A report on the geologic and stratigraphic logging project of Semiliki Basin-Albertine Graben in Ntoroko District Western Uganda from 03th Jan 2022 to 10th Jan 2022
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The field work accrued to this report took place from 15th to 28th July, 2017 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 stratigra+phy, 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 non tectonic 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 stratigraphic sequence exhibited in the basin is divided into seven Formations (in decreasing age) namely; the Kisegi, Kasande, Kakara, Oluka, Nyaburogo, Nyakabingo and Nyabusosi formations. Lithofacies were identified indicating different depositional environments (fluvial, deltaic and lacustrine). The basin is affected by intensive tectonic activity, that led to the formation of vast types of structures that include faults, joints, bedding, cross-bedding, laminations, unconformities, mud diapirs, and plunging folds among others. Geophysical data of semliki basin and shallow, high resolution (150-200 Hz) seismic data from an intraslope salt withdrawal minibasin in the Gulf of Mexico were availed for interpretation. The sediments of the Semliki Basin represent a petroleum play for hydrocarbon accumulations as all elements of a petroleum system were identified in the field. The presence of oil seeps in kibuku indicates that organic rich source rocks are present, an indicator of an active system thus great petroleum potential.