A report on the geologic and stratigraphic field study of the Semliki Basin, Ntoroko District, Western Uganda
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The geological and stratigraphic field exercise was carried out in the Semliki Basin, Ntoroko district in western Uganda. The field exercise lasted a period of 12 days, during which a number of activities were carried out, including but not limited to sedimentary logging, depositional system reconstruction, stream sediment studies, and structural measurements among others. The aim of the field study was to apply the geological, geophysical and other relevant theoretical knowledge attained during the course of the program to study the petroleum system of the Semliki Basin. This was particularly focused in the study of the depositional environments and depositional processes that took place in the area. Sediments found in this area comprise fluvial, lacustrine and deltaic sediments. 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.