Abstract
A new gravity survey was carried out in the northern part of the onshore Kribi- Campo sub-basin in Cameroon. The data were incorporated to the existing ones and then analyzed and modeled in order to elucidate the subsurface structure of the area. The area is characterized in its north-western part by considerably high positive anomalies indicative of the presence of a dense intrusive body. We find, 1) from the analysis of the gravity residual anomaly map, the high positive anomalies observed are the signature of a shallow dense structure; 2) from the multi-scale analysis of the maxima of the horizontal gradient, the structure is confined between depths of 0.5 km and 5 km; 3) from the quantitative interpretation of residual anomalies by spectral analysis, the depth to the upper surface of the intrusive body is not uniform, the average depth of the bottom is h1 = 3.6 km and the depths to particular sections of the roof of the intrusion are h2 = 1.6 km and h3 = 0.5 km; 4) and the 3D modeling gives results that are suggestive of the presence of contacts between rocks of different densities at different depths and a dense intrusive igneous body in the upper crust of the Kribi zone. From the 3D model the dense intrusive igneous block is surrounded by sedimentary formations to the south-west and metamorphic formations to the north-east. Both formations have a density of about 2.74 g/cm3. The near surface portions of this igneous block lie at a depth range of 0.5 km to 1.5 km while its lower surface has a depth range of 3.6 km to 5.2 km. The shape of the edges and the bottom of the intrusive body are suggestive of the fact that it forms part of a broader structure underlying the Kribi-Campo sub-basin with a great influence on the sedimentary cover.
Highlights
According to [1], the Aptian salt basin of Equatorial West Africa is a combination of seven basins among which are the Rio del Rey and the Douala/Kribi-Campo basins
There is a slide shift of the depth of the center of the body that extends to 5.2 km approximately. This value agrees with the results provided by the spectral analysis method which give the average depth of the intrusive body between 0.5 km and 3.6 km
The depth of 1.6 km obtained for some sections of the body by spectral analysis has been confirmed by the approximately 1.5 km obtained for particular sections of the roof of the body
Summary
According to [1], the Aptian salt basin of Equatorial West Africa is a combination of seven basins among which are the Rio del Rey and the Douala/Kribi-Campo basins. The Doula/Kribi-Campo basin has two sub-basins: the Douala sub-basin to the North and the Kribi-Campo sub-basin to the South. The Kribi-Campo sub-basin is located between 2 ̊20'N and 3 ̊20'N, and extends over 6150 km offshore and 45 km in a triangular onshore area [2]. It is limited to the South by the Campo high, to the east by the Precambrian basement, and to the North by a possible Aptian salt and/or the northern end of the Kribi Fracture Zone noted Kribi FZ (Figure 1). The western limit of the sub-basin seems to be broadly defined by the Kribi Fracture Zone [2]. The green rock belts (GRB) and gneiss are part of a geological unit called “Nyong Unit”
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