, basement disinte-gration and subsidence consequent to the Cretaceous opening of theSouth Atlantic Ocean. The northern segment is commonly called the Bidasub-basin while the southern segment is referred to as Lokoja sub-basin.The Bida Formation lies unconformably on the Basement Complex in thenorthern segment of the basin. The Lokoja Formation which is itsequivalent in the southern segment also unconformably overlies thebasement. The Bida and Lokoja Formations are immature mineralogi-cally and texturally, and consist of massive, clast to matrix supportedconglomerate, that fine upwards to conglomeratic-sandstone, mediumgrained sandstone, siltstone and subordinate-claystone (Ojo and Akande,2013). Overlying the Lokoja Formation is the Patti Formation which ismade up of shale, sandstone, ironstone and claystone (Ojo et al., 2020).In the northern portion of the basin, the Bida Formation is overlain by theEnagi Formation which consists of siltstone, sandstone and claystone(Ojo 2012). The Enagi and Patti Formations are directly overlain by theBatati and Agbaja Formations respectively (Adeleye, 1974; Akande et al.,2005). The Batati Formation is made up of oolitic, goethitic and argil-laceous ironstones with ferruginous siltstone and claystone intercalationsand shaly beds occurring in small proportions, some of which yieldednear-shore shallow marine to fresh water fauna (Adeleye, 1973). TheAgbaja Formation (probably Late Maastrichtian) consists of oolitic andpisolitic ironstones (Ojo et al., 2020). The structural style of the MiddleNiger Basin is portrayed by a system of NW-SE trending faults at the

Figure 4. Color-shaded first vertical deriva-tive (FVD) map produced from the reduced-to-pole aeromagnetic anomaly data of Mid-dle Niger Basin and the surrounding base-ment complex terrane. The FVD enhancesdetails of near surface sources and is suitablefor delineating the edges and shape of sour-ces. In the northeast and northern zones,high frequency pattern is seen in the base-ment complex terrane. The continuousdotted lines represent the boundary of theMiddle Niger Basin. Solid black lines: majorshear zones from previous study of Salawuet al., (2020). Abbreviations: AYI – Anka-Yauri-Iseyin shear zone; KZI – Kalangai-Zungeru-Ifewara shear zone.

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boundaries of the basin with the surrounding crystalline basementterrain (Kogbe et al., 1983; Rahaman et al., 2018), which suggests a riftorigin for the Middle Niger Basin. No prominent morphological features,lineaments or intrusions were observed within the sedimentary basin(Salawu et al., 2020). In contrast, the underlying basement is charac-terized by prominent structural features, including the lateral continuityof the NNE-SSW trending Kalangai–Zungeru-Ifewara shear zones formedduring the Pan-African orogeny (Salawu et al., 2020).

3. Data and methodology

The magnetic data investigated in this study was provided by theNigerian Geological Survey Agency (NGSA). The high resolution aero-magnetic data is not publicly available but can be acquired from theNGSA. The data is part of the regional aeromagnetic data of Nigeria ac-quired by a geophysical company (Fugro Airborne Surveys Limited) forthe NGSA between 2004 and 2009. The datasets were acquired at aconstant flight altitude of 80 m on a series of NW-SE flight lines(perpendicular to regional trends). The flight lines are spaced and tied at500 m and 2000 m respectively. The data were corrected for diurnalvariation effects and the main component of the geomagnetic field(IGRF) was removed. A range of standard digital processing techniqueswere utilized for the interpretation of the aeromagnetic anomaly data toinvestigate the subsurface structural fabric of the Middle Niger Basin.These methods are commonly used for the interpretation of potentialfield dataset for locations and depth estimations of structural featuressuch as faults, contacts and intrusive bodies. All processing of the aero-magnetic anomaly data was accomplished using the Oasis Montaj(Geosoft™) software package.

Processing routine of the magnetic data comprised of the followingsteps: (a) the total magnetic intensity (TMI) anomaly data (Figure 2) wastransformed to reduced-to-pole (RTP) data (Figure 3), to simplify theinterpretation of magnetic anomalies which are influenced by the di-rections of the magnetic field and sourcemagnetization (Saibi et al. 2015;

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Abdel Zaher et al., 2017). This transformation was achieved with aninclination: -4.978� and declination: -2.082 degrees of the Earth's field.The magnetic field parameters (inclination and declination) were chosenat the midpoint of the studied region (longitude: 6� 000 E and latitude: 9�

300N). Additionally, we implemented a pseudo-inclination 80� to stabi-lize the results of this filter, which is unstable in low-latitude regions.Considering the rock types and ages within the region, remanentmagnetization is generally not an interfering factor, which allows theaccurate use of the RTP transformation to correctly shift anomaliesdirectly above their sources, (b) the application of first vertical derivativefilter to enhance high frequency anomalies, in order to suppress theregional effects (long-wavelength) of deep magnetic sources. Hence, weexamine the magnetic patterns of shallow source bodies, (c) applicationof total gradient technique to improve the magnetic signature of struc-tures (faults or dykes), (d) calculation of depths to themagnetic basementusing source parameter imaging technique for the tectonic framework.The enhancement filters and depth estimation technique utilized in thisstudy are discussed below.

3.1. First vertical derivative

The first vertical derivative (FVD) technique is normally applied toaeromagnetic data to accentuate near surface structural features andshallow sources generating magnetic anomalies. The zero values of FVDof the reduced-to-pole (RTP) aeromagnetic field normally correspond tothe geological structures. The FVD with respect to depth (z) is given inEq. (1) as (Evjen, 1936):

FVD¼ ∂F∂z (1)

where F is the detected RTP aeromagnetic anomaly field. Here, weapplied the FVD technique to the RTP aeromagnetic data to distinguishthe Middle Niger Basin from the surrounding basement terrane based onthe patterns of the FVD frequencies. Sedimentary basins are normally

Figure 5. Color-shaded total gradient map of Middle Niger Basin and its surrounding crystalline basement terrane, computed from the aeromagnetic anomaly data.The continuous dotted lines represent the boundary of the Middle Niger Basin. Solid black lines: major shear zones from previous study of Salawu et al., (2020).Abbreviations: AYI – Anka-Yauri-Iseyin shear zone; KZI – Kalangai-Zungeru-Ifewara shear zone.

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characterized by low anomaly values (high frequency) and the bound-aries are marked by contrast of high and low anomaly values (Salawuet al., 2020).

3.2. Total gradient

The application of total gradient method to observed aeromagneticanomaly field normally provides good horizontal locations for structures(suchas contacts, intrusions, faults and sheet sources) independentof theirmagnetic latitude (Phillips 2000; Azizi et al., 2015). The amplitude of totalgradient exhibits maxima over structural features, regardless of sourcemagnetization directions and ambient magnetic field (Roest et al., 1992).The absence of the magnetization direction in the shape of the totalgradient amplitude is an attractive characteristic for the analysis of aero-magnetic datameasured aroundmagnetic equator (MacLeod et al., 1993).The total gradient is derived from the three orthogonal gradients of themagnetic anomalyfield using Eq. (2) (Roest et al. 1992), which is given as:

TGðx; yÞ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�∂F∂x

�2

þ�∂F∂y

�2

þ�∂F∂z

�2s

(2)

where TGðx; yÞ is the total gradient of the aeromagnetic anomaly field. Thetotal gradient filter was applied to the aeromagnetic anomaly data of thestudy area to assess the existenceof volcanic rocks in theMiddleNiger Basinand to map structural features within the surrounding basement terrane.

3.3. Source parameter imaging

Interpretation of aeromagnetic anomalies requires determining eachof the entity that characterized the sources of themagnetic anomalies. Thesource parameter imaging (SPI) is a major technique commonly used forthe estimation of depth values of sources, which is an entity that is mostly

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sought (Smith et al., 1998). The estimateddepth values are independent ofmagnetic declination, inclination, remanentmagnetization, strike and dip(Thurston and Smith 1997). These characteristics make the SPI techniquevery useful for aeromagnetic anomaly data measured at low magneticlatitude regions such as the studied region. The SPI technique uses thelocal wavenumber in Eq. (3) for depth estimation which is given as:

K ¼∂2F∂x∂z

∂F∂x þ ∂2F

∂y∂z∂F∂y þ ∂2F

∂z2∂F∂z�

∂F∂x

�2

þ�∂F∂y

�2

þ�∂F∂z

�2 (3)

SPI assumes a 2-D sloping contact model and maximum values of Kare located above the sloping contact. In addition, depth values ofmagnetic sources are computed by substituting Eq. (3) into the expres-sion for depth estimate in Eq. (4), given as:

Depthx¼0 ¼ 1Kmax

(4)

where, Kmax in Eq. (4) is the maximum value of K (equation 3) above 2-Dsloping contact. The SPI technique was applied to the aeromagnetic dataof the Middle Niger Basin and surrounding basement complex terrane toestimate depth values of sources within the basin and its surroundingareas. This is to obtain the sedimentary thickness of the basin and varia-tions of depth values of sources within the surrounding basement terrane.

4. Result

4.1. Reduced-to-pole map

The Reduced-to-pole (RTP) map (Figure 3) shows magnetic highand low anomalies with different patterns within the study area. The

Figure 6. (a) Structural map of the studyarea produced from the extracted maxima ofthe total gradient amplitude, which was usedfor the identification of magnetic lineamentslocations. (b) Rose diagram generated fromthe maxima of the total gradient amplitudereveals that lineaments are majorly orientedin the E-W, NE-SW and ENE-WSW directions.The continuous dotted lines on Figure 6arepresent the boundary of the Middle NigerBasin. Solid red lines on Figure 6a are majorshear zones from previous study of Salawuet al., (2020). Abbreviations: AYI –

Anka-Yauri-Iseyin shear zone; KZI –

Kalangai-Zungeru-Ifewara shear zone.

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RTP anomaly field ranges between �60 nT and 135 nT, revealing thehigh magnetic signature of the Middle Niger Basin and the surroundingbasement complex areas. The RTP map can be classified generally intotwo main domains; the first domain which is characterized by scat-tered, high frequency magnetic anomalies correspond to the basementcomplex terranes of Kwimu, Zungeru, Minna, Lapai, and south ofLafiagi. The high frequency with low to moderate amplitudes anoma-lies within the basement terrane are interpreted as linked to shallowstructures such as contacts, fractures and intrusive bodies. The seconddomain which reveals low frequency of high amplitude magneticanomalies with prominent large elongated patterns corresponds to theMiddle Niger Basin on the RTP map. This pattern of low frequencyanomalies are attributed to deep-seated magnetic sources within thebasement.

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4.2. Structural features of the Middle Niger Basin and its basement

4.2.1. First vertical derivativeThe reduced-to-pole first vertical derivative (FVD) map (Figure 4)

reveals rough relief, with negative and positive FVD anomalies ofvarious amplitudes that ranges from �0.162 to 0.189 nT/m. The mainmagnetic trends are in the, NW-SE, N–S, NE–SW and E-W orientationwithin the basin and surrounding crystalline basement complex. In thebasement terrane, elongated regional gradients with NNE–SSW trendsare related to the Kalangai-Zungeru-Ifewara (KZI) shear zone aroundZungeru area and Anka–Yauri-Iseyin (AYI) shear zone to the west. Thelow amplitude magnetic anomalies inside the basin, which extend fromBokani through Bida to Abaji areas are produced by a series of magneticminerals of the Campano-Maastrichtian ironstones within the

Figure 7. Color-shaded source parameter imaging depth map of Middle Niger Basin with surrounding basement areas derived from the total aeromagnetic data of thestudy area. The continuous dotted lines represent the boundary of the Middle Niger Basin. Solid black lines: major shear zones from previous study of Salawu et al.,(2020). Abbreviations: AYI – Anka-Yauri-Iseyin shear zone; KZI – Kalangai-Zungeru-Ifewara shear zone.

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sedimentary formation that has been previously discussed, by Ojo andAkande (2013) and Ojo et al., (2020). This reveals possible lack ofvolcanic rocks within the sedimentary layers of the basin. These lowamplitude magnetic anomalies are elongated and trends mainly in theNW-SE and E-W directions. A few elongated low amplitude magneticanomalies with NE–SW trends are revealed within the central parts ofthe basin on the FVD map. Ojo and Akande (2013) have presented adetailed study of the southern portion of the Middle Niger Basin, andtheir results show heavy metal mineral assemblages such as magnetite,hematite, limonite and ilmenite within the Lokoja Formation of thebasin. Generally, the FVD map reveals magnetic signature produced byshallow sources of the Middle Niger Basin and its surrounding crystal-line basement areas.

4.2.2. Total gradientThe total gradient map (Figure 5) shows negative and positive

anomalies of various amplitude and wavelengths ranging from 0.08 to0.32 nT/m (Figure 5). Inside the Middle Niger Basin (which extend fromBokani through Bida to Abaji areas), amplitude of the total gradient isminima which revealed a smooth surface on the total gradient map (seeFigure 5). This denotes low magnetic contents of the Cretaceous sedi-mentary fill in the basin as well as probable non-volcanic rocks within thebasin. The boundaries of the basement complex terrane with the sedi-mentary basin are marked by differences between low (0.08 nT/m) andhigh (0.32 nT/m) values of the total gradient amplitude, which aretentatively interpreted as series of faults. Dominating maxima of the totalgradient amplitude becomes widely distributed towards the north andnortheastern portion of the map (Figure 5) signifying an intensivelyfractured rocks within the basement complex terrane. In order to high-light the locations, lateral extent, and trends of structural features shownon the map, the maxima of the total gradient amplitude were extractedand used to produce the structural map (Figure 6) of the region under

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study. The visual inspection of the map (Figure 6) illustrates numerousmagnetic structures which revealed the superficial shapes of the MiddleNiger Basin. It also shows that the boundary of the basin is marked bysystems of E-W, NW-SE and NE-SW trending lineaments. These trendpatterns reveal the structural control architecture of the basin, therebyindicating a rift origin of the Middle Niger Basin. Additionally, the pro-duced Rose diagram from the maxima of the total gradient amplitudereveals major orientation of lineaments in the E-W, NE-SW and ENE-WSW directions.

4.2.3. Source parameter imagingThe Middle Niger Basin is underlain and surrounded by the Nigerian

Basement that carries imprints of the Pan-African tectonic event (600Ma), with dominant N–S and NE-SW shears that define the major struc-tural fabrics (foliations, lineations, folds, etc.) of the entire region (Dada2008). One method which estimates the depth to the top of sources (suchas sloping contact and thin sheet model) is by the application of thesource parameter imaging (SPI) technique. These estimates can be usedto represent the basin floor morphology, which has direct significance tothe structural history of the region. The SPI map (Figure 7) reveals esti-mated depth values of sources within the studied region between 50 mand 1050 m. The depth values that relate to penetrative structural fea-tures within the crystalline basement complex terrane are mostly <150m. A major fascinating feature on the map is the higher and consistentdepth values of the entire Middle Niger Basin, which extends fromBokani through Bida to Abaji areas, in contrast to the lower depth valuesof the surrounding basement complex areas. The pattern of depth valuesin Figure 7 permits the visual assessment of the SPI map with thedelineated boundaries of the Middle Niger Basin (revealed by thetermination of structural features) on the structural map (Figure 6). Theconsistent depth values <1100 m depict the internal geometry of theMiddle Niger Basin. Additionally, the extent of the Middle Niger Basin

Figure 8. Color-shaded sedimentary thickness map estimated from the source parameter imaging depth map of Middle Niger Basin with surrounding basement areas.

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was extracted from the SPI Map to isolate the basin from the surroundingbasement terrane. The value of 80 m sensor mean terrain clearance wassubtracted from the resulting Middle Niger Basin SPI map to establish asedimentary thickness map (Figure 8) of the basin. The map representsthe estimated thickness of non-magnetic geological material above themagnetic basement.

5. Discussion

From recent studies that have added to our understanding of theorigin of sedimentary basins resulting from structural controls (Zieglerand Cloetingh 2004; Lopes de Castro et al., 2012), we have sought todecipher the link between the underlying structural framework of thecrystalline basement and the development of the Middle Niger basin.The interpretation of aeromagnetic data in this study has identifiedimportant structural features associated with geologic formations in thestudy area. It was observed that the reduced-to-pole (RTP) magneticmap (Figure 3) shows prominent high amplitude long wavelength RTPanomalies in Middle Niger Basin (Bokani and Bida areas) which aretentatively interpreted to be caused by magnetic sources within thebasement that underlies the basin. These interpretations agree with theresults of aeromagnetic investigation across various section of the basinby researchers such as Salawu et al., (2020) and Ojo (1990). The firstvertical derivative (FVD) map of the RTP data was produced to focus oninvestigating shallow sources within the basin. The map reveals a clearcontrast between the basin and surrounding crystalline basement. Onthe FVD map (Figure 4) many low amplitude magnetic anomalies areapparent inside the Middle Niger Basin (extending from Bokani throughBida to Abaji areas). Based on the magnitudes and narrow FVD anom-alies, many of these appear to result from contrasts within the Creta-ceous sedimentary formation of the basin. This is because anomaliesproduced by non-igneous magnetic sources within sedimentary

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formations are normally much weaker compared to those of the intru-sive igneous rocks within the basement, which commonly contains ahigher concentration of magnetic minerals (Gunn 1997). Additionally,the lack of maximum amplitude values of FVD anomalies inside thesedimentary layer of the Middle Niger Basin reveals a possible lack ofvolcanic rocks in the basin. In contrast, the basement complex showsseveral high amplitude anomalies attributed to shallow structural fea-tures such as intrusions, faults and fractures. The FVD map and itsinterpretation satisfy the results of the previous aeromagnetic investi-gation (Salawu et al., 2020; Ojo 1990) of the Middle Niger Basin, whichsuggests that the basin sedimentary pile is characterized by the absenceof non-igneous intrusions. The total gradient map (Figure 5) reveals theproliferation of structures such as faults, folds and intrusions throughoutthe crystalline basement. The map equally shows the Middle Niger Basinto have fewer structures especially revealing the possible lack of vol-canic rocks within the sedimentary layers of the basin. The producedstructural map (Figure 6a) reveals basement fabrics and the superficialshapes of the Middle Niger Basin which is marked by E-W, NW-SE andNE-SW structural trends. The clouds of SPI depth solutions with NW-SEtrends reveal the internal basin architecture. These trend patterns areorthogonal or oblique to the main basement fabric within the MiddleNiger Basin, coupled with the presence of faults through the margin ofthe basin; thereby attributing its origin to a major rifting followed bysedimentation. The patterns of bounding lineaments of the Middle NigerBasin are parallel with basement fabrics. Hence, the bounding linea-ments justify that the rift basin was controlled by the reactivation ofpre-existing basement fabrics.

6. Conclusion

Aeromagnetic maps of the Middle Niger Basin and surrounding areasallow a comparison to be made between the structural signatures of the

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basin and its surrounding area. The presence of the shear zones and othermagnetic lineaments within the crystalline basement complex terrane areoutlined by prominent aeromagnetic lineaments. The first vertical deriv-ativemapdepicts a possible lack of volcanic rockswithin theMiddleNigerBasin. The total gradientmap revealedmagnetic patterns,which allow themapping of the basin boundaries. In contrast, the source parameter im-aging map shows clouds of depth solutions, which suggest internal basinstructures, trending mainly in the NW-SE direction perpendicular to themain basement fabric (NE-SE and E-W) deduced from the total gradientmethod.Weuse the source parameter imaging technique presentedhereinto establish magnetic depth estimates within the study area, though themagnetic basement topography varies considerably, the depths to themagnetic basement are generally not more than 1100 m.

Declarations

Author contribution statement

Naheem Banji Salawu, Silas Sunday Dada, Julius Ogunmola Fatoba,Olusola Johnson Ojo, Leke Sunday Adebiyi, Toyin Yusuf Abdulraheem:Analyzed and interpreted the data; Wrote the paper.

Abayomi John Sunday: Contributed reagents, materials, analysis toolsor data.

Funding statement

This research did not receive any specific grant from funding agenciesin the public, commercial, or not-for-profit sectors.

Data availability statement

The authors do not have permission to share data.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.

Acknowledgements

The authors thankfully acknowledge the support of the NigerianGeological Survey Agency and BS Geophysical and Consultancy Ltd., fortheir immense contribution and the facilities made available during thecourse of this research.

References

Abdel Zaher, M., Saibi, H., Mansour, K., Khalil, A., Soliman, M., 2017. Geothermalexploration using airborne gravity and magnetic data at Siwa Oasis, Western Desert,Egypt. Renew. Sustain. Energy Rev. 82 (3), 3824–3832.

Adeleye, D.R., 1974. Sedimentology of the fluvial Bida Sandstone (Cretaceous), Nigeria.Sediment. Geol. 12, 1–24.

Adeleye, D.R., 1973. Origin of ironstones: an example from the Mid-Niger Basin, Nigeria.J. Sediment. Petrol. 43, 709–727.

Adeleye, D.R., Dessauvagie, T.F.J., 1972. Stratigraphy of the Niger Embayment near Bida,Nigeria. In: Desssauvagie, T.F.J., Whiteman, A.J. (Eds.), African Geology. Universityof Ibadan Press, pp. 181–186.

9

Akande, S.O., Ojo, O.J., Erdtmann, B.D., Hetenyi, M., 2005. Paleoenvironments, organicpetrology and Rock-Eval studies on source rock facies of the Lower MaastrichtianPatti Formation, Southern Bida Basin, Nigeria. J. Afr. Earth Sci. 41, 394–406.

Azizi, M., Saibi, H., Cooper, G.R.J., 2015. Mineral and structural mapping of the Aynak-Logar Valley (Eastern Afghanistan) from hyperspectral remote sensing data andaeromagnetic data. Arab. J. Geosci. 8, 10911–10918.

Dada, S.S., 2008. Proterozoic evolution of the Nigeria–Boborema province. In:Pankhurst, R.J., Trouw, R.A.J., de Brito Neves, B.B., de Wit, M.J. (Eds.), WestGondwana: Pre-cenozoic Correlations across the South Atlantic Region, 294.Geological Society, London, Special Publications, pp. 121–136.

Evjen, H.M., 1936. The place of the vertical gradient in gravitational interpretations.Geophysics 1, 127–136.

Farhi, W., Boudella, A., Saibi, H., Bounif, M.O.A., 2016. Integration of magnetic, gravity,and well data in imaging subsurface geology in the Ksar Hirane region (Laghouat,Algeria). J. Afr. Earth Sci. 124, 63–74.

Gunn, P.J., 1997. Application of aeromagnetic surveys to sedimentary basin studies.AGSO J. Aust. Geol. Geophys. 17 (2), 133–144.

Kogbe, C.A., 1989. Cretaceous and tertiary of the iullemmeden basin in Nigeria. In:Kogbe, C.A. (Ed.), Geology of Nigeria, second ed., pp. 377–421.

Kogbe, C.A., Ajakaiye, D.E., Matheis, G., 1983. Confirmation of a rift structure along theMid-Niger valley, Nigeria. J. Afr. Earth Sci. 1, 127–131.

Lopes de Castro, D., Bezerra, F.H.R., Sousa, M.O.L., Fuck, R.A., 2012. Influence ofNeoproterozoic tectonic fabric on the origin of the Potiguar Basin, northeastern Braziland its links with West Africa based on gravity and magnetic data. J. Geodyn. 54,29–42.

MacLeod, I.N., Jones, K., Dai, T.F., 1993. 3-D analytic signal in the interpretation of totalmagnetic field data at low magnetic latitudes. Explor. Geophys. 24, 679–688.

Megwara, J.U., Udensi, E.E., 2014. Structural analysis using aeromagnetic data: Casestudy of parts of southern Bida basin, Nigeria and the surrounding basement rocks.Earth Sci. Res. 3 (2), 27–42.

Mohamed, H., Mizunaga, H., Saibi, H., 2020. Computation of geophysical magnetic datafor a buried 3-D hexahedral prism using the Gauss-Legendre Quadrature Method.Near Surf. Geophys.

Nabighian, M.N., 1972. The analytic signal of two-dimensional magnetic bodies withpolygonal cross-section: its properties and use for automated anomaly interpretation.Geophysics 37, 507–517.

Ojo, S.B., 1990. Origin of a major aeromagnetic anomaly in the Middle Niger Basin,Nigeria. Tectonophysics 185, 153–162.

Ojo, O.J., 2012. Depositional environments and petrographic characteristics of BidaFormation around share-pategi, northern Bida basin, Nigeria. J. Geogr. Geol. 4 (1),224–241.

Ojo, O.J., Akande, S.O., 2013. Petrographic facies, provenance and paleoenvironments ofthe Lokoja Formation southern Bida basin, Nigeria. J. Min. Geol. 49 (2), 93–109.

Ojo, O.J., Bamidele, T.E., Adepoju, S.A., Akande, S.O., 2020. Genesis andpaleoenvironmental analysis of the ironstone facies of the maastrichtian PattiFormation, Bida basin, Nigeria. J. Afr. Earth Sci. 174.

Phillips, J.D., 2000. Locating magnetic contacts: a comparison of the horizontal gradient,analytic signal, and local wavenumber methods. In: SEG Technical ProgramExpanded Abstracts, 2000, pp. 402–405.

Rahaman, M.A.O., Fadiya, S.L., Adekola, S.A., Coker, S.J., Bale, R.B., Olawoki, O.A.,Omada, I.J., Obaje, N.G., Akinsanpe, O.T., Ojo, G.A., Akande, W.G., 2018. A revisedstratigraphy of the Bida Basin, Nigeria. J. Afr. Earth Sci.

Roest, W.R., Verhoef, J., Pilkington, M., 1992. Magnetic interpretation using the 3-Danalytic signal. Geophysics 57, 116–125.

Saibi, H., Aboud, E., Gottsmann, J., 2015. Curie point depth from spectral analysis ofaeromagnetic data for geothermal reconnaissance in Afghanistan. J. Afr. Earth Sci.111, 92–99.

Salawu, N.B., Fatoba, J.O., Adebiyi, L.S., Ajadi, J., Saleh, A., Dada, S.S., 2020.Aeromagnetic and remote sensing evidence for structural framework of the middleNiger and Sokoto basins, Nigeria. Phys. Earth Planet. In. 309.

Salawu, N.B., Fatoba, J.O., Adebiyi, L.S., Eluwole, A.B., Olasunkanmi, N.K., Orosun, M.M.,Dada, S.S., 2021. Structural geometry of Ikogosi warm spring, southwestern Nigeria:evidence from aeromagnetic and remote sensing interpretation. Geomech. Geophys.Geo- energ. Geo-resour. 7, 26.

Smith, R.S., Thurston, J.B., Dai, T., MacLeod, I.N., 1998. iSPITM – the improved sourceparameter imaging method. Geophys. Prospect. 46, 141–151.

Thurston, J.B., Smith, R.S., 1997. Automatic conversion of magnetic data to depth, dipand susceptibility contrast using the SPI (TM) method. Geophysics 62, 807–813.

Udensi, E.E., Osazuwa, I.B., 2004. Spectra determination of depths to magnetic rocksunder the nupe basin, Nigeria. Nigerian Assoc. Petrol. Exploration. Bullet. 17, 22–37.

Zaborski, P.M., 1998. A review of the Cretaceous systems in Nigeria. Afr. Geosci. Rev. 5,385–483.

Ziegler, P.A., Cloetingh, S., 2004. Dynamic processes controlling evolution of riftedbasins. Earth Sci. Rev. 64, 1–50.