A report on the Geological and Stratigraphic field study of the Semiliki basin in the Albertine Graben, Ntoroko district in Western Uganda.

Abstract

The field study was carried out in Semliki basin located (0186809, 79572 1614M) in the southern part of the Albertine Graben, Ntoroko district in western Uganda. The area is bounded by an escarpment to the east and south and then by river Semliki to the west. It lies onshore south of Lake Albert.

The major aim of this study was to enable us apply the geological, geophysical, stratigraphic and any other knowledge we have acquired during the different lectures to understand the geology, scrutinize and analyze the petroleum system of the area practically relating to the petroleum system.

We worked in groups and I belonged to group 5. While carrying out the field work studies, we identified the lithologies and structures present in the area as well as determined the environments of deposition and depositional processes that took place in the rift area. This was done through the critical analysis of the stratigraphy and structures of the sediments that filled up the basin. The geological, structural and stratigraphic data collected was then analyzed and conclusions about their usefulness in the petroleum potential of Semliki basin were made. The major source of sediments in the Semiliki basin is the Rwenzori mountain region and many different types of facies were identified in the area along with their significance in the formation of a good petroleum system. The basin was greatly affected by intensive tectonic activity which led to the formation of the different types of structures with in the basement and sediments in Semiliki basin such as beds, joints, faults, folds and veins. The sediments ranged from fluvial to lacustrine sandstones, clays and siltstones while the basement lithological comprised of weathered and altered granite gneisses, mafic and felsic rocks.

We visited other areas such as the Turaco wells and the Sempaya hot springs (Buranga geothermal project) which indicated the presence of a high geothermal gradient for maturation of source rocks within the region.

The sedimentology, stratigraphy and tectonic data collected was used to develop a full interpretation of the geologic history and evaluate the economic importance of the rocks encountered in the Semiliki basin.

We concluded that the study area has a good petroleum potential due to the presence of all the petroleum system elements such as source rocks (organic rich shales), reservoir rocks (thick sandstones), seals (shales and evaporites), traps (faults) and migration pathways (cross beds, faults, and beds).