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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Tectonic Evolution of the Albertine Graben of the East African Rift System; Constrained from Geological and Geophysical Data Recently Acquired in the Graben

Dozith Abeinomugisha1; Frank Mugisha1; Nurudin Njabire1

(1) Petroleum Exploration and Production, Ministry of Energy and Mineral Development, Entebbe, Uganda.

The Albertine graben forms the northernmost termination of the western arm of the East African Rift System. Rifting was initiated from the western side of the rift during the Miocene with the accumulation of thick sediments in asymmetric basins along strike of the rift system and the subsequent formation of Lakes Albert, Edward and George on the rift floor. Later faulting of the ramping eastern margin especially over the Lake Albert region created an almost full graben structure and diverted the originally east - west drainage patterns away from the basin thus limiting clastic sediment supply. This created anoxic conditions in the deep lakes allowing deposition of source rocks. Uplift of the eastern rift shoulders created the Lakes Victoria and Kyoga saga basins.

The Rwenzori uplift during the Pliocene right in the middle of the rift, provided a sediment barrier to the Lake Albert basins but also to the southern areas. Secondly, with increased uplift and the breakthrough of some of the drainage channels, the mountains became a major sediment source into the Lake Albert basins creating huge sedimentary section in the Pliocene especially in the semliki basin. Most researchers have concentrated on the southern part of the East African Rift System (Malawi and Tanganyika rifts) leaving the northern most part(the Albertine Graben)little studied.

The Albertine graben is a frontier basin currently under exploration for hydrocarbons. Gravity and Magnetic data, together with 2D and 3D seismic data have been acquired in the graben. A number of wells have also been drilled with commercial discoveries of oil and gas. Interpretation of this data has revealed the major tectonic regimes that have shaped the graben and the sediment facies that fill up to six kilometer deep basins. Contrary to the long held view, that the Albertine Graben is purely controlled by extensional tectonics, seismic data interpretation shows a late compression episode in the Graben generating an inversion tectonic regime and creating major hydrocarbon traps.