Stratigraphic and geological field study report of Semliki Basin in the Albertine Graben, Ntoroko District, Western Uganda.

Abstract

A field work and excursion study to the Albertine graben under the guidance of our lecturers during the recess term of third year of our study for 12 days. The area of study was Semliki basin located in the southern part of the Albertine graben in Uganda. The study area lies onshore south of Lake Albert, it is bounded by an escarpment to the east and south and River Semliki to the west. The aim of this study was to enable us apply the geological, geophysical and other knowledge we have acquired during the course of the programme to understand the geology, scrutinize and analyze the petroleum system of the area practically; then make conclusions whether the petroleum system is working or not. While carrying out the field work studies, environments of deposition as well as the depositional processes that took place in the area through the critical analysis of the stratigraphy and structures of the sediments were studied using various field equipment and various methods that aided in the success of the set objectives. The area has a pre-rift basement lithology which consists of altered Granites and Granite Gneisses, Felsic and Mafic rocks and the post-rift lithology which is made up of sedimentary rocks mainly of the fluvial, deltaic 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, Kakara Formation, Oluka Formation, Nyaburogo Formation, Nyakabingo Formation and the youngest being Nyabusozi Formation. Vast structural and stratigraphic data collected were then analyzed to make conclusions about the petroleum potential of Semliki basin. Many different facies types were identified in the area, as well as their significance in the formation of good reservoir rocks and seals. The basin was affected by intensive tectonic activity, that led to the formation of vast types of structures with in the basement and sediments that were observed. Examples of these structures include faults, joints among others. Sedimentary structures such as mud diapirs, faults, plunging folds (anticlines) would be good structural traps for petroleum. The presence of hot springs with in the area indicated the presence of high enough thermal gradients for oil maturation. It was concluded that the study area had a good petroleum system (working petroleum play).