ISSN 1794-6190 e-ISSN 2339-3459 https://doi.org/10.15446/esrj.v27n3.105868 EARTH SCIENCES RESEARCH JOURNAL Earth Sci. Res. J. Vol. 27, No. 3 (September, 2023): 251- 258 G EO PH Y SI C S An integrated approach of advanced methods for mapping geologic structures and sedimentary thickness in Ukelle and adjoining region (Southeast Nigeria) Stephen E. Ekwok1, Ahmed M. Eldosouky2, Ubong C. Ben3, Ogiji-Idaga M. Achadu3, Anthony E. Akpan1, Abdullah Othman4, Luan Thanh Pham5* 1. Applied Geophysics Programme, Department of Physics, University of Calabar, PMB 1115, Calabar, Cross River State, Nigeria. 2. Department of Geology, Suez University, Suez, 43518, Egypt 3. Department of Geology, University of Calabar, PMB 1115, Calabar, Cross River State, Nigeria 4. Department of Environmental Engineering, Umm Al-Qura University, Makkah, Saudi Arabia 5. Faculty of Physics, University of Science, Vietnam National University, Hanoi, Viet Nam *Corresponding author: luanpt@hus.edu.vn How to cite item: Ekwok, S. E., Eldosouky, A. M., Ben, U. C., Achadu, O. I. M., Akpan, A. E., Othman. A., & Pham, L. T. (2023). An integrated approach of advanced methods for mapping geologic structures and sedimentary thickness in Ukelle and adjoining region (Southeast Nigeria). Earth Sciences Research Journal, 27(3),v251-258 https://doi.org/10.15446/esrj.v27n3.105868 Manuscript received: 17/11/2022 Accepted for publication: 05/10/2023 Keywords: Edge detection; Tilt-depth; Geologic structures; Ukelle; Southeast Nigeria. Palabras clave: detección de bordes; método de inclinación y profundidad; estructuras geológicas; Ukelle; Sudeste de Nigeria. ABSTRACT High-resolution aeromagnetic data were enhanced using recent and advanced filters to map the geologic structures of the Ukelle and adjoin region (Southeast Nigeria). Aeromagnetic data were reduced to the equator (RTE) and upward continued to 100 m. Subsequently, enhancement operations like the tilt angle of the horizontal gradient (TAHG), lo- gistic function of the horizontal gradient (LTHG), and fast sigmoid function (FSED) operations were carried out. The results from these filters indicated that the ENE-WSW, NE-SW, NNE-SSW, and NNW-SSE orientations dominate the structural pattern of the Ukelle region. In addition, the edge filters delineated NE-SW trending synclinal structures that match the location of thick (500-1400 m) sedimentation obtained by the tilt-depth (TD) method. Furthermore, the structural map obtained from remote sensing data validated the lineament orientations and position of the NE-SW trending synclinal structure. The results also showed that the study location’s southeastern and northwestern flanking portions, controlled by extensive Santonian igneous intrusions and metamorphisms, are characterized by high linea- ments and thin (0-500 m) sedimentation. The observed thin sedimentation is believed to be caused by widespread Santonian tectonic events in the area. At the same time, related geologic structures served as migration pathways and accumulation zones for rift mineralization. Acercamiento integrado de métodos avanzados para el mapeo de estructuras geológicas y espesor sedimentario en Ukelle y regiones adyacentes, en el sudeste de Nigeria RESUMEN En este trabajo se usaron filtros recientes y avanzados para mejorar la información aeromágnetica de alta resolución que permitiera mapear las estructuras geológicas de Ukelle y las regiones con las cuales limita (en el sudeste de Nigeria). A la información aeromagnética se le aplicó la Reducción al Ecuador y continuó hasta los 100 metros. Luego se reali- zaron operaciones de mejoría como el ángulo de inclinación del gradiente horizontal, función logística del gradiente horizontal, y la función rápida sigmoide. Los resultados obtenidos con estos filtros indicaron que las orientaciones ENE-OSO, NE-SO, NNE-SSO y NNO-SSE dominan el patrón estructural de la región Ukelle. Adicionalmente, los filtros de borde delinearon que la tendencia NE-SO de las estructuras sinclinales coinciden con la ubicación de la densa masa sedimentaria (entre 500 y 1400 metros) obtenida con el método de inclinación y profundidad. Además, el mapa structural obtenido con la información de teledetección validó las orientaciones de lineamiento y la tendencia en la posición de NE-SO de la estructura sinclinal. Los resultados también muestran que las áreas del sureste y del noroeste que flanquean la zona de estudio están controladas por grandes intrusiones y metaformismo ígneo del Santoniano y se caracterizan por grandes lineamientos y sedimentación delgada (0-500 metros). Se estima que la sedimentación delgada que se observó fue causada por los extendidos eventos tectónicos durante el Santoniano en el área. Simultánea- mente, las estructuras geológicas relacionadas sirvieron como caminos de migración y zonas de acumulación para la mineralización en zanjas de hundimiento. https://doi.org/10.15446/esrj.v27n3.105868 mailto:luanpt@hus.edu.vn https://doi.org/10.15446/esrj.v27n3.105868 252 Stephen Ekwok, Ahmed Eldosouky, Ubong Ben, Ogiji-Idaga Achadu, Anthony Akpan, Abdullah Othman, Luan Thanh Pham 1. Introduction Airborne magnetic method is one of the most suitable procedures for mapping near surface and underlying basement geologic structures (Ben et al., 2022a; 2022b). Analysis involving high resolution airborne magnetic data can be used to resolve the challenges involved in delineating subtle geologic features (Eldosouky, 2019; Almasi et al., 2014), detecting regional geological borders (Cooper and Cowan, 2008; Pham et al., 2019), delineation of depo- centres and basement framework (Ekwok et al., 2021a; 2021b; 2021c) as well as mapping of zones of mineralization and hydrothermal modifications (Ekwok et al., 2020a). The evaluation of linear edges and borders of magnetic sources which commonly reveal subsurface faults, fractures, contacts, as well as associated tectonic bodies, are useful in the interpretations of geological structures. Previous research has shown that the magnetic techniques are extremely useful as an investigative delineating tool when there are disparities between the different rock units (Dentith et al., 2000). Tectono-magnetic events of the area control development and expression of the geologic features of the region (Eldosouky et al., 2022). The tectonic settings, the structural framework, occurrence of rift minerals as well as the discovery of oil and gas in commercial quantity triggered extensive geoscience studies in the Benue Trough (Ekwok et al., 2022a; 2019). Nonetheless, due to the low degree of resolution, the boundaries cannot be directly mapped from the observed potential field data (Fedi and Florio, 2001). Several enhancement procedures have been developed by various researchers to properly delineate the geologic structures caused by tectonic events (Eldosouky et al., 2020; Jorge et al., 2023). The gradient amplitude technique (Cordell and Grauch, 1985) is commonly used for improving geologic borders. Hansen and deRidder (2006) used the curvature of the gradient amplitude in identifying linear structures. However, the gradient amplitude filter detects the borders of shallow sources better than deeper bodies (Arısoy and Dikmen, 2015). This is due to the inability of gradient amplitude to provide steady indicators from the borders of low and high amplitude magnetic signatures simultaneously (Eldosouky et al., 2020; Pham et al., 2022a, b). The analytic signal filter developed by Roest et al. (1992), which is also well known, is often used to locate the flank borders of magnetic anomalies (Pham et al., 2021a). Just like the gradient amplitude filter, the analytic signal filter performs defectively in the enhancement of magnetic anomalies created by joint deep and shallow sources (Pham et al., 2018; 2019; 2021b). Other enhancement operators like tilt derivative and theta are often used in mapping lineaments, and describing geologic structures of the bodies (Miller and Singh, 1994; Wijns et al., 2005). Pham et al. (2020, 2021c) introduced the improved logistic function and softsign function to increase the resolution of the edges. Eldosouky et al. (2020), Pham and Prasad (2023) reviewed the effectiveness of the filters in terms of their precision on the detection of borders of magnetic sources on both observed and theoretical data. Other improved enhancement operations like the spectral moments (Sun et al., 2016), TAHG (Ferreira et al., 2013), LTHG (Pham et al., 2019), and FSED (Oksum et al., 2021), can reveal lineaments of different anomalies. Previous studies in the Lower Benue Trough using magnetic data with low resolution obtained by Geological Survey of Nigeria (GSN) in 1974, were centered on the mapping of major intrusive structures, fault systems, stratigraphy, sediment thickness, spatial distribution of igneous intrusions, and delineation of depo-centres (Oha et al., 2016; Ofoegbu, 1984; Ofoegbu and Mohan, 1990). Later, increased interest amongst researchers were later generated on the geologic structural complexity caused by igneous intrusions, and associated rift-minerals in the area (Oha et al., 2016; Ofoegbu, 1984; Ofoegbu and Mohan, 1990). These geologic structural studies were investigated involving derivatives, analytic signal, low pass filtering, upward continuation, source edge detection, etc (Ekwok et al. 2019; 2020a). However, some local and subtle geologic structures were suppressed by these filters. The availability of improved filters (like the TAHG, LTHG, FSED, etc.) has made it easier to determine subtler anomalies and generate more detailed geologic structural information. These filters generate peak responses directly over source borders, and produce better resolution and distinctive lineament maps (Eldosouky et al., 2020; Pham et al., 2022b; Oksum et al., 2021; Kamto et al., 2023). This research involved the application of some recent filters such as the TAHG, LTHG and FSED to airborne magnetic data from the Ukelle and adjacent area (Southeast Nigeria) to map geologic boundaries. The mapping of these boundaries is expected to help determine lead-zinc, brine conduit, barite and ironstones accumulation zones within the Ukelle and environs. These minerals are reported in commercial quantity in other geologic units within the Abakiliki Anticlinorium (Uma and Lohnert, 1992; Uma, 1998). Moreover, the TD method was also applied to the magnetic dataset to determine the depth to the geologic structures, as well as sedimentary cover of the basement rocks. The findings from this research are expected to improve the existing knowledge on the geological structures and patterns, as well as thickness of the sediments in Southeast Nigeria. 2. Geologic setting The Ukelle region is sited in the Lower Benue Trough, on the northeastern flank of the Santonian Abakaliki Anticlinorium (Fig. 1). The investigated region is positioned between longitude 8000’ and 8030’E and latitude 6030’ and 7000’N. Figure 1. Geological map of the Ukelle and adjacent area. The series of events which resulted to the development of the Benue Trough and its constituent parts have been well documented (Onuoha and Ofoegbu, 1988). A thick sedimentary successions of the Cretaceous age occupy the Lower Benue Trough, and overlies the Precambrian basement mainly of composed of migmatic and granitic rocks. The Precambrian basement is overlain by the Albian Asu-River Group (ARG), which is composed of bluish black sandstone. The Eze-Aku Formation (EAF), which sits directly on the Asu-River Group, is made up of calcareous siltstone and shale, calcareous sandstones, and shelly and sandy limestone (Reyment, 1965). The Coniacian Awgu-Shale (AS) is dominated by marine fossiliferous, grey bluish shale, limestone, and calcareous sandstone. The Campanian Nkporo Shale (NS) which overlies the Agwu-Shale, is characterised by mostly marine arenaceous sandstone members. In general, tectonism has had a significant impact on the sedimentary series, which happened in two stages and resulted in the folding of the overlying sedimentary materials (Nwachukwu, 1972). The folding event that occurred in the Santonian period was the primary cause of the formation of the Abakaliki-Anticlinorium. The asymmetry and reversed faults linking with the folds that were created in this period indicate that they were majorly compressional in pattern. Benkhelil (1987) characterised the Abakaliki Anticlinorium happenings as a whole orogenic cycle encompassing sedimentation, compressive tectonics, magmatism, and metamorphism. The related magmatic happenings caused the introduction of numerous intrusions into the overlying ARG and EAF. The NS sits unconformably over the folded EAF and the ARG (that is, Abakaliki Anticlinorium) (Whiteman, 1982). The Ukelle area which is part of the Abakaliki Anticlinorium, is a prominent geological structure formed as a result of series of tectonic processes. It is situated within the larger Benue Trough, a major intra-continental rift basin that extends across several countries in West Africa (Benkhelil, 1989). The Abakaliki Anticlinorium is characterized by its distinct folding pattern, where rock layers are bent upwards into an arch-like structure known as an anticline. The primary tectonic process responsible for the formation of the Abakaliki 253An integrated approach of advanced methods for mapping geologic structures and sedimentary thickness in Ukelle and adjoining region Anticlinorium is compressional tectonics (Benkhelil, 1989). As a result, the originally horizontal sedimentary strata in the Abakaliki region were folded and uplifted, forming the characteristic anticlinal structure observed today (Benkhelil, 1989). The folding process is believed to have occurred during the Santonian period, as indicated by radiometric dating of the sedimentary rocks in the area (Benkhelil, 1989). Figure 2. Total magnetic intensity map of the Ukelle and adjacent area. 3. Data and method Data The high resolution airborne magnetic data used for this study which covers an area of about 25,000 km2, were purchased from the Nigerian Geological Survey Agency (NGSA). Fugro Airborne Surveys (FAS), Canada, under contract to the NGSA, acquired aero-geophysical data between the period of 2005 and 2010, covering the whole country. The dataset was acquired using a Flux-Adjusting Surface Data Assimilation System with 100 m of flight- line space, 500 m of tie line space, and terrain-clearance ranging from 80-100 m. Furthermore, Fugro Airborne Surveys, Canada, subtracted the regional field from measured magnetic data engaging the tenth generation of the International Geomagnetic Reference Field. Following the wide acceptance and availability of the IGRF, the main advantage of the IGRF is the reliability it offers in potential field survey practice (Reeves et al., 1997). The dataset used in this paper was converted to total magnetic intensity (Fig. 2) and then reduced to the equator before being upward continued to 100 m. (Fig. 3). Because the data was gathered at a low latitude, the magnetic data was reduced to the equator. Jain (1988) and Leu (1981) reported that RTE generates more reliable results, especially at middle and lower latitudes. Also, the data were upward continued to attenuate the geologic effects associated with very short wavelength anomalies. All the enhancement operations were carried out using the RTE upward continued to 100 m data. Figure 3. RTE data upward continued to 100 m. Methods Edge detection methods Ferreira et al. (2013) proposed the TAHG operator to outline the lateral boundaries, which is based on the derivatives of the horizontal gradient (THG). The filter is expressed as: TAHG = atan + �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� THG Z THG THG Y 2 2 (1) where ∂THG/∂x, ∂THG/∂y and THG/∂z are the THG derivatives, which is expressed as: THG= �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� F X F Y 2 2 (2) where (∂F/∂x) and (∂F/∂y) are the derivatives of the field F. Figure 4c shows the TAHG of synthetic magnetic data (Fig. 4b) of the bodies M1 and M2 in Figure 4a. We can see that the TAHG can balance different anomaly amplitudes, but it cannot provide the sharp edges. The LTHG technique is the enhanced type of the THG, which is centred on the logistic function and given by Pham et al. (2019): LTHG= exp1 2 2 �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� THG Z THG THG Y ���� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� ���� (3) Pham et al. (2019, 2022b) proved that 2 ≤ α ≤ 10 will produce the best solutions. As shown in Figure 4d, the LTHG can equalize different amplitudes, and provides sharper edges than the TAHG. 254 Stephen Ekwok, Ahmed Eldosouky, Ubong Ben, Ogiji-Idaga Achadu, Anthony Akpan, Abdullah Othman, Luan Thanh Pham The fast sigmoid function (FSED) is another detector, developed by Oksum et al. (2021). This technique is centred on the fast sigmoid function of the ratio of the derivatives of the THG. Its maximum values are used to detect the source borders. This technique is given by: FSED R R �� �� �� 1 1 ´ (4) where R THG Z THG X THG Y �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� 2 2 (5) As displayed in Figure 4e, the FSED also provides balanced anomalies and sharper edges than the TAHG. Figure 4. (a) Synthetic model, (b) magnetic anomaly, (c) TAHG, (d) LTHG, (e) FSED. As shown in Figures 4c and 4d, the depth of the source bodies has no effect on the TAHG and LTHG, and their peak values are near the true boundaries even for deep bodies. This is one of the benefits of the TAHG and LTHG over the horizontal gradient, which cannot delineate boundaries originating from deep magnetic bodies (Pham et al., 2022b; Eldosouky et al., 2020). The FSED also enhances the boundaries of both deep and shallow bodies and its peak values are near the real boundaries (Fig. 4e). Depth estimation method The TD technique is based on the relationship between tilt angle derivative (TDR) (Miller and Singh, 1994), horizontal position and depth of a vertical 2-D contact as (Salem et al., 2007): TDR F z F x F y �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� atan 2 2 (6) and TDR h z c == atan (7) where zc is the contact depth, and h is the horizontal location. Equation 7 shows that the contact location (h = 0) relates to the zero values of the TDR, and the depth relates to the horizontal distance between TDRs of 0 and and ±π/4. 4. Results In an attempt to offer better understanding of the location, trend and pattern of geologic structures in the Ukelle and adjoining regions of Southeast Nigeria, enhanced filters like the TAHG, LTHG and FSED were applied on the high resolution RTE magnetic data that were upward continued to 100 m (Fig. 3). Figure 5 signifies the output of the TAHG. The maxima of the method revealed lineaments caused by magnetic bodies. Nevertheless, sharp edges cannot be detected by this filter. The LTHG of upward continued RTE magnetic data is shown in Figure 6. This map displays a clearer delineation of geologic structures, which are much easier to visually interpret qualitatively. Figure 7 shows the output of the FSED. Like other methods, the FSED generates the edges with the same amplitude. Figure 5. TAHG map of the Ukelle and adjacent area. As shown in the synthetic model, the peak responses obtained from the TAED (Fig. 5), LTHG (Fig. 6), and FSED (Fig. 7) were positioned directly over magnetic source borders. The filters applied in this study (Figs. 5-7) delineated horizontal geologic structures with ENE-WSW, NE-SW, NNE-SSW, and NNW-SSE orientations. Figure 5 generated more connective linear features that are somewhat diffused. The low resolution of source edges in Figure 5 makes geologic interpretations more difficult. The LTHG and FSED simultaneously balanced the low and high amplitudes (Figs. 6 and 7). These filters also provide greater resolution and distinctiveness compared to the TAHG (Fig. 5). By comparing the results from the methods, we can say that the LTHG and FSED are precise and highly effective in identifying several geologic features associated with the Santonian Abakaliki Anticlinorium (Benkhelil, 1987), which were not clear in Figure 5. Since the TAED, LTHG, and FSED peaks respond to the source edges, we determined these peaks using the improved crest detection technique (Pham et al., 2023). Magnetic boundaries are then identified from the locations of the peaks. The overlay of the locations of the peaks is presented in Figure 8. Here, the peaks of the TAHG are shown by black dots, the peaks of the LTHG are displayed by cyan dots, while red dots respond to the FSED peaks. By mapping the maxima locations of the filters, the results for the edge locations are similar (Fig. 8). 255An integrated approach of advanced methods for mapping geologic structures and sedimentary thickness in Ukelle and adjoining region Figure 6. LTHG map of the Ukelle and adjacent area. Figure 7. FSED map of the Ukelle and adjacent area. Furthermore, the TD method (Salem et al., 2007) was applied to assess the depths of geologic structures within the study area. The main advantage of the TD method is that, unlike standard Euler deconvolution, it doesn’t require the window size (Ekwok et al., 2022a; 2020a; 2021b). The depth map (Fig. 9) revealed depth range of approximately 0-1400 m. This thin sedimentation is thought to be caused by the extensive invasion of the sediments by the Santonian intermediate-mafic igneous intrusions, as well as tuffs and calc-alkaline lavas intrusions (Benkhelil, 1987; Murat, 1970) in the study area. The tectonic event caused extensive baking of sediments, generation of metamorphosed rocks and creation of geologic structures in the region. Figure 8. Peaks of the TAHG (black dots), LTHG (cyan dots) and FSED (red dots). Figure 9. Tilt-depth map of the Ukelle and adjacent area. 5. Discussion The northeast-southwest structural trend controlled the basement framework and sedimentation pattern in the southeastern part of Nigeria (Benkhelil, 1987; Benkhelil et al., 1975; Burke et al., 1970). The lineaments within the investigated area that trend in NW-SE, NE-WS, NNE-SSW, and E-W directions were easily traced (Figs. 5-7). The LTHG (Fig. 6) and FSED (Fig. 7) filters are additionally efficient in mapping edges of the NE-SW trending synclinal structures associated the Abakaliki Anticlinorium. This NE-SW synclinal structure previously mapped by Ekwok et al. (2020a), partitioned the study area into northwest and southeast flanks (that is, folds/uplifts), that coincide with the zone characterised by relatively thick (500-1400 m) sedimentation (Fig. 7). The northwest and southeast flanks 256 Stephen Ekwok, Ahmed Eldosouky, Ubong Ben, Ogiji-Idaga Achadu, Anthony Akpan, Abdullah Othman, Luan Thanh Pham that correlated strongly with zones dominated by thin (0-500 m) Cretaceous sedimentary series, are controlled by widespread near-surface igneous, tuffs and calc-alkaline lavas intrusions (Benkhelil, 1987; Murat, 1972) as well as metamorphosed Albian shales (Ekwok et al., 2022c; 2021b; Benkhelil et al., 1975). The coexistence of uplifts/folds (positive anomalies) and synclines (negative anomalies) in Southeast Nigeria have been reported by previous studies (Benkhelil, 1987; Burke et al., 1970; etc). Generally, the uplifted regions are controlled by high concentration of lineaments (Fig. 8), caused by a series of elongated narrow folds within the ENE-WSW, NE-SW, NNE-SSW and NNW- SSE configurations of the Abakaliki sedimentary area triggered by the invasion of alkaline dolerites, basalts, and syenites (Murat, 1972) into the overlying sediments. The major structural pattern of the Benue Trough and Abakaliki Anticlinorium is NE-SW (Benkhelil, 1987; Murat. 1972; Burke et al., 1970), while some E-W lineaments pattern are described as transverse fractures to the major NE-SW fault along which massive intrusions were placed. Lineament maps (Fig. 10) were generated from magnetic data (Fig. 10a) and remote sensing involving shuttle radar topographic mission (SRTM) data (Fig. 10b). Fig. 10a is characterised by a wide range of geologic structures, while Fig. 10b is dominated by short lineaments and some regional structures. Besides, the NE- SW trending synclinal structure (Fig. 10a) with thick sedimentation was mapped also mapped (Fig. 10b). Generally, it was observed that the trending pattern of Fig. 10b correlates strongly with lineaments determined in Fig. 10a generated from the edge filters. Comparatively, the various results of the enhancement operation applied in this research showed that the LTHG and FSED methods generated sharper and more distinct geologic structures of the Ukelle and adjacent area, than the TAHG. In addition, there is a good correlation between lineaments in Fig. 10a and 10b, and the rose petals (Fig. 11) show trends in the ENE-WSW, NE-SW, NNE-SSW and NNW-SSE orientations. These geologic trends have been previously reported in the Lower Benue Trough (Ekwok et al., 2021a; 2021b; 2021c). The main strike orientation in the Lower Benue Trough and Abakaliki-Anticlinorium is represented by the ENE-WSW, NE-SW and NNE-SSW directions. The ENE, NE and NNE characterise the regional-strike of the lineaments that correspond to region (the Lower Benue Trough) that was tectonically disturbed during the Santonian period (Murat, 1970). Figure 10. (a) Magnetic lineaments map obtained from the edge filters, (b) GIS generated lineaments map from SRTM of the Ukelle and adjacent area. Figure 11. Rose diagrams of magnetic lineaments obtained from the edge filters (a) and (b) GIS lineaments. 257An integrated approach of advanced methods for mapping geologic structures and sedimentary thickness in Ukelle and adjoining region Conclusions Delineation of geologic structures and contacts in the Ukelle and adjoining area (Southeast Nigeria) involved the TAHG, LTHG, FSED, and the RTE total magnetic intensity data that were upward continued to 100 m. The filters generated geologic structures that trend in the ENE-WSW, NE-SW, NNE-SSW, NNW-SSE and NW-SE directions. Remote sensing involving SRTM data generated structural map that validated the structural orientations of lineaments obtained by the enhanced filters. Furthermore, the lineament maps delineated the NE-SW trending synclinal structures that coincide with the zone characterised by relatively thick (500-1400 m) sedimentary series revealed by the TD map. Also, the enhanced filters as well as the TD result mapped folds/ uplifts in the northwest and southeast flanks with thin (0-500 m) sedimentation, controlled by widespread Santonian igneous intrusions and metamorphism that caused high concentration of lineaments in these portions. Acknowledgments The authors thank the editors and three anonymous reviewers for their constructive comments and recommendations. References Almasi, A., Jafarirad, A., Kheyrollahi, H., Rahimi, M., & Afzal, P. (2014). Evalua- tion of structural and geological factors in orogenic gold type minera- lization using airborne geophysical data, Kervian area, NW of Iran. Ex- ploration Geophysics, 45(4), 261-270. https://doi.org/10.1071/EG13053 Arısoy, M. O., & Dikmen, U. (2015). Edge enhancement of magnetic data using fractional order derivative filters. Geophysics, 80(1), J7–J17. https://doi. org/10.1190/geo2013-0473.1 Ben, U. C., Ekwok, S. E., Achadu., O-I. M., Akpan, A. E., Eldosouky, A. M., Ab- delrahman, & Gómez-Ortiz, D. (2022b). A novel method for estimating model parameters from geophysical anomalies of structural faults using the manta-ray foraging optimization. Frontiers in Earth Science, 10, 870299. https://doi.org/10.3389/feart.2022.870299 Ben, U. C., Ekwok, S. E., Akpan, A. E., Mbonu, C. C., Eldosouky, A. M., Ab- delrahman, K., & Gómez-Ortiz, D. (2022a). Interpretation of magnetic anomalies by simple geometrical structures using the manta-ray fora- ging optimization. Frontiers in Earth Science, 10, 849079. https://doi. org/10.3389/feart.2022.849079 Benkhelil, J. (1987). Cretaceous deformation, magmatism and metamorphism in the lower Benue Trough. Nigeria. Geological Journal, 22(S2), 467-493. https://doi.org/10.1002/gj.3350220629 Benkhelil, J. (1989). The origin and evolution of the Cretaceous Benue Trough (Nigeria). Journal of African Earth Science, 8(2-4), 251-282. DOI: ht- tps://doi.org/10.1016/S0899-5362(89)80028-4 Benkhelil, M. G., Ponsard, J. F., & Saugy, L. (1975). The Bornu-Benue Trough, the Niger Delta and its Offshore: tectono-sedimentary reconstruction during the cretaceous and tertiary from geophysical data and geology. In: Kogbe, C. A. (Ed.). Geology of Nigeria. Elizabethan Press, Lagos, 277–309. Burke, I. C. C., Dessauvagie, T. F., & Whiteman, A. J. (1970). Geological history of the Benue Valley and adjacent areas. In: Dessauvagie, T. F. J., Whiteman, A. J. (Eds). African Geology, Ibadan University Press, Ibadan, 187-205. Cooper, G. R. J., & Cowan, D. R. (2008). Edge enhancement of potential-field data using normalized statistics. Geophysics, 73(3), H1–H4. https://doi. org/10.1190/1.2837309 Cordell, L., & Grauch, V. J. S. (1985). Mapping basement magnetization zones from aeromagnetic data in the San Juan basin. New Mexico. In: Hinze, W. J. (Ed.). The utility of regional gravity and magnetic anomaly maps. Society of Exploration Geophysicists, 181-197 Dentith, M. C., Cowan, D. R., & Tompkins, L. A. (2000). Enhancement of subtle features in aeromagnetic data. Exploration Geophysics, 31(1/2), 104-8. https://doi.org/10.1071/EG00104 Ekwok, S. E., Achadu, O. I. M., Akpan, A. E., Eldosouky, A. M., Ufuafuonye, C. H., Abdelrahman, K., & Gómez-Ortiz, D. (2022c). Depth estimation of sedimentary sections and basement rocks in the Bornu basin, Northeast Nigeria using high-resolution airborne magnetic data.  Minerals,  12, 285. https://doi.org/10.3390/min12030285 Ekwok, S. E., Akpan, A. E. Kudamnya, E. A., & Ebong, D. E. (2020b). Assessment of groundwater potential using geophysical data: a case study in parts of Cross River State, south-eastern Nigeria. Applied Water Science, 10, 144. https://doi.org/10.1007/s13201-020-01224-0 Ekwok, S. E., Akpan, A. E., Achadu, O. I. M., & Eze, O. E. (2021a). Structural and lithological interpretation of aero-geophysical data in parts of the Lower Benue Trough and Obudu Plateau, Southeast Nigeria. Advances in Space Research, 68(7), 2841-2854. https://doi.org/10.1016/j.asr.2021.05.019 Ekwok, S. E., Akpan, A. E., Achadu, O. I. M., Thompson, C. E., Eldosouky, A. M., Abdelrahman, K., & Andráš, P. (2022a). Towards understanding the source of brine mineralization in Southeast Nigeria: Evidence from hi- gh-resolution airborne magnetic and gravity data. Minerals, 12, 146. https://doi.org/10.3390/min12020146 Ekwok, S. E., Akpan, A. E., & Ebong, D. E. (2019). Enhancement and mode- lling of aeromagnetic data of some inland basins, southeastern Nigeria. Journal of African Earth Sciences, 155, 43-53. https://doi.org/10.1016/j. jafrearsci.2019.02.030 Ekwok, S. E., Akpan, A. E., & Ebong, E. D. (2021c). Assessment of crustal struc- tures by gravity and magnetic methods in the Calabar Flank and ad- joining areas of Southeastern Nigeria-a case study. Arabian Journal of Geosciences, 14(308), 1-10. https://doi.org/10.1007/s12517-021-06696-1 Ekwok, S. E., Akpan, A. E., Ebong, E. D., & Eze, O. E. (2021b). Assessment of depth to magnetic sources using high resolution aeromagnetic data of some parts of the Lower Benue Trough and adjoining areas, Southeast Nigeria. Advances in Space Research, 67(7), 2104-2119. https://doi.or- g/10.1016/j.asr.2021.01.0071000260 Ekwok, S. E., Akpan, A. E., & Kudamnya, E. A. (2020a). Exploratory mapping of structures controlling mineralization in Southeast Nigeria using high resolution airborne magnetic data. Journal of African Earth Science, 162, 1-11. https://doi.org/10.1016/j.jafrearsci.2019.103700 Ekwok, S. E., Akpan, A. E., Achadu, O. I. M., & Ulem, C. A. (2022b). Impli- cations of tectonic anomalies from potential field data in some parts of Southeast Nigeria. Environmental Earth Sciences, 81, 6. https://doi. org/10.1007/s12665-021-10060-7 Eldosouky, A. M. (2019). Aeromagnetic data for mapping geologic contacts at Samr El-qaa area, North Eastern Desert, Egypt. Arabian Journal of Geos- ciences, 12, 2. https://doi.org/10.1007/s12517-018-4182-2 Eldosouky, A. M., Ekwok, S. E., Akpan, A. E., Achadu, O. I. M., Pham, L. T., Ab- delrahman, K., Gómez-Ortiz, D., & Alarifi, S. S. (2022). Delineation of structural lineaments of Southeast Nigeria using high resolution aero- magnetic data. Open Geosciences, 14, 331–340. https://doi.org/10.1515/ geo-2022-0360 Eldosouky, A. M., Pham, L. T., Mohmed, H., & Pradhan, B. (2020). A comparati- ve study of THG, AS, TA, Theta, TDX and LTHG techniques for impro- ving source boundaries detection of magnetic data using synthetic mo- dels: A case study from G. Um Monqul, North Eastern Desert, Egypt. Journal of African Earth Sciences, 170, 103940. https://doi.org/10.1016/j. jafrearsci.2020.103940 Fedi, M., & Florio, G. (2001). Detection of potential fields source boundaries by enhanced horizontal derivative method. Geophysical Prospecting, 49(1), 40–58. https://doi.org/10.1046/j.1365-2478.2001.00235.x Ferreira, F. J. F., de Souza, J., de B. e S. Bongiolo, A., & de Castro, L. G. (2013). Enhancement of the total horizontal gradient of magnetic anomalies using the tilt angle. Geophysics, 78(3), J33–J41. https://doi.org/10.1190/ geo2011-0441.1 Hansen, R. O., & deRidder, E. (2006). Linear feature analysis for aeromagnetic data. Geophysics, 71 (6), L61–L67. https://doi.org/10.1190/1.2357831 https://doi.org/10.1071/EG13053 https://doi.org/10.1190/geo2013-0473.1 https://doi.org/10.1190/geo2013-0473.1 https://doi.org/10.3389/feart.2022.870299 https://doi.org/10.3389/feart.2022.849079 https://doi.org/10.3389/feart.2022.849079 https://doi.org/10.1002/gj.3350220629 https://doi.org/10.1016/S0899-5362(89)80028-4 https://doi.org/10.1016/S0899-5362(89)80028-4 https://doi.org/10.1190/1.2837309 https://doi.org/10.1190/1.2837309 https://doi.org/10.1071/EG00104 https://doi.org/10.3390/min12030285 https://doi.org/10.1007/s13201-020-01224-0 https://doi.org/10.1016/j.asr.2021.05.019 https://doi.org/10.3390/min12020146 https://doi.org/10.1016/j.jafrearsci.2019.02.030 https://doi.org/10.1016/j.jafrearsci.2019.02.030 https://doi.org/10.1007/s12517-021-06696-1 https://doi.org/10.1016/j.asr.2021.01.0071000260 https://doi.org/10.1016/j.asr.2021.01.0071000260 https://doi.org/10.1016/j.jafrearsci.2019.103700 https://doi.org/10.1007/s12665-021-10060-7 https://doi.org/10.1007/s12665-021-10060-7 https://doi.org/10.1007/s12517-018-4182-2 https://doi.org/10.1515/geo-2022-0360 https://doi.org/10.1515/geo-2022-0360 https://doi.org/10.1016/j.jafrearsci.2020.103940 https://doi.org/10.1016/j.jafrearsci.2020.103940 https://doi.org/10.1046/j.1365-2478.2001.00235.x https://doi.org/10.1190/geo2011-0441.1 https://doi.org/10.1190/geo2011-0441.1 https://doi.org/10.1190/1.2357831 258 Stephen Ekwok, Ahmed Eldosouky, Ubong Ben, Ogiji-Idaga Achadu, Anthony Akpan, Abdullah Othman, Luan Thanh Pham Jain, S. (1988). Total magnetic field reduction-the Pole or Equator? A model study. Canadian Journal of Exploration Geophysics, 24(2), 185-192. Jorge, V. T., Oliveira, S. P., Pham L. T., & Duong, V. H. (2023). A balanced edge detector for aeromagnetic data. Vietnam Journal of Earth Sciences, 43(3), 326–337. https://doi.org/10.15625/2615-9783/18461 Kamto, P. G., Oksum, E., Pham, L. T., & Kamguia, J. (2023). Contribution of ad- vanced edge detection filters for the structural mapping of the Douala Sedimentary Basin along the Gulf of Guinea. Vietnam Journal of Earth Sciences, 43(3), 287–302. https://doi.org/10.15625/2615-9783/18410 Leu, L. K. (1981). Use of reduction-to-the-equator process for magnetic data in- terpretation. Geophysics, 47, 445. Miller, H. G., & Singh, V. (1994). Potential field tilt a new concept for location of potential field sources. Journal of Applied Geophysics, 32(2-3), 213–217. https://doi.org/10.1016/0926-9851(94)90022-1 Murat, R. C. (1970). Stratigraphy and paleogeography of the Cretaceous and lower Tertiary in Southern Nigeria. In: Dessauvagie, T. F. J., Whiteman, A. J. (Eds.). African Geology, Ibandan University Press, Ibanan, 251-266. Nwachukwu, S. O. (1972). The tectonic evolution of the the southern portion of the Benue Trough, Nigeria. Geological Magazine, 109(05), 411-419. ht- tps://doi.org/10.1017/s0016756800039790 Ofoegbu, C. O. (1984). A model of the tectonic evolution of the Benue Trou- gh of Nigeria. Geological Rundschau, 73(3), 1007-1018. https://doi. org/10.1007/BF01820885 Ofoegbu, C. O., & Mohan, N. L. (1990). Interpretation of aeromagnetic anoma- lies over part of Southeastern Nigeria using three-dimensional Hilbert transformation.  Pure and Applied Geophysics,  134, 13–29. https://doi. org/10.1007/BF00878077 Oha, I. A., Onuoha, K. M., Nwegbu, A. N., & Abba, A. U. (2016). Interpreta- tion of high resolution aeromagnetic data over southern Benue Trough, southeastern Nigeria. Journal of Earth System Science, 125, (2) 369–385. https://doi.org/10.1007/s12040-016-0666-1 Oksum, E., Le, D. V., Vu, M. D., Nguyen, T. H. T., & Pham, L. T. (2021). A novel approach based on the fast sigmoid function for interpretation of poten- tial field data. Bulletin of Geophysics and Oceanography, 62(3), 543-556. https://doi.org/10.4430/bgta0348 Onuoha, K. M., & Ofoegbu, C. O. (1988). Subsidence and evolution of Nigeria’s continental margin: implications of data from Afowo-1 well Mar. Ma- rine and Petroleum Geology, 5, 175-181. https://doi.org/10.1016/0264- 8172(88)90022-0 Pham, L. T., Le, M. H., Oksum, E., & Do, T. D. (2018). Determination of maxi- mum tilt angle from analytic signal amplitude of magnetic data by the curvature-based method. Vietnam Journal of Earth Sciences, 40(4), 354–366. https://doi.org/10.15625/0866-7187/40/4/13106 Pham, L. T., Oksum, E., & Do, T. D. (2019). Edge enhancement of potential field data using the logistic function and the total horizontal gradient. Acta Geodaetica et Geophysica, 54(1), 143–155. https://doi.org/10.1007/ s40328-019-00248-6 Pham, L. T., Vu, T. V, Le Thi, S., & Trinh, P. T. (2020). Enhancement of po- tential field source boundaries using an improved logistic filter. Pure and Applied Geophysics, 177(11), 5237–5249. https://doi.org/10.1007/ s00024-020-02542-9 Pham, L. T., Kafadar, O., Oksum, E., & Hoang-Minh, T. (2021a). A comparative study on the peak detection methods used to interpret potential field data: A case study. Geocarto International, 37(13), 3679-3696. https:// doi.org/10.1080/10106049.2021.2007297 Pham, L. T., Oliveira, S. P., Le, M. H., Trinh, P. T., Vu, T. V., Duong, V. H., Ngo, T. N. T., Do, T. D., Nguyen, T. H., & Eldosouky, A. M. (2021b). Delineation of structural lineaments of the Southwest Sub-basin (East Vietnam Sea) using global marine gravity model from CryoSat-2 and Jason-1 satelli- tes. Geocarto International, 37(25), 7681-7698. https://doi.org/10.1080/ 10106049.2021.1981463 Pham, L. T., Oksum, E., Le, D. V., Ferreira, F. J. F., & Le, S. T. (2021c). Edge de- tection of potential field sources using the softsign function. Geocarto International, 37(14), 4255-4268. https://doi.org/10.1080/10106049.20 21.1981463 Pham, L. T., Oksum, E., Kafadar, O., Trinh, P. T., Nguyen, D. V., Vo, Q. T., Le, S. T., & Do, T. D. (2022a). Determination of subsurface lineaments in the Hoang Sa islands using enhanced methods of gravity total horizontal gradient. Vietnam Journal of Earth Sciences, 44(3), 395-409. https://doi. org/10.15625/2615-9783/17013 Pham, L. T., Oliveira, S. P., Eldosouky, A. M., Abdelrahman, K., Fnais, M. S., Xa- yavong, V., Andráš, P., & Le, D. V. (2022b). Determination of structural lineaments of Northeastern Laos using the LTHG and EHGA methods. Journal of King Saud University - Science, 34(3), 101825. https://doi.or- g/10.1016/j.jksus.2022.101825 Pham, L. T., & Prasad, K. N. D. (2023). Analysis of gravity data for extracting structural features of the northern region of the Central Indian Rid- ge. Vietnam Journal of Earth Sciences, 45(2):147–163. https://doi. org/10.15625/2615-9783/18206 Pham, L. T., Oksum, E., & Eldosouky, A. M. (2023). High precision subsurface structural mapping of the Trompsburg complex (South Africa) from gravity and magnetic data. Advances in Space Research, 71(5), 2348- 2356. https://doi.org/10.1016/j.asr.2022.10.019 Reeves, C., Reford, S., & Millingan, P. (1997). Airborne geophysics: old methods, new images. In: Gubins, A. (Ed.). Proceedings of the Fourth Decennial International Conference on Mineral Exploration, Australia, 13-30. Reyment, R. A. (1965). Aspects of the Geology of Nigeria. Ibadan University Press, Ibadan. Roest, W., Verhoef, J., & Pilkington, M. (1992). Magnetic interpretation using 3-D analytical signal. Geophysics, 57, 116–125. https://doi. org/10.1190/1.1443174 Salem, A., Williams, S., Fairhead, J. D., Ravat, D., & Smith, R. (2007). Tilt-dep- th method: a simple depth estimation method using first-order magnetic derivatives. Leading Edge, 26(12), 1502–1505. https://doi. org/10.1190/1.2821934 Sun, Y. Y., Yang, W. C., & Zeng, X. Z. (2016). Edge enhancement of potential fi eld data using spectral moments. Geophysics, 81(1), G1–G11. https:// doi.org/10.1190/geo2014-0430.1 Uma, K. O. (1998). The brine fields of the Benue Trough, Nigeria: a comparative study of geomorphic, tectonic and hydrochemical properties. Journal of African Earth Sciences, 26(2), 261-275. https://doi.org/10.1016/S0899- 5362(98)00009-8 Uma, K. O., & Lohnert, E. P. (1992). Research on the saline groundwaters in the Benue Trough, Nigeria: Preliminary results and projections. Zentralbla- tt fur Geologie und Palaontologie, 11, 2751-2756. Whiteman, A. J. (1982). Nigeria: Its Petroleum Geology, Resources and Potential. Graham and Trotham, London, 394 pp Wijns, C., Perez, C., & Kowalczyk, P. (2005). Theta map: edge detection in magne- tic data. Geophysics, 70(4), L39-L43. https://doi.org/10.1190/1.1988184 https://doi.org/10.15625/2615-9783/18461 https://doi.org/10.15625/2615-9783/18410 https://doi.org/10.1016/0926-9851(94)90022-1 https://doi.org/10.1017/s0016756800039790 https://doi.org/10.1017/s0016756800039790 https://doi.org/10.1007/BF01820885 https://doi.org/10.1007/BF01820885 https://doi.org/10.1007/BF00878077 https://doi.org/10.1007/BF00878077 https://doi.org/10.1007/s12040-016-0666-1 https://doi.org/10.4430/bgta0348 https://doi.org/10.1016/0264-8172(88)90022-0 https://doi.org/10.1016/0264-8172(88)90022-0 https://doi.org/10.15625/0866-7187/40/4/13106 https://doi.org/10.1007/s40328-019-00248-6 https://doi.org/10.1007/s40328-019-00248-6 https://doi.org/10.1007/s00024-020-02542-9 https://doi.org/10.1007/s00024-020-02542-9 https://doi.org/10.1080/10106049.2021.2007297 https://doi.org/10.1080/10106049.2021.2007297 https://doi.org/10.1080/10106049.2021.1981463 https://doi.org/10.1080/10106049.2021.1981463 https://doi.org/10.1080/10106049.2021.1981463 https://doi.org/10.1080/10106049.2021.1981463 https://doi.org/10.15625/2615-9783/17013 https://doi.org/10.15625/2615-9783/17013 https://doi.org/10.1016/j.jksus.2022.101825 https://doi.org/10.1016/j.jksus.2022.101825 https://doi.org/10.15625/2615-9783/18206 https://doi.org/10.15625/2615-9783/18206 https://doi.org/10.1016/j.asr.2022.10.019 https://doi.org/10.1190/1.1443174 https://doi.org/10.1190/1.1443174 https://doi.org/10.1190/1.2821934 https://doi.org/10.1190/1.2821934 https://doi.org/10.1190/geo2014-0430.1 https://doi.org/10.1190/geo2014-0430.1 https://doi.org/10.1016/S0899-5362(98)00009-8 https://doi.org/10.1016/S0899-5362(98)00009-8 https://doi.org/10.1190/1.1988184 _Hlk117383605 _Hlk140744517 _Hlk117383699 _Hlk117384045 _Hlk117383717 _Hlk117384107 _Hlk117384164 _Hlk117384629 _Hlk140744117 _Hlk140744971 _Hlk117384677 _Hlk140745779 _Hlk117384690 _Hlk117385327 _Hlk117384894 bau010 bau015 bau020 _Hlk140744829