By Ekpa, Moses Member Mark
Integrated geophysical study involving aeromagnetic and aerogravity methods were carried out
to investigate the Niger Delta in Nigeria. This was aimed at investigating the cause and nature of
anomalous bodies within parts of Niger Delta studied. The airborne gravity and magnetic data
used in this research work were obtained from the Nigerian Geological Survey Agency (NGSA)
Abuja. The airborne data were collected by Fugro Airborne Survey Limited for the agency using
Scintrex CG-3M Autograv gravimeter for the gravity data and Optical Pumped Caesium Vapour
Magnetometer for the magnetic data. Four sheets each of digital airborne gravity and magnetic
data, totaling eight sheets covering the study area were used in the study. Spectral analysis,
standard Euler deconvolution, source parameter imaging (SPI), forward and inverse modeling
techniques were employed in quantitative interpretation to determine depth/thickness of the
sedimentary basin, basement topography, structural trends, curie point depth, thermal gradient,
heat flow, density contrasts, magnetic susceptibility and types of mineralization prevalent in the
area. The residual anomalies were enhanced by applying a high pass filter of order zero and then
gridded. The data were modeled using Oasis Montaj, Winglink, Microsoft Excel, Fourpot and
Surfer 10 software. The analyses were carried out for both aeromagnetic and aerogravity data.
The Bouguer anomaly of the study area varied from -7.0 to 37.7mGal while the residual Bouguer
anomaly varied from -19.6 to 25.7mGal. The total magnetic intensity (TMI) anomalies had
values of between -53.7nT and 119.5nT while the residual magnetic intensity ranged from -52.5
to 58.0nT. The spectral analysis revealed the depth to magnetic sources varying from 2.5 to
5.5km while the shallow magnetic sources varied from 0.89 to 1.47km. The geothermal analysis
revealed the curie point depth ranging from 11.782 to 18.048km and the calculated geothermal
gradient ranged from 32.137 to 49.231o???−1. The heat flow values ranged from 80.343 to
7
123.080???−2. The SPI gave values ranging from -249.7 to -5031.7m for shallow and deep
lying magnetic anomalous bodies, -539.7 to -4276.0m for shallow and deep lying gravity
anomalous bodies. The windowed Euler-3D for TMI field revealed depths ranging from 644.6m
to -1892.2m for structural index of one; 1135.2m to 4036.6m for structural index of two and
615.3m to -6175.3m for structural index of three. The Bouguer gravity result revealed the depth
range of 1355.5 to -1518.1 m for structural index of one; 2384.5 to -3283.2m for structural index
of two and 2426.0 to -5011m for structural index of three. The forward and inverse modeling
gave the susceptibility values for the modeled profiles 1, 2, 3, 4 and 5 as 0.0100, 0.0002, 0.0120,
0.0250 and 0.0003SI respectively, with their respective depths of 4742, 4792, 2614, 5169 and
3873m. The modeled profiles 6, 7, 8, 9 and 10 gave density values as 1.820, 2.410, 0.720, 2.310
and 2.100 ???−3respectively, with their respective depths of 3872, 4228, 4880, 3560 and
2527m. The results from this study have thrown more light to the understanding of the depth to
basement, basement topography, structural trends, density contrasts, magnetic susceptibility,
curie point depth, thermal gradient and heat flow in the study. These will be of economic benefit
to the country if well harnessed.