Hidden Sub-Basins Beneath Nigeria’s Chad Basin Revealed by High-Resolution Aeromagnetic Survey

Deep beneath the dusty plains of northeastern Nigeria, one of the country’s largest onshore sedimentary basins has just been mapped in unprecedented detail, and the results could reshape the search for oil and gas in West Africa. A team of geologists at Abubakar Tafawa Balewa University in Bauchi has re-evaluated the petroleum prospects of the Nigerian sector of the Chad Basin, known locally as the Bornu Basin, using high-resolution airborne magnetic data that cover the entire basin and its surrounding basement terrains. Their analysis, published in Discover Geoscience, identifies six buried sub-basins, two of which stand out as prime candidates for hydrocarbon accumulation, with sedimentary fill reaching roughly six kilometres in thickness in places.

The Bornu Basin is no ordinary piece of real estate. It is the Nigerian portion of the vast intracontinental Chad Basin, which touches five countries: Cameroon, the Central African Republic, Chad, Niger and Nigeria. Bordered to the south by the Benue Trough and to the west by the Central Nigerian Basement Complex, the basin belongs to the broader West and Central African Rift System, a network of rift-related sedimentary basins that share a common tectonic history. Renewed interest in Nigeria’s inland basins has been fuelled by recent petroleum discoveries in neighbouring basins, including the Upper Benue Trough, the Muglad Basin of Sudan and South Sudan, Chad’s Doba, Doseo and Salamat basins, and Niger’s Termit Basin, all of which evolved under similar tectonic regimes.

Earlier geochemical and heat-flow studies had already suggested that the Bornu Basin holds promise, particularly for gas generation, but a viable petroleum system requires more than mature source rocks. Explorers need to know where sediments are thick enough to have buried organic matter to the right temperatures, and where faults and fractures can act as traps and migration pathways. That is precisely where the new study makes its mark: by combining basin-wide coverage with modern interpretation techniques, the researchers produced a far more complete picture of the basin’s hidden architecture than previous, more localised efforts.

The data came from the Nigerian Geological Survey Agency, acquired by Fugro Geophysical Company, and the team applied a battery of processing steps designed to sharpen the magnetic signal. They first separated regional and residual magnetic components using Gaussian filtering, then applied a reduction-to-pole transformation to shift anomalies directly above their source bodies. Because the study area sits at low magnetic latitude, where that transformation is notoriously unstable, the researchers also computed the analytic signal, an enhancement that works regardless of the direction of magnetisation. Total horizontal derivative maps, upward-continued to 500 metres and 2 kilometres, highlighted lithologic contacts and basin boundaries, while tilt-derivative analysis and CET Grid Analysis extracted linear structures representing faults and fractures.

For the crucial task of estimating how deep the buried basement lies, the team turned to three-dimensional Located Euler Deconvolution, a technique prized for its accurate source positioning and its independence from assumptions about magnetisation direction. The resulting depth-to-basement map spans values from about 5,800 metres below the reference datum to 220 metres above it, with the deepest sedimentary accumulations concentrated in the central and eastern portions of the basin, around Baga, Monguno, Maiduguri, Gashua, Geidam, Potiskum, Azare and east of Damaturu. The western part of the study area, by contrast, is dominated by shallow or exposed basement with less than two kilometres of sedimentary cover.

The basement topography reconstructed from the Euler solutions turned out to be strikingly undulating, especially in the eastern half of the basin. Six sub-basins emerged from the analysis, separated by igneous and volcanic highs. Two of them dominate the picture. The largest, located in the northeastern part of the basin, trends northeast to southwest, stretches roughly 250 kilometres in length and 95 kilometres in width, and reaches thicknesses of about six kilometres in places. The second major sub-basin sits in the central region, extends about 140 kilometres and exceeds three kilometres in thickness. The remaining four sub-basins are shallower, with sedimentary fills of less than 2.5 kilometres.

The extracted lineaments, ranging from about 10 to more than 150 kilometres in length, weave an interconnected structural network across both the exposed basement and the sediment-covered basin. Their dominant orientation is northeast to southwest, particularly east-northeast to west-southwest, with subordinate northwest to southeast and north-northeast to south-southwest trends. This structural grain matches the regional tectonic fabric documented in earlier studies of the Bornu Basin and the nearby Upper Benue Trough, and is interpreted as reflecting reactivated Pan-African basement fabrics and Cretaceous rifting. In petroleum terms, such fault and fracture systems matter enormously: they can enhance reservoir permeability, provide migration pathways for hydrocarbons, and create structural traps where faults are sealed laterally or capped by impermeable strata.

One of the most intriguing findings concerns volcanic intrusions. The analytic signal and Euler deconvolution results suggest that volcanic bodies within the Gongola arm of the Northern Benue Trough extend northward into the Bornu Basin, corroborating earlier reports and even the penetration of such intrusions by the Kanadi exploratory well. Igneous intrusions are a double-edged sword in petroleum geology. On one hand, they can locally heat adjacent sediments and accelerate the maturation of organic matter into oil and gas; on the other, they can alter reservoir quality and disrupt fluid pathways. The authors stress that their study did not specifically assess thermal maturity, so the precise role of these intrusions in the basin’s petroleum system remains an open question that demands geochemical, thermal and basin-modelling follow-up work.

The depth estimates also invite comparison with earlier studies, which reported maximum basement depths beneath the giant northeastern sub-basin ranging from about 3 to 6.2 kilometres depending on the method used. The 5.8-kilometre maximum identified in the new work sits near the upper end of that range and is consistent with estimates from spectral and source-parameter imaging techniques, while some prior estimates in the central part of the basin appear to have overestimated depths relative to the new results. The discrepancies underscore how sensitive depth estimates are to data resolution, processing choices and spatial coverage, which is exactly why a consistent, basin-wide dataset and a single, robust interpretation method can add so much value.

Taken together, the findings point to two highly prospective sub-basins characterised by substantial sedimentary thickness, intersections of regional fault systems and proximity to volcanic intrusions, a combination that the authors argue makes them the most favourable segments of the basin for hydrocarbon occurrence. The exploration wells Kanadi and Albarka, which encountered total sedimentary thicknesses of 3,048 and 3,470 metres respectively within the Bima, Gongila, Fika and Chad Formations, provide independent support for the substantial accumulations inferred from the magnetic data. The sedimentary succession itself, spanning continental Bima sandstones, shallow-marine Gongila Formation, the organic-rich Fika Shale, deltaic Gombe deposits and the younger Kerri-Kerri and Chad Formations, includes the source-rock intervals that geochemists have long flagged as promising. What the new study adds is a roadmap: by pinpointing where thick sediments coincide with dense structural fabric, it gives explorers a rational basis for prioritising seismic acquisition and, eventually, exploratory drilling. For a nation eager to grow its petroleum reserves beyond the mature Niger Delta, the buried depocentres of the Bornu Basin may represent one of the most compelling frontier plays on the African continent, and the next chapter of the story will be written with seismic surveys, geochemistry and, ultimately, the drill bit.

Subject of Research: Aeromagnetic re-evaluation of petroleum prospectivity in the Nigerian sector of the Chad (Bornu) Basin

Article Title: Petroleum prospect re-evaluation of the Nigerian sector of the Chad (Bornu) Basin using high-resolution aeromagnetic data

Article References: Petroleum prospect re-evaluation of the Nigerian sector of the Chad (Bornu) Basin using high-resolution aeromagnetic data. (n.d.). https://doi.org/10.1007/s44288-026-00730-z

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00730-z

Keywords: Bornu Basin, Chad Basin, aeromagnetic data, depth to basement, hydrocarbon prospectivity, sub-basins, Euler deconvolution, analytic signal, lineaments, volcanic intrusions, West and Central African Rift System, Nigeria