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Abstract:The Albertine Graben is one of the most petroliferous onshore rifts in Africa. It forms the northernmost termination of the western arm of the East African Rift System. Its surface exposures were first studied by Wayland [1] and Pickford et al.[2] among others. Pickford et al. [2] especially developed the basic stratigraphic framework of the graben which was later modified by the government geoscientists and international oil companies using subsurface data. However, the stratigraphic units were not fully and formally described, and have been used informally in different and often confusing ways. The current study therefore aims to solve this challenge by establishing a coherent stratigraphic scheme for the entire graben through an integral study of surface and subsurface data.The study involves precise description of the type and reference sections for various formations both in exposure and wells; and has therefore led to the development of lithostratigraphic columns of different basins in the graben. The approach reveals that the Semliki area, south of Lake Albert, has the most complete sedimentary succession in the graben, spanning the period from middle Miocene (ca 15 Ma) to Recent. It also reveals that platform deposits, which form a small fraction of the thickness of the basinal succession, represent a highly condensed sequence which only saw deposition at times of Lake highstand.

A multiproxy provenance approach (heavy mineral analysis, U‐Pb zircon geochronology, and Pb isotopic analysis of K‐feldspar) has constrained sediment supply within the Upper Nile drainage system in the Miocene‐Pliocene. Provenance data from sandstones were obtained from three exploration wells, two situated on the north‐eastern margin and one on the eastern flank of the Lake Albert Basin, NW Uganda. Data suggest that high‐grade to low‐grade metamorphic rocks and granitoids have variably supplied the heavy mineral assemblages around the Lake Albert Basin during the Miocene‐Pliocene, with contributions from the isotopically heterogeneous Archean Cratons (including the local Ugandan Craton, Tanzanian, and Congo Cratons) and the Pan‐African rocks (the Mozambique Belt) with possible contributions from the Neoproterozoic and Paleoproterozoic rocks. These data also highlight clear differences between supply to the eastern basin margin, compared with the northeast, which is reconcilable with current models for Miocene‐Pliocene drainage in the region. Supply to northeastern Lake Albert during the Miocene‐Pliocene appears to have been through a proto‐Albert Nile (draining from NE to SW) and from a proto‐Victoria Nile or similarly oriented palaeo‐river systems draining from the east. In contrast, the eastern flanks of the basin were likely supplied via the palaeo‐Nkusi river, tapping local hinterland sources and more distal basement to the far‐east (Mozambique Belt). This study highlights the importance of utilizing a multiproxy approach in provenance analysis as no one signal is capable of distinguishing the different source lands and constraining the evolving drainage patterns.

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Glaciers on the world's highest tropical mountains are among the most sensitive components of the cryosphere, yet the climatic controls that influence their fluctuations are not fully understood. Here, we present the first 10 Be ages of glacial moraines in Africa and use these to assess the climatic conditions that influenced past tropical glacial extents. We applied 10 Be 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 10 Be ages document expanded glaciers at ca. 24.9 and 21.5 ka, indicating that glaciers in equatorial East Africa advanced during the global Last Glacial Maximum (LGM; 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 subsequent to ca. 21.5 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 fluctuations of Rwenzori glaciers were strongly influenced by air temperature.