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Albertine rift, Uganda : deformation-sedimentation-erosion relatioships

Abstract : The Albertine Rift corresponds to the northern section of the western branch of the East African Rift System which runs over a distance of about 2100 m from Lake Albert in the north to Lake Malawi in the south. Lake Albert basin is considered as a classical half-graben oriented NNW-SSW, with a major northeasterly bounding fault, the Bunia fault system, located along the western shoreline. Pre-rift stage has started around 12 Ma while major rifting episode is assumed to begin around 8 Ma (Ebinger, 1989; Pickford & al., 1993). Referring to Van Damme and Pickford (2003), a palaeo-lake (Lake Obweruka) existed from 7.5 to 2.5 Ma and covered the entire area of the Albertine Rift during of that period. This study attempts to characterize the tectono-sedimentary evolution of the rift through time by restoring (1) the kinetic of vertical movements and the subsidence evolution, (2) the geometry and paleoenvironments variations of the sedimentary infilling and (3) the geomorphological evolution and associated deformations. Compilation of field vertical sections and correlations with sub-surface data led to highlight three majors lacustrine flooding events with a maximum occuring between 7 and 8,5 Ma. Comparison with Cenozoic vegetation evolution in tropical Africa (Bonnefille, 2010) confirmed the ages based on molluscs and vertebrates fossils scales (Gautier, 1970; Pickford et al., 1993; Van Damme and Pickford, 2003). Seismic interpretations will help to characterize the 3D geometry of the rift and the relationship between tectonic and sedimentation. Coupled with these data, identification and characterization of paleo-surfaces allow us to propose a first model of geomorphological evolution which highlights successive weathering and erosional periods since 50 Ma. Around 3 Ma, uplift of a metamorphic basement block (the Ruwenzori Mountains) led to the tearing up of the paleo-lake Obweruka ant to the creation of two local base levels: the Albert and Edward lakes. We assume that present-day scarp is related to a recent final uplift stage causing a regional tilting of the basins between 14 and 12 Ka (Ebinger, 1989; Pickford et al., 1993). It results a reversal of the flow directions in the whole western Uganda and the formation of Lake Victoria.
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Conference papers
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Submitted on : Tuesday, December 3, 2013 - 3:30:21 PM
Last modification on : Friday, April 5, 2019 - 8:17:34 PM

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Brendan Simon, François Guillocheau, Cécile Robin, Martine Bez, Philippe Lays, et al.. Albertine rift, Uganda : deformation-sedimentation-erosion relatioships. 14 ème congrès français de sédimentologie, Nov 2013, Paris, France. pp.59. ⟨insu-00913361⟩

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