OJG  Vol.4 No.10 , October 2014
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 km2. On its onshore portion, the Douala sub-basin has a trapezoic shape and covers a total surface area of about 6955 km2 while the offshore part covers an area of about 5850 km2. 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 potential 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/cm3. 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/cm3 at a depth of about 5.88 km below the surface and an average thickness of about 26.95 km.
Cite this paper: Ndikum, E. , Tabod, C. , Essimbi, B. , Koumetio, F. , Tatchum, N. , (2014) Gravity Model for an Anomalous Body Located in the NW Portion of the Douala Sedimentary Sub-Basin, Cameroon (Central Africa). Open Journal of Geology, 4, 524-541. doi: 10.4236/ojg.2014.410039.

[1]   Kenfack, P.L., Njike, P.R.N., Ekodeck, G.E. and Ngueutchoua, G. (2012) Fossils Dinoflagellates from the Northern Border of the Douala Sedimentary Sub-Basin (South-West Cameroon): Age Assessment and Paleoecological Interpretations. Geosciences, 2, 117-124. DOI: 10.5923/j.geo.20120205.03

[2]   Brownfield, M.E. and Charpentier, R. R. (2006) Geology and Total Petroleum Systems of the West-Central Coastal Province (7203), West Africa. US Geological Survey Bulletin 2207-B.

[3]   Tokam, K.A.P., Tabod, C.T., Nyblade, A.A., Julia, J., Wiens, D.A. and Pasyanos, M. (2010) Structure of the Crust Beneath Cameroon, West Africa, from the Join Inversion of Rayleigh Wave Group Velocities and Receiver Functions. Geophysical Journal International, 183, 1061-1076.

[4]   Ndikum, E.N., Tabod, C.T. and Tokam, A.-P.K. (2014) Frequency Time Analysis (FTAN) and Moment Tensor Inversion Solutions from Short Period Surface Waves in Cameroon (Central Africa). Open Journal of Geology, 4, 33-43.

[5]   Ndikum, E.N., Tabod, C.T., Tokam, A.-P.K. and Essimbi, B.Z. (2014) Fault-Plane Solution of the Earthquake of 19 March 2005 in Monatele (Cameroon). Open Journal of Geology, 4, 289-293.

[6]   Ngon, G.F.N., Etame, J., Ntamak-Nida, M.J., Mbog, M.B., Mpondo, A.M.M., Martine, G., Yongue-Fouateu, R. and Bilong, P. (2012) Geological Study of Sedimentary Clayey Materials of the Bomkoul Area in the Douala Region (Douala Sub-Basin, Cameroon) for the Ceramic Industry. C. R. Geoscience, 344, 366-376.

[7]   Kenfack, P.L., Ngaha, P.R.N., Ekodeck, G.E. and Ngueutchoua, G. (2012) Mineralogic Characterization and Petroleum Potential of Clays (Shales) of the N’Kapa Formation (Paleocene-Eocene) in the Douala Sedimentary Sub-Basin (South-West Cameroon). International Journal of Geosciences, 3, 696-709.

[8]   Nguene, F.R., Tamfu, S., Loule, J.P. and Ngassa, C. (1992) Paleoenvironnements of the Douala and Kribi/Campo SubBasins in Cameroon, West African. Géologie Africaine: Colloque de Géologie Africaine, Libreville, Recueil des Communications, 6-8 May 1991, 129-139.

[9]   Regnoult, J.M. (1986) Synthèse Gélogique du Cameroun. D.M.G, Yaoundé, Cameroun, 118 p.

[10]   SNH/UD (2005) Stratigraphie Séquentielle et Tectonique des Dép?ts Mésozo?ques Syn-Rifts du Bassin de Kribi/ Campo. Rapport Non Publié, 134 p.

[11]   Ross, D. (1993) Geology and Hydrocarbon Potential of Rio Muni Area, Equatorial Guinea. Oil and Gas Journal, 91, 96-100.

[12]   Pauken, R.J. (1992) Sanaga Sud Field, Offshore Cameroon, West Africa. In: Halbouty, M.T., Ed., Giant Oil and Gas Fields of the Decade 1978-1988, American Association of Petroleum Geologists Memoir, Tulsa, 217-230.

[13]   Turner, J.P. (1995) Gravity-Driven Structures and Rift Basin Evolution: Rio Muni Basin, Offshore West Africa. American Association of Petroleum Geologists Bulletin, 79, 1138-1158.

[14]   Coward, M.P., Purdy, E.G., Ries, A.C. and Smith, D.G. (1999) The Distribution of Petroleum Reserves in Basins of the South Atlantic Margins. In: Cameron, N.R., Bate, R.H. and Clure, V.S., Eds., The Oil and Gas Habitats of the South Atlantic, Geological Society (London) Special Publication, London, 101-131.

[15]   Selley, R.C. (1997) African Basins, Sedimentary Basins of the World. 3rd Edition, Elsevier Science B.V., Amsterdam, 173-186.

[16]   Abdelrahman, E.M., Riad, S., Refai, E. and Amin, Y. (1985) On the Least-Squares Residual Anomaly Determination. Geophysics, 50, 473-480.

[17]   Radhakrishna, I.V. and Krishnamacharyulu, S.K.G. (1990) Polyfit: A Fortran 77 Program to Fit a Polynomial of Any Order to Potential Field Anomalies. Journal of Association of Exploration Geophysicists, 11, 99-105.

[18]   Telford, W.M., Geldart, L.P. and Sheriff, R.E. (1990) Applied Geophysics. 2nd Edition, Cambridge University Press, Cambridge, 6-61.

[19]   Pirttij?rvi, M. (2009) FOURPOT. Department of Physics, University of Oulu, Oulu, Geophysics.

[20]   Blakely, R.J. and Simpson, R.W. (1986) Approximating Edges of Source Bodies from Magnetic or Gravity Anomalies. Geophysics, 51, 1494-1498.

[21]   Noutchogwe, T.C., Tabod, C.T., Koumetio, F. and Manguelle-Dicoum, E. (2011) A Gravity Model Study for Differentiating Vertical and Dipping Geological Contacts with Application to a Bouguer Gravity Anomaly over the Foumban Shear Zone, Cameroon. Geophysica, 47, 43-55.

[22]   Zeng, H., Xu, D. and Tan, H. (2007) A Model Study for Estimating Optimum upward Continuation Height for Gravity Separation with Application to a Bouguer Gravity Anomaly over a Mineral Deposit, Jilin Province, Northeast China. Geophysics, 72, 145-150.

[23]   Koumetio, F., Njomo, D., Tabod, C.T., Noutchogwe T.C. and Manguelle-Dicoum, E. (2012) Structural Interpretation of Gravity Anomalies from the Kribi-Edea Zone, South Cameroon: A Case Study. Journal of Environmental & Engineering, 9, 664-673.

[24]   Abdelrahman, E.M., Bayoumi, A.I., Abdelhady, Y.E., Gobashi, M.M. and El-Raby, H.M. (1989) Gravity Interpretation Using Correlation Factors between Successive Least-Squares Residual Anomalies. Geophysics, 54, 1614-1621.

[25]   Cordell, L. (1979) Gravimetric Expression of Graben Faulting in Santa Fe Country and the Espanola Basin, New Mexico. Guidebook to Santa Fe Country. In: Ingersoll, R.V., Ed., New Mexico Geological Society Guidebook: 30th Field Conference, 59-64.

[26]   Cordell, L. and Grauch, V.J.S. (1985) Mapping Basement Magnetization Zones from Aeromagnetic Data in the San Juan Basin, New Mexico. In: Hinze, W.J., Ed., The Utility of Tegional Gravity and Magnetic Anomaly Maps, Society of Exploration Geophysicists, Tulsa, 181-197.

[27]   Marson, I. and Klingele, E.E. (1993) Advantages of Using the Vertical Gradient of Gravity for 3-D Interpretation. Geophysics, 58, 1588-1595.

[28]   Khattach, D., Keating, P., Mostafa, M.L., Chennouf, T., Andrieux, P. and Milhi, A. (2004) Apport de la gravimétrie à l’étude de la structure du bassin des Triffa (Maroc nord-oriental): Implications hydrogéologiques. Comptes Rendus Geoscience, 336, 1427-1432.

[29]   Grauch, V.J.S. and Cordell, L. (1987) Limitations of Determining Density or Magnetic Boundaries from the Horizontal Gradient of Gravity or Pseudogravity Data. Geophysics, 52, 118-121.

[30]   Fedi, M. and Florio, G. (2001) Detection of Potential Fields Source Boundaries by Enhanced Horizontal Derivative Method. Geophysical Prospecting, 49, 40-58.

[31]   Florio, G., Fedi, M. and Pasteka, R. (2006) On the Application of Euler Deconvolution to the Analytic Signal. Geophysics, 71, L87-L93.

[32]   Gunn, P.J. (1975) Linear Transformation of Gravity and Magnetic Fields. Geophysical Prospecting, 23, 300-312.

[33]   Jacobsen, B.H. (1987) A Case for Upward Continuation as a Standard Separation Filter for Potential-Field Maps. Geophysics, 52, 1138.

[34]   Phillips, J.D. (1997) Potential-Field Geophysical Software for the PC, Version 2.2. US Geological Survey Open-File Report 97-725, 34.

[35]   Parker, R.L. (1974) Best Bounds on Density and Depth from Gravity Data. Geophysics, 39, 644-649.

[36]   Parker, R.L. (1975) The Theory of Ideal Bodies for Gravity Interpretation. Geophysical Journal International, 42, 315-334.

[37]   Safon, C., Vasseur, G. and Cuer, M. (1977) Some Applications of Linear Programming to the Inverse Gravity Problem. Geophysics, 42, 1215-1229.

[38]   Ander, M.E. (1980) Geophysical Study of the Crust and Upper Mantle beneath the Rio Grande Rift and Adjacent Great Plains and Colorado Plateau. Ph.D. Thesis, University of New Mexico, Albuquerque/ Los Alamos National Laboratory Reo, Los Alamos, LA-8676-T.

[39]   Ander, M.E. and Huestis, S.P. (1982) Mafic Intrusion beneath the Zuni-Bandera Volcanic Field, New Mexico. Geological Society of America Bulletin, 3, 1142-1150.<1142:MIBTZV>2.0.CO;2

[40]   Huestis, S.P. and Ander, M.E. (1983) IDB2—A Fortran Program for Computing Extremal Bounds in Gravity Data Interpretation. Geophysics, 48, 999-1010.

[41]   Luyendyk, B.P. (1984) On-Bottom Gravity Profile across the East Pacific Rise at 21 North. Geophysics, 49, 21662177.

[42]   Huestis, S.P. and Parker, R.L. (1977) Bounding the Thickness of the Ocean Magnetized Layer. Journal of Geophysical Research, 82, 5293-5303.

[43]   Huestis, S.P. (1979) Extremal Temperature Bounds from Surface Gradient Measurements. Geophysical Journal International, 58, 249-260.

[44]   Huestis, S.P. (1981) Temperature Bounds from Heat Flow Data on Irrerular Non-Isothermal Surfaces. Geophysical Journal International, 65, 165-170.

[45]   Huestis, S.P. (1984) The Inverse Problem for Heat Flow Data in the Presence of Thermal Conductivtty Variations. Geophysical Journal International, 78, 119-137.

[46]   Vasco, D.W., and Johnson, L.R. (l985) Extremal Inversion of Static Earth Displacement Due to Volume Sources. Geophysical Journal International, 80, 223-239.

[47]   Ander, M.E. and Huestis, S.P. (1987) Gravity Ideal Bodies. Geophysics, 52, 1265-1278.

[48]   Koumetio, F., Tabod, C.T. and Manguelle-Dicoum, E. (2009) Evidence for upper Mantle Intrusion in the West African Coastal Sedimentary Basins from Gravity Data: The Case of the Southern Part of the Douala Basin, Cameroon. Global Journal of Geological Sciences, 7, 181-187.

[49]   Cooper, G.R.J. (1998) GRAV2DC for Windows User’s Manual (Version 2.05). Geophysics Department, University of the Witwatersrand, Johannesburg.

[50]   (2014) Rock Property Tables for Specific Gravity, Density and Porosity. EduMine On-Line Bulletin.

[51]   (2014) Rock Density Chart in Imgarcade. On-Line Image Arcade.