New geochemical and palynological data and a sedimentological reinterpretation of two cores from Lake Albert allow a revision of the paleoclimatic and paleohydrologic history of northwest Uganda over the last 30,000 C-14 yr BP. Our findings document one and possibly three periods of significantly reduced inflow to the Nile River system from the White Nile. Based on sediment fabric and mineralogy, shifts in percentages of total organic carbon (TOC) and total organic nitrogen (TON), hydrogen index (HI), and delta(13)C and delta(15)N, as well as poor preservation of sporopollenin and siliceous microfossils, we recognize two mature paleosols that formed between 18,000 and 12,500 C-14 yr BP at the surface of exposed lacustrine muds. A thin fossiliferous zone between the two soils documents a brief period of flooding. Lake Albert was below the level of the coring site, and thus a closed basin, for several thousand years during the late Pleistocene. Around 12,500 C-14 yr BP the younger vertisol was flooded by a major rise in lake level. Relatively deep-water conditions were established soon after this transgression, but an apparent change in sedimentation rate sometime between 8,000 and 3,400 C-14 yr BP may reflect another, briefer period of low water, which resulted in interruption of sedimentation at the coring site. Palynological data document a rapid and abrupt shift to drier conditions around Lake Albert from 11,400 to 9,900 C-14 yr BP coincident with the cool Younger Dryas event of the Northern Hemisphere. Geochemical evidence suggests that throughout the terminal Pleistocene and early Holocene, and again in the late Holocene, the water column was relatively well-mixed with little tendency to persistent anoxia. (C) 1997 Elsevier Science B.V.
