Lithostratigraphy and distribution of Pleistocene sediments of the Munyu wa Gicheru Formation in South Kenya Rift Valley

Pleistocene sediments of the eastern African Rift Valley have been subjecte d to intensive study over the last few years, because they are very useful in the study of pal ae olakes, climatic changes and the study of lacustrine diatomite deposits, which are a source of industrial raw materials. In thi s paper, the results of field study on the lithostratigraphical divisions a nd distribution of Pleistocene sediments in South Kenya Rift Valley is docu mented. The pal ae olake beds at Munyu wa Gicheru lie in a trough, which occurs on a platform at the eastern flank of the South Rift Valley of Kenya. The beds have been divided into three lithostratigraphical members, which form the Munyu Formation. At the base of the Gicheru Sequence, the lower member is c omposed of basal massive obsidian layers, which are overlain by gravel beds . The upper parts of the member consist of a massive diatomite bed, which c ontains intercalations of greyish clay. The middle member is composed of ma ssive beds of clean white diatomite with varying amounts of silt. The unit is capped by pumiceous volcanic ash. The upper member, which experienced se veral breaks in sedimentation, consists of reworked, silty diatomite overla in by a phonolite layer. Within the diatomite beds are irregular and discon tinuous laminations of tuff. Diatom species and lithological relationships indicate that the lacustrine sediments were deposited on a westdipping plat form bounded by the Kedong Fault on the west and the Kiriri Fault in the ea st. (C) 1999 Elsevier Science Limited. All rights reserved.