A report on the sedimentary history, stratigraphic analysis, basin fill and structural interpretation of the Semliki Basin in the Albertine Graben in relation to its hydrocarbon accumulation
MetadataShow full item record
The Albertine Graben is one of the most petroliferous onshore rifts in Africa. It forms the northern most termination of the western arm of the East African Rift System. Its surface exposures were first studied by Wayland and Pickford et al. among others. Pickford et al. especially developed the basic stratigraphic framework of the graben which was later modified by the government geoscientists and international oil companies using subsurface data. This field project employs various techniques of geology and geophysics to investigate various aspects of Semliki sedimentary basin. The observations, analyses, interpretations and results of this study have all been documented herein. The Semliki basin is located in the Southern part of the Albertine graben, Ntoroko district in Western Uganda. Semliki area lies onshore South of Lake Albert and it is bounded by the escarpment to the East and South and by rivers Lamia and Semliki to the West. It covers an area approximately 1200 km². The Semliki basin is covered by sediments that represent Middle Miocene to Recent, which are described from outcrop and well data, underlain by possible Jurassic or Permo-Turassic to Early Tertiary sediments which rest uncomfortably on Basement described by seismic data. The basement rocks are dominated by fractured gneisses and granites while sedimentary rocks are dominated by sands and clays. The stratigraphic sequence exhibited in the basin is divided into seven Formations, namely; Kisegi, Kasande, Kakara, Oluka, Nyaburogo, Nyakabingo and Nyabusosi in that order of ascent. The provenance of the detritus in the basin was deduced to be in the Rwenzori Mountains, with water as the main agent of transport. It was observed that environments in the basin shifted over time from alluvial plain, lacustrine, deltaic plain in semi arid, humid and tropical climatic conditions; and as such enabled the deposition of the distinctive Formations. The rock record in Semliki as shown by the gravity, magnetic and seismic data acquired depicts several structures, primary and secondary, that enabled paleocurrent and paleoenvironment reconstruction through characteristic facies associations. These structures include joints, faults,stratification, and flower structures, among others. However, the structural lineaments generally manifest as short discontinuous arrays in a given trend.