A geologic and stratigraphic logging project report of Semiliki Basin, Albertine Graben, Ntoroko District, Western Uganda

Abstract

The sediments are stratigraphically divided into Kisegi formation at the base, Kasande formation, Karaka formation Oluka formation, Nyaburogo formation and the youngest formation being Katorogo formation. From the basin and facies analysis, the depositional environment of the Kibuku sediments along the road cut ranged from fluvial, lacustrine to deltaic. 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. These sediments represent a petroleum play for hydrocarbon accumulations in which necessary elements of valid petroleum system were identified such as potential reservoirs and source rocks, possible seals, traps and migration pathways of hydrocarbons. The Semliki Basin is a sub-basin in the south of greater Albertine Graben, the most prospective region for oil and gas exploration in Uganda. Sediments in this basin are of Mid-Miocene to recent age, which are underlain by possible Jurassic to Early Tertiary age sediments resting unconformably over the Basement rocks. Sediments are mainly fluvial-lacustrine and deltaic in nature, predominantly comprising sandstones, siltstones and claystones, and the basement comprises igneous and high-grade metamorphic rocks such as granites, granite gneiss, among others. Valuable structural and stratigraphic data was collected and interpreted to make informed conclusions about the petroleum system and potential of the Semliki Basin. Due to the intensive tectonism, a number of structures are present both in the basement rocks and sediments. These include faults, joints, and veins, bedding, crossbedding, laminations, unconformities, mud diapirs, and folds among others. v The surface manifestation of Sempaya Hot spring is evident for the early maturation of the organic matter to expel oil in the young sediments of the Albertine graben. The sediments in the Semliki Basin represents petroleum play for hydrocarbon accumulations, in which the necessary elements of a valid petroleum systems were identified. These include good potential for reservoir and seal as well as circumstantial evidence of regionally mature source rocks, possible seals, traps and hydrocarbon-migration pathways.