Tectonic Control on Hydrocarbon Accumulation in the Intracontinental Albertine Graben of the East African Rift System

Abstract

The Albertine Graben is a Tertiary intracontinental rift that developed on the Precambrian orogenic belt of the African craton. It forms the northern termination of the western arm of the East African rift system (EARS). The western branch of the EARS consists of three sectors, the Rukwa rift in the south, the Tanganyika rift in the central, and the Albertine rift in the north. The Albertine rift stretches from the border between Uganda and Sudan in the north and to Lake Edward in the south. It is commonly referred to as the Albertine Graben and is composed of the four lakes of Albert, George, Edward, and Kivu. These lakes overlie discrete depocenters offset by northwest–southeast or east–west-trending transfer zones. Although fundamentally, the Albertine Graben has been considered an extensional province, undeniable evidence of transpression exists, suggesting a component of lateral shear stress at a late stage in basin evolution. The available geologic and geophysical data indicate that the graben has gone through extension and transpressional episodes, resulting in structures that are typical to both settings. The prevalence of deformation documented by flower structures in the shallow sedimentary sections in some basins in the graben indicates that the neotectonic processes are transpressional. The Albertine Graben has undergone substantial tectonic movements that created accommodation space for thick sediments (6 km [3.7 mi]) that were deposited in lacustrine and fluviodeltaic environments. The sedimentary layers dip gently toward the depocenter on the western margin of the rift. Rapid tectonic subsidence coupled with limited sediment input led to deep stratified lakes with the accompanying deposition of source rocks. Significant oil discoveries during the past few years on the eastern margins of Lake Albert have fueled considerable interest in the hydrocarbon prospectivity within the Albertine Graben. The hydrocarbon exploration wells drilled in the Albertine Graben have proved deposition of source, reservoir, and cap rocks and development of structural and stratigraphic traps.