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A Tectono-Stratigraphic Development of the Albertine Graben of Uganda, Western Arm of East African Rift System Based on Sedimentary Exposures, Seismic and Well Data

Abstract

The Albertine Graben is a Tertiary rift system with a complex evolution history. Though it is essentially an extensional province, there is undeniable evidence of compressional tectonics. The Graben, comprises a number of structural and topographic basins, lying in a general north-easterly (NE) trend in en-echelon pattern. The basins have varying ages, younging both to the north and south. Therefore, correlation of the different Stratigraphic units from one basin to the next has been a complex task. Since Miocene, when rifting was initiated in the Albertine Graben, there has been several tectonic episodes that have shaped the geometry of the basins. The observed structural styles from seismic data, is due to a combination of (1) pre-rift basement fabric and (2) secondary modification as a result of extensional and strike-slip tectonics that has been going on since Miocene. The Albertine Graben, forms the northernmost termination of the western arm of the East African Rift System. Since Miocene, thick sediments up to 6Km in some basins have accumulated. The fault systems that comprise this rift are highly segmented, separated by relay ramps and accommodation zones which sometimes are basement highs. The graben, can be divided into three structural domains based on structural geometry and trend namely; the southern, central and northern domains. The structural elements in the southern domain trend in a NNE–SSW direction, structural elements in the central domain change to a NE–SW direction while the structural elements in the northern domain return to a NNE–SSW trend. Different stratigragraphic schemes have been developed by oil companies and researchers that have operated in Uganda. These schemes have largely been uncoordinated and gives varying ages to same sedimentary packages. The petroleum Exploration and Production Department in the Ministry of Energy and Mineral Development of the Uganda Government is coordinating a study to harmonize the different stratigraphic schemes. This paper will discuss the work that has been done to harmonize the different stratigraphic schemes using sedimentary exposures, seismic and well data that have been acquired in the Albertine Graben.