Late Quaternary Sedimentation and Climate in the Lakes Edward and George Area, Uganda — Congo

Abstract

Sedimentological and geochemical analyses of four cores from Lake Edward, East Africa, provide a detailed record of climate and lake-level changes during the Late Pleistocene and Holocene. Our record suggests that the lake was lower during the Late Pleistocene, in agreement with previous records of lake-level change in East Africa, Following an Early Holocene high stand, during which Lakes Edward and George were connected as one large water body, lake levels dropped as a result of a shift to drier climates, possibly combined with tectonic lowering of the Semliki outlet. This fall in lake level led to the desiccation of Lake George, was accompanied by tectonic activity in the basin, and exposed a >10 m fault scarp associated with the Kasindi Fault Zone. This fault zone divides the basin into a western and an eastern section and the exposed fault scarp caused damming of rivers that entered the basin from the north and northeast, leading to the creation of two separate water bodies. Low Lake Edward in the west, which was a closed lake and where extensive beaches formed along the eastern shore, and Lake Mweya located east of the fault zone. Lake Mweya was at a higher elevation than low Lake Edward and was apparently a well-flushed basin, receiving water from several rivers and possibly draining into low Lake Edward. Sediments deposited during this low stand have different geochemical characteristics, suggesting that limnological conditions in the two basins were different, Lake levels began to rise around 4.5 ka BP, uniting the two lakes and creating modern Lake George some time before 3.6 ka BP. The transgression caused drowning of extensive swamps and marks a change to gradually more lacustrine conditions in the Edward and George basins. There are indications of a shift to a slightly more and climate around 1.7 to 1.8 k-a BP, correlating with climate records from other East African lakes.