Gravity Model for an Anomalous Body Located in the NW Portion of the Douala Sedimentary Sub-Basin, Cameroon (Central Africa)

Abstract

Gravity studies have been carried out in the Douala sub-basin which is a sedimentary basin located both onshore and offshore on the South coast of Cameroon between latitudes 3˚03'N and 4˚06'N and longitudes 9˚00' and 10˚00'E, covering a total surface area of 12,805 km 2 . On its onshore portion, the Douala sub-basin has a trapezoic shape and covers a total surface area of about 6955 km 2 while the offshore part covers an area of about 5850 km 2 . Gravity data used in this study are constituted of 912 gravity data points located between longitudes 8˚10.2' to 10˚59.4'E and latitudes 2˚30.6' to 4˚59.4'N and the study area is located to the NW section of the onshore portion of the Douala sub-basin. This study area is characterised by considerably high positive anomalies attaining peak values of about 104.1 mGals at longitude 9˚9.9' and latitude 4˚1.1' with contour lines which are mostly oriented in the NNE direction. Residual anomalies were extracted by upward continuation of the Bouguer anomaly field at an optimum height of 30 km. This residual field and those obtained by the separation of polynomial of order 4 had a very high correlation coefficient factor of 0.979. The multi-scale horizontal derivative of the vertical derivative (MSHDVD) method was applied on the extracted residual anomalies for the delimitation of possible contacts in the source while the amplitude spectrum was used to estimate the depth to the top of the po-* Corresponding author. E. N. Ndikum et al.525 tential field source. The MSHDVD method did not delimite any clear cut contacts in the source but the amplitude spectrum estimated the potential field source at a depth of about 4.8 km. The ideal body theory was used to determine the density contrast along a 65 km NW-SE profile yielding a value of 0.266 g/cm 3 . 2.5D modelling aimed at bringing out the underlying structural layout of this study area presents a source body which is very probably an intrusive igneous block surrounded by sedimentary formations and having a density of 2.77 g/cm 3 at a depth of about 5.88 km below the surface and an average thickness of about 26.95 km.

Gravity study of the Douala sub-basin (Cameroon) using Euler 3D deconvolution, source edge detection (SED) and special function analysis

“…5a, b and 6b) clearly portray the outline of a near circular geologic body which extends deep into the crust beneath this study area. This of course confirms the presence of a deeper structure of intrusive origin [13,14]. The absence of depth location plots toward the south of these plots further suggests that this intrusive body in its southern section stretches beyond this study area.…”

“…From the works of [13,14], results of spectral analysis which were further backed by those of 2.5D modeling suggested the presence of an intrusive body of density 2.77 g/ cm 3 of igneous origin in this study area located at a depth of about 4.2 km. This body was shown to have a thickness of about 26 km.…”

“…2) was obtained by gridding the data using the minimum curvature grid and then plotted with contour intervals of 3 mGal. It had been shown earlier on [13] that the optimum height of upward continuation required to completely carry out a residual-regional separation in this area of study is equal…”

“…The Douala sedimentary sub-basin which constitutes the upper section of the Douala-Kribi/Campo sedimentary basin is one of the main basins of the Cameroon Atlantic basin located in the Gulf of Guinea. This sub-basin, unlike the adjacent Kribi/Campo sub-basin which has been subject to a number of geophysical studies [1][2][3][4][5][6][7][8][9][10][11][12], has in recent times recorded a few number of geophysical studies like those of [13][14][15]. Using audio magnetotellurics soundings, [12] were able to highlight two blocks with different morphologies on the basement-sedimentary transition zone around the eastern margin of the Douala basin and they as well estimated the total sedimentary thickness at 1.1 km.…”

Impact of the South Atlantic Opening on the Origin and the Tectonic of the Mamfe, Douala and Rio Del Rey Sedimentary Basins, Geodynamics Implication

“…The geophysical works carried out in these basins aimed at the structural study and the realization of the anomaly and geological maps from the gravity, electrical, aeromagnetic and magnetotelluric data. These include those of Dumort [20], Collignon [21], Petters et al [22], Fairhead et al [23], Manguéllé-Dicoum et al [24], Poudjom Djomani et al [25], Benkhellil et al [26], Ndougsa Mbarga [27], Nouayou [28], Brownfield and Charpentier [29], Nvondo Owono [30], Nguimbous et al [31], Ndikum et al [32], Koum et al [33], Nzeuga et al ([34], [35], [36]).…”