Sand supply to the Lake Albert Basin (Uganda) during the Miocene-Pliocene: A multiproxy provenance approach

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.