Late Quaternary environments in the White Nile region, Sudan

Both the channel of the lower White Nile and the soils adjacent to the river have a number of special characteristics, which are a direct reflection of its unique late Quaternary history. These attributes include a straight channel pattern (despite a flood gradient of 1 in 100000 and a very fine suspension load) and localised concentrations of buried evaporites, carbonates, and highly saline subsoils at intervals alongside the river. Late Quaternary aeolian, fluviatile and lacustrine deposits in and near the lower White Nile valley reveal a strong contrast between the often dry, cold and windy late Pleistocene climates characteristic of the Last Glacial Maximum (18000 +/- 3000 BP) and the wetter and warmer climates prevalent in those regions towards 11500-11000 BP, 9500 BP and 8500-7000 BP. Buried shell-beds and recessional strandlines indicate a sudden and rapid regression of the vastly expanded terminal Pleistocene White Nile in possible Younger Dryas times (11000-10000 BP) coinciding with probable temporary closure of Lake Victoria in the Ugandan upper reaches of the White Nile. The stable carbon and oxygen isotopic composition of freshwater gastropod shells in the lower White Nile region is consistent with a stronger summer monsoon towards 11500-11000 BP and again towards 8500-7000 BP. At intervals between ca. 18 000 and 12000 BP, the lower White Nile was a strongly seasonal river, which shifted course frequently and carried large quantities of medium and coarse sand. The present Sudd swamps in the southern Sudan cannot have been in existence during those times, but came into existence (or became reestablished), during the Holocene. (C) 2000 Elsevier Science B.V. All rights reserved.