A geologic and stratigraphic field study of Kibuku Area (Semliki Basin)

Abstract

The area of study was Semliki basin located in the southern part of the Albertine graben (Ntoroko district) western Uganda. The aim of this study was to enable us apply the geological, geophysical and general class knowledge we have acquired during the course of the program to understand the geology, scrutinize and analyze the petroleum system of the area, study the environments of deposition and the depositional processes that took place in the area. The area’s basement lithology consists of altered granites and undifferentiated gneisses with some dolerite intrusions as well. Overlying the basement rocks are sedimentary rocks that is sands, clays and silt, mainly of the fluvial and lacustrine nature believed to have originated in the Rwenzori ranges. The contact between the sediments and the basement is marked with a basal conglomerate. The basin was affected by intensive tectonic activity, that led to metamorphism of the basement rocks and formation of vast types of structures with in the basement and sediments, examples of these structures include faults, joints, folds, veins and banding. Formation of these lines of weaknesses within the rocks allowed percolation of mineral rich fluids. The minerals later precipitated to form gypsum deposits, which is very abundant in the area, mainly within the sands and clays. Several other structures exist in the sedimentary rocks some of which include; cross beds, mud diapirs and bioturbation structures. At the Makondo fault area, thick clays had plenty of fresh water oyster shells, bivalves, fish bones and fins which confirmed the lacustrine and fluvial origin of the sediments. The presence of hot springs with in the area indicated the presence of high enough geothermal gradients for maturation and expulsion of hydrocarbons. We concluded that the study area has a working petroleum system characterized with all the required system components that is source rocks, reservoir rocks, seals, traps and migration pathways.