A Field Study Report of Semliki basin in the Albertine Graben in Ntoroko District, Western Uganda

Abstract

This report gives a detail of fieldwork activities carried out from 1st to 9th July 2024 within the Semliki basin in Albertine graben. The fieldwork was carried out in areas of Kichwamba, Kibuku at the quarry, along the seasonal Kisegi River, along Kibuku road cut, and Sempaya hot springs. The main objective of the field work was to study the environment and processes of deposition of sediments and make deductions about the petroleum potential of the area. The specific objectives of the fieldwork were; to identify lithologies in the Semliki basin, to identify and relating structures observed in the basement and in the sediments, to identify different elements of the petroleum system and to identify the facies and depositional environments. Different materials used were to measure, record and store geological data. The manuals provided to each group were used to guide group members in the study process. Most of the activities done were in groups though some of the activities like presentation of results were individual work. Vast structural and stratigraphic data was collected and then analyzed to make conclusions about the petroleum potential of Semliki basin. The study area comprised of fluvial, deltaic and lacustrine sediments, all affected by intensive tectonic activity. This led to the formation of different structures with in the basement and sediments that we observed. Examples of these structures include faults, joints, folds, veins. Sedimentary structures observed include cross bedding, unconformities, faults and mud cracks. Faults and folds would be good structural seals. Different lithologies like thick sands, thick clay beds, silts were encountered which form potential reservoirs and source rocks for the petroleum system. The presence of Sempaya hot springs within the area indicated the presence of a high geothermal gradient which is important factor for source rock maturation. Sedimentology, stratigraphy and tectonics are applied to develop a full understanding of the rocks and the sediments that fill Semliki sedimentary basin and this information was used to interpret the geologic history and evaluate the economic importance of these rocks. A conclusion was made that the study area had a good (working) petroleum system characterized with all the required system components that is source rocks, reservoir rocks, seals, traps and migration pathways and there is a chance of discovery of petroleum and a recommendation that petroleum exploration programs should be continued in this basin.