Abstract

Gravity data were acquired along two profiles in some parts of the Njaba River sub-basin. Profile A-A’ and B-B’ run for about 30 and 12 km respectively with the end of the two profiles meeting at Oguta Lake. The Bouguer gravity anomaly along Profile A-A’ revealed initial positive gravity values to a wavelength of about 21 km and then followed by a sudden drop of the observed gravity showing a significant gravity minimum. Profile B-B’ showed an alternating gravity high and low which was followed by a sudden extremely low value in the observed gravity. Further investigation showed that the structure modeled is graben and horsts bounded by two normal faults. The high gravity observed is due to the lesser density contrasts between the sediments and the basement which had resulted from the up-warping of the crust. The area showing low gravity revealed thick sedimentary accumulation of recently deposited alluvium deposits deposited in the subsided area bounded by these two faults. The structural framework of the parts of the sub-basin studied suggested an environment favorable for large scale entrapment of hydrocarbons. This is justified by the ongoing exploration and exploitation of petroleum resources in the study area.

Key words: Gravity profiles, gravity anomaly, density contrasts, sub-basin, graben and horst, Oguta Lake.