GRAVITY INVESTIGATIONS IN THE MIDDLE NIGER BASIN AREA, NIGERIA

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OJO, Samuel Bakare
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Abstract
Gravity measurements carried out in the Middle Niger Basin area show that the area is characterised by negative Bouguer anomalies ranging in value from -67 mgal to +15 mgal. The free-air anomalies are distributed about a mean value of approximately +5 mgal. which suggests that the area is approximately compensated. A regional anomaly ranging in value from about -20 mgal in the sourthern parts of the area to about -20 mgal in the northern parts of the area is correlated with a gradual thickening of the crust from the South to the North. Major negative residual anomalies centred on the basin are explained by the presence of thick Cretaceous sedimentary rocks in the area. Positive residual anomalies also occur over parts of the basin and these are attributed to a high-density metamorphic basement, and to masses which are probably of scirest composition. From two dimensional modelling based on gravity profiles it is estimated that the maximum possible thickness of the 6retaceous sediments is generally of the order of 2km, and is nowhere considered to exceed 2.7 km. The gravity pattern at the boundaries of the basin indicates that the contacts at the edges of the basin are probably not faulted. The basin is therefore thought to be an area of local subsidence.
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Thesis submitted to the Ahnadu Bello University for the degree of Master of Science Department of Physics Ahmadu Bello University Zaria - Nigeria
Keywords
GRAVITY, INVESTIGATIONS, MIDDLE, NIGER, BASIN, AREA,, NIGERIA
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