A report on the geological findings obtained during the study trip to Kibuku area in Karugutu, Ntoroko district, Western Uganda.

Abstract

The Kibuku area is located within the Semliki basin of the western arm of the East African Rift System. It forms part of petroleum exploration license Block 3, which is in the Albertine Graben, Uganda. Both Uganda and the Democratic Republic of Congo share the Semliki basin. The Ugandan portion of the Semliki basin covers the southern part of the Lake Albert, plus a landward area to the south of the lake.The provenance of these sediments is probably the basement rocks of the Rwenzori Mountains because the pebbles of the conglomerates observed to be in contact with the basement had a similar mineralogy with the basement rocks of the Rwenzori Mountain. The Semliki Basin is covered by sediments that represent the Middle Miocene to Recent, which are described from outcrop and well data, underlain by possible Jurassic or Permo-Triassic to Early Tertiary sediments, which rest unconformably on basement, described from seismic data. The study has allowed a better understanding of the stratigraphic relationship of the different rock units. The sediments are stratigraphically divided into Kisegi Formation at the base, Kasande Formation, Kakara Formation, Oluka Formation, Nyaburogo Formation, Nyakabingo Formation and Nyabusosi Formation. From the basin and facies analysis, the depositional environment of the Kibuku sediments along the road cut ranged from fluvial, lacustrine to deltaic. These sediments predominantly comprise sandstones, siltstones and claystones and the basement comprises igneous and high grade metamorphic rocks such as granites, granite gneiss among others. The sediments in the Semliki Basin represent a petroleum play for hydrocarbon accumulations, in which the necessary elements of a valid petroleum system were identified. These include excellent or good potential for reservoirs and top seals as well as circumstantial evidence of regionally mature source rocks, possible seals, traps and hydrocarbon- migration pathways.