Structure and Stratigraphy of the Lake Albert Rift, East Africa

Abstract Modern lake basins set within active continental rifts provide useful analogs for exploration efforts in ancient extensional basins that are known to be rich in hydrocarbons. Lake Albert is one of the Great Lakes of Africa and is located at the northern end of the western branch of the East African rift system. This large, but comparatively shallow, eutrophic, and probably geologically ephemeral lake basin serves as an end-member example of the modern tropical lake systems that occupy this extensional province. Seismic reflection and gravity data sets indicate that the basin contains a maximum of 5 km (3.1 mi) of synrift, dominantly lacustrine sedimentary fill, in two subbasins separated by a midbasin high. In contrast to other large rift basins in the western branch of the rift valley, the Lake Albert Rift is not a highly asymmetrical half-graben basin, but instead has subsided nearly symmetrically and continuously in the late Cenozoic along two extensive boundary fault systems on either side of the basin. Seismic sequences from across the basin were correlated to borehole stratigraphy from a deep well drilled on the Ugandan margin. These observations suggest that the basin has experienced a long-term change from a continuously open lacustrine, possibly deep lake system in the Miocene or early Pliocene, to an alternating shallow lacustrine and fluvial system in the mid and late Pleistocene. This history of basin evolution has led to the development of a rich hydrocarbon system.