Geologic field Study of the Semliki Basin, Albertine Graben

Abstract

The field work accrued to this report took place from 21st/07/2019 to 1st/08/2019 at Kibuku within the Semliki Basin in Ntoroko district, Western Uganda. The report is made up of a seven-fold dissection of chapters that a give a detailed account of the objectives, materials and methods, lithology and stratigraphy, basin and facies analysis, structures and Geophysics of the Semliki basin which altogether summarize the petroleum system of the study area. Outcrop studies near Kichwamba about the basement showed a highly metamorphosed and complex assemblage of volcanic, intrusive, igneous and metamorphic rock types majorly quartzite and gneisses. The area was marked by distinct structural features in the basement which included faults and zone of intensive fracturing comprising different sets of joints. Prevalence of deformation documented by flower structures in the shallow sedimentary section of former Turaco sites in the Graben indicates that nontectonic processes are transpressional. Synthesis studies of the evolution of the Albertine Graben suggest that the Albertine Graben basin is a tertiary intra-continental rift basin that developed on the Precambrian orogenic belt of the African Craton. The sediment sequence within the Kibuku study area comprised sands, clays and siltstone ranging from tertiary to recent in age representing a prolonged and nearly continuous phase of cyclic sedimentation in the biggest part of the basin. The prominent cyclic pattern of clays and sands in the study area reflected changing depositional environments whereby sands were probably deposited by high energy water in the fluvial system and finer sediment such as clays were deposited with decrease in energy in the lacustrine system. The interpretation of gravity data helped to understand the crustal thickness variation while magnetic data enabled the mapping of basement depth, composition and the presence of intra sedimentary volcanics. Integration of the gravity and magnetic interpretation suggested that the Northern part of the Semliki basin consisted of many faults with many structural trends. A summary and economic assessment of petroleum system showed that there was no possibility of having petroleum. This was because potential source rocks were clays with little thickness; a few fossils with some being oxidized indicating that the organic matter had been destroyed.