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Nicholas C.J.,Trinity College Dublin | Newth I.R.,Count Geophysics Ltd | Abeinomugisha D.,Ministry of Energy and Mineral Development | Tumushabe W.M.,Ministry of Energy and Mineral Development | Twinomujuni L.,Plot 21 29
Journal of Maps

The Lake Edward basin lies within the Albertine Rift Valley of Uganda and the Democratic Republic of Congo which forms the northern end of the western arm of the East African Rift System. It is a frontier petroleum prospective area, which, at the outset of this study, had no exploration wells drilled within it or any deep reflection seismic surveys. There have been some previous studies in the basin, but none produced a geological map subdividing the onshore rift-fill sediments or established a workable stratigraphic framework for them. Between 2007 and 2010, Dominion Uganda Ltd., in collaboration with Trinity College Dublin and the Petroleum Exploration and Production Department of the Ministry of Energy, Uganda, undertook a geological mapping survey of the south-eastern onshore part of the basin, known as petroleum ‘Exploration Area 4B’ (EA4B). Five rift sediment formations were identified and mapped across the area to produce a new geological map of EA4B. Palynological analyses suggest that all exposed rift sediments are (Late to Mid) Pleistocene–Holocene. EA4B is dominated by a north-east to south-west trending fault zone which underwent significant extension within the last 130,000 years to produce a trough, or sub-basin, to the south-east against the rift margin. This trough subsequently filled, initially with ponded swamp clays, followed by coarse fluvial and alluvial clastics. There is field evidence for minor inversion and ‘pop-up’ structures along some footwall crests, suggesting that the neotectonic phase is compressional or transpressional, and this has caused stream rejuvenation and incision. © 2015 Christopher J. Nicholas. Source

Kelly M.A.,Dartmouth College | Russell J.M.,Brown University | Baber M.B.,Dartmouth College | Howley J.A.,Dartmouth College | And 4 more authors.

Glaciers on the world's highest tropical mountains are among the most sensitive components of the cryosphere, yet the climatic controls that infl uence their fl uctuations are not fully understood. Here we present the fi rst 10Be ages of glacial moraines in Africa and use these to assess the climatic conditions that infl uenced past tropical glacial extents. We applied 10Be surface exposure dating to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains (~1°N, 30°E), located on the border of Uganda and the Democratic Republic of Congo. The 10Be ages document expanded glaciers ca. 23.4 and 20.1 ka, indicating that glaciers in equatorial East Africa advanced during the global Last Glacial Maximum (ca. 26-19.5 ka). A comparison of these moraine ages with regional paleoclimate records indicates that Rwenzori glaciers expanded contemporaneously with dry and cold conditions. Recession from the moraines occurred after ca. 20.1 ka, similar in timing to a rise in air temperature documented in East African lake records. Our results suggest that, on millennial time scales, past fl uctuations of Rwenzori glaciers were strongly infl uenced by air temperature. © 2014 Geological Society of America. Source

Tumushabe W.M.,Ministry of Energy and Mineral Development
1st EAGE Eastern Africa Petroleum Geoscience Forum - Sharing Lessons Learned: What's Next?

The geochemical results from this study have shown that rift-fill sediments in the southeast Lake Edward basin are similar internally apart from a few sand rich beds which were depleted of most elements compared to basement and bulk continental crust. This is due to reworking and winnowing during transportation to final deposition. The siliceous sedimentology showed that the area is dominated by alluvial fans and fluvial distributary fan complexes. Five individual fan complexes could be recognized fringing the edge of the rift and these merge distally towards the present day lake shoreline. Within the fan complexes, five broad lithofacies were recognized. The study showed that the sediments were sourced from the south and southeast of the basin, and no major internal differences exist within the documented formations. Source

Tumushabe W.M.,Ministry of Energy and Mineral Development
1st EAGE Eastern Africa Petroleum Geoscience Forum - Sharing Lessons Learned: What's Next?

Lake Edward basin forms the extreme southern part of the Albertine graben in southwestern Uganda. This graben forms the northern most part of the western arm of the East African Rift System (EARS).This basin has been explored to understand its paleoclimate, tectonics and depositional history and its petroleum potential. With these efforts, still its depositional, tectonic history and petroleum potential is less understood. Dominion (U) limited carried out seismic studies to ascertain its subsurface geology and this led to the drilling of Ngaji-1 well in 2010. This well did not encounter any hydrocarbon shows. Even a potential source rock was not encountered. However from surface investigations, there is some evidence for the existence of a source rock somewhere in the basin. From This study, potential reservoir facies, seal/cap facies and traps were encountered. At this scale of investigations, it is not possible to elucidate the extent of a pre-rift sedimentary basin which appears to host the source rock, and even to ascertain the location of hydrocarbon traps. This could be the subject for further investigations. Source

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