Chesowanja (Baringo Basin), Kenya

The Pleistocene localities of Chesowanja lie to the east of Lake Baringo in Kenya, near the foot of the Laikipia escarpment at 0.65οN, 36.2οE (Fig. 1). The sites occupy a fault-step raised 200 m above the level of the present-day lake. Finds include remains of robust australopithecines (Australopithecus boisei, or Paranthropus boisei) (cf., Wood and Constantiono 2007) from two localities, as well as a remarkable series of archaeological remains of different ages. The geology and paleontology of the study area, including the hominin finds, were first published by Carney et al. (1971), but the presence of artifacts was noted only later by Bill Bishop in 1973 (Bishop et al., 1975). Chesowanja is unusual among major early Pleistocene localities in eastern Africa in featuring a set of exposures on a relatively restricted scale, and especially in having a sequence that is laid out horizontally (Fig. 2). The sediments containing archaeology extend from older to younger from west to east, across about one kilometer. The geological sequence is made up of a series of major units ranging in age from the Lower Pleistocene to the Holocene, starting with the Chemoigut Formation, and continuing with the Chesowanja Formation. Description of the geological sequence has been amended with each successive phase of fieldwork in the area. The initial paper by Carney et al. (1971), reporting the first find of a robust australopithecine (A. boisei) from the Chemoigut Formation, interpreted the Chesowanja basalt as a dyke thrust vertically through the sediments. Bill Bishop in his surveys developed a new understanding of the structure, realizing that the Chesowanja basalt formed an integral part of the sequence, overlying the Chemoigut Formation, and underlying a series of later sediments. The basic stratigraphy given in Bishop et al. (1975), and especially Bishop et al. (1978), has thus stood the test of time, although successive archaeological investigations have both clarified and posed new questions, through uncovering detailed evidence of local stratigraphy and dips of sediments (Gowlett, 1999; Gowlett et al., 1981; Harris et al., 1981, 1983).