Field study report of the Albertine Graben Area
Muziransa, Huq Shaffi
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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 area‟s pre-rift basement lithology consists of altered granites and granitic gneisses, felsic and mafic rocks and the post-rift lithology is made up of sedimentary rock mainly of the fluvial and lacustrine nature believed to have their source of provenance in the Rwenzori ranges. 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, amphibolites among others. Valuable structural and stratigraphic data was also collected and interpreted to make informed conclusions about the petroleum system and potential of the Semliki Basin. Due to the intensive tectonism the area has been subjected to, a number of structures are present both in the basement rocks and sediments. These include faults, joints, and veins among others. In addition, a number of structures are also present in the soft sediments, such as bedding, cross-bedding, laminations, unconformities, mud diapirs, and plunging folds among others. 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 excellent or good potential for reservoir and seal as well as circumstantial evidence of regionally mature source rocks, possible seals, traps and hydrocarbon-migration pathways.