Aeromagnetic Data Analysis for Subsurface Investigation of Benue Trough and Bornu Basin in Northeast Nigeria.
Abstract:
In this study, we conducted a geophysical investigation of subsurface structures in parts of Benue Trough and Bornu Basin, located in northeast Nigeria, using aeromagnetic data. The study area is bounded by latitude 9.50 N to 12.00 N and longitude 9.50 E to 12.00 E, and it is covered by 25 aeromagnetic maps. These maps were digitized on a 3 km by 3 km grid and combined to create a comprehensive aeromagnetic data file for the region, consisting of 7921 data points. The 3 km spacing interval imposed a Nyquist frequency of 0.167 km-1.
To facilitate interpretation, the obtained data underwent a filtering process to isolate the deep-seated (long wavelength) anomaly from the shallow (short wavelength) anomaly. The analysis revealed that low magnetic values were prevalent in the northern part of the study area. The magnetic (structural) trends observed were east-west, northeast-southwest, and northwest-southeast, with the northwest-southeast trend being dominant.
Various magnetic lineaments were identified in the study area, which were suggested to be extensions of landward oceanic fracture zones. Through the application of Centre for Exploration Targeting (CET) grid plug-ins, 2D subsurface modeling, and depth analysis using spectral analysis and source parameter imaging, we found that both Bornu Basin and Benue Trough exhibited similar structural relationships, with more structural activities observed in Bornu Basin, particularly in the basement complex region and the volcanic areas in the eastern part.
The analysis also revealed a maximum sedimentary thickness of 3.72 km, centered around Gombe and south of Damaturu and Bulkachuwa, according to spectral analysis. However, Source Parameter Imaging (SPI) indicated a maximum sedimentary thickness of about 5.0 km in the same areas. The 2D modeling results displayed sedimentary thicknesses ranging from 0.0 km to a maximum of 4.60 km, with the thickest regions around Gombe, Ako Gombe, Bulkachuwa, and Damaturu, where thicknesses ranged from 3.00 km to 4.60 km. These findings suggest that the area can potentially host hydrocarbons.
The agreement among the results obtained from different analytical methods further validated their accuracy. Additionally, the boundary between Bornu Basin and Upper Benue Trough was successfully delineated through trend analysis of the total magnetic intensity, upward continuation filter, and 2D modeling of subsurface structures, identifying the separation at approximately latitude 11.00 N, corresponding to the “Dumbulwa-Bage High.”
The subsurface lithology revealed two main units: a sedimentary rock unit underlain by basement rocks. The sedimentary unit comprised shales, sandstones, limestones, siltstones, clay, and non-marine facies, while the basement rocks consisted of pegmatite, granite gneiss, and migmatites.
Aeromagnetic Data Analysis for Subsurface Investigation of Benue Trough and Bornu Basin in Northeast Nigeria.