Project report for Semliki basin field study

Abstract

This is a field observation and post-field data analysis report of a geologic and stratigraphic logging exercise in the Albertine Graben, south and east of Lake Albert in Ntoroko District, Western Uganda. Targeted areas were the Kichwamba, Itojo, Kibuku, and Semliki Basin. The principal objectives were to investigate the depositional environments and sediment processes, and acquire knowledge on the physical, sedimentological, and sequence stratigraphic character of the region. Semliki Basin, part of the western branch of EARS, defines its northern boundary. It is a halfgraben rift basin with the shallow margin in Uganda and the deeper segment extending into the Democratic Republic of Congo. The basin consists of two large lithological packages: the Basement and sedimentary sequences, developed as a half-graben under extensional tectonics. The Basement consists mainly of low-grade metamorphic rocks such as granitic gneisses overlain by sedimentary cover greater than 6,000 meters in thickness. The sediments are divided into seven formations based on lithology and age: Kisegi, Kasande, Kakara, Oluka, Nyaburogo, Nyakabingo, and Nyabusosi (Lukaye, 2016). Extensive tectonic activity has formed a wide range of structural features in the basin, from faults, joints, and bedding planes to cross-bedding, laminations, unconformities, and plunging folds. These were identified in outcrops in the field as well as by interpretation of seismic reflection data. Cross-stratification, for instance, shows that fluvial processes exist. Geophysical surveys on the Semliki Basin show that its sedimentary sections are full of promise for hydrocarbon potential, as all the essential elements of a petroleum system were observed. The presence of the Sempaya hot springs signals a high geothermal gradient, a prevailing condition for the thermal maturation of source rocks. Furthermore, the discovery of the oil seeps in the Kibuku area confirms the presence of organic-rich source rocks that again point to an active petroleum system and high hydrocarbon potential.