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The continental basins in East Africa are important sediment storage systems that have long been of interest to sedimentologists. The architecture of the basin and rift infill is a complex composite of several factors, e.g., sediment-supply rates, accommodation space, regional drainage and climate pattern, most of them determined by the displacement geometry along the border fault system. The long-term record of the numerous rift sectors represent excellent natural archives documenting the climatic, environmental and tectonic history of eastern Africa during the past million years (e.g., deMenocal, 2004; Pickford, 1990).

Numerous investigations of the sedimentary record exposed in the EARS have been carried out during the last decades, whereas in the beginning of East African research more attention was paid to the eastern branch of the EARS. For one thing, this is because the structure and location of the older rift branch allows to study all aspects concerning rifting, including the transition from continental to oceanic rifting (Logatchev et al., 1972), and secondly, because of spectacular fossil remains that have been found within the valleys of the eastern rift branch. A large amount of studies have been published that deal with late Pleistocene to Holocene global and local climate changes (e.g., Hecky and Kilham, 1973; Richardson and Dussinger, 1986; Gasse, 2000; Verschuren et al., 2000; Gasse et al., 2008; Scholz et al., 2007, 2011), and its possible connection with tectonically driven uplift of rift shoulders (e.g., Sepulchre et al., 2006), orbital forcing (Olsen, 1986; Johnson and Odada, 1996; Trauth et al., 2003; Maslin and Christensen, 2007), and/or human evolution (e.g., Trauth et al., 2005, 2007; Holmes, 2007; Maslin et al., 2014, 2015). As in the ongoing ‘Hominin Sites and Paleolakes Drilling Project’,

which addresses the causal link between geohistorical processes, especially climatic and environmental ones, with events in hominin evolution (Campisano et al., 2017), most of these studies have been applied on Pliocene-Holocene fluvio-lacustrine marine sediments deposited in the numerous rift lakes. The high resolution marine records in the shallow rift lakes of the EARS are sensitive environments for quantifying paleoprecipitation, water balance and paleotemperature changes, including seasonality (Trauth et al., 2007). Few authors also considered terrestrial outcrop- based studies for addressing the linkage between paleoclimate/-environmental changes and hominin evolution (Stollhofen et al., 2008; Simon, 2015; Mtelela et al., 2016). Besides for paleoenvironmental archives, several of the rift basins bear important hydrocarbon resources and are thus attractive targets for petroleum exploration (e.g., Robbins, 1983; Katz, 1990; Lambiase, 1995; Lambiase and Morley, 1999). To better understand the basin geometry and its sedimentary infill, many exploratory drilling campaigns were initiated and a variety of investigations, including magneto telluric, gravity surveys and geophysical modelling (e.g. Ebinger et al., 1989) have been conducted. Moreover, intensive seismic subsurface mapping has been carried out in many of the rift sections, e.g., Lake Tanganyika (Rosendahl, 1988), Lake Malawi (Scholz et al., 1989), Lake Turkana (Dunkelman et al., 1989) and in the Rukwa Basin (Morley et al., 2000), many of them sponsored by the oil companies. Further published data include conceptual models for the evolution of syntectonic sedimentary architecture of rift basins (Gawthorpe and Leeder, 2000), volcanic dating (e.g. Wichura et al., 2011) and lakebed lithological studies (e.g., Tiercelin et al., 1992). So far, two special papers on African Rift sedimentation were edited by Frostick et al. (1986) and Renault and Ashley (2002), in which results and the progress in rift tectonics, volcanism, and fluvial-lacustrine depositional systems are compiled in several articles.

Despite the relatively large volume of literature on rift sediments, information about the onset and long-term evolution of the rift is rare. Sedimentary provenance studies, which provide a perfect tool for addressing uncertainties concerning the detailed chronology of uplift, volcanism and rifting in eastern Africa, remain insufficient in the EARS. Until now, only few compositional studies on the rift deposits have been undertaken. Mathisen and Vondra (1983) studied heavy-mineral associations of Plio-Pleistocene fluvio-lacustrine sediments in the East Turkana Basin to unravel the timing of rifting, magmatism and drainage development. Roberts et al. (2012) studied the paleoenvironmental and paleoclimatic history of the Rukwa Basin by using sedimentological, paleontological and geochronological approaches. Multi-proxy provenance studies are completely absent for most rift basins and are also lacking in the northern section of the western branch of the EARS (Albertine Rift). Although the Albertine Rift is a key region for understanding the evolutionary history of eastern Africa and preserves some of the oldest and most complete sedimentary successions in the EARS, research activity remained relatively poor during the last century. Existing sedimentological studies date back to the early 20th century (Wayland, 1926; Solomon, 1939; Lepersonne, 1949; Bishop and Trendall, 1966; Bishop, 1969; overview in Pickford et al., 1993). The first deep well was drilled in the Kaiso area (WAKI) in 1938; however, well data were not published (Davies, 1951). More systematic paleontological and biostratigraphical studies, as well as mapping were carried out since the 1960th by various authors, including De Heinzelin (1963), Gautier (1970), Pickford (1986), Senut et al. (1987), Pickford et al. (1993), and VanDamme and Pickford (1995, 1998, 2003). Major parts of the present knowledge about the geological and paleontological evolution of the rift valley bases on fossil founds gathered during several expeditions, such as the Uganda Paleontological Expedition (Pickford et al., 1993). Pickford et al. (1993) and Senut and Pickford (1994) especially reviewed the molluscan and mammalian biostratigraphy and introduced most of the formations in the Albertine Rift, which are still of fundamental relevance and provide the base for this thesis. Based on their studies, same authors also provided a more detailed overview about tectonic events affecting that particular rift sector.

Figure 1-9. (A) Rift valley in the Nkondo-Kaiso region east of Lake Albert (619 m a.s.l.) with the uplifted rift shoulder (in the back), reaching altitudes of ~ 1300 m a.s.l. (B) Road cut unveiling Miocene sediment successions in the southern Lake Albert sub-basin (Kisegi-Nyabusosi area; photo courtesy D. Brüsch). (C) Rift sediment exposed at the Warwire Cliff near the Lake Albert Safari Lodge east of Lake Albert (Nkondo-Kaiso area; photo courtesy S. Roller).

The relative little research activity on the rift sediments in the Albertine Rift during the last century has several reasons: (i) sedimentary outcrops are rare and only exposed in few scattered patches around Lake Albert, (ii) outcrops are often of poor quality (e.g., dense vegetation), (iii) no possibility of high-resolution tephrochronology especially in lower parts of the stratigraphy because of only sporadically occurring tephra layers, (iv) no spectacular fossil finds, (iv) poor infrastructure and accessibility of the area, (v) the region has been of great political conflict throughout the past decades with civil wars in Uganda, Rwanda, and the Democratic Republic of Congo and is now and then still affected by political instabilities in some parts.

Sedimentological studies in the Albertine Rift were only intensified in the recent years in the course of the interdisciplinary RiftLink research program (Bauer et al., 2010a, Rümpker and Mertz, 2016), established to address rifting dynamics, uplift, and climate change in Equatorial Africa with special focus on the Rwenzori Mountains and surrounding rift sectors. In this context, Roller et al. (2010) developed a depositional model for the southern Albertine Rift (Kisegi-Nyabusosi area) based on logged sedimentary sequences on the northern side of the Rwenzori Mountains. Moreover, much attention has been paid to the Albertine Rift lately, because of its large volumes on hydrocarbon resources that can be found at the margin of the basin. Since the Albertine Rift represents one of the most petroliferous onshore rifts in Africa, oil companies and the Uganda government have put much effort in sedimentary research. Intensive seismic profiling was conducted that covers the entire lake area by a grid of transversal and longitudinal lines to better understand the overall morphology of the basin. In 2002, a deep well (Turaco-1) was drilled to depths of almost 2500 m, but without significant hydrocarbon discoveries (Logan et al., 2009). This was followed by several successful deep wells drilled in and around Lake Albert (Kingfisher 1-3, Ngassa 2, Waki-1). Research data from the wells are only sparsely available; some of them only presented at conferences and investors presentations (Macgregor, 2015). Published studies attempt to provide a broader understanding of the structure and stratigraphy of the basin by integrating seismic reflection and gravity data. Palynological studies were applied to better understand the climate and environmental conditions of the basin through time (Lukaye, 2009; Shaw et al., 2009). Simon (2015) and Lukaye et al. (2016) attempted to refine the existing stratigraphic scheme for the Albertine Rift by integrating surface data and subsurface data. However, the time of onset of the rift valley is still controversially discussed between industry and academics with proposed ages ranging from early Miocene (Lepersonne, 1949; Lukaye, 2009), mid- Miocene (Abeinomugisha and Kasande, 2012; Lukaye et al., 2016) to late Miocene (Pickford and Senut, 1994; Yasui et al., 1992). Information about sediment sources is rare. Authors consider that most of the sediment was delivered into the valley by fluvial means (Pickford et al., 1993). Several attempts have been carried out to reconstruct the Miocene to recent drainage network of east Africa (Cooke, 1958; de Heinzelin, 1962). Authors suggest that before the mid-Pleistocene, the hydrological system of Uganda was dominated by westward directed rivers that flowed from Kenya to join the great Congo system (Wayland, 1929; de Heinzelin, 1962; Bishop, 1965; Taylor and Howard, 1999). Thermally induced uplift of continental crust caused disruption of this surface drainage, by the so- called ‘axis of upwarping’ located 13–32 km east of the western rift, leading to river reversal (Doornkamp, 1968) and formation of Lake Victoria some 400.000 years ago (Johnson et al., 2000). Provenance studies are completely absent for the sedimentary infill of the Albertine Rift, but have recently been applied to modern river sediments along the western rift branch of the EARS, including the Albertine Rift, and the River Nile system to study modern erosional processes and products (Garzanti, 2013a, 2013b, 2015). Despite the fact that research activity has been strongly enhanced during the last couple of years and new well data provide a broader insight into the evolution of the Albertine Rift, the data acquisition remains still insufficient to develop a profound understanding of the regional and local tectonic, climatic and sedimentary history of the northern part of the western rift branch.