TITLE:
Gravity Model for an Anomalous Body Located in the NW Portion of the Douala Sedimentary Sub-Basin, Cameroon (Central Africa)
AUTHORS:
Eric N. Ndikum, Charles T. Tabod, Bernard Z. Essimbi, Fidèle Koumetio, Noutchogwe C. Tatchum
KEYWORDS:
Douala Sub-Basin, Sedimentary Basin, Bouguer Anomaly, Residual Field, Upward Continuation, 2.5D Model, Intrusive Igneous Block
JOURNAL NAME:
Open Journal of Geology,
Vol.4 No.10,
October
29,
2014
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.